Design and Construction of High Current Winding for

DEGREE PROJECT IN ELECTRICAL ENGINEERING, SECOND CYCLE, 30 CREDITS STOCKHOLM, SWEDEN 2018

Design and Construction of High Current Winding for a Transverse Flux Linear Generator Intended for Wave Power Generation AHMED AMINE RAMDANI SEBASTIAN RUDNIK

KTH ROYAL INSTITUTE OF TECHNOLOGY SCHOOL OF ELECTRICAL ENGINEERING AND COMPUTER SCIENCE

Design and Construction of High Current Winding for a Transverse Flux Linear Generator Intended for Wave Power Generation AHMED AMINE RAMDANI SEBASTIAN RUDNIK

Master in Electrical Power Engineering Date: September 6, 2018 Supervisor: Anders Hagnestål Examiner: Oskar Wallmark Swedish title: Design och Framtagning av Lindning Ämnad en Linjär Transervsalflödesgeneratorprototyp School of Electrical Engineering and Computer Science

iii

Abstract There is currently a high demand for electric power from renewable sources. One source that remains relatively untapped is the motion of ocean waves. Anders Hagnestål has been developing a uniquely efficient and simplified design for a point-absorb buoy generator by converting its linear motion directly into alternating electric power using a linear PM engine. To test this method, a smaller prototype is built. Its characteristics present some unusual challenges in the design and construction of its winding. Devices of this type typically use relatively low voltage (690V typically for a wind turbine, compared to the 10kV range of traditional power plants). To achieve high power, they need high current, which in turn requires splitting the conductors in the winding into isolated parallel strands to avoid losses due to eddy currents and current crowding. However, new losses from circulating currents can then arise. In order to reduce said losses, the parallel conductors should be transposed in such a way that the aggregate electromotive force the circuits that each pair of them forms is minimized. This research and prototyping was performed in absence of advanced industrial means of construction, with limited space, budget, materials, manpower, know-how, and technology. Manual ingenuity and empirical experimentation were required to find a practical implementation for: laying the cables, fixing them in place, transferring them to the machine, stripping their coating at the ends and establishing a reliable connection to the current source. Using theoretical derivations and FEM simulation, a sufficiently good transposition scheme is proposed for the specific machine that the winding is built for. A bobbin replicating the shape of the engine core is built to lay down the strands. The parallel strands are then organized each into their respective bobbin, with a bobbin rack and conductor funneling device being designed and constructed to gather them together into a strictly-organized bundle. An adhesive is found to set the cables in place. Problems with maintaining the orientation and configuration of the cables in the face of repeated torsion are met and solved. A chemical solution is used to strip the ends of the conductors, and a reliable connection is established by crimping the conductors into a bi-metal Cu-Al lug.

iv

In conclusion, the ideal transposition schemes required to cancel out circulating currents due to magnetic flux leakage are impossible to put in practice without appropriate technological means. The feasible transposition scheme turns out to be a simple mirroring of conductors’ positions, implemented by building each half of the winding separately around replicas of the core and then connecting them using crimping lugs. Keywords: Wave-power, transverse flux generator, winding, aluminum conductor, magnetic flux leakage, ocean energy, wave energy, wave energy generator, electromotive force, parallel strands, circulating currents, crowding effects, skin effect, proximity effect, eddy currents, racetrack effect, cable twisting, AlCu connection, enamel, polyamide-imide, dicloromethane.

v

Sammanfattning Efterfrågan på el från förnybara källor är hög och inget tyder på att det kommer ändras den närmsta tiden. En källa till förnybar el som än idag står relativt orörd är den där man använder energin från havsvågor. Det är denna förnybara källa Anders Hagnestål haft i åtanke när han nu bygger en unikt effektiv generator med syftet att i ett senare skede utvinna el med hjälp av flytande punktabsorberande vågkraftsystem. Generatorn är av den linjära typen och omvandlar det punktabsorberande systemet rörelse till el. För att testa denna generatormodell så påbörjades bygget av två fullskaliga prototyper 2017. Denna uppsats behandlar specifikt arbetet med generatorlindningen till prototyperna och innefattar processen från design till själva byggnationen. Lindingen består av flertalet mindre och isolerade lindningsledare med uppgift att bland annat minska skinneffekt och virvelströmsförluster. När man använder denna metod så uppkommer dock ett nytt problem vilket härstammar från att lindningsledarna är samman n kopplade i vardera ända och bildar på så sätt 2 slutna strömkretsar. Konsekvensen kan vara stora förluster från cirkulerande strömmar på grund av det magnetiska ströflöde som finns runt järnkärnan som lindningen omsluter. Utgångspunkten för att minimera dessa cirkulerande strömmar är att transponera alla lindningsledare på ett sätt så att den resulterande elektromotoriska spänningen för varje strömkrets blir så liten som möjligt. Med hjälp av förenklade modeller samt FEM simuleringar så bestämdes ett lämpligt sätt att transponera lindningstrådarna utifrån olika kriterier. Lösningen blev att lindningstrådarna endast transponerades en gång med en så kallad 180 grader transponering. Detta ger en tillräckligt god minimering av de cirkulerande strömmarna, men den stora fördelen med denna lösning är att det är möjligt att linda maskinen med de små resurser projektet hade tillgång till, dock var detta till en stor nackdel då väldigt mycket tid gick till att hitta egna tillvägagångsätt för att utföra byggandet av lindningen på ibland okonventionella sätt. Nyckelord: Vågkraft, transversalflödesgenerator, lindningsledare.

vi

Foreword This thesis constitutes the end of our Master’s program in electrical power engineering. The work has been conducted at the School of Electrical Engineering and Computer Science at the Royal Institute of Technology in Stockholm.

vii

Acknowledgments We would like to thank our supervisor Anders Hagnestål for the opportunity to work with this project and for all the encouraging words we got to believe in our work and ideas. Jesper Freiberg and Stefan Bosniak for their help with the material and tools to execute our designs. Brian Timmer, Post Doc at the Organic Chemistry division of the Department of Chemistry of KTH, who helped us test a chemical solution to quickly and safely strip the enamel from the cable, which is indispensable in preparing the extremities of the bundles for safe connection. Hendrik Klein, our contact at Elpress AB, who helped us find an appropriate solution for a bi-metal connection between the aluminum winding and the copper bus bars of the power electronics. Malin Nordgren, of Gleitmo Technic AB, who sent us multiple types of glue for the assembly of the winding. Zachary Ross and the rest of the staff at the Model Workshop of the School of Architecture of KTH, who kindly allowed us to use the CNC milling machine at the school and gave us the guidance to program and handle it. Our families and loved ones, for supporting us through this period.

Contents 1

Introduction 1 1.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.2 Aim and Purpose . . . . . . . . . . . . . . . . . . . . . . . 4 1.2.1 Research Questions . . . . . . . . . . . . . . . . . . 4 1.3 Limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.4 Delimitations . . . . . . . . . . . . . . . . . . . . . . . . . 8 1.4.1 Literature . . . . . . . . . . . . . . . . . . . . . . . 8 1.4.2 Simulation . . . . . . . . . . . . . . . . . . . . . . . 9 1.4.3 Testing . . . . . . . . . . . . . . . . . . . . . . . . . 10 1.5 Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . . 10 1.5.1 Scientific Consensus . . . . . . . . . . . . . . . . . 10 1.5.2 FEM Simulation . . . . . . . . . . . . . . . . . . . . 11 1.5.3 Winding Choice . . . . . . . . . . . . . . . . . . . . 11 1.5.4 Construction . . . . . . . . . . . . . . . . . . . . . 11 1.6 Choice of Conductor Material . . . . . . . . . . . . . . . . 11 1.7 Literature Review . . . . . . . . . . . . . . . . . . . . . . . 12 1.8 Current Crowding . . . . . . . . . . . . . . . . . . . . . . 12 1.8.1 Joule effect and conductor section: . . . . . . . . . 13 1.8.2 Conductor bending . . . . . . . . . . . . . . . . . . 14 1.8.3 Skin and proximity effects . . . . . . . . . . . . . . 15 1.8.4 Eddy Currents: . . . . . . . . . . . . . . . . . . . . 17 1.8.5 Circulating Currents: . . . . . . . . . . . . . . . . . 18 1.9 Transposition . . . . . . . . . . . . . . . . . . . . . . . . . 19 1.9.1 Defining the language . . . . . . . . . . . . . . . . 19 1.9.2 Minimization . . . . . . . . . . . . . . . . . . . . . 24 1.9.3 Flux Density Distributions And Transposition Schemes 27 1.9.4 Linear Magnetic Field In Both Transversal Directions . . . . . . . . . . . . . . . . . . . . . . . . . . 29 1.9.5 Generalized Magnetic Flux Density . . . . . . . . 29

ix

x

CONTENTS

1.9.6 2

3

4

The usefulness of the simple crossing: . . . . . . . 30

Methods 2.1 FEM Study Of The Magnetic Flux . . . . . . . . . . . . . 2.2 Study of the behaviour of the flux leakage through FEM simulation . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3 Winding Transposition . . . . . . . . . . . . . . . . . . . 2.3.1 The Ideal Solution . . . . . . . . . . . . . . . . . 2.3.2 One Transposition per Run . . . . . . . . . . . . 2.3.3 The simplest solutions . . . . . . . . . . . . . . . 2.4 Winding Choice . . . . . . . . . . . . . . . . . . . . . . . 2.5 Winding construction method . . . . . . . . . . . . . . . 2.5.1 Building the Core-Replica Bobbin . . . . . . . . 2.5.2 Winding the bobbin . . . . . . . . . . . . . . . . 2.5.3 Damage to the Insulation: Prevention and Correction . . . . . . . . . . . . . . . . . . . . . . . . 2.6 Stripping The Wires . . . . . . . . . . . . . . . . . . . . . 2.7 Aluminum Conductor Terminations . . . . . . . . . . . 2.7.1 AlCu Bundle-Electronics Termination . . . . . . 2.7.2 Al-Al Wire-Wire Connection . . . . . . . . . . . Results 3.1 Material . . . . . . . . . . . . . . . . . . . . 3.1.1 Materials . . . . . . . . . . . . . . . . 3.2 Construction: Materials and Methods . . . 3.3 Bobbin Construction . . . . . . . . . . . . . 3.3.1 The Core-Replica Bobbin . . . . . . 3.3.2 Raw Materials . . . . . . . . . . . . . 3.3.3 Ideal Bobbin Construction Method . 3.3.4 The Stadium-Shape . . . . . . . . . . 3.4 Winding Construction . . . . . . . . . . . . 3.4.1 Final and Working Winding Method 3.5 Cable-Stripping . . . . . . . . . . . . . . . . Discussion and Conclusions 4.1 Simulation . . . . . . . . . . . 4.2 Winding Choice . . . . . . . . 4.2.1 Aluminum or Copper 4.2.2 Cross-Section Shape . 4.2.3 Hollow Conductors .

. . . . .

. . . . .

. . . . .

. . . . .

. . . . .

. . . . .

. . . . .

. . . . .

. . . . . . . . . . .

. . . . .

. . . . . . . . . . .

. . . . .

. . . . . . . . . . .

. . . . .

. . . . . . . . . . .

. . . . .

. . . . . . . . . . .

. . . . .

. . . . . . . . . . .

. . . . .

. . . . . . . . . . .

. . . . .

33 . 33 . . . . . . . . .

34 38 38 39 40 42 43 44 45

. . . . .

52 53 56 56 57

. . . . . . . . . . .

63 63 63 64 65 65 65 66 70 72 72 78

. . . . .

79 79 80 80 80 81

CONTENTS

4.3 4.4

4.5 4.6

4.2.4 Current crowding effects. . . . 4.2.5 Insulation . . . . . . . . . . . . 4.2.6 Safer Handling of the Winding 4.2.7 Cable-stripping . . . . . . . . . Transposition . . . . . . . . . . . . . . Construction . . . . . . . . . . . . . . . 4.4.1 Connections and Resistances . 4.4.2 The CRB Construction . . . . . Instrumental improvements . . . . . . Conclusion . . . . . . . . . . . . . . . .

. . . . . . . . . .

. . . . . . . . . .

. . . . . . . . . .

. . . . . . . . . .

. . . . . . . . . .

. . . . . . . . . .

. . . . . . . . . .

. . . . . . . . . .

. . . . . . . . . .

. . . . . . . . . .

xi

. . . . . . . . . .

References A Appendix A.1 Statistical Fitting of Data . . . . . . . . . . . . . . . . A.2 Importing and Fitting the Goodness of Data . . . . . A.3 Configuring the Geometric Parameters in COMSOL A.4 Tools . . . . . . . . . . . . . . . . . . . . . . . . . . . A.4.1 Drawing and Measuring Instruments . . . . A.4.2 Holding Tools . . . . . . . . . . . . . . . . . . A.4.3 Boring Tools . . . . . . . . . . . . . . . . . . . A.4.4 Cutting Tools . . . . . . . . . . . . . . . . . . A.5 Schematics . . . . . . . . . . . . . . . . . . . . . . . . A.5.1 Cores . . . . . . . . . . . . . . . . . . . . . . . A.5.2 Bobbin . . . . . . . . . . . . . . . . . . . . . . A.6 Cable Lug instructions . . . . . . . . . . . . . . . . . A.7 Datasheet for hot-melt adhesive . . . . . . . . . . . . A.8 Datasheet for low viscous hot-melt adhesive . . . . A.9 Datasheet for LCR bridge . . . . . . . . . . . . . . . A.10 Datasheet for Micro-ohmmeter . . . . . . . . . . . . A.11 Datasheet for infrared camera . . . . . . . . . . . . . A.12 Datasheet for Pro 950 Tape . . . . . . . . . . . . . . .

81 81 82 82 82 83 83 83 85 87 89

. . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . .

93 93 93 95 97 97 101 101 103 105 105 106 107 112 113 114 115 116 117

xii

CONTENTS

Nomenclature Bundle - The collection of parallel strands that carries the total current in one phase of the winding Conductor - The aluminum core of each strand Core Replica Bobbin, CRB - A bobbin that is designed so that the winding can be constructed around it, then removed and taken away to be incorporated into the electrical machine on its own. Electromotive force - The voltage generated between the extremities of one loop of conductor by the variation along time of the magnetic flux that traverses the surface that the loop is the border of. Magnet Wire - Also known as winding wire or enameled wire. The material constituting the strands; an aluminum conductor coated with insulating enamel. Solidary Bobbin - A bobbin that is designed so that the winding, once constructed around it, remains fixed to it. The bobbin, containing the winding, is then added into the electrical machine as an integral part thereof. Strand - Each individual insulated magnet wire Translator - The column of steel and magnets that moves up and down the center of the device.

xiii

Chapter 1 Introduction 1.1

Background

Since the industrial revolution, energy demand increased exponentially. While it was possible to rely on the combustion of fossil fuels for a time, they are a non-renewable, finite resource, and burning them results in the release of gasses that increase the greenhouse effect in the atmosphere, causing a man-made global warming with potentially catastrophic and irreversible consequences. As the problem became more urgent, economies around the globe sought to transition to renewable energy sources. The use of hydraulic, wind, solar, biomass, and even geothermal power is abundant and growing exponentially, as shown in Fig. 1.1. The energy of the oceans, however, remains largely untapped to this day in comparison; the insignificant sliver that it represents in the previous graph is expanded upon in Fig. 1.2. Based on possibly the highest quality global database available at present[3], it is estimated that the global gross resource is about 3.7 TW, which lies in the range of earlier evaluations (1-10 TW). However the exclusion of areas with very low energy (P ≤ 5kW/m) and in particular areas impacted by sea ice decreases this resource by about 20%, resulting in 2.985 TW globally. The total flux of ocean wave energy resource that goes through a line 30 nautical miles away from the coast is estimated to be 18 484 TWh, of which only 850 TWh (4.6%) can be extracted with state-of-theart generators[4]. This represents 3.5% of the total electricity generated in 2015 is estimated to be 24 255 TWh [5].

