sensors Article
Wireless Monitoring of Induction Machine Rotor Physical Variables Jefferson Doolan Fernandes 2 , Francisco Elvis Carvalho Souza 1 , Glauco George Cipriano Maniçoba 1, * ID , Andrés Ortiz Salazar 1 1
2
*
ID
and José Alvaro de Paiva 2
Programa de Pós-Graduação em Engenharia Elétrica, Universidade Federal do Rio Grande do Norte, Campus Universitário Lagoa Nova, Centro de Tecnologia, CEP 59078-970 Natal, Brazil;
[email protected] (F.E.C.S.);
[email protected] (A.O.S.) Instituto Federal de Educação, Ciência e Tecnologia do Rio Grande do Norte, Campus Parnamirim, CEP 59143-455 Parnamirim, Brazil;
[email protected] (J.D.F.);
[email protected] (J.A.P.) Correspondence:
[email protected]; Tel.: +55-84-99100-3581
Received: 29 August 2017; Accepted: 25 October 2017; Published: 18 November 2017
Abstract: With the widespread use of electric machines, there is a growing need to extract information from the machines to improve their control systems and maintenance management. The present work shows the development of an embedded system to perform the monitoring of the rotor physical variables of a squirrel cage induction motor. The system is comprised of: a circuit to acquire desirable rotor variable(s) and value(s) that send it to the computer; a rectifier and power storage circuit that converts an alternating current in a continuous current but also stores energy for a certain amount of time to wait for the motor’s shutdown; and a magnetic generator that harvests energy from the rotating field to power the circuits mentioned above. The embedded system is set on the rotor of a 5 HP squirrel cage induction motor, making it difficult to power the system because it is rotating. This problem can be solved with the construction of a magnetic generator device to avoid the need of using batteries or collector rings and will send data to the computer using a wireless NRF24L01 module. For the proposed system, initial validation tests were made using a temperature sensor (DS18b20), as this variable is known as the most important when identifying the need for maintenance and control systems. Few tests have shown promising results that, with further improvements, can prove the feasibility of using sensors in the rotor. Keywords: wireless communication; energy harvesting; electrical machines maintenance; induction motor control systems; rotor temperature
1. Introduction Electric machines play an extremely important role in industry, many of them making up 100% of their driving power. Misuse, failure to manage maintenance, and late detection of defects can cause months of repair and result in actual production losses or overspending with replacements [1]. By monitoring the physical variables of electrical machines it is possible to perform a more efficient and more reliable maintenance. This requires the use of suitable apparatus capable of recording various phenomena, such as: vibrations; temperature; performance; acceleration; among others. Based on the knowledge and analysis of the phenomena, it is possible to indicate, in advance, any defects or failures in the machines and equipment [2,3]. It is relatively easy to measure variables in the stationary part of the motor (stator), the difficulty appears when you want to observe the phenomena that occurs in the rotor. For this, one can make use of estimations from the variables of the stator, or use sensors in the rotor which brings great challenges due to the rotation [4–6].
Sensors 2017, 17, 2660; doi:10.3390/s17112660
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The monitoring of the physical variables of the rotor is very important for the detection of failures, as well as in the application of control systems. A widely used method for controlling induction motors (called control by rotor flow orientation) requires knowledge of the rotor time constant that is very sensitive to rotor temperature by measuring the temperature it is possible to more accurately estimate the time constant and thus improve the performance of the controller. But because of the complexity of implementation and the high cost of placing sensors in the rotor, parameter estimation methods are most commonly used to obtain values close to the exact local temperature [6]. There are basically two challenges for placing sensors in the rotor, energizing the transducer/sensor and transmitting data. With the rotation, the options found to solve these problems are:
•
Wireless energizing: # # # # #
•
Batteries [5,7,8]; Collector rings; RFID (Radio Frequency Identification) [9]; SAW (Surface Acoustic Wave) [10]; WPT (Wireless Power Transfer) [4].
Wireless data transmission: #
RF (Radio Frequency);
# # #
2.4 GHz [5,7,10,11]; 433 MHz [12].
RFID (Radio Frequency Identification) [9]; SAW (Surface Acoustic Wave) [10]; IrDA (Infrared Data Association) [8].
Energy harvesting (EH) technology could play a significant role harvesting various sources of ambient energy such as vibration, electromagnetic, thermal, etc. EH can be used to power the network nodes while storing the surplus in storage units (e.g., batteries, supercapacitor) [13–17]. The objective of this work is to develop a wireless embedded system for monitoring the physical variables of the rotor of electric machines. For this, the works were divided in two parts: 1.
2.
Design and develop a circuit for reading rotor variables and wireless information transmission. Following with the magnetic field effect study of the motor and analysis of packet losses in the wireless transmission. Design and develop a device responsible for converting magnetic energy of the rotating field into electrical energy, which will power the circuit of the embedded system. The device consists of a magnetic generator responsible for capturing magnetic energy, an AC/DC rectifier, a regulation stage, and an energy storage module using supercapacitor.
2. Proposed System Overview As previously mentioned, the objective of this work is to develop an embedded system to monitor physical variables in an induction motor rotor. The embedded system can be characterized as combining the use of hardware and software in a device with a predefined purpose. The embedded system has the purpose of controlling processes or acting on a problem. This is done using the peripherals, which are chosen and sized based on the problem [18–20].
