Electrical Engineering Department. King Fahd University of Petroleum & Minerals (KFUPM). Dhahran, Saudi Arabia. Abstract-This paper presents a menu-driven ...
Human-Computer Interaction of Single/Three Phase Transformer Design and Performance Farrukh Shahzad
M. H. Shwehdi, Senior Member
Electrical Engineering Department King Fahd University of Petroleum & Minerals (KFUPM) Dhahran, Saudi Arabia
Abstract-This paper presents a menu-driven easy to use computer package which has been tailored at this stage to asssit: 1- Young Electrical Engineer in industry to visualize and enhance the practical use of theoretical and analytical brief notes learned in typical energy conversion course taken at undergraduate level, and enable him or her of having confidence, industry know-how process, and sufficient design and performance evaluation skills on the different types of transformers. 2- In teaching Electrical machines laboratory for Power Enginnering students by an interactive step-by-step approach. All experiments performed on transformers and more can be handled by the software to illustrate transformer design and performance details. The scope of this package is to present in an interactive logical design procedure and to calculate: corelyokelsheets dimensions, low and high voltage winding’s number of turndlayers, axial length and other related dimensions.
Key words: Electric machines, Transformers, Machine design, Computer aided design, Power Engineering Education, Engineering software. 1. 1NTRODUCTlON
The general problem of design may be defined as that of determining the most suitable form of equipment, if both technical consideration and cost are taken into account. A satisfactory result is not obtained simply by the solution of a series of equations. The design process is basically iterative, whether performed by hand or by computer [ 1-31. Supplementary use of personal computers in electrical engineering education can provide an effective learning environment for introductory as well as advanced studies. In addition, sufficient exposure to PC as a design and analysis tool is consistent with the ever expanding industrial applications of
0-7803-3825-1/97/$10.00 1997 IEEE
these devices. The purpose of this paper to present an interactive software programmed to design and analyze transformers. The software is useful to obtain the optimum transformer designs. Also, it can calculate all the performance characteristics of the transformer including but not limited to efficiency, Copper and Iron losses. The design is based on core HIW ratio, core material, shape, conductor diameter, type of windings of each side, percentage loading and KVA and voltage rating as specified by the user. The objective of the package is to be a human-computer interactive aid for design, calculation, and the analysis of single/three phase, distribution/power, shelllcore type, dryloil filled, natural/forced cooled transformer, and useful training and teaching tool for power utilities and industry engineers as well as electrical power engineering students and educators. This software is a part of a big project to develop an interactive electrical machine analysis and design package. 11. PROBLEM FORMULATION
A transformer is essentially a static electromagnetic device consisting of two or more windings which link with a common magnetic field. One of these windings, the primary, is connected to an alternating voltage source, and alternating flux is produced whose amplitude depends on the primary voltage and number of turns. The primary induced voltage is E, = 44.4 f q5,, T, (1) where f =frequency, 4m=mutual flux and T,, = number of turns in the primary winding. This flux linking with the secondary winding induces in it a voltage whose value depends on the amplitude of flux and number of secondary winding turns. The secondary induced voltage is E, = 44.4 f bmT, (2) where T, = number of turns of secondary winding. Ratio of voltage is E, I E,, = T, I T,,. Therefore, any desired value of secondary voltage can be attained by using a suitable number of turns. The transformer designer has to have certain information before a design can be created; the major items are as follows: Rating of the transformer. 0 Primary and secondary line voltages. 0 Primary and secondary winding connection (star, delta, etc.)
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Number of phases (Single or Three). Frequency of operation. Type of cooling (ON, OB, OFB, etc.). Tapping type, range and steps. Temperature rise limits. e Test conditions. e Mass dimensional restrictions. With this information a design can be produced which would give the designer a choice to decide upon the reactance, load loss and iron (core) loss. To minimize the cost of the transformer he would invariably work to the maximum permissible flux and current densities keeping with good design practice for the size and type of transformer being considered. The resultant design would, therefore, have natural values for the reactance and losses in keeping with the particular manufacturer’s design techniques. The problems involved in arriving at such a design are considerably reduced where the reactance and losses are specified by the customer. In practice it is found that the majority of customers specify the reactance since this has to comply with the electrical system in which the transformer is to be installed. Sometimes the losses are specified, or alternatively the capitalized cost of the losses. In recent years the maximum noise level of power transformer has also been specified. Therefore, these four parameters could also be specified : e Reactance or impedance. Load loss or capitalized cost of the loss per kilowatt. Iron loss or capitalized cost of the loss per kilowatt. Noise level. Following specification are governed by the particular manufacturer’s code of practice or standards for the design considered. e General arrangement of the windings with respect to the core leg. e Type of winding design (helical, layer, disk, etc.). e Type of winding conductor ( copper, aluminum, transposed cable or normal strand). e Type of core( one-, two-, three-, four-, or five-, limbed mitred or non-mitred joints.) e Type and grade of core steel. e Type and cooling arrangement (radiators on the tank or separate bank, pumps, fans, etc.). e Maximum thermal gradient in the windings. e Maximum current densities in the windings. e Maximum winding eddy current losses expressed as a percentage of the winding (12R) losses. e Maximum flux density in the core leg. e Major insulation clearances (inter-winding and windings to core insulation). e Minor insulation thickness (paper covering on the conductor, radial duct widths in the windings, etc.). Type of tap-change gear and position of the tapping winding. e Type of material for the tank (steel or aluminum).