1

2

CHAPTER 1. INTRODUCTION

Figure 1.1: Total Renewable Energy Installed Capacity[1] On the other hand, [6] makes a similar estimate of the net theoretical energy resource at 2.985 TW, that is, 26148.6 TWh excluding areas where the wave power is below 5kW/km and areas with ice coverage. At the present time and on a global scale it is a very respectable energy source. This is even more the case when considering its local significance in the high-latitude countries where it reaches the highest levels. Currently, waves provide a gross power of 120 kw/m in the South Indian ocean, 90 kw/min the South Pacific, and 80 and 90 kw/m in the North Atlantic between 40°and 60°of latitude. Furthermore, due to the effects of global warming, these magnitudes can be expected to increase. 1 due to man-made global warming have consequences that drastically affect this status-quo. 1

Since 1948, "the regions in the Southern Hemisphere with highest values of wave energy are increasing at the highest rates with values from 0.4 to 0.8 kW/m/yr", while "North Atlantic and North Pacific are experiencing a moderate increase of 0.2 kW/m/yr". Furthermore, the impact of rising ocean levels, which should be expected to [7] ocean levels are between 30 and 180 cm by 2100, relative to levels in 1990


3

Figure 1.2: Total Ocean Energy Installed Capacity[2] Nevertheless, the imminent threat of said global warming is the very reason governments and private entities are investing in developing all available forms of renewable energy. The current project approaches the extraction of the wave energy by approximating perfect extraction of the wave front’s energy as it traverses the buoy’s location. The main purpose of the thesis is to design and manufacture a suitable winding for a transverse flux machine that is intended for wavepower generation. The specific type of transverse flux generator that the will be contributed to is the idea and work of Anders Hagnestål, researcher at the Royal Institute of Technology in Stockholm. He has come up with a design making it possible to convert the unusually slow motion of the waves to electricity in an efficient and low-cost way.[8] [9] [10] To be specific, the task undertaken in the thesis was the design and construction of windings for a prototype to test the machine. Said prototype involves both a generator and a motor. They are identical in every dimension save the thickness of the cores, where the motor’s are wider, as shown in Fig. A.13. The problem is complex; many interlocking parameters need to be considered in the design of the winding. A (non-exhaustive) breakdown into smaller tasks and problems that had to be addressed in the work therefore can be seen in 1.2.

4


1.2

Aim and Purpose

The topic at hand is the design and construction of the winding of a linear three-phase electrical machine which is used for the direct conversion of ocean wave energy into electrical power. The purpose is to find out how to configure said winding in such a way as to minimize or eliminate the losses caused by circulating currents through parallel winding due to magnetic flux leakage around the iron core, and how to construct the physical winding, or a prototype thereof, in practice. This research should help the reader better understand the problem of flux-leakage-induced circulating currents in machines that use parallel conductors in their winding to conduct large currents, as well as the practical challenges that building and connecting such a winding raises. Solving this problems allows for the construction of any similar machine with greater efficiency and power density, thus increasing the viability of any similar application, where energy needs to be extracted from a movement with a very wide and low range of frequency, and where the conditions require the usage of a high-current, low-voltage configuration. In particular, it should establish the fundamental guidelines and tools for the completion of the construction of the winding for this specific prototype, as well as provide an example on how to proceed with the construction of windings for similar machines in the future, saving the reader time in exploration and experimentation.

1.2.1

Research Questions

The following questions were explored in this thesis, with an answer being proposed for each of them, and tested whenever possible: • What is the shape and magnitude of the magnetic flux density field around the magnetic core in the areas occupied by the winding? • How to best transpose the windings to reduce induced voltages between parallel windings to a negligible level? • Does this solution remain the optimal alternative in practice, given the challenges of its construction and maintenance?


5

• How to easily, cheaply, and quickly strip the insulation enamel from the extremities of the conductors that are going to connect to the power electronics? • How to best connect the aluminum conductors of the generator with the copper bus bars of the power electronics? • How to construct the winding in such a way that it can easily be fastened around both sides of the iron core of the electric machine, which are physically separate from each other? • How to construct a physical live-sized model of said iron core to function as a bobbin around which to build and consolidate the winding previous to its insertion? • How to ensure that the winding holds its configuration once in the machine and subjected to the thermal and mechanical constraints of its nominal functioning conditions? • How much manpower would it take to construct the winding according to the method that we designed using the materials available? What changes in design or construction would improve this construction time?

1.3

Limitations

Technique and Know-how: Neither we nor anyone in the school had any experience winding machines of this size and characteristics nor the knowledge of the materials needed to do it correctly. The winding of forty parallel conductors in a single bundle around each core posed a peculiar challenge. Time Constraints: Access to the lab and workshop were limited to only specific hours of the day. Due to continually trying new techniques, it was difficult to plan how long each task would take until it was well underway. Many unexpected difficulties in planning were encountered. Simulations were intensely timeconsuming. Budget: The project assigned to this team has been assigned very limited resources, which led to most of the following limitations.

6


Tools and Technology: It was not possible to acquire machines that would have accelerated the processes. There were no machines for winding and unwinding the cables, or for stripping them, or for holding them together in the most desirable position. The very basic tools available required ingenuity and improvisation on the authors’ part. In particular: • There were no wire-stripping tools suitable for the type of magnet wire that was given. After many different tries, the best solution found was chemical: after research and experimentation, a combination of chemical solvents was found that could reliably and quickly dissolve the cable’s coating. • The stands that were used to support the bobbins in the process of unwinding them had structural flaws in the shape of the shaft, the inertial, balance, and the friction, that made the process unwieldy and complex. Manual additions had to be implemented in order to make them functional, see Fig. 1.3.

(a) Right side fix

(b) Left side fix

Figure 1.3: Bobbin Stand Fix • To contain the conductor needed for each strand in the simultaneous winding solutions, new bobbins had to be expressly constructed, as shown in Fig. 1.4.


7

Figure 1.4: Bobbins to be wound with single strand • To hold said bobbins in position, a dedicated rig had to be set, as shown in Fig. 1.5

Figure 1.5: Bobbin rack Manpower: It was not possible to hire manual labor for the timeconsuming tasks, or for those that would be physically demanding or require manual skill. Logistics: It was not possible to order any products with significant lead time in a project where needs were discovered in an exploratory way. Any acquisitions in addition to the pre-existing materials needed to be made from nearby distributors using the transportation means available. Much of the materials was recycled from the school’s workshop leftovers. Space: It took a lot of time to get space to work in. From a small desk in a shared office, to a spot at the bottom of the stairs, to a corridor area between power cabinets and heavy electrical machinery in the building’s basement.

8


Material: A specific type of magnet wire was provided, thus strongly influencing design choice and reducing flexibility in the design of the winding.

1.4

Delimitations

Due to the limitations as seen in 1.3, the priorities set by the thesis supervisor are as follows: • Design build one functional winding that can be used for testing the electrical machine. • Come up with a transposition method that can be reasonably expected to minimize the winding losses. • Stay within budget, finish on time, with the means at your disposal. Therefore, the following choices were made: • Instead of a detailed, dynamic, 3D simulation of the behaviour of the machine, including different types of winding transposition methods, a rudimentary 2D simulation of the machine and its flux leakage at different current phase angles was deemed sufficient. • Instead of building the six winding pairs needed for the machines, only one pair of windings was deemed enough. • Instead of going into extreme detail on the Calculus and electrophysics involved in the phenomena here covered, an introductory overview within the fundamentals was deemed sufficient. Instead, the focus of the thesis was directed towards the practical considerations of the winding’s construction.

1.4.1

Literature

There’s a number of avenues of investigation that were deemed unnecessary or non-pertinent.


9

Most literature regarding losses in conductors due to eddy currents and/or current-crowding phenomena that reduce the effective crosssection of the conductors, is developed for high-frequency and/or highvoltage applications, and therefore does not apply to the problem at hand. There’s a certain amount of debate regarding estimations of the total wave potential, both locally and globally. There’s also a large body of literature regarding present experiments in the ocean wave energy sector and the state of the art therein. This was not explored beyond the broad strokes needed for the Background section (1.1).

1.4.2

Simulation

COMSOL Multiphysics was used for electromagnetic simulations. It might have been possible to make a more detailed simulation of the behaviour of the conductors. • On COMSOL, the large, uniformed conductor could have been split into parallel strands of solid aluminum, linked in series according to each chosen transposition method. Running the simulation could have then yielded more exact distributions of the current in the winding, and a more exact estimation of the losses. • The original COMSOL simulation could have been changed from a series of stationary simulations that identify a phase shift in the current with a position shift in the translator, to a time-dependent simulation that has the current be organically caused by the movement of the translator, rather than imposed as a simulation precondition. • The whole machine could have been simulated in full 3D detail. All three suggestions share the same problem, in increasing levels: it is very time-consuming to do, be it in terms of implementing and configuring the simulation, or in terms of running it, as they require considerable processing power. Even the simple simulations that were actually run could leave our computers running at full power for several hours. Because those simulations weren’t performed, it was not possible to obtain the parameters necessary to perform a full analytic model allowing a reasonably quick study of the different transposition schemes

10


that could have been tried. Said results would include the flux linkage in each strand, and therefore each conductor’s self-inductance as well as the mutual inductance between each pair of conductors. [11] Had those parameters been obtained, implementing the analytic model and performing a systematic search for an optimal transposition scheme would not have been a trivial effort either. In short, while more detailed simulation work would have been indispensable to obtaining an optimal result, the lack of time and resources, or, in other words, the urgency of building the physical bobbins within a short time and with a small budget...

1.4.3

Testing

Given that by the time the winding were constructed and the thesis’ time was coming to an end, there was no magnetic core around which the materials could be tested, it was not possible to obtain the empirical parameters of the circuit other than the resistance of the cables and of the lug connection. Furthermore, as of the time of this writing, there isn’t a power source or sink available to provide or absorb the 180 kVA needed to simulate the circuit’s behaviour, and it is uncertain that the instrumentation available would be up to the task of measuring its behaviour.

1.5

Assumptions

The study begun with a number of assumptions, which were necessary to move forward. While some of them were tested, challenged, and rejected during the project, others remained in place, either because it was impractical or impossible to verify them before the end of the project, or because doing so falls far beyond its scope.

1.5.1

Scientific Consensus

Well-established theoretical foundations such as Maxwell’s Laws and their correlates are taken as a given. Likewise, practical formulae, results, and estimations, that were found in peer-reviewed scientific papers and graduate theses, are treated as credible, and taken at face value. While it is not uncommon for published, peer-reviewed scientific papers to contain serious errors, verifying them falls outside of the


11

scope of this thesis, as such verification efforts can constitute enough work to be publications and theses in their own right.

1.5.2

FEM Simulation

• The geometry and characteristics of the simulated machine is considered to be sufficiently close to that of the finished machine, even though the simulation employs a uniformly distributed current density. • It is assumed that the COMSOL simulation is a sufficiently accurate representation of the behaviour of the electromagnetic field around the magnetic core.

1.5.3

Winding Choice

• It was assumed that the winding would bend easily around the desired direction, and maintain straight orientation. • It was also assumed that it would be a simple matter to keep track of forty parallel conductors and place them well. • Aluminum was chosen because of its low cost, and issues relating to the quality of terminations were not put into question. • It was assumed that the removal of the magnet wire’s polymer coating would be a simple task.

1.5.4

Construction

• It was assumed that the methods employed for bonding the windings together were sufficiently robust. • The initial construction was made with the assumption that the windings would be forming large bundles.

1.6

Choice of Conductor Material

Some of the properties of copper and aluminum are compared in Table 1.1

12


The quantified ratios between Cu and Al Material Weight Cost Conductivity

Cu 3 2.5 1.5

Al 1 1 1

Table 1.1: Relative properties of aluminum and copper, given the same resistance per length The cost of the winding is estimated to be in the order of 5-10% of the total cost of the machine, but the winding losses represent 0.5% of the total power, in the order of 200 W per coil. This is also the reason why cooling is not a big concern: the windings produce barely more heat than a light-bulb. Therefore, the increased cost of using copper rather than aluminum is not justified by the corresponding increase in ampacity 1.6.

1.7

Literature Review

There is a fair amount of literature on topics resembling what is covered in this thesis. Two common traits have emerged: • The literature presents a solution but skips steps on how they got there, making replication difficult. • The literature covers a specific topic which is close to the subject at hand. However, the methods presented in the former do not generalize to the latter. In conclusion, the most crucial elements in this thesis build upon documents [12] and [11].

1.8

Current Crowding

The selected cabling given at the beginning of the thesis was chosen in consideration of the following effects: • Joule effect. • Skin effect.


13

• Proximity effect. • Leakage-driven eddy currents. • Racetrack effect. However, this created a new concern, circulating currents. Minimizing it it is the topic of this thesis. Below is a more detailed review of each of these effects and how they affect this specific problem.

1.8.1

Joule effect and conductor section:

Figure 1.6: Current Flux Through Conductor Section J J2 dQ =J·E=J· = dV σ σ

Figure 1.7: Joule-effect heating of a section of conductor

(1.1)

14


Joule effect: electric charges traversing a conductive material causes volumetric heat losses in direct proportion to the resistivity of the material and to the square of the density of the charge flow. See Fig. 1.6 and Eq. 1.1. Fig. 1.7 is a typical example. Given the limitations in the voltage of the power electronics available to provide the machine’s power source (with a rating of around 600V), and the power rating envisioned (180kVA), the current needed to be increased to a relatively large 300A. Consequently, in order to reduce Joule losses, it was decided that the total conductor section of one phase needed to be as large as possible. The maximization of filling factor and power density of the winding determined the choice of a quadrangular section shape. Regardless of section shape, however, such a thick conductor would not only be difficult to bend and wield, but would leave a lot of room for eddie currents of different kinds to circulate within it, which would result in the various types of unnecessary losses listed above, and expanded upon below.

1.8.2

Conductor bending

Racetrack effect: When a conductor is bent with a small bend radius, current density increases towards the axis around which it is bent, as the current seeks to take the shortest path1.9. The sharper the turn, the stronger the effect, as seen in Fig. 1.8.

Figure 1.8: Streamlines Of Current Density In Bent Cable[13]


15

Figure 1.9: Current Density Variation[14]

1.8.3

Skin and proximity effects

Skin effect: The frequency of alternating current causes a synchronous change in the magnetic field within conductor (Fig. 1.10), which causes current density to migrate to the edges of the conductor (Fig. 1.11).

Figure 1.10: Skin Effect Cause[15] The avoidance of the skin effect determined the splitting of the conductor in multiple parallel wires of equal section. According to [16], the generic equation for skin effect depth, below which the current density drops below 1/e = 0.37 of the current at the

16


Figure 1.11: Skin Depth δ[15] surface in a circular conductor, as long as the current is at frequencies far below fmin = 2π/(ρAl A l is given by 1.2. r 2ρ δ= (1.2) ωµ Constant

Value

Unit

Source

ρAl σAl r,Al epsilon0 f µr,Al µ0 δ

2.82E-08 3.54E+07 1.7 8.85E-12 1 < f < 40 1 4π · 10− 7 13.36 < δ < 84.5

Ω · m [17] S/m [17] [18] F/m [19] Hz [20] H/m mm

Table 1.2: Skin Depth Of Aluminum At 1 to 40 Hz Table 1.2 shows all the relevant properties of Aluminum and estimates a skin depth above 13mm. The 4x2 mm aluminum conductors chosen are more than small enough for the skin effect to be negligible. The magnitude of the external magnetic flux leakage is in turn large enough that what little internal flux leakage there is might be entirely drowned out[21]. verifying this would be a topic for further research. This separation in parallel strands reduces how far the current in the winding can migrate away from the center of the cross section,


17

leaving only a proximity effect. Proximity effects: The fluctuating magnetic field caused by the alternating main current of one conductor causes in a nearby conductor a back EMF which makes current density migrate away from said other conductor, as illustrated in Fig. 1.12.

Figure 1.12: Graphic Representation for the Proximity Effect[22] The increase in apparent resistance due to this effect is assumed to be negligible at the application’s frequency range.

1.8.4

Eddy Currents:

The need to reduce leakage-driven eddy currents determined the choice of a rectangular section, which was originally oriented so that the longer side would be parallel to the direction where the flux leakage density was expected to be largest, namely, transversal to the magnetic core. Construction constraints overrode that choice when it came to the individual conductors: see 2.5.2. Eddy Currents: Fluctuating magnetic field leakage coming from the magnetic core causes eddy currents in the conductor section plane perpendicular to the field, as seen in Fig. 1.13

18


Figure 1.13: Eddy Current In Flat Conductor Due To Transversal Magnetic Flux[23]

1.8.5

Circulating Currents:

Circulating currents: A bundle of parallel conductors under a fluctuating magnetic flux form a mesh of conducting loops through which the flux induces a back-EMF and circulating currents that leave the total current entering and leaving the bundle unchanged.