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The proposed system represented by the block diagram in Figure 1 is formed by an energy Sensors 2017, 17, 2660 and a hardware. The hardware is divided into two printed circuit boards, one 3 ofto 14 generating device Sensors 2017, 17, 2660 3 of 14 house the data acquisition and communication circuit and one to the power circuit.
Figure 1. Embedded System Block Diagram. Figure 1. 1. Embedded Embedded System System Block Block Diagram. Diagram. Figure
2.1. Data Acquisition and Communication Circuit Data Acquisition Acquisition and Communication Circuit 2.1. Data The data acquisition and communication circuit consists basically of transducer, and communication consists basically microcontroller, The data dataacquisition acquisition andIn this communication circuitschematically consistsof transducer, basically of transducer, microcontroller, and RF module. work,circuit the structure shown in Figure 2 is used, and RF module. In this work, the structure schematically shown in Figure 2 is used, it is microcontroller, and RF module. In this work, the structure schematically shown in Figure 2 is used, it is composed of two parts. The first is a circuit A that is coupled to the rotor and rotates composed along with of two parts. The first is a circuit A that is coupled to the rotor and rotates along with it, here a it is composed of two parts. The first is a circuit A that is coupled to the rotor and rotates along with it, here a microcontroller receives the temperature values supplied by the sensor, processes the microcontroller receives the temperature values supplied by the sensor, processes the information it, here a microcontroller receives the temperature values supplied by the sensor, processes the information and sends to the RF module (Radio Frequency), it transmits the temperature values and sendsradio toand the RF module Frequency), itFrequency), transmits the radio information sends to signals. the(Radio RF module (Radio it temperature transmits thevalues temperature values through frequency The second part is a receiving circuit B external tothrough the motor in frequency signals. The second part is a receiving circuit B external to the motor in which a second RF through radio frequency signals. The second part is a receiving circuit B external to the motor in which a second RF module receives the signals containing the temperature information and sends it module themodule signals containing temperature information and sends it to a microcontroller which a receives second RF receives thethe signals containing thea temperature information and sends it to a microcontroller which in turn passes the information to computer. which in turn passes the information to a computer. to a microcontroller which in turn passes the information to a computer.
Figure Figure 2. 2. Data Data acquisition acquisition and and communication communication circuit. circuit. Figure 2. Data acquisition and communication circuit.
The The characteristics characteristics of of the the main main components components will will be be described described below below where, where, at at this this point point in in the the The characteristics of theinformation main components will be described where, at point in the research, the is current consumption of all research, the most most important important information is the the maximum maximum currentbelow consumption ofthis all components, components, research, the importantdevice information the to maximum current of all components, to the will power the circuitconsumption in consumption peak. to certify certify that thatmost the generating generating device will be beisable able to However, to certify that the generating device will be able to power the circuit in consumption peak. However, component component choices choiceswere weremade madewith withexpectation expectationfor foraalow lowpower powercircuit. circuit. component choices were made with expectation for a low power circuit. 2.1.1. 2.1.1. RF RF Module Module 2.1.1. RF Module To RFRF module would be most appropriate for our the following criteria Tochoose choosewhich which module would be most appropriate forapplication, our application, the following To choose which RF module would be most appropriate for our application, the following were considered: small size, low power consumption, low cost and the possibility to send and receive criteria were considered: small size, low power consumption, low cost and the possibility to send criteria were(transceiver). considered: (transceiver). small size, low power consumption, low costthese and the possibility to send information The one that most approached characteristics was the NRF24L01 of and receive information The one that mostthese approached characteristics was the ® and receiveof information one that approached these the manufacturer Nordic (transceiver). Semiconductor , shown in most Figure 3. in Figure ®, shown NRF24L01 the manufacturer NordicThe Semiconductor 3. characteristics was the NRF24L01 of the manufacturer Nordic Semiconductor®, shown in Figure 3.
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Figure 3. 3. RF RF module module NRF24L01. NRF24L01. Figure Figure 3. RF module NRF24L01.
The NRF24L01 is a ULP (Ultra Low Power) transceiver that has a data transfer rate of 2 Mbps The NRF24L01 NRF24L01 is Power) transceiver that hashas a data transfer raterate of 2of Mbps and is aaULP ULP(Ultra (UltraLow Lowband. Power) transceiver that data transfer 2 Mbps and The operates in the 2.4 GHz frequency Its peak consumption ina the transmission or reception operates in the 2.4 GHz frequency band. Its peak consumption in the transmission or reception of data and operates in the 2.4 GHz frequency band. Its peak consumption in the transmission or reception of data is 14 mA. is 14 mA. of data is 14 mA. 2.1.2. Microcontroller 2.1.2. Microcontroller 2.1.2. Microcontroller Like the RF module, the choice of the microcontroller was subject to the same criteria: reduced Like the RF module, the choice of the microcontroller was subject to the same criteria: reduced RF consumption; module, the choice of the microcontroller subject to the the same reduced size;Like low the power and low cost. It must also bewas compatible with SPIcriteria: communication size; low power consumption; and low cost. It must also be compatible with the SPI communication size; low power and low cost.with It must also be compatible with the SPI protocol in orderconsumption; to exchange information the RF module. Thus was chosen thecommunication microcontroller protocol in order to exchange information with the RF module. Thus was chosen the microcontroller protocol in order tothe exchange information with the RF module. Thus wasin chosen PIC18f14K50 from manufacturer Microchip Technology Inc., shown Figurethe 4. microcontroller PIC18f14K50 from the manufacturer Microchip Technology Inc., shown in Figure 4. PIC18f14K50 from the manufacturer Microchip Technology Inc., shown in Figure 4.