The number of ways in which the design problem can be solved by a computer are virtually unlimited. The method evolved is dependent upon which parameters of the design are considered to be the most important. The computer can be used in nearly all aspects of the transformer design where the fundamental principle is understood and where mathematical equations have to be solved [ 11.
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111. SOFTWARE FEATURES e
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This software can be run on any IBM-compatible computer (XT to Pentium). Completely menu driven with user-friendly input and output. It supports math co-processor (8087/80287/80387). The execution speed increases many fold, if a co-processor is present. Complete error checking with abnormal-termination protection. It performs all computation in extended i.e. long double precision (20 significant decimal digits) using IEEE floating point arithmetic. Complete mouse support. Expression entry support. Interactive help provided. Operating system shell support. User can take print out of every result and graph. IBM proprinter (Epson & Panasonic compatible), Laser jet printer support. Workspace can be saved as text file for later processing. It supports almost all types oi graphics driver including CGA, EGA, VGA etc. The quality of graph is dependent on the driver resolution. Graphical output can be copied to clipboard or bitmap file (*.bmp) in color or B/W with user defined background. Online cross-hairing support to read the curves point directly and accurately. IV. EXAMPLE
As an example, a 25KVA, 2.2KVl220V, 400 Hz is designed using the software. It is a 3-phase, distribution, coretype, natural-cooled, oil-immersed, staddelta transformer [3]. A. CORE DESIGN:
From table(for 50 hz.) : k = 0.45 F o r f = 4 0 0 H z , k = 1.273 Volts/turn (E,) = 6.36 Flux, 4 = 0.00358 Weber Selected flux density, B = 1.OO Wb/m’ Iron area, A, = 35.83 cm2 Dimensions of step(s) : d = 8.00 cm a = 6.80 cm,
b = 4.24 cm
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Window space factor: K, = 0.2484 Selected current density: - = 2.30 A/mmz Window area : A, = 0.00917 mz Selected H/W ratio = 2.50 Window height : H = 15.138 cm 15.00 (adjusted) 6.50 (adjusted) Window width : W = 6.055 cm New window area : A, = 97.500 cmz Distance blw centers of adjacent core leg : D = 13.30 cm Yoke area (20% increased) = 43.000 cmz Yoke flux density, By = 0.833 Wb/mz Gross yoke area = 47.777 cmz Yoke height = 7.027 cm, Yoke Width = 6.799 cm Length = 33.398 cm, Frame dimensions : Height = 29.054 cm B. LOW VOLTAGE WINDING : Voltlphase = 127.017 V No. of turns = 20 turns Currentlphase = 65.608 Amps Cross section of conductor = 28.525 mmz width = 16.00 mm, From table, bare conductor thickness = 1.SO mm conductor c/s = 28.800 mm2 New current density = 2.278 A/mmz Insulation thickness = 0.250 mm width = 16.500 mm Insulated conductor thickness = 2.300 mm Winding type : Helical Turnsllayer = 9 No. of layers required = 2.22 + 3 {to provide clearance} Actual turndayer = 7 Layer-layer voltage = 89.10 V Axial depth = 13.200 cm Clearance with yoke = 0.900 cm Inter-layer insulation = 0.500 mm Radial depth of LV winding = 7.900 mm Insulation between core & first layer =' 1.50 mm LV winding dia's : inside = 8.299 cm, Outside = 9.879 cm C. HIGH VOLTAGE WINDING : Voltlphase = 2.200 KV No. of turns = 346 turns Currentlphase = 3.788 Amps Cross section of conductor = 1.647 mmz Conductor dia = 1.448 mm bare conductor dia = 1.50 mm, From table, overall dia (ins.) = 1.745 mm New current density = 2.144 A/mmz Winding type : Cross over No. of coils needed = 1.47 4 2 Tumskoil = 173.00 + 174 tums Coil arrangement : 5 layers * 35 tums/layer + 175 turndcoil Tums covered by 1 coils = 175 Turns left = 171