Figure 1.14: Circulating Current One Pair Of Flat Conductors Due To Transverse Magnetic Flux[23] It is possible to minimize the magnitude of said currents by transposing the conductors so that each pair of conductors crosses each other in the plane orthogonal to the direction of the leakage flux, in such a way the surface that is defined between each pair of parallel conductors is divided in two areas, where the flux traverses them in opposite directions. Thus, the EMF generated along the perimeter of one surface is equal and opposite that of the other, resulting in a suffi-


19

ciently small EMF that the circulating current is negligible, and so are the losses it causes. The purpose of this assignment is, given all the previous design decisions, to generate a suitable transposition method and implement it in practice while constructing the winding.

1.9 1.9.1

Transposition Defining the language

Bundled Wires The construction of this linear generator requires the usage of a lowvoltage, high current configuration. In this configuration, the cable section needs to become very large to reduce Joule Losses (see 1.8.1). However, this opens it up to skin effect (1.8.3) and eddy current (1.8.4) losses. In order to avoid this, the current is divided among parallel strands, the sum of the sections of conductor therein adding up to the desired total section. Hereafter, the following terminology will be used: bundle refers to the collection of parallel conductors that carries the total current, while strand will refer to the individual conductors, and cable to the conductor plus its insulating layer. In this section, conductors will be treated as idealized to a single line, so they will be named ’strand’, ’cable’, or ’conductor’ interchangeably. Time as a spatial metaphor By envisioning the layout of the strands in terms of the process of winding them, one can phrase their spatial progress as a temporal one. One then says that the cable "spends time" in a position to say that it is laid at that position during a given spatial interval, or that the spatial regions between the bundle positions need to be "covered" by a pair of cables (that is to say, encircled or delimited) "for an equal amount of time". Hereafter, this temporal language will be used alongside the spatial to facilitate ease of understanding. This temporal terminology is not to be confused with the time variable in the electrical machine’s

20


Figure 1.15: 180° transposition movement. In this document, save for the formulation of the electromotive force as a time derivative of the flux, the time variable will only be used in the context of phase angle when examining the state of the system at specific instants, as a perfectly regular periodic functioning is assumed. Transposition Types [11] helps us define two main transposition patterns, for a bundle made of two columns: Rotation/Continuous The conductors switch places at regular intervals. Each conductor moves one slot above until it reaches the bottom, then rises up to the top of the next column. 360° transposition The rotation is at 360° each wire is back to the position in the bundle that it occupied at the beginning of the transposition, so that the bundle’s disposition is the same it was originally. See Fig. 1.16 and 1.17, as well as Fig 1.21 (c). 180° transposition The rotation is at 180° when the topmost wire at left column has reached the bottom of the same column. In other words, each wire occupies the opposite position to the one it was originally in, relative to the center of the bundle. See Fig. 1.15. Mirroring/Discrete The positions are flipped alongside either the horizontal or the vertical symmetry axis of the bundle. See Fig. 1.18, as well as Fig 1.21 (a) and (b).


Figure 1.16: 360° transposition

Figure 1.17: A classic Roebels bar continuous 360° transposition

21

22


Figure 1.18: Mirror transposition around the horizontal axis


23

Figure 1.19: Strand Circuit [24] Circulating Currents And The Losses They Cause The splitting of the current into a bundle of strands, however, creates a new problem. As shown in 1.19 each pair of parallel strands forms its own closed circuit, and any variation of an electromagnetic flux traversing the surface the circuit encloses results in an electromotive force (emf) that propels a circulating current through that circuit, adding itself to the main current on the strand in which they share a direction, and subtracting itself to it in that in which their directions are opposite, as seen in (1.3) and (1.4).    I1 = i1 + I/n .. (1.3) .   I = i + I/n n

n

In those parallel strand circuits, there is very little to impede the current caused by each emf. The resistance of the cable is small to begin with, and the reactance is likewise very small at the expected frequencies. Therefore, even small emfs due to otherwise negligible flux leakage can cause relatively large currents, and, therefore, relatively large losses, which may create heat problems in the generator. From the perspective of the stator’s electric terminals, where all the bundle’s conductors come together, those electric currents end up cancelling out; they increase the current in one conductor the same as they decrease it in the other, and so they amount to a null sum (1.5). However, the Joule effect heat losses are proportional to the square of

24


the total current in each conductor (1.6). Therefore, a given increase in current produces a greater increase in heat loss than the same decrease produces a reduction thereof. In conclusion, the increase in heat losses due to Joule effect will be strictly positive in every instance (1.9). n X

n X

Ik =

k=1

(ik + I/n) =

I

(1.4)

0

(1.5)

k=1 n X

ik =

k=1

X

X

Ik2 R X =R (ik + I/n)2   X X X 2  ik + 2 ik I/n + (I/n)2  = R | {z } | {z } 0 ≥0 X X P ≥ (I/n)2 R P =

(1.6) (1.7) (1.8) (1.9)

In the present case, the magnetic flux leakage outside the motor core is sufficiently large that the circulating currents in the parallel strands resulting from it cannot be neglected, and require a countermeasure.

1.9.2

Minimization

In general, the method employed is to minimize the emf by setting the parallel strands in such a way that the magnetic flux leakage traversing the surface enclosed between them is made as small as possible, if not null. Each circuit’s emf can be cancelled out by crossing the cables over in such a way that the flux leakage causes a positive emf in one region and a negative emf in the other, the latter cancelling the former out. As the total flux encircled by the circuit is a result of the linear addition of each component of the flux density, the problem is made more tractable by looking into each Cartesian component separately, as shown in 1.20 and (1.10).


25

Figure 1.20: Flux Density Decomposition Vs. Surface Normal Vector

Z S

~ S ~= B·d

Z

Z (Bx , By , Bz )·(dSx , dSy , dSz ) = S

S

Z Z Bx dSx + By dSy + Bz dSz S

S

(1.10) Furthermore, in the case of electrical machines, in the relatively small regions containing the electric conductors, and given the relatively small magnitude of the flux density, the original assumption was that it would be fair to approximate the variation of said flux density as linear in the space the conductors occupy. In that local context, it was estimated to be diminishing linearly as the distance from the air gap and from the iron core increases. This was the approach used in [12]. The following subsections show how the problem was approached theoretically with increasingly-complex behaviour of the flux. Figure 1.21 is used as reference.

26


Figure 1.21: Examples of transposition of bundles along one place.[12]


1.9.3

27

Flux Density Distributions And Transposition Schemes

Uniform Flux Density When the normal flux density component is constant along the plane, each pair of parallel conductors must, as seen from that plane, cross each other in such a way that two regions so enclosed are of equal surface. The first region will have a normal vector pointing out of the plane, the second pointing in, and the sum total of the flux over each surface will therefore be equal and opposite. To compensate the flux, it is enough that each pair of cables cover the same total area in positive and negative. The simplest solution is then to perform one single transposition in the middle, where all cables will change position to the one opposite the occupied originally. Case (b) in Fig 1.21 is an example of such a solution. This is also the rationale behind twisted pair cables, as seen in Fig 1.22 and Fig 1.23. Flux Density Variable On The Cross-Section But Constant Along The Bundle Length This is the case when the transversal flux density is constant alongside the length of the bundle, but varies relative to height or depth. It is trivial to generalize from the case where the flux density will vary along the ’depth’ or ’height’ but not both at the same time. The bundle is then modeled as flat, with all the cables existing in one plane. The greyscale transition in Fig. 1.21 represents how the flux density normal to the plane is constant along the "length" coordinate and de-

Figure 1.22: Generic Example of Twisted Pair Cables

28


creases linearly along the "height". Another way to represent this would be using isolines of magnetic flux density, which would then are parallel to one of the coordinate axes and uniformly spaced as the magnitude increases linearly along the other coordinate. One algorithm that achieves that is to have each conductor "descend" one "step" each interval, until it reaches the bottom, whereupon, on the next step, it will return to the "top". When the conductors are bus bars and are stacked in a single column, the resulting type of bundle is known as Roebels Bar. In the literature, we have found it most commonly associated with long cylindrical engines. However, this method can be generalized to cases when we have more than one "column" of conductors, and the field varies along the "depth" as well as along the "height". Once the "first" conductor, that was initially at the top of the first column, reaches the bottom rung, it will then move on to the "top" of the next column, with the one at the bottom of the deepest/last column taking its place in the first, and so on. The process, whereby the "first" conductor undergoes such a journey until it is back in its original "position" in the bundle section, will be hereafter known as a 360° transposition sequence. Several approaches present themselves: • The simplest and roughest is to assume that the field is unifrom and apply a simple mirroring. All emfs won’t be cancelled, but if the average flux across the plane is non-null, the component of the emf due to said average flux will be cancelled out. • The most complex one is to modify the separation between cables accordingly so that the flux enclosed between two successive cable positions remains identical. If so, then a simple mirroring would work well. This would be possible only if the linear distribution of the flux density remains constant: as soon as the gradient changes, the spacing among the cables would need to change accordingly. Furthermore, it is quite difficult to space conductors this way in practice. This approach is therefore plainly impractical. • The most effective approach is to have each pair of parallel conductors enclose each "height" interval of the plane in equal amounts, both "in positive" (with the normal component of flux density pointing in the same direction as the surface vector) and "in negative" (with the flux density pointing in the opposite way), so


29

that the total sum of normal flux density over surface amounts to zero. If one were to envision the layout of the strands in terms of the process of winding them, one could also say that the regions need to be covered "for an equal amount of time". This can be achieved by having each cable spend an equal amount of ’time’ at each ’position’. This can be achieved by using: – A 180° transposition sequence. (see Fig. 1.21 (d)). – If the number of conductors is a power of two, a main mirror transposition of all wires in the bundle’s midpoint, then two secondary mirror transpositions for the top and bottom subsets of cables at the quarter- and there-quarter-point, etc. (see Fig. 1.21 (c)). The mirror transposition method (Fig 1.21 (a) and (b)) remains sufficient if there is only one pair of cables.

1.9.4

Linear Magnetic Field In Both Transversal Directions

So far, the different possibilities have been be examined from the perspective of a single plane, upon which the bundle is laid flat, and where only the magnetic flux density perpendicular to the plane will be taken into account. Because the total emf is a linear combination of the projection of the magnetic flux on each direction alongside the plane between cables, as long as the behaviour of the magnetic field is constant alongside the longitudinal axis of the bundle, it is possible to consider each plane separately, and freely combine the corresponding transposition solutions defined for each plane. This is roughly the case inside the slots of long electrical machines, such as the turbines studied in [11]. However, this doesn’t apply if the flux density does not behave according to this assumption, which turns out to be the case in the machine studied in this report.

1.9.5

Generalized Magnetic Flux Density

When the flux density varies alongside the longitudinal axis of the bundle, things become much more difficult. It becomes essential to find symmetries and regularities for which to design ad-hoc transposition schemes. In the worst case scenario, the field may turn out to be

30


too complex to properly design for. An organized bus bar distribution with a regular scheme of discrete "intervals" and "positions" may not be practical or cost-effective to execute. Hence, one may use what is known as a Litz Wire[25], where the cables are uniformly randomized along the bundle.

1.9.6

The usefulness of the simple crossing:

It is common practice to twist cables in pairs to increase electromagnetic compatibility by reducing electromagnetic radiation and crosstalk between neighboring pairs, and to improve rejection of external electromagnetic interference, as seen in 1.23. In fact, the simple crossing remains useful when dealing with a two-wire bundle, in every instance where the magnetic field’s component normal to the plane containing the wires presents an even symmetry relative to the plane that’s transversal to the cables’ direction and bisects them at the middle of their length. It also remains useful if the flux density is spatially periodic along the length of the bundle and the wires are made to cross at regular intervals equal to the spatial period. This can further be generalized to apply in


Figure 1.23: The Twisted Pair With Variable Density

31

Chapter 2 Methods The study was performed in the Department of Electrical Power Engineering at the Royal Institute of Technology in Stockholm between January and August 2018. The materials used include, in the exploratory phase, digital CAD software SolidWorks®, FEM simulation software COMSOL®, and mathematics software MATLAB®. This allowed the determination of the optimal transposition system. In the secondary and most important phase, implementation was performed manually, including the construction of relatively complicated systems to attempt the winding without interruption.

2.1

FEM Study Of The Magnetic Flux

On [11] and [12], methods are proposed for the analysis of the behaviour of circulating currents between parallel strands, and for the study of how one current would interact with another. However, a feasibility difficulty was met immediately: while these studies dealt with 10 and 16 strands at a time respectively, the current design was initially meant to be 100 parallel strands. This increased the difficulty of both formulating the problem mathematically and processing the simulations numerically, to the point that the hardware we were granted couldn’t even handle a CAD sketch of 100 rectangles together, let alone solid figures with twisting and winding. A later downsizing of the machine made the number of parallel windings in one bundle to be revised downward, settling at 40 parallel strands. Nevertheless, the simulation results ended up suggesting a method

33

34

CHAPTER 2. METHODS

that would substantially simplify both the calculations and the execution.

2.2

Study of the behaviour of the flux leakage through FEM simulation

On the COMSOL model of the machine provided by the supervisor, the simulation results suggested symmetries in the electromagnetic field in the core, that could be exploited for a simple generic solution using only one twist, no matter how many layers of winding are used.

Figure 2.1: Magnetic Flux Density and Flux Lines Across the Whole Model. The figures suggest the following: • The magnetic flux density’s magnitude, as well as the magnetic flux lines, form a mirror symmetry alongside the middle plane of the machine. • In other words, the magnetic flux leaves one side of the core to

CHAPTER 2. METHODS

35

Figure 2.2: Magnetic Flux Density and Flux Lines: detail. penetrate the other side with the same intensity in the horizontal axis, but the opposite one in the vertical. • This is true within the space occupied by the conductor itself. That is to say, this applies to the flux leakage. This hypothesis is tested by taking a large number of measuring points of the magnetic flux leakage in the conductors, and exporting the Bx and By values, as shown in Fig 2.4 and 2.5 into tables. The

36

CHAPTER 2. METHODS

Figure 2.3: Magnetic Flux Density: magnitude and vectors plot within the conductors. tables were then imported into Matlab, where they were separated by axis, and a statistical estimation of the data fit between the following values was made. If one sets the origin of coordinates at the center of the machines, then the hypothesis being tested is

CHAPTER 2. METHODS

37

Figure 2.4: Magnetic Flux Density: vectors plot within the conductors.

Figure 2.5: Magnetic Flux Density: vectors plot within the conductors, meshing quality test.

Bx (x, y) = Bx (−x, y)

(2.1)

By (x, y) = −By (−x, y)

(2.2)

The relevant Matlab code is referred to in the Appendix.

38

CHAPTER 2. METHODS

2.3

Winding Transposition

From the simulation results discussed in 2.1 and the theoretical background on how to handle transpositions in 1.9, the following observations can be made: • The magnetic field’s horizontal component presents an even symmetry along the x axis, relative to the middle plane 2.1. • Its axial/horizontal component presents an odd symmetry along the y axis, relative to the middle plane 2.2. Other than that, the magnetic field is very irregular and far from linear, especially as one draws close to the middle of the machine (see Fig. 2.3 and others in 2.2).

2.3.1

The Ideal Solution

Assuming that the field is constant along the z dimension (the one perpendicular to the plane in wich the COMSOL 2D simulation is made), one can propose treating each "run" that the bundle does across the top or the bottom of the core like one would a slot in a rotating machine, with the transition between top and bottom treated here as that between two slots is treated there. Fig. 2.6 shows a similar transition as one bundle leaves one layer and enters another in a lower position. According to the results found in [11], a transposition method consisting of a 360° process performed once for each pass above or below the core, with a mirror-flip transition in the "end" side, would practically eliminate all circulating currents. However, as seen later in 2.5.2, even winding a single bundle with all cables straight and parallel was impossible to in a timely manner do while keeping all cables properly oriented, within the limitations of this project. Doing so with the cables performing a full transposition in a uniform and orderly fashion was not at all within the realm of practicality. It should be noted that, for the solution to be entirely perfect, the cable should be laid on the core along the edge (the shortest side) to reduce eddy current losses. This is further discussed in 2.3.3.

CHAPTER 2. METHODS

39

Figure 2.6: Ending of a double layer of winding in a rotating machine, flattened

2.3.2

One Transposition per Run

Keeping the cables in the same order during one run and transposing them between runs would be a reasonable method if the magnetic flux were uniform along the length as well as the height. In that case, the simple transposition methods discussed in [12] would suffice in dealing with such a field. However, that is not the case: transpositions based on the logic of "each pair should spend an equal amount of time in each region" break down when the region’s field varies along the length. Then one needs to consider the symmetries of the field. By ’s odd symmetry for two-column vertical bundle configurations, each pair of cables’ φy is cancelled so long as the layers remain at the same height when they are in the same turn (at the same distance relative to the center), and undergo a mirror flip over the vertical plane. With more than two columns, however, this becomes less and less true as the number of columns increases. Bx ’s even symmetry As long as the bundles are in narrow vertical columns, the y field is cancelled so long as the layers remain at the same height and don’t cross.