Figure Figure 4. 4. Microcontroller. Microcontroller. Figure 4. Microcontroller.
A 12 12 MHz MHz crystal crystal was was used used as as oscillator, oscillator, multiplied multiplied by by four four in in the the PIC PIC giving giving aa processing processing A A 12 MHz crystal was used as oscillator, multiplied by four in the PIC giving a processing frequencyof of48 48MHz. MHz.With Withthis thisfrequency frequencyand andpower powerofof3.3 3.3V V estimated maximum consumption frequency itsits estimated maximum consumption is frequency of 48 MHz. With this frequency and power of 3.3 V its estimated maximum consumption is 12 mA. 12 mA. is 12 mA. 2.1.3. Transducer Transducer 2.1.3. 2.1.3. Transducer Several types types of of sensors sensors and/or and/or transducers Several transducers can connect to the proposed embedded system, Several types of sensors and/or transducers canand connect to the proposed embedded system, since the the microcontroller analog digital inputs and supports various since microcontroller usedused allowsallows analog and digital inputs and supports various communication since the(SPI, microcontroller used analog and digital inputs and supports various communication protocols I2C, allows UART, 1-WIRE). protocols I2C, UART, (SPI, 1-WIRE). communication protocols (SPI,thermometer I2C, UART, DS18b20, 1-WIRE). For this this work work the digital digital thermometer DS18b20, manufactured manufactured by by Maxim Maxim®® (San José, California, For the CA, USA), ® For this work the thermometer DS18b20, manufactured Maxim (San José, California, EUA), was It is digital a transducer digital transducer that provides data calibrated in degrees Celsius. It uses was used. Itused. is a digital that provides data calibrated inby degrees Celsius. It uses 1-Wire EUA), used.communication It is a digital thatto provides data calibrated in Celsius. uses 1-Wirewas protocol whichtoallows connect several sensors in degrees the bus occupying protocol communication which transducer allows connect several sensors in the same bussame occupying aItsingle 1-Wire protocol communication which allows to connect several sensors in the same bus occupying a single pin of the microcontroller that monitoring temperature of several points of the rotor. pin of the microcontroller that allows monitoring temperature of several points of the rotor. a single pin of the microcontroller that allows monitoring temperature of several points of the rotor. 2.2. 2.2. Power Power Circuit Circuit 2.2. Power Circuit To circuit andand the generating device it is necessary to knowtothe current Todesign designthe thesupply supply circuit the generating device it is necessary know thedemand current of theToload, is, the acquisition board. of information the components of design supply circuit andcommunication the generating deviceFrom it isinformation necessary to know the current demand of that the the load, that is, the and acquisition and communication board. From of the this, a maximum expected consumption of approximately 33 was reached, shown Table 1.as demand of the is, the acquisition and communication board. From information of the components of load, this, athat maximum expected consumption of mA approximately 33as mA was in reached, components of this, shown in Table 1. a maximum expected consumption of approximately 33 mA was reached, as shown in Table 1.
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Table 1. Maximum expected current for the PCB of acquisition and communication of data. Table 1. Maximum expected current for the PCB of acquisition and communication of data. Component Maximum Current
NRF24L01 (RF Module) 14 mA Component(Microcontroller) Maximum Current PIC18F14K50 12 mA NRF24L01 (RF Module) 144mA DS18b20 (Transducer) mA PIC18F14K50 (Microcontroller) 12 mA LED 3 mA DS18b20 (Transducer) 4 mA TOTAL 33 mA LED 3 mA TOTAL
33 mA
With this, it was decided to design a power circuit with output voltage of 3.3 V and capacity for a maximum current of 50 mA, leaving a margin to avoid overload. With this, it was decided to design a power circuit with output voltage of 3.3 V and capacity for a maximum currentDevice of 50 mA, leaving a margin to avoid overload. 2.3. Generator 2.3. Generator Device on which the embedded system was installed is a three-phase four-pole The motor squirrel-cage rotor whose nominal parameters listed in 2. Fromfour-pole the characteristics of this The motor on which the embedded system wasare installed is aTable three-phase squirrel-cage motor it was dimensioned the generator device of the embedded system. rotor whose nominal parameters are listed in Table 2. From the characteristics of this motor it was dimensioned the generator device of the embedded system.
Table 2. Motor Parameters.