Reinforced coil : 5 layers * 34 turnSAayer + one layer of 1 turns Layer-layer voltage = 63.64 V Radial depth = 10.000 mm Axial depth of one coil = 6.107 cm Insulation between coils = 5.00 mm Axial depth of h.v. winding = 12.715 cm Clearance with yoke = 1.143 cm Insulation between windings = 6.980 mm HV. winding dia's : inside = 11.275 cm, Outside = 13.275 cm D. PERFORMANCE : Low side resistance = 0.004 Ohms High side resistance = 1.586 Ohms Resistance refer to high side = 2.832 Ohms Full load copper loss = 121.898 Watts
a) Iron loss Density of core material = 7600 Kg1cub.m Core volume = 0.00161 cub.m Total core mass = 12.255 Kg From curve, at B = 1.O Loss/Kg = 1.20 W Total core loss = 3 1.863 Watts Yoke volume = 0.00287 cub.m Total yoke mass = 2 1.829 Kg From curve, at B = 0.833 Loss/Kg = 0.80 W Total yoke loss = 26.195 Watts Total Iron loss = 58.057 Watts Full load efficiency (pf=l) = 99.29 YO V. CONCLUSIONS In this paper, a very user-friendly software have been introduced for power engineering students and design engineers. Due to limitation of space, complete coverage of all the options have not been possible, but because of it's wide applications and large number of options, the authors feel that this package could be very useful for teaching, learning, and designing purposes. The availability of personal computers in laboratories have offered new possibilities in power engineering education. With this software, lab instructors can demonstrate and explain the transformer design concept on this screen and can quickly respond to student's queries with on-line explanation. The students can learn more by using the program and exchanging ideas and questions with fellow students. The engineering intuition of the students is greatly developed by moving the emphasis from the numerical analysis and computer programming to the comprehension of fundamental principles of transformer design [4]. VI. ACKNOWLEDGMENT The authors acknowledge the computing and publishing support of NED University of Engineering and Technology,
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Karachi, Pakistan and King Fahd University of Petroleum and Minerals, Dhahran, Saudi Arabia.
VII. REFERENCES [I]
A. B. Crompton and K. S. Rowe, Principles ofTransformer Design.
[2] M. G. Say, Alternating Current Machines, 4“’ edition, Pitman, London, 1976.
131 A. K. Sawhney, A Course in Electrical Machine Design, Dhanpat Rai and Sons, India, 1980. [4]
A. Z. Khan and F. Shahzad, “A challenging Laboratory for the Comprehension of Power System Transient Stability,” IEEE proc. Of the 28”’NAPS, MIT, Boston, USA, Nov. 10-12, 1996.
VIII. BIOGRAPHIES Farrukh Shahzad was born in Karachi, Pakistan, on August 6, 1969. He did his BE(EE) from the NED University of Engineering & Technology, Karachi, Pakistan in 1992 and his MSEE from King Fahd University of Petroleum & Minerals (KFUPM), Dhahran, Saudi Arabia in 1996. He worked with Philips (Consumer Electronics) in Karachi in 1993. Currently, he is working at a Telecommunication company in NJ, USA. His areas of interest are power systems, Control systems and signal processing with emphasis on software development and computer applications. He is US copyrigth holder of four Engineering Softwares.
M. H. Shwehdi (S’74, M’85, SM’90) received his BSc(EE) from University of Tripoli, Libya in 1972. He obtained his MSEE from the University of Southern California and Ph.D. from Mississippi State University in 1975 and 1985 respectively. He was a consultant to A.B. Chance Company from 1981-1987, and Flood Engineer from 1990 to 1993. Dr. Shwehdi held teaching positions with the University of MissouriColumbia (1986-87), Texas A&I University (1987-88), University of Florida (1988-91) and Penn. State University from 1991-1993. At present he is with the King Fahd University of Petroleum & Minerals (KFUPM), Saudi Arabia. Dr. Shwehdi is active in IEEE activities both locally and nationally. He was named and awarded IEEE/IAS oustanding Supervisor for Student Research 1989, 1990 and the IEEE outstanding student advisor in 1990.
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