40

CHAPTER 2. METHODS

2.3.3

The simplest solutions

Single-column and single-file solutions When attempting to construct the winding, it was found that multiple columns were not a viable construction method (see 2.5.2). When the bundle is designed to be a single vertical column, wrapped like a helix around the core, the vertical flux leakage cannot create circulating currents: the only remaining concern are the eddy currents. Conversely, when the bundle is designed to be a single horizontal file, wrapped around the core like a spiral, the horizontal flux leakage is similarly disarmed, leaving eddy currents as the only concern. Since the vertical field is estimated to be an order of magnitude larger than the horizontal, a vertical configuration was chosen for the construction. Single-transposition solutions Single-transposition solutions are the simplest to achieve: they require transposing the cables only once, when making the jump from the left core to the right one. However, when combining with symmetry effects in the flux, the results can be tricky. Nevertheless, the rule of thumb is as follows: • When faced with odd symmetry in the flux, mirroring the configuration across the symmetry axis has the best chance of roughly reducing the total flux across each pair. This entails performing no transposition between the cores. • When faced with even symmetry, doing the opposite is what is required, and a mirror transposition between the cores is recommended. This is achieved by folding the bundle around the Y axis. It is possible to combine both solutions by interlacing the windings as they are being folded. In the device built for this project, this could have been achieved by opening the funnel and interchanging the cables’ positions alongside the the machine’s X axis (which, in the rig, happens to be the vertical direction, because the bobbin is being wound on its side). In simple terms, open the rig, and trade the cables’ positions vertically, two by two.

CHAPTER 2. METHODS

41

However, combining both solutions undermines the cancellation of the vertical flux, as the vertical flux is not uniform along the vertical axis (on average, it drops significantly as one moves away from the core), and thus the flux each horizontal pair is exposed to is no longer cancelled. However, it is better than not doing it at all. Edge vs. Flat Bending the cable around the edge side is much more difficult and delicate to do well than bending it around the flat side. However, when it comes to avoiding eddy current losses, bending it around the edge side is preferable. The flux density in the winding is much larger in the vertical than the longitudinal direction, by an order of magnitude (see 2.1). For equal magnetic flux density, the losses due to eddie current are proportional to the transversal dimension of of the cable that is orthogonal to the magnetic field, squared. Here it is called the width. Given that the conductor’s flat side is twice as wide as its edge side, as shown in Fig 2.7, when the conductor is turned, from lying on its edge relative to the core, to lying on its flat instead, the eddy currents are expected to quadruple (2.6) [26].

Figure 2.7: Eddy Currents Due To Side

42

CHAPTER 2. METHODS

loss Peddy ∝ D2

(2.3)

0

loss Peddy ∝ D02

(2.4)

0

(2.5)

D = 2D loss Peddy =

2.4

loss 0 4Peddy

(2.6)

Winding Choice

Magnet wire is the winding material commonly used in electrical machines that needs tight coils of insulated conductors. There are a lot of different types of magnet wires with different kinds of shapes, sizes and heat properties. By reading into the price and physical differences between aluminum and copper magnet wires of different kinds together with the practical knowledge we gained during the construction work of the winding we would say that it would be smart to choose something that is square instead of rectangular. The aluminum strands we used were very pliable but at similar sizes even copper would be pliable Below are some given/wanted specifications from the thesis supervisor:

VLL = 750V ILN = 300A f = 4to40Hz Bmax = 1.7T Sf e = 0.0531m2 ΦB = B · S = 0.09027Wb While the power electronics system is rated for 1200V, the supervisor determined that 750V should be the voltage to be aimed for. Roughly 300A is what the power electronics setup for this prototype can handle. The voltage thereby generated is given by (2.7): Emf = −N

∂(Bmax ∗ Sf e ) ∂t

(2.7)

CHAPTER 2. METHODS

43

Therefore, the number of turns should be the one given by (2.8): N=

2.5

Emf Bmax Sf e 2π ∗ f

(2.8)

Winding construction method

When the transposition scheme was determined, the work on constructing the prototype began. This was not a straightforward process: it required the improvisation of intermediate technical solutions to put it into practice. As new obstacles were encountered, new necessities appeared, and new ways of overcoming them had to be put forward. A lot of careful thinking and precautions are natural when doing something for the first time, and these were the conditions the project was under. • The winding needed to be constructed around a bobbin. • Said bobbin needed to replicate the geometry of the magnetic core. Standard procedure is to construct the winding around a portable bobbin, and then coating the whole in resin or glue, so that they remain one solidary unit. This solidary bobbin is then used to carry the winding and slide it into the machine. However, in this case, it was given as a specification that the winding should be built in such a way that it could be incorporated into the machine without a bobbin to support it. The motive for this instruction was a drive to include as much aluminum into the space between the iron core structure as possible, in order to reduce electric losses, without concern for guaranteeing structural support to the winding in the way bobbins usually do. It was estimated that the metal structure of the motor would keep the windings in place well enough by itself. Therefore, instead of building a solidary bobbin for each core winding, there would be a assembly bobbin, around which each and every winding would be built, and then removed, to be stored until the time came to build the core. Said assembly bobbin will hereafter be known as the core-replica bobbin, or CRB, as wooden replica of the core was deemed as the best option originally.

44

CHAPTER 2. METHODS

2.5.1

Building the Core-Replica Bobbin

The construction of the CRB was already by default non-trivial, but the construction that was eventually executed was more complicated than it needed to be, out of a desire to increase its structural integrity. In 3.3, a suggested simplified solution is presented, and in 4.4.2, possible improvements are discussed. Design The design is the same as shown in Fig. 3.1, minus the supplementary augmentations to upgrade it to the motor core’s dimensions. The details are shown in the schematics in Fig. A.14. Materials The CRB was made out of wooden panels cut into rectangular shapes as seen in the technical drawings. This material was chosen because it was the most readily-available in the electrical department’s workshops, as well as the easiest to ’work on’. The thickness of the panels themselves didn’t matter much, so long as the external shape of the core was faithfully reproduced. Maintaining reasonably straight lines and surfaces along the sides was, however, quite important for structural integrity. Therefore, the type of wooden panel chosen didn’t matter much, so long as it was stable. The edges of the wood panels were not quite straight originally, and errors in tool manipulation could have perpetuated the problem. Therefore, it was important to proactively and parsimoniously determine the lines along which the wood panel should be cut. The accurate drawing of the perimeters on the timber was achieved through the combined usage of redundant drawing tools, similar to the kind used in paper technical drawing, but with characteristics specific to wood- and metal-working. The tools were: • an edge square (see Fig. A.1): it allows the drawing of lines perpendicular to the edge against which the broad section is held. • a straightedge ruler (see Fig. A.3): allows the drawing or confirmation of straight segments on flat surfaces, the measurement thereof, and can be a support for the flat square.

CHAPTER 2. METHODS

45

• a flat square: allows the drawing or confirmation of straight angles, and, slid alongside the straight edge, can be used to draw parallel lines. • a compass (see Fig. A.6): allows the drawing of arc circles and the confirmation of equal distances. • a caliper (see Fig. A.5): allows the measurement of distance between surfaces. The method described in Fig. A.6a complements the straightedge, while the one in Fig. A.6b complements the usage arithmetically dividing a length and then using a graded ruler to measure whenever segments need to be divided in equal lengths, such as when determining where to place the drill-holes. Then, using a table circular saw (Fig. A.12) to cut down the preexisting, very large wooden panels to a manageable size, then a bandsaw (see Fig. A.11 to further cut it down to roughly the exact desired dimensions. Any further irregularities would be sanded off using files or sandpaper. The aforementioned geometric methods were also useful for the purpose of drawing upon the surface of the base of the bobbin the positions where the side panels should go, as well as where the holes for the wood screws should be pre-drilled. This decision is further discussed in 3.3.3 and 4.4.2

2.5.2

Winding the bobbin

The following subsections describe in detail the construction of the winding cable bundle and winding procedure of the winding-coils. The following procedures to perform the winding were chosen with the desire to avoid cutting the winding in the middle, due to the difficulties surrounding Aluminum terminations. This was thought to make the process less complex, but it turned out to instead increase the complexity. Roughly 600kg corresponding to 28 000m of magnet wire were already bought and stocked prior to the start of this thesis work, Consequently, that was the material that had to be used. The magnet wire came divided in 12 wooden bobbins, each weighing around 50 kg. The magnet wire stocked was an rectangular 2x4 mm aluminum strand with and 0.1 mm polyester-imide/polyamide-imide coating rated 180◦C.

46

CHAPTER 2. METHODS

Figure 2.8: Magnet wire bobbins in wooden boxes ordered from Zheng Zhou LP Industry Co,.LTD.

Figure 2.9: Schematic view of the different section lengths of the winding The 20x2 edge wound configuration The bundle was made of two layers of twenty strands and having the total width of 84 mm and a height of 4.4 mm. Both the bundle and strands will be wound on the edge side in a pancake manner(bending on the short 2 mm side of each strand and on the 4.4 mm side of the bundle). This was due to the transversal magnetic flux being estimated a factor ten larger than the axial magnetic flux in the space where the winding shall sit as explained in 2.3.3. Each strand in the bundle was approx. 115 m long thus corresponding to the length of having it wound 76 turns around the CRB. The construction of the bundle and winding began by building forty bobbins, one for each of the 115 m strands. The material for the 40 boobins: • 8 pieces of 2.5 meter wooden 45mm x 45mm beams • 10 pieces of 1220x2440x3 mm hard-board for the circular sides Because of the large amount of bobbins to be made they were made a CNC milling machine able to take 1220x2440 mm boards was used as aid.

CHAPTER 2. METHODS

47

Figure 2.10: 8 circular parts milled and pre-drilled holes made for the six 40 x 40 x 55 mm spacers

Figure 2.11: Bobbins made for holding around 120 m of strand The result was a stand that was able to hold one bobbin in place while winding them with 115 m of magnet wire from the 50 kg manufacturer bobbin. A weighing scale was used instead of measuring the actual length of the strand. When the weight was increased to a certain point the bobbin had the amount of winding co-responding to the weight. [] When all the 40 strands were wounded the bobbins were put into a bobbin rack, separated into two rows holding 20 bobbins each, as seen in Fig. 2.12. The purpose of this contraption was to make it possible to feed each strand independently of one another. This was very important because of the way the bundle was to be wound, where the inner part of the bundle would unreel each turn less strand from its bobbin than the strands on the outer side of the bundle. Basically, the contraption was meant to permit this: if one strand is unreeled from the bobbin

48

CHAPTER 2. METHODS

Figure 2.12: Bobbin rack

Figure 2.13: Midway strand support rack, all the other strands should stay still. Because of the large width of the bobbin rack, it was necessary to be able to get the strands near each other, with the purpose of forming the 2x20 strand bundle for this a "node"/"funnel" contraption was designed as seen in Fig. 2.14

Figure 2.14: Funnel for bringing strands into the desired configuration

CHAPTER 2. METHODS

49

To further bring the strands together and keep them from crisscrossing without control, a device was improvised using zipties. Furthermore, colored zipties were added in sequence to help in keeping track of the cables, as seen in Fig. 2.15.

Figure 2.15: Ziptie device The bundle was now ready to be wound around the CRB, and, for this to work, the CRB was standing on a table that stood on wheels2.16, which made it possible to translate and at a fixed height on the horizontal plane as needed, and rotate it around the vertical axis (see Fig. 2.17 and 2.18). It was quickly seen that it was impossible to wind it because of the twisting of the strands each time a corner was turned around the CRB. The problem was so grave that there was a need to clamp the cables down on the bobbin using a wide beam in order to simply be able to turn the corners. The process was physically strenuous, as the bobbins needed to be turned around consistently. It was mentally stressful, as one had to constantly keep track of all cables’ positions; the ziptie device was very helpful in this regard, but, ultimately, utterly insufficient. All of this together made the process extremely time-consuming. Despite all those efforts and costs, the result remained inaccurate, and the cables couldn’t remain organized (see Fig. 2.19). The winding was therefore aborted. The conclusion reached was that what made the bending the most difficult was the fact that it was being done edge-side, that is to say, along and against the shortest side of the conductor. Any irregularities in the deformation were amplified and, due to the plasticity of aluminum, difficult to rectify. We therefore decided to rotate the strands 90° despite the fact that this would increase the eddy currents by a factor of four (see 2.3.3), it decreased the difficulty in the construction so much that it was deemed the only way to move forward.

50

CHAPTER 2. METHODS

Figure 2.16: Core replica bobbin on table with wheels

Figure 2.17: What the winding around the core could have looked like

Figure 2.18: Top view of the 20x2 attempt The 40x1 flat side bent configuration The flat side bent configuration however, turned out to be catastrophic, as can be seen in 2.20, 2.21 and 2.22; bending on the broadside when the cables were coming from the bobbins oriented towards edge required each of them to undergo a twist along the way. Despite strenuous efforts, to perform such a transition while simultaneously maintaining a consistent column organization turned out to be completely

CHAPTER 2. METHODS

51

Figure 2.19: The clamp does not help much unfeasible.

Figure 2.20: Top view of the 40x1 attempt

Figure 2.21: Side view of the 40x1 attempt

One conductor at a time Finally, the only viable remaining solution was to build the winding one conductor at a time. This necessitated abandoning the idea of having continuous cabling between both bobbins in a phase across the gap between cores, as it was not possible to move on to a next conductor while remaining linked to the previously winded conductor’s bobbin

52

CHAPTER 2. METHODS

Figure 2.22: The ziptie device at the 40x1 attempt without carrying said bobbin along with the CRB; it would be neither practical nor sensible to carry forty bobbins of winding under the table. The solution is explain in thorough detail below in the Results section.

2.5.3

Damage to the Insulation: Prevention and Correction

During the construction, the winding was damaged on several occasions. As this was in the middle of the winding, there was no possibility of using common shrinking tube, and abandoning a whole winding was deemed excessive. A solution was found in dielectric tape, as shown in 2.23; the data-sheet for it is in A.12. Rated 7.5kV, it was deemed sufficient.

Figure 2.23: Dielectric Tape The enamel was easily damaged when being handled by pliers and

CHAPTER 2. METHODS

53

other hard metal tools. However, manipulating it with them was indispensable in orienting it properly. In order to avoid further damaging the enamel, and in the absence of gentler tools (see 4.5), a solution was found in covering the pliers’ tips with shrinking tube (see 2.24). In retrospect, a simpler solution, such as wrapping them with tape, might have been adequate.

Figure 2.24: Pliers With Shrink-Tube Tips

2.6

Stripping The Wires

Ends of winding-coils are to be connected electrically to power electronics and each separate strand in each winding-coil will be joined at the place of the mirror transposition. Because of this it is very important to strip the enamel from the wires’ terminations to a specific length determined by the lengths of the Al-Cu cable lugs and the Al-Al connection lugs used. Because of the large number of wire strands needed to be stripped (768 strands, assuming that the design developed with a 256 m2 winding cable will be used for all coils, an effective solution was needed to do the stripping within budgetary and time constraints. First, manual/mechanical approaches were tested was. Filing the enamel with various files proved to be a very hard and time-consuming job, and because the winding threads are relatively thin and fragile, it didn’t take much to scuff or bend the aluminum. Sandpaper didn’t work because the space between the grains was quickly clogged by enamel dust, requiring constant interruptions to clean the sandpaper or replace it. Furthermore, it was very time consuming and demanding work.