Table 2. Motor Parameters.Value Nominal Parameter Power 5.0 HP Nominal Parameter Value Voltage(∆/Y) 220/380 V PowerCurrent (∆/Y) 5.0 HP 14.1/8.19 A Voltage(∆/Y) 220/380 V Speed 1725 RPM Current (∆/Y) 14.1/8.19 A 60 Hz Speed Frequency 1725 RPM Frequency
60 Hz
2.3.1. Math Analysis 2.3.1. Math Analysis In order to make a qualitative analysis about the parameters and how they influence the induced voltage, mathematical equation was developed on influence the basic In order to make aaqualitative analysis about the parameters and based how they theconcepts induced of electromagnetism. voltage, a mathematical equation was developed based on the basic concepts of electromagnetism. Figure illustrate the four-pole magnetic field within the motor at atime given timeand point, Figure 5a,b5a,b illustrate the four-pole magnetic field within the motor at a given point, howand how the coils of the generator device interact with this magnetic field. the coils of the generator device interact with this magnetic field.
Figure 5. Arrangement of the generator coils in relation to the fourfour poles generated by the stator. Figure 5. Arrangement of the generator coils in relation to the poles generated by the stator. (a) Physical device; (b) simplified representation; (c) stator magnetic flux wave form. (a) Physical device; (b) simplified representation; (c) stator magnetic flux wave form.
rotational traverses the coils the generator with velocity v, which in ainterval time interval TheThe rotational fieldfield traverses the coils of theofgenerator with velocity v, which in a time ∆t ∆t travels the space S. Figure 6a shows top view of Figure 6b,small the small circles are tips the tips of the travels the space S. Figure 6a shows a topaview of Figure 6b, the circles in b in areb the of the magnetic arrows magnetic fluxflux arrows in a.in a.
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Figure 6. Representation of the relative displacement between coil conductors and the stator magnetic Figure 6. Representation of the relative displacement between coil conductors and the stator field. (a) Frontal view; (b) top view. magnetic field. (a) Frontal view; (b) top view.
Faraday’s Faraday’s Law Law states states that that in in aa conductor conductor subjected subjected to to aa magnetic magnetic flux flux variation variation φφan aninduced induced electromotive where absolute value for N conductors is given as: electromotiveforce forcearises ariseseeind ind where absolute value for N conductors is given as: eeind = N =N ind
dφ dφ. dtdt .
(1) (1)
Considering toto thethe area swept by by thethe conductor, it can be Consideringthat thatthe themagnetic magneticflux fluxisisperpendicular perpendicular area swept conductor, it can calculated by: by: Z be calculated φ=
BdA.
(2) (2) The flux density B in the air gap, shown in Figure 5c, can be described approximately by The flux density B in the air gap, shown in Figure a sinusoidal 5c, can be described approximately by a 2 sinusoidal B(s) = B0 sin s (3) r
φ = BdA .
2
= B0rsin s ( s )B(s), (3) where B0 is the maximum value assumedBby is the of the generator, and s is the space radius r traveled along the circumference. TheB0area canmaximum be calculated by:assumed by B(s), r is the radius of the generator, and s is the space where is the value traveled along the circumference. The area can be calculated by: A(s) = l.s
=>
dA = lds.
(4)
. Figure 6b. A( s )cutting = l.s the => flux dAlines, = ldssee Since l is the length of the conductor Substituting Equations (3) and (4) into (2), determine the magnetic flux: Since l is the length of the conductor cutting the flux lines, see Figure 6b. magnetic Substituting equation (3) and (4) determine the flux: Zsinto(2), 2 B0 lr 2 s ds = 1 − cos s . φ(s) = B0 l s sin B2 lr 2r r2 φ ( s ) = B0l0 sin s ds = 0 1 − cos s .
Knowing that, Knowing that,
0
r
2
s = v.t, and v =
ω r. 2
r
(4)
(5)
(5) (6)
ω the conductor relative to the magnetic In which v and ω are the linear and angular velocities r. s = v.t , and v = of (6) flux lines. If the rotor is rotating ω will be in function of the 2 slip frequency. The value 2 dividing ω refers to the number of pole pairs. In which v and ω are the linear and angular velocities of the conductor relative to the magnetic The expression of the flux becomes: flux lines. If the rotor is rotating ω will be in function of the slip frequency. The value 2 dividing ω refers to the number of pole pairs. B0 lr φ(t) = (7) [1 − cos(ωt)]. The expression of the flux becomes: 2
φ (t ) =
B0lr 1 − cos (ωt ) . 2
Substituting (13) into (7) and solving the derivative, we have:
(7)
eind =
NB0lrω sin(ωt ) . 2
(8)
This equation calculates the induced voltage in the conductors of one side of the coil, the induced voltage in the complete coil is twice this value, therefore: Sensors 2017, 17, 2660
eind = NB0lrω sin(ωt ) .
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(9)
This expression reveals that solving the maximum value ofwe thehave: induced voltage depends directly on the Substituting (7) into (1) and the derivative, dimensions of the generator l and r, the number of turns that is limited by the dimensions, the slip NBmotor 0 lrω supply current. frequency ω and B0 which is associatede with the sin(ωt). (8) ind = 2 2.3.2.This Prototype Construction equation calculates the induced voltage in the conductors of one side of the coil, the induced voltage in the complete coil is twice this value, therefore: The rotor has a diameter of 99.0 mm, so a core diameter of 96.0 mm was defined for the generator in order to avoid collisions with the stator. The generator device core was laminated to eind The = NB ). (9) 0 lrωsin ( ωtsystem minimize eddy current losses [11,21,22]. embedded will be fixed to the rotor, more specifically to the extensions of the aluminum bars shown in Figure 7. This expression reveals that the maximum value of the induced voltage depends directly on the The blades were made with galvanized steel sheet number 22, material chosen for being dimensions of the generator l and r, the number of turns that is limited by the dimensions, the slip ferromagnetic and easily accessible. Each blade is 0.80 mm thick. Twelve blades were made which, frequency ω and B0 which is associated with the motor supply current. after being ready, received a layer of varnish to electrically isolate one blade from the other. The thickness of the Construction core was approximately 10.0 mm, so as not to compromise the total available space 2.3.2. Prototype that is 30.0 mm, because there will be 20.0 mm remaining for the coils, 10.0 mm for each side of the core.The rotor has a diameter of 99.0 mm, so a core diameter of 96.0 mm was defined for the generator in order to 30 avoid collisions with thefour stator. generator core connected was laminated to minimize Using AWG enameled wire, coilsThe with 180 turnsdevice each were in series. Figure 7 eddy current losses [11,21,22]. The embedded system will be fixed to the rotor, more specifically to the shows the prototype ready. extensions of the aluminum bars shown in Figure 7.
Figure 7. Prototype generator set. Figure 7. Prototype generator set.
The blades were made with galvanized steel sheet number 22, material chosen for being 2.3.3. PCBs Prototyping ferromagnetic and easily accessible. Each blade is 0.80 mm thick. Twelve blades were made which, after circuits wereofdesigned PCBs were made, one for supply (1) and beingAfter ready,the received a layer varnish totwo electrically isolate one blade fromthe thepower other. The thickness of another for the acquisition 10.0 andmm, datasocommunication (2) as seen in Figure 8a,b. They attached the core was approximately as not to compromise the total available space thatare is 30.0 mm, through there terminals that them This configuration the system more because will be 20.0also mmconnect remaining forelectrically. the coils, 10.0 mm for each side makes of the core. versatile, it is necessary to change the acquisition andturns communication circuit for in another with Usingif 30 AWG enameled wire, four coils with 180 each were connected series. one Figure 7 more sensors or that ready. has some modifications, just replace the corresponding plate. Figure 8c shows shows the prototype the assembled system with all its parts ready. 2.3.3. PCBs Prototyping After the circuits were designed two PCBs were made, one for the power supply (1) and another for the acquisition and data communication (2) as seen in Figure 8a,b. They are attached through terminals that also connect them electrically. This configuration makes the system more versatile, if it is necessary to change the acquisition and communication circuit for another one with more sensors or that has some modifications, just replace the corresponding plate. Figure 8c shows the assembled system with all its parts ready.
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Figure 8. 8. PCBs. PCBs. (a) Top Top view; view; (b) (b) bottom bottom view; view; (c) (c) PCBs PCBsset seton ongenerator generatordevice. device. Figure Figure 8. PCBs. (a) Top view; (b) bottom view; (c) PCBs set on generator device.
2.3.4. Assembly Assembly 2.3.4. 2.3.4. Assembly With the the generator built built and and the the circuits circuits designed, designed, the the PCBs PCBs of of the the rectifier rectifier circuit circuit and and the the data data With With the generator generator built and the circuits designed, the PCBs of the rectifier circuit and the data acquisition and communication circuit were made. The parts were joined and the whole system was acquisition and and communication communication circuit circuit were were made. made. The The parts parts were were joined joined and and the the whole whole system system was was acquisition coupled to the rotor, as shown in Figure 9. With the machine running the system will rotate along coupled to Figure 9. 9. With thethe machine running the system will will rotate alongalong with coupled to the therotor, rotor,asasshown showninin Figure With machine running the system rotate with the and rotorthe and the PCBs will be supplied by energy captured by the generating device. the rotor PCBs will be supplied by energy captured by the generating device. with the rotor and the PCBs will be supplied by energy captured by the generating device.
Figure 9. System coupled to the rotor. (a) Outside the stator; (b) inside the stator. Figure 9. System coupled to the rotor. (a) Outside the stator; (b) inside the stator. Figure 9. System coupled to the rotor. (a) Outside the stator; (b) inside the stator.
3. Results 3. Results 3. Results The first tests have been done without the presence of the rotor, in order to make a previous The first tests have been done without the presence of the rotor, in order to make a previous analysis thetests system behavior. Without thethe rotor the motor cannot theto nominal at The of first have been done without presence of the rotor,receive in order make avoltage previous analysis of the system behavior. Without the rotor the motor cannot receive the nominal voltage at its terminals, the behavior. inductanceWithout is muchthe smaller, it presents lownominal impedance which analysis of thesince system rotor consequently the motor cannot receiveathe voltage at its terminals, since the inductance is much smaller, consequently it presents a low impedance which would lead tosince high the current values. is much smaller, consequently it presents a low impedance which its terminals, inductance would lead to highthe current values. To circumvent problem a VARIAC (Autotransformer) was used, with it was applied a voltage would lead to high current values. To circumvent the problem a VARIAC (Autotransformer) was used, with it was applied a valueTo necessary to generate the nominal current of the motor. circumvent the problem a VARIAC (Autotransformer) was used, with it was applied a voltage value necessary to generate the nominal current of the motor. Thevalue tests necessary performedtoingenerate the laboratory used the structure voltage the nominal current of theshown motor.in Figure 10. A is the computer The tests performed in the laboratory used the structure shown in Figure 10. A is B the computer screen that provides the graphics with theused temperature values received by the10. circuit (connected The tests performed in the laboratory the structure shown in Figure A is the computer screen that provides the graphics with thethe temperature values received by the circuit B (connected to to the USB of the computer), sent the by embedded system locatedby inside the motor C which to is screen that port provides the graphics with temperature values received the circuit B (connected the USB port of the computer), sent by the embedded system located inside the motor C which is energized by the three-phase VARIAC the USB port of the computer), sent byD.the embedded system located inside the motor C which is energized by the three-phase VARIAC D. In E there is three-phase also a gray induction machine, used as a generator that feeds a set of lamps with energized by the VARIAC D. In E there is also a gray induction machine, used as a generator tests. that feeds a set of lamps with 180 W F, serving a load for the motor during InofE power there isinalso a gray as induction machine, used as a laboratory generator that feeds a set of lamps with 180 W of power in F, serving as a load for the motor during laboratory tests. 180 W of power in F, serving as a load for the motor during laboratory tests.