54

CHAPTER 2. METHODS

Various power tools available in the department were tested, but none of them turned out to improve or accelerate the process. It stood to reason that there would be special machines for stripping the enamel from magnet wires. While there were no such machines in the department, a company was found that builds special machines for this purpose, known as the Eraser Company. They have a product that is suitable to the wire here used; a portable and airdriven stripper named PD9, costing 1440 USD + accessory. This was outside the budgetary bounds of the project. While different manual/mechanical ways to remove the insulation were being tried, chemical solutions were being simultaneously tested, by having small 5 cm samples submerged in various solvents. The following chemicals that were tested without any success in stripping the magnet wires: Acetone, Xylene, Toluene, Ethanol, and Methane. The chemistry department at KTH were then sought for their expertise and their equipment in order to acquire and test some of stronger and more dangerous solvents, of a type similar to those that are used in manufacturing the enamel itself. There, success was finally found. A solvent that proved to be effective and that the chemistry department had in stock was Dichloromethane. After a couple of hours bathed in the solvent (as seen in Fig. 2.25, most of the enamel swelled and loosened from the aluminum wire. However, left behind was a thin layer that did not go away even after days in the solvent, as Fig. 2.26 shows. With the help of a suitable steel wool together with a gel for removing furniture paint1 and manual work gave the sufficient final result. The stripped wires were then cleaned with isprophyl alcohol and a soft rag. The final result is shown in Fig. 2.27 To be able to strip the final two machines with this method it was estimated that around 5 liters of dichloromethane would be needed. At a price of 289 SEK per 2.5 l, this was deemed to be perfectly within budget.

1

Libero Fine Wood Stripper ™

CHAPTER 2. METHODS

55

Figure 2.25: The magnet wires bathed in Dichloromethane

Figure 2.26: Residual Coating Layer

Figure 2.27: The final result is a stripped wire as can be seen compared to the wire still having the black enamel coating

56

CHAPTER 2. METHODS

Figure 2.28: Al-Cu Bundle Lug

2.7 2.7.1

Aluminum Conductor Terminations AlCu Bundle-Electronics Termination

The connection between the bundle of aluminum conductors and the copper bus bar feeding into the power electronics presents a particular challenge. To build such a connection reliably, professional expertise is required. Thankfully, this project has benefited from the help of Elpress, a Swedish company specializing in crimping technologies, and with considerable expertise in AlCu bi-metallic pin and ring terminals. Given the total aluminum cross-section in the expected terminals was 40 × 2 × 4=320mm, they provided a 240mm lug with a frictionwelded AlCu interface, which provides an excellent connection. The aluminum conductor is pressed from a recommended rectangular 4 × 10 matrix configuration into the smaller, circular 320mm cross-section with the help of a ’round-shaping tool’ (rundformningverktyg). Then it is inserted into the lug, the inside of which is lubricated, and the termination is then crimped with an appropriate crimping tool. For further reference, see Ap. A.6 and contact Elpress. Given that the number of wires in a bundle ended up being reduced from 40 to 32, the present solution is no longer valid, and the dimensions of the lug and the corresponding presses need to be updated accordingly.

CHAPTER 2. METHODS

2.7.2

57

Al-Al Wire-Wire Connection

The winding and transposition solution that was ultimately chosen requires cutting the wires between the windings, and connecting them again. Connections of aluminum to aluminum are non-trivial, as even without the issue of galvanic corrosion and bad interface, there’s the insulating layer of aluminum oxide and the creep problems between aluminum wires. After looking into brazing solutions, contacting the leading companies in Sweden, which ABB hire as experts, they explained that soldering Aluminum is a high-skill endeavor, and recommended against attempting it without skills. The catalogues of distributors of electric crimped connections, such as Elfa, contained no few Aluminum-exclusive connectors with 8mm cross-sections, and none in stock. While there were some Aluminumdedicated 16mm lugs, they were likewise not readily available, and fairly expensive: at a rate of roughly 100 SEK/unit, each pair of windings would require around 3200 SEK to connect to each other. However, considering that this machine was only a prototype, and not intended to run continuously or in the tough environmental conditions of its intended maritime use, it was determined that, for the sake of expediency, a simple joint using a crimped copper lug would suffice. Nevertheless, tests were performed to verify that the connection had an appropriately low resistance. As the resistance in such a cable connection is very low, a simple multimeter is not enough. Instead, the tests were performed using first an LCR link (see A.9) and later a micro-ohmmeter (µΩ-meter, see A.10). On the LCR link (see Fig. 2.30), the measured resistance is estimated at 11mΩ: that amounts to an increase of 3 to 5% in the overall resistance. For 30 conductors at an expected 5.7A RMS, the expected losses at the connection would aggregate to 11 W. In a machine rated for 180kV A, that is in the order of 1 × 10−8 : insignificant. On the Microohmmeter (see Fig. 2.31), running a 30A current through the connection registers merely a 7.8mV voltage drop, the resulting resistance is estimated at to be of 0.26mΩ. The resulting expected losses would be even more insignificant. It is difficult to get accurate thermal radiation observations from the highly reflective surface of the lug and conductor. In order to observe

58

CHAPTER 2. METHODS

CHAPTER 2. METHODS

Figure 2.30: LCR-bridge Test

59

60

CHAPTER 2. METHODS

Figure 2.31: Microohmmeter Test

CHAPTER 2. METHODS

61

Figure 2.32: Heat Losses the temperature change in the connection as the current traversed it, a small black strip was glued to the lug, as can be seen in Fig. 2.29. Then a thermal imagery camera (see A.11) was used to estimate the temperature of the lug when subjected to 30A of current. As shown in Fig. 2.32, the temperature in the surface of the lug is estimated to rise to 37◦C, which suggests a rating of 5A[27].

Chapter 3 Results 3.1

Material

3.1.1

Materials

Raw Materials For one winding: • 32 strands worth of magnet wire, cut in 115 m lengths • 32 tubular connection joints Consumables • 2L of dichloromethane1 . • Libero Fine Wood Stripper™ • 1 roll of steel wool. • 4x32=128 zip ties to tie the loose ends in place. • Tape: masking tape should be enough. One roll of dielectric tape as well. • Drill bits, of a smaller diameter than the screws.

1

The KTH Organic Chemistry department can help in acquiring it affordably

63

64

CHAPTER 3. RESULTS

Tools • 1 stand for the conductor bobbin. • 1 stand for the winding bobbin. • 1 padding for the cable not to slack and drag on floor. • 5 metal strips (roughly 1 for each 5 turns). • Cardboard • 1 band-saw. • 1 stationary circular saw. • 1 metal compass • 1 straight angle • 1 large caliper. • 1 file. • 1 stationary drill. • 1 countersink drill bit. • Clamps. • Crimping tool

3.2

Construction: Materials and Methods

The result of the construction work is a functional winding assembly line. Readers are invited to modify and optimize it according to their circumstances. Suggestions to this effect are covered in 4.4.

CHAPTER 3. RESULTS

3.3 3.3.1

65

Bobbin Construction The Core-Replica Bobbin

The winding is constructed around the bobbin, to be later transferred into the electrical machine. The mold-bobbin is originally designed to reproduce the shape of the metal core of the generator. The schematics for the relevant dimensions of the core and all the dimensions needed to construct the bobbin are given in While the motor core is identical to that of the generator in nearly every dimension, it differs crucially in that it has a wider cross-section. While an entirely new bobbin is not necessary, two extra plates (and, optionally, four extra columns) of 25 mm thick will have to be added when the time comes to build the motor’s windings (in Fig. 3.1, they are the pale ones). These can be built to be removable with appropriate usage of screws.

3.3.2

Raw Materials

These are the materials that will be an integral part of the bobbin itself. • Wood planks of consistent width and sufficient sturdiness. • Screws of appropriate length and diameter. • Tecbond 260 glue or equivalent. • Masking tape: to cover the surfaces of the bobbin so that any adhesives used on the winding do not flow into the bobbin. The extension for the motor bobbin will require: • 2 additional planks of wood of 25mm thickness each, or equivalent • 4 additional screws Consumables The materials that will be used for the construction, don’t remain with the bobbin, but have a non-negligible chance of breaking or otherwise ending up diminished or replaced in the process.

66

CHAPTER 3. RESULTS

• Drill bits: they should be chosen to have a diameter congruent with that of the drill itself. They are easy to break, so it’s good to have several exemplars of the same. • 1 countersink drill bit. • 1 screw bit. (Fig. A.10) • 1 pencil Tools Items that remain unaffected by usage and can be reused for other things later. • 1 band-saw. • 1 stationary circular saw. • 1 metal compass, optionally. • 1 straight angle. • 1 large caliper. • 1 file of appropriate grain for the chosen wood. • 1 stationary drill. • 1 ruler. • Ratcheting and spring Clamps (Fig. A.7)

3.3.3

Ideal Bobbin Construction Method

The fundamentals in constructing the Core Replica Bobbin are shown in schematics A.14 and A.13. The base needs to be at least as large as the expected maximum footprint of the bobbin. While it’s not necessary for it to match its shape, there should be a clear marking of said footprint, either by drawing it or by scratching/engraving it. The proposed design involves two redundant ways of ensuring the rectitude and structural integrity of the assembly:

CHAPTER 3. RESULTS

67

Figure 3.1: Final Core Replica Bobbin Design the structural cross it is formed composed by the three wooden panels in the center of the bobbin. the lid it is formed by one rectangular panel placed on top of the bobbin. As long as the structural cross is maintained, the lid is unimportant: its only role is to hold the extra lengths of cable of every winding that need to be stored above it while the bobbin is being wound, as long as the bundle isn’t being wound all at once. Therefore, it can be made of any flat material. If there’s leftover wood available, it can be cut out of that. Otherwise, a sheet of fiberglass, aluminum, or even simple cardboard, may well suffice. If instead one chooses to dispense with the cross, the lid needs to be sufficiently tough and rigid itself. Setting aside supplementary wood for this purpose is therefore recommended. The final bobbin, as shown in 3.1, can be used for both the generator and the motor’s cores (Fig. 3.2 and 3.3). In its base form, it reflects the dimensions of the generator core, and includes a mark-

68

CHAPTER 3. RESULTS

Figure 3.2: Electrical Generator Iron Core ing showing the limits of the space the generator winding can occupy. As the only difference between the motor and the generator’s core is its thickness, the bobbin can be easily modified to be used for motor windings, by adding wooden elements of the appropriate thickness (25mm) to the system. It should be noted that only the large plates are strictly necessary for the winding of the bobbin: while the four extra square columns added to the short end panels guarantee that the bobbin has the same outer perimeter as the motor core, the winding is not expected to lie against those end sides. Rather, it is expected to bend back around away from that part, most likely according to the stadium-shaped design, which is strongest recommendation. The existing bobbin was not built with this modification in mind, and so the base is almost wide enough, but not quite: there’s a distance of 120mm between the edge of the base and the side panel in the prototype bobbin (see Fig. 3.4), when the distance required according to the schematics is 126.6 mm. For those wishing to continue working on the project, it should be possible to add an extension of 6.6mm or

CHAPTER 3. RESULTS

Figure 3.3: Electrical Motor Iron Core

69

70

CHAPTER 3. RESULTS

Figure 3.4: Present Width of the Bobbin Track more by using the cardboard. The outer-panel wood planks and the bottom can be of any thickness so long as the outer surface sits at the appropriate position to reproduce the outer shape of the core. However, note that using smaller thickness will require increasing the length of the cross planks: the arms of the cross should be increased by the same amount, and the center of the cross by the twice that. Note that, in the prototype, the wood planks used happened to be of 25mm thickness, which is the thickness of the wood used in the construction of the existing bobbin, and which happens to be the very same thickness increase that is required to upgrade the generator template to that of the motor.

3.3.4

The Stadium-Shape

A stadium shape makes it much easier to bend the bobbin, as it dramatically increases the curve radius that the winding must go through. The straight segment at the sides of the stadium is also a slight problem in that it can be difficult for the wires to follow a straight line as easily as they could bend around a large curve. It also helps maintain the tension of the cardboard augmentation over the long side. For maximum ease of construction, the bobbin was augmented with a cardboard filling that gave it the desired shape, as seen in Fig. 3.5.

CHAPTER 3. RESULTS

Figure 3.5: Oval Cardboard Filling

71

72

3.4 3.4.1

CHAPTER 3. RESULTS

Winding Construction Final and Working Winding Method

Figure 3.6: Final Execution of the Winding The bobbin was, as usual, fixed to the table using two clamps, diametrically opposed relative to its center. However, its height was raised using a hollow plastic box, which made it more comfortable to perform the winding, and which allowed the storage of the winding "beginnings" within itself, with the "endings" being stored atop the bobbin itself. The hollow box had the added benefit of increasing the distance between the bottom of the metal bars that formed the backbone of the clamps, and the ground, reducing the chance of accidents and interferences. To address the concern that the cable might slip from its position and cross with itself or the winding, each time a cable finished winding, forming a layer or coil, the latter would be covered in tape at regular intervals, as seen in 3.7, and, especially, near the top, where there was nothing to hold the cable flat and where discrepancies in height were the most common. To keep track of the number of turns at any given time, leftover iron core lamination strips were placed at intervals of 5 widths of cable. They were deemed thin enough to perform this function without

CHAPTER 3. RESULTS

73

affecting significantly the height that the windings could reach. The cardboard inner lining made it easy to support them in position from the first turn. To ensure that their relatively hard and sharper edges would not damage the cable’s enamel, as they in fact did on a couple of occasions, they were covered in tape (see Fig. 3.10). To keep the cable coming vertical, that is to say, on the broadside, the funnel was pushed aside and kept there by mechanical means. At the same time (see Fig. 3.11), a special glue was used to guarantee that, at the beginning and end of the winding, each cable would be solidly laid parallel to the previous one; Tecbond 260 A.7. The glue also helped ensure the solidarity of the top and bottom layers, removing any chance of the winding’s inner layers dropping down under their own weight like a released spring. A paper plate was kept to accumulate the glue gun’s frequent and abundant leakings while idle. Before each cable was wound, it was cut and extended (dragged from its storage bobbin) to a sufficient length that would allow a comfortable margin of manipulation when the time came to build the connections in the generator. Then it was fixed to the side of the bobbin or glued to the side of the previous cable, so that it would maintain an ideal beginning position. After that, the supplementary length was wound around a small empty bobbin to give it a regular shape, and stored inside the hollow box supporting the bobbin. Upon completion of the winding, the CRB was flipped over and the winding was easily removed. Then, it was tested for width, as shown in Fig. 3.9, given that this was the most critical dimensions to ensure it fit in the generator core alongside other windings.

74

CHAPTER 3. RESULTS

Figure 3.7: Taping the first coil

Figure 3.8: Winding removed from CRB

CHAPTER 3. RESULTS

75

Figure 3.9: First part of the winding removed and width-checked, width check an important dimension not to exceed its tolerance

76

CHAPTER 3. RESULTS

Figure 3.10: Tape-Covered Lamination Strips

CHAPTER 3. RESULTS

Figure 3.11: Glue Gun and Funnel

77

78

3.5

CHAPTER 3. RESULTS

Cable-Stripping

In the absence of a dedicated tool, the cable terminations needs to be stripped using dicloromethane to remove most of the enamel, and a generic paint stripper to remove the remaining residual coating, as was found in 2.6. The paint stripper is easy to acquire in retail shops: Libero Fine Wood Stripper™works just fine with the help of some steel wool. The dicloromethane, however, is a more specialized chemical product. A company named Fisher Scientific sell the solvent, identified under article number 10458210: "Dichloromethane, 99+ percent, Extra Pure, Stabilized with Amylene, SLR, Fisher Chemical." The price per bottle of 2.5L was, in Aug. 2018, 296 SEK. There is probably a discounted price if ordered in the name of KTH. Dicloromethane is a potent and dangerous substance and needs to be handled with care. In manipulating the solvent, it is important to make sure to work in a safe environment, as dichloromethane is a suspected carcinogen. Minimum precautions are adequate ventilation (to avoid inhalation, exposure limit is 70 ppm/15 minutes) and to use personal protective equipment (to avoid skin, eye and clothing contact).[28]

Chapter 4 Discussion and Conclusions 4.1

Simulation

In the COMSOL model of the machine, there were several simplifying assumptions made. There is considerable work to be done if one would wish to extract more faithful results and test out possible transposition schemes in simulation before building them in practice. • Splitting the conductor could have been split into parallel strands, and bundles in series, linked according to each chosen transposition method. Then the current distribution and the losses could be observed and compared with the baseline. • Changing from a series of stationary simulations that identify a phase shift in the current with a position shift in the translator, to a time-dependent simulation that has the current be caused by the movement of the translator, rather than imposed as a simulation pre-condition. • Building a 3D model of the machine, windings and all. It would be useful to obtain the parameters necessary to perform a full analytic model allowing a reasonably quick study of the different transposition schemes, as done in [11]. Among such parameters would be the flux linkage in each strand, and therefore each conductor’s self-inductance as well as the mutual inductance between each pair of conductors.