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Figure (A)(A) Computer Monitor; (B) Receiver Circuit;Circuit; (C) Motor.; VARIAC; 10. Experimental Bench. Computer Monitor; (B) (C) Motor.; (D) Figure 10. 10.Experimental ExperimentalBench. Bench. (A) Computer Monitor; (B) Receiver Receiver Circuit; (C) (D) Motor.; (D) (E) Generator; (F) Load (Lamps). VARIAC; (E) (F) VARIAC; (E) Generator; Generator; (F) Load Load (Lamps). (Lamps).
3.1. 3.1. Generator Generator Rating Rating The generator device underwent aa test to it the voltage and a test to verify if it if meets the required voltage and output power The generator generatordevice deviceunderwent underwent test to verify verify if it meets meets the required required voltage and output output power (to supply the embedded system). For that a load of 35 Ω corresponding to the internal (to supply embedded system). For that aFor loadthat of 35 corresponding to the internal of power (to the supply the embedded system). a Ω load of 35 Ω corresponding to resistance the internal resistance of according to maximum transfer theorem, it the generator wasgenerator applied, was according to the maximum power transferpower theorem, it is in this condition resistance of the the generator was applied, applied, according to the the maximum power transfer theorem, it is is in in this condition that the generator will provide its maximum power. that the generator will provide its maximum power. this condition that the generator will provide its maximum power. During blue waveform), aa with aaa 12 12 A Arms currentapplied appliedon onthe thestator statorwinding winding(light (light blue waveform), During the the test, test, with with 12 A rms current applied on the stator winding (light blue waveform), rmscurrent peak ) was measured at the output (dark blue waveform), which corresponds apeak peakvoltage voltageof (4.24V ) was measured at the output (dark blue waveform), which corresponds voltage ofof666V VV(4.24 (4.24 VVrms rms ) was measured at the output (dark blue waveform), which corresponds rms to to aa power power of of approximately approximately 500 500 mW. mW. The The system system requires requires at at least least 5.5 5.5 V V peak peak and and aa minimum minimum power power of mW, the result shown Figure 11. Therefore the generating device meets requirements device meets thethe requirements of of 165 mW, mW,the theresult resultisis isshown showninin inFigure Figure11. 11.Therefore Thereforethe thegenerating generating device meets the requirements of the system. the system. of the system.
Figure 11. Waveform showing the voltage generated in the generator device. Figure showing the the voltage voltage generated generated in in the the generator generator device. device. Figure 11. 11. Waveform Waveform showing
The The next next test test was was based based on on the the embedded embedded system system (PCBs (PCBs ++ Prototype) Prototype) using using PCBs PCBs as as load, load, which which The next test was based on the embedded system (PCBs + Prototype) using PCBs as load, which means means that that all all components components are are powered powered by by the the generator generator device device (Figure (Figure 12). 12). The The voltage voltage at at the the means that all components are powered by the components: generator device (Figure 12). The voltage at the regulator regulator output output reached reached 3.3 3.3 Vdc. Vdc. In In this this test, test, all all components: temperature temperature sensor; sensor; microcontroller; microcontroller; and and RF RF module module are are working working as as proposed. proposed.
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regulator Sensors 2017,output 17, 2660reached 3.3 Vdc. In this test, Sensors 2017, 17, 2660 and RF module are working as proposed.
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Figure 12. Voltage value generated after passing through the regulator. Figure 12. 12. Voltage Voltage value value generated generated after after passing passing through through the the regulator. regulator. Figure
3.2. Evaluation of Data Transmission 3.2. Evaluation of Data Transmission In order to verify interference of the magnetic field of the machine on the data acquisition and In order to verify interference of the magnetic field of the machine on the data acquisition and communication circuit, the embedded system was confined inside the motor after the rear and front communication circuit, the embedded system was confined inside the motor after the rear and front covers were placed for interference analysis. The temperature reading, with the transducer in covers were interference analysis. TheThe temperature reading, with the transducer in contact wereplaced placedforfor interference analysis. temperature reading, with the transducer in contact with the generator core, is sent to the computer with a sampling rate of one second. Figure 13 with thewith generator core, is sent with a sampling rate of one Figure Figure 13 shows contact the generator core,to is the sentcomputer to the computer with a sampling rate second. of one second. 13 shows the temperature values read for 1000 s. The graph shows the motor temperature increases. the temperature values values read forread 1000for s. 1000 The graph motor increases. shows the temperature s. The shows graph the shows the temperature motor temperature increases.
Figure 13. 13. Temperature Temperature values, values,inside insidethe themotor, motor,received receivedand andplotted plottedon onthe thecomputer. computer. Figure Figure 13. Temperature values, inside the motor, received and plotted on the computer.
The next tests were performed with the system coupled to the rotor and the machine set to The next with thethe system coupled to thetorotor machine set to operate. The nexttests testswere wereperformed performed with system coupled the and rotorthe and the machine set to operate. To verify if the rotating radio would interfere with the communication, a test was performed operate. To verify if the rotating radio would interfere with the communication, a test was performed energizing the embedded system with a battery of 12 with V andthe 23communication, mAh. This battery was was chosen because To verify if the rotating radio would interfere a test performed energizing the embedded system with a battery of 12 V and 23 mAh. This battery was chosen it has dimensions that fit the available space. In order to reduce the power consumption for longer energizing the embedded system with a battery of 12 V and 23 mAh. This battery was chosen because it has dimensions that fit the available space. In order to reduce the power consumption for battery life, since it has a low electric charge, this test was done using a time of 2 s between because it has dimensions that fit the available space. In order to reduce the power consumption the for longer battery life, since it has a low electric charge, this test was done using a time of 2 s between the transmissions, resulting 793 asamples (thatcharge, corresponds approximately to 26a min) complete longer battery life, since in it has low electric this test was done using time until of 2 sthe between the transmissions, resulting in 793 samples (that corresponds approximately to 26 min) until the discharge of theresulting battery asincan be samples seen in Figure transmissions, 793 (that 14. corresponds approximately to 26 min) until the complete discharge of the battery as can be seen in Figure 14. complete discharge of the battery as can be seen in Figure 14.
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Figure 14. Wireless communication test. A: 50 V in the stator windings; B: 220 V in the stator windings; C: 100 V in the stator windings.
In order to analyze the response of the generating device, a test was performed with the rotor blocked, the stator received a current of A: 10 A.V With the oscilloscopeB:the for Figure 15 were Figure communication test. in V thein stator 220 images VB:in 220 the stator windings; Figure 14. 14.Wireless Wireless communication test. 50 A: 50 the windings; stator windings; V in the stator obtained. C: 100 V inC: the100 stator windings; V inwindings. the stator windings. Approximately 25 s after the engine was energized, the computer started to receive the temperature information sent by the prototype. At that time, the voltage in the data acquisition and In order to thethe generating device, a test was was performed with with the rotor In to analyze analyzethe theresponse responseofof generating device, a test performed the communication circuit reached 2.42 V. In approximately 70 s the voltage stabilized at 3.3 V until the blocked, the stator received a current of 10 of A. 10 With the oscilloscope the images for Figure 15 were rotor blocked, the stator received a current A. With the oscilloscope the images for Figure 15 motor shutdown, as seen in Figure 15b. obtained. were obtained. Approximately 25 s after the engine was energized, the computer started to receive the temperature information sent by the prototype. At that time, the voltage in the data acquisition and communication circuit reached 2.42 V. In approximately 70 s the voltage stabilized at 3.3 V until the motor shutdown, as seen in Figure 15b.
Figure 15. 15. (a) (a) Stabilized Stabilized voltage; voltage; (b) (b) Voltage Voltage after Figure after stopping stopping transmitting. transmitting.
Approximately 25 s has after was motor energized, the computer started the The generator device notthe yetengine run at rated speed, since at this speed theto slipreceive frequency temperature sent by the prototype. that time, the voltage in compensated the data acquisition is low, aboutinformation 5% of the synchronous speed. TheAt low slip frequency can be by the and communication reached V. In approximately 70 s the voltage at 3.3data, V until increase of the othercircuit parameters in 2.42 Equation (9). Based on Equation (9) andstabilized experimental an Figure 15. (a) Stabilized voltage; (b) Voltage after stopping transmitting. the motor shutdown, as seen in for Figure analytical estimate was made the 15b. induced voltage in the generating device for two different The generator has not16. yet run at rated motor speed, since at this speed the slip frequency situations, the resultdevice is in Figure The generator device has not yet run at rated motor speed, since at this speed the slip frequency is low, about 5% of the synchronous speed. The low slip frequency can be compensated by the increase is low, about 5% of the synchronous speed. The low slip frequency can be compensated by the of the other parameters in Equation (9). Based on Equation (9) and experimental data, an analytical increase of the other parameters in Equation (9). Based on Equation (9) and experimental data, an estimate was made for the induced voltage in the generating device for two different situations, analytical estimate was made for the induced voltage in the generating device for two different the result is in Figure 16. situations, the result is in Figure 16.
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12 of 14 12 of 14 10 Generator Divice 1 (Prototype) Generator Divice 2 Required Peak Voltage
9
Induced Voltage (V)
8 7 6 5 4 3 2 1 0
0
10
20
30 slip(%)
40
50
60
Figure Figure16. 16.Estimation Estimationfor forthe theinduced inducedvoltage voltagein intwo twogenerating generatingdevices deviceswith withdifferent different dimensions. dimensions.