79

80

CHAPTER 4. DISCUSSION AND CONCLUSIONS

Other data to look into with separate windings would be the dynamic forces the flux leakage would subject them to, and how the machine’s behaviour could be affected by the circuit. One could also simulate the machine’s thermal behavior. [11] seem to have gotten good results using a software called MagNet®: the electrical machine division at the department of electrical power engineering could consider acquiring this software.

4.2 4.2.1

Winding Choice Aluminum or Copper

There is an ongoing debate on the use of aluminum vs copper magnet wires in electrical machines, with advantages and drawbacks depending on the application. Aluminum provides significant advantages in turns of weight and cost (see Table 1.1). However, in this project, the use of aluminum led to some difficulties in the construction process 2.5.2. Its softness and plasticity made it so that any irregularities, rough edges, or bends, would cause deformations and damages that it was possible to mitigate but not eliminate with the means available to the project. These slight damages accumulated over each turn, causing the winding to have a smaller fill factor than it would if the material had been more elastic. Aluminum’s softness, along with its tendency to form a resistive film of oxide when in contact with air, and the galvanic corrosion and contact problems inherent in any interfacing it may need to do with copper conductors, presented further challenges. 2.7.

4.2.2

Cross-Section Shape

h While in theory a flat winding allows for better fill factor, in practice, a round profile for the magnet wire may be the easier to use because of not having issues with unwanted twisting of each separate strand. Using a round copper magnet wire instead of using the aluminum flat (rectangular) magnet wire here used us could drastically simplify the construction process.


4.2.3

81

Hollow Conductors

A rather unusual technology that might be worth looking into are hollow magnet wires, being traversed with cooling fluid, might allow for the possibility of a higher performance with less conductor material. Besides the immediate advantages of inside cooling, the advantage of using such a fluid is that it can be chosen so that it evaporates whenever the machine is working at a certain degree of overload, allowing the generator to more easily handle the sudden bursts of power that come from extreme waves. It should be noted that said technology only reaches its maximum usefulness in high-frequency applications, such that the skin depth is comparable to the hollow conductor’s tube wall thickness. and in situations with high current de

4.2.4

Current crowding effects.

Since the cable strands are only 2 mm, the current crowding effects should be very small. Certainly, given how small the conductors are relative to the skin depth, as seen in 1.8.3, it might not be worth the time to investigate the matter further. However, a fairly comprehensive paper was written on the topic[29], and, if the reader attempts the more complex simulations suggested in 4.1, it may be advantageous to check on the current density distribution in the windings and whether it doesn’t change significantly within each strand and from center to periphery of the winding. An effect similar to the racetrack effect can happen if parallel stranded windings are of different strand lengths: the shorter ones have less resistance, and, as they are subjected to the same voltage, they will carry more current. This is, however, not the case with the transposition pattern here chosen.

4.2.5

Insulation

Given that the winding functions at a relatively low voltage of around 750 V, the insulation problems are not the ones one would typically find in the more common 11 kV turbo-generators, nor are standard 230V practices sufficient. Although the winding’s enamel is rated for a sufficiently high voltage, no further consideration was given to the problem of insulation, and this matter can be crucial. A breakdown of the enamel due to friction, vibration, or over-voltage, might cause a

82


short-circuit and burn the whole machine. The problem is well worth examining.

4.2.6

Safer Handling of the Winding

Despite strenuous efforts, the winding got damaged on several occasions. Though dielectric tape was a reasonable stopgap, it may be useful to study the vulnerabilities of the enamel and, in particular, grade it in Mohs’ hardness scale, as well as establishing an awareness of the hardness of the tools around it, so as to ensure which ones can be allowed to be in contact with it.

4.2.7

Cable-stripping

The current solution is very cost-effective, but relatively dangerous. Perhaps there is some sort of cheap machine that could be bought, or built using available materials and ingenuity.

4.3

Transposition

The transposition scheme here presented is clearly not the best option possible, only the best option that the authors could ideate and execute within their time and budgetary constraints. Its value should be challenged, and better alternatives should be sought. For instance, while it is difficult to wind a full column of strands simultaneously in flat, it might be practical to wind a double column by doing so layer by layer, two by two, especially once the bobbin’s edges have been softened into the stadium/oval shape. This could reduce losses due to eddy currents in the flat of the winding by a factor of four. However, unlike the single-column method, it could allow the transversal component of the flux leakage to create a circulating current. Due to the odd symmetry of said component, the flux could cancel out by itself, at the expense of not performing any vertical transpositions (moving conductors up or down a position in the bundle) (see 1.9 and 2.3), but that would leave the longitudinal leakage flux to operate freely.


4.4 4.4.1

83

Construction Connections and Resistances

The results of the tests on the Al-Al lugs showed a degree of discrepancy of two orders of magnitude (see 2.7.2). The dramatic difference between these results (two orders of magnitude) suggests inaccuracy and merits further investigation, until a coherent measurement can be obtained, or, at least, until the reasons it’s difficult to get are properly established. It might also be worth it to test the behaviour of the connection over time. It could be the case that connecting the individual cables this way is actually cost-effective and reliable. Furthermore, it could be worthwhile to test the resistance of each individual winding, as well as the terminal-to-terminal resistance of the two of them connected. Given that the strands are now independent, having been cut in the middle, it becomes possible to reconfigure them at will to include as many conductors in one bundle as is desired. This may invite the usage of a screw-type cable terminal as opposed to the current crimp type. The reader is encouraged to research connection methods between cables and to test whether it is possible to reduce the voltage drop relative to the solution here presented. The matter of galvanic corrosion needs to be properly addressed, ideally within budget limits.

4.4.2

The CRB Construction

There was a particular effort to install the screws in sufficient number and evenly spaced. Unfortunately, said effort might have been counter-productive, as the screws may have ended up causing the panels to bend out of the desired positions. This may be either be due to the pre-drilling holes penetrating the material at an angle, or it may be because the surfaces were not as straight and even as was intended. It is tentatively suggested that the reader try to use fewer screws or even dispense with them altogether in favor of simple glue. Furthermore, the current design may not be ideal: it is time-consuming and complex, and the resulting bobbin is quite heavy and unwieldy. It is suggested that the reader find ways to make it simpler, lighter, and faster to build.

84


Geometry and Graphic Calculations When it comes to making the graphic calculations and drawing all the relevant elements on the wood, the reader is welcome to familiarize themselves with basic engineering drawing techniques[30] and basic geometry[31][32]. Tolerances and removal Not being able to use a bobbin to carry the winding, there was a need to make space between the permanent bobbin and the winding to facilitate removal of the completed winding. To do so, we cardboard was employed, which is deformable and cannot guarantee dimensional consistency between replications of the winding. The cardboard was used because of a desire to ensure that the bobbin fits around the core;. This can be mitigated by measuring the dimensions inside the winding for comparison with the dimensions of the cardboard construct around the winding. Extension to the stadium shape On the topic of cardboard, and regarding the extension of the bobbin to a stadium shape, the reader is encouraged to find a better way to build said stadium shape than imprecise cardboard. Adding a lid A common problem during the previous windings was that the top layer was open, without a ceiling to stop it. While this made removal easiest, it caused time-consuming concerns regarding the cables slipping across each other, ending up at irregular heights, or otherwise getting disorganized, and necessitated careful application of adhesive tape and fluid to ensure good behaviour. A removable lid of sufficient size, perhaps one using drills or pins, could help deal with this problem handily. Spacing of the Spacers The core lamination strips used to keep track of the number of turns of a cable being wound are stacked vertically. Perhaps this arrangement is sub-optimal, as, small though their effect on the column’s total


85

height is, placing them all along the same vertical maximizes said effect. It would perhaps be advisable to try staggering them alongside the side of the winding. Solidary bobbins Alternately, the paradigm might be altogether wrong, and it could make sense to build solidary bobbins that would be bound to the windings permanently. The reader is encouraged to seek to build such a bobbin to carry the winding in, and verify its viability within the project.

4.5

Instrumental improvements

Budget constraints have severely restricted the options available to this project when it came to building the bobbin. Had more resources been available, other tools might have been used. The following are a series of suggestions regarding the tools to be used. The stands of the bobbins The most appropriate kind of bearing or support for the supply bobbin is yet to be found. In the strand by strand method of winding, it becomes unnecessary to pre-load intermediary bobbins: one can use the supplier’s bobbin directly. However, it is heavy, and needs to be well-balanced, and move with just enough friction. On the one hand, while one winds up the CRB, the supply bobbin’s movement should not be so light that it keeps on unwinding on its own and creating unwanted slack and bends in the cable. On the other hand it shouldn’t be so heavy that it’s too difficult to turn. Clamps If one is to keep using a table on wheels instead of a support that can actually rotate on its vertical axis, it would be useful to find a good replacement to the current type of clamps. They consistently get in the way of the winding during roughly the first ten turns, causing irregularities in the shape of the cable and requiting unnecessary care and attention from the operators.

86


Special pliers If one still wishes to bend the wire while keeping it straight, in an artisanal way, several options present themselves, as can be borrowed from the jewelry industry. Nylon-jawed Plier : regular and thin-nosed, are coated with a thin nylon layer and can flatten and harden wire without nicking or changing the diameter of the wire, and can also be used for removing bends and kinks[33]. Parallel or channel-type pliers are useful because the jaws open and close parallel to each other, unlike ordinary pliers. The jaws are smooth, but grip well, as they hold along their length rather than at just one point. These pliers are good for straightening bent wire or for bending angles.[34] Double Cylinder Pliers: to give the wire a specific radius curve. Note that, if things have reached the point where using such a tool becomes viable, one should consider whether the best method is being used, as such minute corrections are only useful when the operation becomes very complex and time-consuming. Adhesives and Insulation Glue, resin, lacker: there should be a better way of holding the bobbin together than just covering part of some of the layers in masking tape. Winding Operation The reader is otherwise encouraged to research methods for winding the cable flat in a less time-consuming way, as well as wind all the cables together simultaneously in a practical way. The appropriateness of a proper winding machine is to be investigated. Cable Height Management Device Regarding the current winding configuration proposed in the results (see 3.4), a frequent problem was that the cable was being fed at a constant height by the stand, while its height in the bobbin changed continuously. This led to constant readjustment. The resulting bendings


87

and irregularities damage the fill factor and slow down the winding process. If the bobbin were placed on a fixed stand, it could be relatively simple to develop a mechanical device that would use the bobbin’s rotation and a system of pulleys to lift the cable continuously during each turn so that it is fed at the right height always. As long as the process between the end of winding one conductor and beginning with the next one is not automated, it would be preferable for resetting of the height to be manual.

4.6

Conclusion

The magnetic flux leakage of an electrical machine is a complicated phenomenon. Determining the best way to nullify the induced voltage from said flux leakage in the closed loops of parallel conductors by transposing them is challenging at the best of times. Likewise, while aluminum has a low cost per weight, the considerable difficulty in providing good aluminum interfaces and terminations can more than offset that economical advantage. This is all the more the case when the material means available to execute the transposition are limited and force sub-optimal options. Building a winding, with or without transpositions, is a complex task to be undertaken with care, but said limitations can make it insurmountable. Nevertheless, it is possible to find a least bad solution. Hopefully this thesis work will facilitate the completion of this prototype, which in turn will help pave the way towards a more sustainable future. In the meantime, two students had a wonderful opportunity to put some of their knowledge in practice, and acquire a humbling experience in solving a practical electrical power problem.

References [1] Renewable energy statistics 2017. [Online]. Available: https:// irena.org/publications/2018/Jul/Renewable-EnergyStatistics-2018. [2] Backoffice-CMS, Oes annual report 2017. [Online]. Available: https: / / www . ocean - energy - systems . org / publications / annual-reports/document/oes-annual-report-2017/. [3] A. Uihlein and D. Magagna, “Wave and tidal current energy – a review of the current state of research beyond technology”, Renewable and Sustainable Energy Reviews, vol. 58, pp. 1070 –1081, 2016, ISSN: 1364-0321. DOI: https : / / doi . org / 10 . 1016 / j.rser.2015.12.284. [Online]. Available: http://www. sciencedirect.com/science/article/pii/S1364032115016676. [4] K. Gunn and C. Stock-Williams, “Quantifying the global wave power resource”, Renewable Energy, vol. 44, pp. 296–304, 2012. [5] F Birol, Key world energy statistics, 2017. [6] G. Mørk, S. Barstow, A. Kabuth, and M. T. Pontes, “Assessing the global wave energy potential”, in ASME 2010 29th International conference on ocean, offshore and arctic engineering, American Society of Mechanical Engineers, 2010, pp. 447–454. [7] R. J. Nicholls and A. Cazenave, “Sea-level rise and its impact on coastal zones”, science, vol. 328, no. 5985, pp. 1517–1520, 2010. [8] A. Hagnestål, “A highly efficient and low-cost linear tfm generator for wave power”, in EWTEC 2017: the 12th European Wave and Tidal Energy Conference 27th aug-1st Sept 2017, Cork, Ireland, 2017. [9] A. Hagnestål, “On the optimal pole width for direct drive linear wave power generators using ferrite magnets”, Energies, vol. 11, no. 6, p. 1356, 2018.

89

90

REFERENCES

[10] A. Hagnestål, “A low cost and highly efficient tfm generator for wave power”, in The 3rd Asian Wave and Tidal Energy Conference AWTEC 2016, 2016, pp. 822–828. [11] P. Roshanfekr Fard, “Roebel windings for hydro generators”, 69, Master’s thesis, 2007. [12] T. Wall, “Development of the winding geometry for an efficient wave power generator”, PhD thesis, 2017. [Online]. Available: http://urn.kb.se/resolve?urn=urn:nbn:se:kth: diva-214754. [13] T. Gerasimenko, P. Aleksandrovich Polyakov, and I. Evgenyevich Frolov, “Elimination of current crowding problem in flat conductors bent at arbitrary angles”, vol. 47, pp. 41–46, Jan. 2014. [14] S. Datta, Computing total normal flux on a planar surface, Jun. 2014. [Online]. Available: https : / / www . comsol . com / blogs / computing-total-normal-flux-planar-surface/. [15] Biezl, File:skineffect reason.svg, Jul. 2008. [Online]. Available: https: //en.wikipedia.org/wiki/File:Skineffect_reason. svg. [16] A. v. A. Vorst, RF/microwave interaction with biological tissues, eng, ser. Wiley Series in Microwave and Optical Engineering. Hoboken, N.J.: John Wiley & Sons : IEEE Press, 2006, ISBN: 1-28034967-0. [17] D. W. Rankin, “Crc handbook of chemistry and physics, 89th edition, edited by david r. lide”, Crystallography Reviews, vol. 15, no. 3, pp. 223–224, Jul. 2009, ISSN: 0889-311X. [18] Siemens dielectric constants guide, Dec. 2007. [Online]. Available: https://www.automation.siemens.com/w1/efiles/ feldg/files/Downloads/7ML19985LB01.pdf. [19] Committee on data for science and technology (codata) value: Electric constant, 2014. [Online]. Available: https://physics.nist. gov/cgi-bin/cuu/Value?ep0. [20] C. Moosbrugger, ASM ready reference. Electrical and magnetic properties of metals, eng. Materials Park, OH: ASM International, 2000, ISBN: 1-68015-956-9.

REFERENCES

91

[21] H. Uppili and B. Daglen, Bi-directional giant magneto impedance sensor, Aug. 2013. [Online]. Available: http://file.scirp. org/Html/3-1510206_36471.htm. [22] Chetvorno, File:proximity effect.svg, May 2017. [Online]. Available: https://commons.wikimedia.org/wiki/File:Proximity_ effect.svg. [23] P. Ponomarev, I. Petrov, N Bianchi, and J Pyrhönen, “Additional losses in stator slot windings of permanent magnet synchronous machines”, May 2015. [24] K. Takahashi, M. Takahashi, and M. Sato, “Calculation method for strand current distributions in armature winding of a turbine generator”, eng, Electrical Engineering in Japan, vol. 143, no. 2, pp. 50–58, 2003, ISSN: 0424-7760. [25] C. R. Sullivan, “Optimal choice for number of strands in a litzwire transformer winding”, IEEE Transactions on Power Electronics, vol. 14, no. 2, pp. 283–291, 1999. [26] A. Hagnestål, personal communication, May 10, 2018. [27] S. Hedin, personal communication, Aug. 10, 2018. [28] B. Timmer, Re: Stripping aluminum, personal e-mail, Aug. 2018. [29] D. Gerling, “Approximate analytical calculation of the skin effect in rectangular wires”, in Electrical Machines and Systems, 2009. ICEMS 2009. International Conference on, IEEE, 2009, pp. 1–6. [30] K. Rathnam, A First Course in Engineering Drawing. Springer Singapore, 2018. [31] A. Goddijn, M. Kindt, and W. Reuter, Geometry with Applications and Proofs Advanced Geometry for Senior High School, Student Text and Background Information. SensePublishers, 2014. [32] Geometry: High school. [Online]. Available: https : / / study . com/academy/course/high-school-geometry.html. [33] Wire working - how to manipulate wire to create art. [Online]. Available: https://www.hsn.com/article/wire- workinghow-to-manipulate-wire-to-create-art/449. [34] Nylon jaws ring holding pliers parallel type jaws jewellery rings crafts 5-5/8

92

REFERENCES

. [Online]. Available: https : / / www . toolsntoolsuk . co . uk/product/nylon-jaws-ring-holding-pliers-paralleltype-jaws-jewelry-rings-crafts-5-58/. [35] Constructing the perpendicular bisector of a line segment. [Online]. Available: https://www.mathopenref.com/printbisectline. html.

Appendix A Appendix

1

A.1

Statistical Fitting of Data

A.2

Importing and Fitting the Goodness of Data

%I m p o r t a t i o n o f Simulated F i e l d Data

2 3 4 5 6 7 8 9 10 11 12 13 14

Bxy_w1= dlmread ( ’ Bxy_w1 . csv ’ , ’ , ’ , 9 , 0 ) ; Bxy_w2= dlmread ( ’ Bxy_w2 . csv ’ , ’ , ’ , 9 , 0 ) ; Bxy_w3= dlmread ( ’ Bxy_w3 . csv ’ , ’ , ’ , 9 , 0 ) ; Bxy_w1_r= dlmread ( ’ Bxy_w1_r . csv ’ , ’ , ’ , 9 , 0 ) ; Bxy_w2_r= dlmread ( ’ Bxy_w2_r . csv ’ , ’ , ’ , 9 , 0 ) ; Bxy_w3_r= dlmread ( ’ Bxy_w3_r . csv ’ , ’ , ’ , 9 , 0 ) ; Bxy_w1_u= dlmread ( ’ Bxy_w1_u . csv ’ , ’ , ’ , 9 , 0 ) ; Bxy_w2_u= dlmread ( ’ Bxy_w2_u . csv ’ , ’ , ’ , 9 , 0 ) ; Bxy_w3_u= dlmread ( ’ Bxy_w3_u . csv ’ , ’ , ’ , 9 , 0 ) ; Bxy_w1_ur= dlmread ( ’ Bxy_w1_ur . csv ’ , ’ , ’ , 9 , 0 ) ; Bxy_w2_ur= dlmread ( ’ Bxy_w2_ur . csv ’ , ’ , ’ , 9 , 0 ) ; Bxy_w3_ur= dlmread ( ’ Bxy_w3_ur . csv ’ , ’ , ’ , 9 , 0 ) ;

15 16 17 18 19

%% %D i f f e r e n c e between magnetic f i e l d s :

20

93

94

21

22

23

24

25

26

27

28

29

30

31

32

33

34

APPENDIX A. APPENDIX

%DBxw1=Bxy_w1 ( : , 3 )−Bxy_w1_r ( : , 3 ) ;%Always moving from l e f t t o r i g h t %DByw1=Bxy_w1 ( : , 4 ) +Bxy_w1_r ( : , 4 ) ;%Coming up and then down f i t _ w 1 x = goodnessOfFit ( Bxy_w1 ( : , 3 ) , Bxy_w1_r ( : , 3 ) , ’ NRMSE ’ ) f i t _ w 1 y = goodnessOfFit ( Bxy_w1 ( : , 4 ) ,−Bxy_w1_r ( : , 4 ) , ’NRMSE ’ ) f it _ w1_u_x = goodnessOfFit ( Bxy_w1_u ( : , 3 ) , Bxy_w1_ur ( : , 3 ) , ’NRMSE ’ ) fit_w1_u_y = goodnessOfFit ( Bxy_w1_u ( : , 4 ) ,−Bxy_w1_ur ( : , 4 ) , ’NRMSE ’ ) f i t _ w 2 x = goodnessOfFit ( Bxy_w2 ( : , 3 ) , Bxy_w2_r ( : , 3 ) , ’ NRMSE ’ ) f i t _ w 2 y = goodnessOfFit ( Bxy_w2 ( : , 4 ) ,−Bxy_w2_r ( : , 4 ) , ’NRMSE ’ ) f it _ w2_u_x = goodnessOfFit ( Bxy_w2_u ( : , 3 ) , Bxy_w2_ur ( : , 3 ) , ’NRMSE ’ ) fit_w2_u_y = goodnessOfFit ( Bxy_w2_u ( : , 4 ) ,−Bxy_w2_ur ( : , 4 ) , ’NRMSE ’ ) f i t _ w 3 x = goodnessOfFit ( Bxy_w3 ( : , 3 ) , Bxy_w3_r ( : , 3 ) , ’ NRMSE ’ ) f i t _ w 3 y = goodnessOfFit ( Bxy_w3 ( : , 4 ) ,−Bxy_w3_r ( : , 4 ) , ’NRMSE ’ ) f it _ w3_u_x = goodnessOfFit ( Bxy_w3_u ( : , 3 ) , Bxy_w3_ur ( : , 3 ) , ’NRMSE ’ ) fit_w3_u_y = goodnessOfFit ( Bxy_w3_u ( : , 4 ) ,−Bxy_w3_ur ( : , 4 ) , ’NRMSE ’ )

35 36

%S t a t i s t i c a l a n a l y s i s : measure o f s i g n i f i c a n c e

37 38 39 40 41 42 43

BMaxx_w1=max ( abs ( v e r t c a t ( Bxyw1 ( : , 3 ) , Bxyw1r ( : , 3 ) ) ) ) ; DBMaxx_w1=max ( abs (DBxw1) ) ; dBMaxx_w1=DBMaxx_w1/BMaxx_w1 ; BMaxy_w1=max ( abs ( v e r t c a t ( Bxyw1 ( : , 4 ) , Bxyw1r ( : , 4 ) ) ) ) ; DBMaxy_w1=max ( abs (DByw1) ) ; dBMaxy_w1=DBMaxy_w1/BMaxy_w1 ;

44 45

sigma_dBxw1=DBxw1.^2/mean (DBxw1)


95

46 47

48

fit_w1x = NRMSE ’ ) fit_w1y = NRMSE ’ )

A.3

1 2 3 4 5 6

goodnessOfFit ( Bxyw1 ( : , 3 ) , Bxyw1r ( : , 3 ) , ’ ; goodnessOfFit ( Bxyw1 ( : , 4 ) ,−Bxyw1r ( : , 4 ) , ’ ;

Configuring the Geometric Parameters in COMSOL

%General : Cl = 0 . 2 ;%Leg l e n g t h r e c t . c o r e Cd= 0 . 1 8 3 3 ; %D i s t a n c e between l e g s Ch = 0 . 2 ; %t h i c k n e s s o f t h e c o r e l e g a g o f f s = −0.1365;%x pos o f c o r e edge a g a i n s t magnets midoffs = 0 ;%y pos mid c e n t e r c o r e

7 8 9 10 11

12 13 14 15 16 17 18 19 20

w_Width=Cl − 0 . 0 2 ; w_Height=Cd/2 −0.015 Leaving some space between windings x1= a g o f f s −Cl + 0 . 0 0 5 ;%t h i s l e a v e s 5 mm o f margin t o the r i g h t %Also bobbin_margin : y0=midoffs+Ch/ 2 ;%Upper edge o f c e n t r a l c o r e l e g . bobbin_margin = 0 . 0 0 5 ; %t h i s l e a v e s 5 mm between t h e winding and t h e c o r e . %f o r t h e bobbin or t h e i n s u l a t i o n y1=y0+bobbin_margin ; y2=y0+Cd−(w_Height+bobbin_margin ) ; %y2=midoffs+Ch/2+Cd−0.005−Cd/ 2 + 0 . 0 1 5 ; y3=y0+Cd+Ch+bobbin_margin ;

21 22 23 24

c_Width = 2 . 2 e −3; c_Height = 4 . 2 e −3; range=y1+c_Height / 2 : c_Height : x1+w_Height−c _ H e i g h t t /2)

96


Table A.1: Table of Parameters in COMSOL model Name

Expression

Description

agoffs Agw Airgap AirgapDisp B0 bIcoil2 Blocking_h Blocking_w bobbin_margin Bulkw c_Height c_Width Ca Cbw Cd Cdi Cdo Ch Cl Core_airgap cosCa Cwc Cwt DemagTh DemagTw Fcti Fcto Fd Fh Ftbh Fttbi Fttbo Ftth Fttti Fttto Holech Holecw Holed Holedc Holeoffs Ia Ib Ic Icoil ICoilAbs Ihat intpostopleg Leg1h Leg1w Leg2w Legfillet Legh Leghext LeghFrac LeghOffs LegOffs Legspacing Legw lh Magh Magstart Magw midoffs mlh NoMagnets Offs OffsCurr OuterPW PoleWidth PWDisp PWOffs PWSpan tanCa Texct Texp Texw Tfb Tft Tmeh Toffs TrIeh TrIew TrIh Tsexct Tsexp Tsexw Tsih Tsoh Vhm_mag_h Vhm_mag_w w_Height w_Width x1 y0 y1 y2 y3

-1*(LegOffs+Legw+Vhm_mag_h+Core_airgap) 0.001 0.001 0 1.3 70*sqrt(2)*sin(OffsCurr*3.141592654/OuterPW) 1*PoleWidth 0.0005 0.005 0.15 4.2[mm] 2.2[mm] 22.305 0.23 0.1833 0.16538 0.03 (NoMagnets-1)*PoleWidth 0.2 0.001 cos(Ca*3.14192654/180) 0.33 Cwc/cosCa 0.002 0.005 0.11 0.05 0.18333 (NoMagnets+1)*PoleWidth 0.03/cosCa 0.05 0.04 0.105/cosCa 0.17 0.05 PoleWidth/10 0.02 0.002 0.003 0.012 Ihat*sin((Offs-4*PoleWidth/3)/PoleWidth*3.141592654) Ihat*sin(Offs/PoleWidth*3.141592654) Ihat*sin((Offs+4*PoleWidth/3)/PoleWidth*3.141592654) sign(Offs+5*OuterPW)*ICoilAbs 120 100 0 0 0.02 Legw-0.01 0 PoleWidth*LeghFrac PoleWidth-Legspacing/2-Legh/2 0.7 Toffs+PoleWidth/2 Legw/2+Airgap+TrIew+Magw+TrIew+Airgap 1.3*PoleWidth 0.05 0.33 0.4*PoleWidth -1*(Fh-2*PoleWidth+Magh)/2 0.05 0 0 9 0+PWOffs Offs-PWOffs PoleWidth-PWDisp 0.025 PoleWidth*PWSpan/(NoMagnets+1) 0.00625 0 tan(Ca*3.141592654/180) 0.0005 0.002 0.01 0.008 0.004 0.0165 -1.2+Offs 0.00075 0.00075 PoleWidth-Magh (Tsoh-Tsih)/2*20/50 0.002 0.01 0.0175 0.0195 0.007 0.025 c_Height*20 Cl-0.02 agoffs-Cl+0.005 midoffs+Ch/2 y0+bobbin_margin y0+Cd-(w_Height+bobbin_margin) y0+Cd+Ch+bobbin_margin

x pos of core edge against magnets

cable height cable width Core angle Core back width Distance between legs Core distance inner Core distance outer Thickness core Leg length rect. core

Core width center Core width top

Funnel x height center inner Funnel x height center outer Distance between funnels y Funnel height Funnel x height bottom inner Funnel x height bottom outer Funnel x height top inner Funnel x height top outer

Thickness of stator "legs"""

Vi lägger nu denna i mitten på translatordelen, när den är mitt för järnet

Leg height (core leg) Magnet height Magnet width y pos mid center core

Mittentranslator extra höjd fram till pigg Mittentranslator piggens höjd Mittentranslator piggens vidd Test för att kompensera för normalkraft Test för att kompensera för normalkraft Mittentranslator höjd vid luftgap Pole shoe edge height Pole shoe edge width Pole shoe internal height Sidotranslator höjdförändring fram till pigg Sidotranslator höjd på pigg från innerkant Sidotranslator bredd på pigg Sidotranslator höjd mot magnetstapel Sidotranslator höjd mot kärna

Winding Height Winding Width start of the left side windings Upper edge of central core leg start of the first left winding start of the second left winding start of the third left winding


A.4 A.4.1

Tools Drawing and Measuring Instruments

Figure A.1: Edge square

Figure A.2: Flat Square

97

98


Figure A.3: Straight Edge Ruler

Figure A.4: Scratch spring compass


Figure A.5: Caliper

99

100


(a) Straight angle, and segment bisection

(b) Segment division in equal parts

Figure A.6: Compass-and-straightedge operations [35]


A.4.2

Holding Tools

(a) Ratcheting Bar Clamp

(b) Spring Clamp

Figure A.7: Clamps

A.4.3

Boring Tools

101

102


Figure A.8: Drill Press

Figure A.9: Countersink Drill Bits


Figure A.10: Screw Bit

A.4.4

Cutting Tools

103

104


Figure A.11: Bandsaw

Figure A.12: Table Circular Saw

A.5 A.5.1

Schematics 4

Cores

3

2

1

F

F

Motor

170 230

Generator

E

180

120

E

D 203,33

203,33

D

C

150

C

255 315

255 315

150

B

B

A

A

Figure A.13: Relevant Dimensions of the Motor and Generator Cores 4

3

2

1

4

3

2

1

F

F A.5.2

Bobbin 230 180 170 120

E

255

315

122,50

30

E

101,65 101,65

130

D

25

5

35

D

25

C

25

150

C

B

B

A

A

4

3

2

1


A.6

Cable Lug instructions

Sebastian Rudnik KTH, Elkraftsteknik

Hendrik Klein Elpress AB

Kramfors, den 18 Maj 2018

Frågeställning: Undersök vilken kabelsko som passar bäst för att kontakta 2x20 Al-lindningsledare till en kopparskena. Al-lindningsledare 2x4 mm – kabelspecifikationen okänt.

Resultat: Elpress AB rekommenderar att använda en Al-Cu kabelsko – AKK240-10. (12 och 16 mm bulthål finns också tillgängliga). Alla 40 ledare kontaktpressas i en kabelsko. Monteringen av kabelskon kräver rundformning av ledarna (13R19ML/DL –AL.) Ledarpaketet bör för bästa resultat formas som en matris 2x 4x5 med horisontal inriktning och staplat vertikal på varann (se bild 2). Kontaktpressningen sker med ett speciellt lindningsledareverktyg (13P32M2/D2.) Presshuvud som verktygen passar till är DV1300 eller V1300. PS710, V1311A eller fotpump P4000 används som drivkälla till presshuvudet. Andra drivkällor på förfrågan!

Viktig: Vid ändringar av kabelspecifikationen, ledaredimensionering eller ändring av den samlade arean blir resultatet ovan ogiltig!

Hendrik Klein Elpress AB

107

Elektriska förbindningar – bultförband 1

Bultförbandet

Montering av en kabelsko med bultförband för elektrisk överföring kräver särskild uppmärksamhet. Det är viktigt att detta görs på ett korrekt sätt, lika viktigt som kontaktpressningen i andra änden av kabelskon som har beskrivits ovan. Förbandet skall åstadkomma tillräckligt hög klämkraft, fördelad på ett önskvärt sätt samt säkerställa de elektriska egenskaperna över mycket lång tid under höga och varierande belastningar av olika karaktär. Det är mycket viktigt att följa monteringsanvisningarna. Dessa är baserade på teoretiska beräkningar, verifierade tester och erfarenhet från fältstudier. Åtdragningen skall ske på ett kontrollerat sätt med hjälp av momentverktyg där aktuell skruv förspänns till rätt nivå med hjälp av angivet moment. Under dessa förhållanden behöver inte ett korrekt utfört bultförband ”efterdras”. Verktygets noggrannhet har stor betydelse.

1.1

Vridmomentet

Vid förspänning med ett visst moment åtgår en stor del av detta till att övervinna friktion i gängor och mot underlaget under skruvhuvud och mutter. Endast 10 % av det totala momentet ger en förspänning av skruven som skall säkerställa funktionen. Se fig. nedan: F= kraft

Vridmoment Mv =FxL Åtdragningsmoment

Fördelningen av åtdragningsmomentet vid normala förhållanden.