The straight blue line (Generator Device 1) is the prototype response of this research. This The straight blue line (Generator Device 1) is the prototype response of this research. This prototype was built based on the dimensions of a 5 HP induction motor as described in Section 2.3.2. prototype was built based on the dimensions of a 5 HP induction motor as described in Section 2.3.2. It can be noted that it will only produce the voltage necessary for the load at a slip frequency of It can be noted that it will only produce the voltage necessary for the load at a slip frequency of approximately 40%. The Generator Device 2 would be the response of a generator with at least approximately 40%. The Generator Device 2 would be the response of a generator with at least double double the dimensions, 220 turns and installed in a machine of at least 10 HP. This device can the dimensions, 220 turns and installed in a machine of at least 10 HP. This device can already feed the already feed the load at a slip frequency of 5% satisfying the rated operating conditions of an load at a slip frequency of 5% satisfying the rated operating conditions of an induction machine. induction machine. In the next step of the research, the data acquisition and transmission circuit will be redone so In the next step of the research, the data acquisition and transmission circuit will be redone so that it can transmit not only the temperature but also the induced voltage in the generating device. that it can transmit not only the temperature but also the induced voltage in the generating device. This can be easily achieved using one of the analog inputs of the microcontroller along with the use This can be easily achieved using one of the analog inputs of the microcontroller along with the use of batteries to power the circuit. This way it will be possible to relate the induced voltage with the of batteries to power the circuit. This way it will be possible to relate the induced voltage with the parameters of Equation (9) including slippage. This study will enable more precise changes in the parameters of Equation (9) including slippage. This study will enable more precise changes in the attempt to make the generating device operate at rated engine speed. attempt to make the generating device operate at rated engine speed. 4. Conclusions 4. Conclusions The research was divided into two parts. The first concerns the development of a data acquisition The research was divided two The first information concerns the of a data and communication circuit, whichinto allows theparts. reading of rotor (in development this case the temperature) acquisition and communication circuit, which allows the reading of rotor information (in this case by rotating inside the motor and transmitting them to the external device, in this case a computer. the by as rotating inside the motor and transmitting themastoit the externalindevice, in this Thistemperature) circuit worked expected, several tests proved the operation, is verified the presented case a computer. This circuit worked as expected, several tests proved the operation, as it is verified results. The second part deals with developing a generator device with the aim of replacing the battery in thethus presented results. second part with developing a generator device with the aimhas of and guarantee moreThe autonomy and deals less cost (purchase of batteries). The generator device replacing the battery andthe thus guarantee more conditions autonomy of and less cost (purchase of batteries). not yet operated under nominal operating the machine, it still requires a highThe slip generator device has not yet operated under the nominal operating conditions of the machine, it still to operate. Improvements are being studied to achieve operation at the rated speed of the machine. requires highthe slip to operate. Improvements arethe being studied of to the achieve operation at the rated The test awith battery in addition to allowing validation circuit data acquisition and speed of the machine. The test with the battery in addition to allowing the validation of the circuit communication was also intended to verify how long the system works being exclusively powered by data acquisition was alsobattery intended toVverify how long thethe system works being the battery. Our and testscommunication found that an alkaline of 12 and 23 mAh kept transmission for a exclusively powered by the battery. Our tests found that an alkaline battery of 12 V and 23 kept period of approximately 26 min. It is a short time for most applications, this justifies themAh search for the transmission for a period of approximately 26 min. It is a short time for most applications, this alternative ways of feeding this type of system. justifies search for alternative ways this type of system. Thethe prototype was developed forof a feeding small motor (5 HP) with little space available for a larger The prototype was developed for a small motor (5 HP) with space available forasa shown larger generator device than the one designed, which directly affects thelittle voltage induced in it, generator device than the one designed, which directly affects the voltage induced in it, as shown in in Equation (9). For a greater asynchronous machine than the one used in this work, the better the Equation (9). For a greater asynchronous machine than the one used in this work, the better the viability of the proposed system, because the generating device will have larger dimensions, increasing viability the its proposed because themotor generating device have dimensions, its radiusof r and thicknesssystem, l. Since the nominal currents will bewill larger, thelarger flux density Bo will increasing its radius r and its thickness l. Since the nominal motor currents will be larger, the flux density Bo will also increase. These considerations and other improvements, such as using a more
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also increase. These considerations and other improvements, such as using a more efficient AC/DC circuit, compensate for the decrease in induced voltage caused by the low slip frequency. Acknowledgments: The authors would like to thank CAPES and CNPq for the financial support. Author Contributions: Jefferson Doolan Fernandes designed and assembled the circuit for data acquisition and transmission, built the generator device, conducted experimental tests, participated in writing and article corrections. Francisco Elvis Carvalho Souza designed and modeled the generator device, participated in the experimental tests, participated in writing and article corrections. Glauco George Cipriano Maniçoba Performed simulations of the generating device, participated in writing and article corrections. Andrés Ortiz Salazar and José Alvaro de Paiva oriented us in project and execution of the system and in the corrections of the article. Conflicts of Interest: The authors declare no conflict of interest.
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