Den klämkraft som en korrekt åtdragen skruv åstadkommer skall i ett elektriskt förband skapa en kontaktarea tillräckligt stor för att säkerställa god ledningsförmåga, utan risk för överhettning. En M12-skruv i klass 8.8 dragen med 70 Nm åstadkommer ca 4 tons klämkraft. Kontaktytorna formas under trycket från skruven. För att den klämkraften skall fördela sig jämt och skapa en tillräckligt stor kontaktarea måste man alltid använda hårda planbrickor, typ BRB HB200 SMS 70, under skruvhuvud och mutter. Se bild nedan. Det gäller oavsett hårdhet på de ledande materialen (som är mjukare än HB200). I annat fall riskeras stor deformation på det ledande materialet så att förspänningen minskar vilket kan ge ökad risk för otillräcklig kontaktarea och överhettning.

Dok.nr: 0901-012900 Revision A

Datum: 2012-01-18 Ändr. nr: 18539

Godkänd av: PF Sida 1(4)

Elektriska förbindningar – bultförband Skruv Kabelsko Plan, hård bricka

Anslutningsskena

Mutter

Ett korrekt skruvförband där både skruvhuvud och mutter anligger på hårda planbrickor

1.2

Sättning

Den elastiska egenskapen i ett korrekt monterat och utformat bultförband säkerställer att det alltid finns en tillräckligt stor klämkraft även efter sättning, relaxation av materialet. Statiska sättningar sker vid montering och kort därefter. Dynamiska sättningar sker vid höga yttre laster på skruvförbandet.

Åtdragning

R = Övergångsresistans F = Klämkraft

Relaxation

Även efter sättning finns tillräckliga spännkrafter kvar till en viss gräns. Sedan ökar resistansen snabbt.

1.3

Spännbrickor

Användningen av olika typer av låselement eller fjäderbrickor ökar ofta risken för sättning. Om en spännbricka typ SB DIN 6796, med mycket hög spännkraft, placeras och fixeras mellan t.ex. mutter och den hårda planbrickan kan det ge en ökad marginal mot alltför stor sättning. Spännbrickans diameter bör vara mindre än eller lika med planbrickans, även efter


Datum: 2012-01-18 Ändr. nr: 18539


Elektriska förbindningar – bultförband full åtdragning. I annat fall ökar risken för sättning vid planbrickans ytterkant dit spännkrafterna då koncentreras. Vid användning av spännbricka räcker det med 1 st och att den helst placeras på motsatt sida kabelskon, se bild nedan. Skruv Hård planbricka Kabelskons fana Anslutningsskena Hård planbricka med stor ytterdiameter Spännbricka DIN 6796 (ej fullt åtdragen på bilden)

Montering med spännbricka

1.4

Rekommenderade åtdragningsmoment

Åtdragningsmoment (Mv) i Nm, förspänningskraft i kN samt plantryck under bricka N/mm² brickstorlek enl. SMS70 (HB200). Förspänningskraft varierar med friktionsförhållanden. Plantrycket bör ligga inom intervallet 90-180N/mm² för kopparkabelskor. Momenten är valda så att skruvarna förspänns till 70% av sin sträckgräns. Syrafast Stål 10.9 Stål 8.8 1 A4/80 FZB, FZY, FZB, FZY, Gänga FZM FZM Mv Ff p Mv Ff p Mv Ff 5,5 6,6 118 8 9,2 164 5.5 6.2 M5 9,5 9,2 114 13 13 160 9.5 8.6 M6 23 17 116 32 24 164 22 16 M8 45 27 92 64 38 129 45 25.5 M10 78 40 125 110 56 175 76 37 M12 200 75 156 280 110 229 185 69 M16 1) FZB= elförzinkad + blankkromaterad, FZY= elförzinkad + gulkromaterad, FZM= mekaniskt förzinkad. Hållfasthetsklass 8.8 och 10.9. Ff= förspänningskraft (kN). p=Plantryck (N/mm²) 1


Datum: 2012-01-18 Ändr. nr: 18539

p 111 107 109 88 116 144


Elektriska förbindningar – bultförband

1.5

Arbetsgång vid montering av kabelsko

1. Rengör kontaktytor från smuts, oxidskikt och fett med hjälp av stålborste och T-sprit. Detta är särskilt viktigt för aluminium. Ytor som är förtenta, förnicklade, försilvrade får ej borstas. 2. Vaselin eller kontaktfett minskar korrosionsrisk på rengjorda ytor 3. Val av fästelement: Skruv och mutter av hållfasthetsklass 8.8. Smord förzinkad skruv ger minst spridning av förspänningskraften. Välj rostfritt A4-80 i miljöer när det är stor risk för korrosionsangrepp. 4. Val av brickor: Välj alltid hård planbricka typ BRB, HB200. Spännbricka kan normalt uteslutas. Om spännbricka typ DIN 6796 används skall den placeras mellan skruvskalle/mutter och planbricka. Den får aldrig placeras direkt mot elektrisk kontaktyta utan en planbricka emellan. Planbrickan skall ha en ytterdiameter minst lika stor som spännbrickan. 1 st spännbricka är tillräckligt och den bör placeras på skenans baksida, mellan mutter och hård planbricka, se skiss på föregående sida. 5. Skruvarna skall dras med momentverktyg så att åtdragningen sker kontrollerat. Momentnycklar skall regelbundet kalibreras. Anolja skruven vid montering. Även om momentet registreras korrekt är förspänningskraften helt beroende av friktionen. 6. Åtdragningsmomentet enligt tabell ovan. Noggrannhet bättre än ±5%. 7. Kabelskons fana och skenan kan vara av olika material. a. Cu/Cu ger det bästa förbandet, god kontakt och liten risk för sättning. b. Cu/Al ger låg risk för galvanisk korrosion när skenan är av Al. Al/Cu ger högre risk för korrosion och sättning, använd kontaktfett. c. Al/Al ger ett vekare förband. Viktigt att rengöra och använda kontaktfett. Spännbricka + planbricka kan minska risken för sättning. 8. Max 2 st kabelskor av samma storlek på samma skruv. Strömlast bör kontrolleras.


Datum: 2012-01-18 Ändr. nr: 18539


A.7


Datasheet for hot-melt adhesive Produktinformation

Tecbond 260 Smältlim

Produktbeskrivning Tecbond 260 är ett högpresterande universallim med lång öppentid som ger en stark men flexibel fog. Tecbond 260 är ett mångsidigt lim som fungerar speciellt bra mellan glas och lättmetaller samt mellan metaller och ABS-plast. Även lämpat får många typer av plaster,

• Temperaturområde: max +70°C • God vidhäftning till många material. • Starkt och flexibelt. • Alla komponenter i detta lim är godkända av amerikanska FDA enligt CFR 21.175.105 (lim).

keramer, aluminium, glasfiber, vissa typer av hårt trä, papper och träfiber.

Borttagning av lim Monterade komponenter kan separeras genom att värma fogen till strax över maxtemperaturen.

Lagring EVA & Polypropylen Rester av smältlim baserade på EVA och polypropylen kan tas bort med lågaromatisk nafta.

Lagra rent och torrt i temperaturer mellan +5°C och +30°C i stängd kartonger. Exponera inte för direkt solljus eller lokala värmekällor.

Riskupplysning Polyamid Rester av smältlim baserade på polyamid kan tas bort med aceton.

Smältlimmer utgör i stort sett ingen hälsorisk när de används på normalt industriellt vis, men eftersom de används i smält tillstånd kan risk för brännskador finnas. Hudkontakt med flytande smältlim skall undvikas och åtgärder skall vidtagas för att undvika att lim i smält form

Övrig information Alla komponenter i detta lim är godkända för användning i livsmedelsapplikationer enligt amerikanska F.D.A under C.F.R.21.175.105 (lim).

kan skvätta eller på annat sätt komma i kontakt med huden. Vi rekommenderar därför användning av skyddskläder av normal typ, bomullshandskar och skyddsglasögon.

En produkt från:

Reviderad 2016-03-12/SB

112


A.8

113

Datasheet for low viscous hot-melt adhesive

Produktinformation

Tecbond 7718 Black Smältlim

Produktbeskrivning Tecbond 7718 Black är ett polyamidsmältlim med mycket låg viskositet avsett för ingjutning och inkapsling. Passar de flesta pistoler avsedda för 12mm stavar. Produkten är

• Temperaturområde: max +135°C. • Svartpigmenterad. • Ingen blandning nödvändig. • Inget restmaterial.

svartpigmenterad för att undvika att inkapslade komponenter syns. Fixeringstiden är normalt mindre än 2 minuter. För små limmängder kan dock ned till 5-10 sek nås. Användningen av ett smältlim ger en snabbare process eftersom ingen blandning behövs och allt oanvänt limsitter kvar i pistolen.

Användningsområden

Riskupplysning Smältlimmer utgör i stort sett ingen hälsorisk när de används på normalt industriellt vis, men eftersom de

Tecbond 7718 Black polyamidsmältlim är ett polyamid-

används i smält tillstånd kan risk för brännskador finnas.

smältlim avsett för ingjutning och inkapsling.

Hudkontakt med flytande smältlim skall undvikas och

Förbehandling av ytor

åtgärder skall vidtagas för att undvika att lim i smält form kan skvätta eller på annat sätt komma i kontakt med

Rengöring: Rengör alla ytor, tag bort all främmande

huden. Vi rekommenderar därför användning av skydds-

materia och föroreningar som t.ex. formsläppmedel,

kläder av normal typ, bomullshandskar och skyddsglas-

korrosionsskyddsmedel, fett, oljor, vatten, gamla lim-

ögon.

rester och andra ämnen som kan påverka produktens vidhäftning.

Övrig information Produkten är testad enligt UL V0 och klarar kraven på brandsäkerhet. 7718 Black är ett polyamidsmältlim och kommer att absorbera en liten mängd fukt från omgivande luft. Detta påverkar inte limmets prestanda men ger ånga vid applicering vilket gör att limmet kan droppa, skumma och få staven att fastna i pistolen. Stavarna skall därför förvaras i originalförpackningen i möjligaste mån. Vid problem

En produkt från:

Reviderad 2017-03-16/SB

kan stavarna torkas i ugn i +70°C under 24 till 48 timmar.

114

A.9


Datasheet for LCR bridge

HM8118

LCR Bridge HM8118

HZ188 4-Terminal SMD Component Test Fixture (included)

R Measurement range: 20 Hz to 200 kHz (69 steps) R Basic accuracy: 0.05 % R Measurement rate: up to 12 values per second R Automatic or manual selection of circuit type (serial, parallel) HZ184 4-Terminal Kelvin Test Cable (included)

R Measurement functions: L, C, R, |Z|, X, |Y|, G, B, D, Q, Θ, Δ, M, N R Transformer measurement: mutual inductance and ratio R T unable DC BIAS (voltage / current): internal: 0 V to 5 V / 0 mA to 200 mA (resolution: 10 mV / 1 mA) external: 0 V to 40 V (voltage BIAS only) R RS-232/USB dual interface for remote control

HZ181 4-Terminal Test Fixture with shorting plate (optional)

R Fanless design


A.10

115

Datasheet for Micro-ohmmeter MOM600A

Micro-ohmmeter

MOM600A

Micro-ohmmeter ▪▪Compact

and rugged

▪▪Easy-to-use ▪▪600

A output current

DESCRIPTION

APPLICATION EXAMPLES

Switchgear breakdowns are frequently caused by excessively high contact resistance at breakpoints and busbar joints. Moreover, overheating risks are becoming more serious due to the fact that today's distribution networks have to carry heavier loads. Checking contact resistances at regular intervals detects faults before they cause overheating. And here, an ounce of prevention is worth a pound of cure.

A. Measuring the resistance of a circuit breaker element

Micro-ohmmeters are used to measure contact resistances in highvoltage breakers, disconnecting switches (isolators), knife-contact fuses, bus joints, line joints etc. The MOM600A™ is in a class apart on world markets. Designed for use from the arctic to the tropics, this rugged, compact micro-ohmmeter is ideal for field work. A complete set of equipment includes a set of highly flexible cables (including separate measurement cables) and a sturdy transport case.

1. Connect the micro-ohmmeter to the circuit breaker.

2. Set the current (100 A in this example). 3. Press the resistance pushbutton. 4. Read the result.

B. Measuring the resistance of busbar joints 1. Connect the micro-ohmmeter’s current cables to the object being tested. Do not connect the sensing cables since measurements will be taken using an external movable voltmeter.

2. Set the current (100 A in this example). 3. Connect an external voltmeter to the bus. 4. Read the voltmeter (0.1 mV = 1 µΩ in this example). 5. Move the voltmeter to the next joint. 6. Repeat step 4.

A

B

116

A.11


Datasheet for infrared camera

ETS320

FLIR

™

Thermal Imaging Solution for Electronics Testing The FLIR ETS320 is an affordable solution for reducing test times and improving product design for electronic board and device evaluation. Whether the goal is R&D or product testing, heat can be an important indicator of how a system is functioning. The ETS320 helps engineers and test technicians collect accurate, reliable data in seconds and analyze it quickly.

Reduce Test Times The FLIR ETS320 takes the guesswork out of thermal testing, for fast discovery of hot spots and potential points of failure. • Sensitive enough to detect temperature shifts smaller than 0.06°C • Wide temperature range, from -20°C to 250°C, for quantifying heat generation and thermal dissipation • Measures small components down to 170 µm per pixel spot size

Improve Product Design The FLIR ETS320 promotes design improvements and shortens product development time by detecting design flaws that materialize as heat. Measure small components down to 170 µm per pixel spot size

• 320 x 240 IR sensor offers 76,800 points of non-contact temperature measurement • True 45° field of view for broad initial scans to identify potential problems • Measurement accuracy of ±3°C promotes quality assurance and factory acceptance of PCBs

Designed for Laboratory Work The ETS320 is designed for hands-free laboratory testing, with simplified features that allow users to focus on their work instead of on the camera controls.

Determine where to add or remove thermal management devices

• Pole mount included for fast and easy setup • Crisp 3” LCD display provides immediate thermal feedback • FLIR Tools+ software for instant analysis, including Time vs. Temperature measurement

Key Features:

• 320 x 240 IR resolution (76,800 pixels) • Vibrant 3” LCD display • 45° field of view • ±3% measurement accuracy • Records standard radiometric JPEGs • FLIR Tools+ software provided Connect over USB a computer to analyze data in FLIR Tools+

www.flir.com/science


A.12

March 2018

117

Datasheet for Pro 950 Tape

PRO® 950 Polyimide Tape Technical Data Sheet Pro® 950 is a polyimide tape that is ideally suited for applications requiring continuous high temperature operating conditions.

Features & Benefits: Thermosetting adhesive provides solvent resistance and outstanding high temperature adhesion. Pro 950 combines a thin conformable backing with outstanding puncture, tear and abrasion resistance at high temperature levels.

Technical Data           

ASTM Test Method

Backing: Polyimide film Adhesive: Silicone, thermosetting Backing Thickness: 1 mil Total Tape Thickness: 2.5 mils Tensile strength: 24 lbs. per inch Elongation: 50% Adhesion to steel: 20 oz./in Dielectric Strength: 7,500 volts Temperature Resistance: 500°F Insulation Class, Centigrade: 350°F/180°C Certifications: UL510 Recognized

D-3652 D-3652 D-882-91 D-882-91 D-3330 D-149-97 Oven Residue Testing (20min)

Application: Pro® 950 is used as a ground barrier and phase insulation in high performance torridal coils, high frequency motors. Pro® 950 can be used for end turn bundling and connection insulation in small motors. Pro® 950 is also used for cross-over insulation and out wraps on bobbin wound and form wound coils for large rotating machines to bundle conductors and reinforce insulation. Pro® 950 can be used as wave solder masking of printed circuit boards. ISO 9001 Certified

621 Route One South. North Brunswick, NJ 08902 Toll Free #1-800-345-0234

Note: The above are typical values and should not be used in writing specifications. The determination of the suitability of this product for any specific use is solely the responsibility of the user. No representatives, guarantees or warranties of any kind are made to the accuracy or suitability for specific applications. Tape should be stored in its original packaging in a cool dry area away from direct sunlight and should be used within 12 months from date of shipment. Surfaces to which tape is applied should be clean, dry and free of grease, oil or other contaminates.

118


Figure A.14: Final Schematics for the Core-Replica Bobbin

TRITA TRITA-EECS-EX-2018:558

www.kth.se