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1. Again for the Leroy Somer Motor the DC Test was performed across only two stator terminals which would have marginally affected the accuracy of the calculated theoretical stator resistance Table 16 DC test data DC Test Channel 1 Channel2 Average Vims V 25 182 25 214 25 198 Ams A 1 023 1 019 1 021 39 Real Power W 25 374 25 421 25 3975 Complex Power VA 25 752 25 700 25 726 Frequency Hz 0 000 0 000 0 000 Power Factor 0 9853 0 9822 0 98375 6 2 1 Calculations Again the calculations are based on the method described in Chan and Shi 2011 DC Test 2R 2E 38 Ipc V a Ri DE 2Ipc _ 25 198 2x 1 021 12 340 No Load Test Qi y 01h P 39 4 239 683 x 0 896 42 846 210 438VAr Xn Y 40 7 _ 210 438 0 8962 262 1250 Because s 0 Xn Xi Xy 41 Determining Losses Pin Psc Peore Pmisc 42 317 Ri Prot 43 3 x 42 846 3 x 0 896 x 12 340 128 538 29 720 Prot Prop 98 818W Locked Rotor Test Performed at 50Hz Qo y Mh P 44 40 61 2433 x 1 022 46 119 42 316VAr _Q Xir 7 1 _ 42 316 1 0222 50 5140 For a Class B motor X 0 4X_R 0 4 x 50 514 20 2062 Xz 0 6X1R 0 6 x 50 514 30 308 From the no load test Xn 262 125 Hence Xm Xn X1 262 125 20 206 241 919 P R Ty _ 46 119 1 022
2. cccesscceceeeeessesseees 46 Figure 20 The total reactance from the no load teSt cccccoconococoonnnnonanononnnnnnnononanonononnnnncnnnnannononons 53 1 Introduction 1 1 Overview The aim of this project was to configure the Voltech PM6000 Power Analyser to measure the voltages currents and power in two different induction motors under various test conditions These measurements were then used to determine the parameters of each motor s equivalent circuit The equivalent circuit is a per phase representation of a three phase induction motor that can be used to model a real world machine Parameters that were determined include the stator and rotor impedances and the magnetising reactance of the motors Also the stator copper losses and rotational losses were found The resistance Rc corresponding to core loss was not considered in the analysis Core losses include hysteresis and eddy current losses which during normal operation are very small and thus have been ignored The calculated parameter values were used to generate torque speed curves in Matlab By measuring the torque of the motors directly and by comparing various points in the stable region of the motors actual torque speed curves with the curves that were generated in Matlab it is possible to verify that the calculated circuit parameters are correct The Voltech PM6000 is a versatile measurement tool with six configurable channels for AC and DC analysis It can
3. V2 rotor phase voltage referred to the stator V l stator current A l2 rotor current referred to the stator A Im magnetizing current A lc core loss current referred to the stator A R stator resistance Q R rotor resistance referred to the stator Q R core loss resistance referred to the stator Q X stator leakage reactance Q X2 rotor leakage reactance referred to the stator Q Xm magnetizing reactance Q Z the total stator impedance per phase Q Z the rotor impedance per phase referred to the stator Q s the slip in p u 3 Test Procedure The circuit parameters of a three phase induction motor as described in the previous section can be found by performing a series of tests that are analogous to the short circuit and open circuit tests on a transformer These tests must be performed under precisely controlled conditions as the operating temperature will affect the internal resistance of the motor and the rotor resistance will also vary with the rotor frequency If these effects are not taken into account this can lead to misleading results and a set of parameter values that do not accurately represent the motor circuit under normal operating conditions The precise details of how each induction motor test must be performed to achieve accurate results are described in EEE Standard 112 Test Procedure for Polyphase Induction Motors and Generators see Appendix 4 Althoug
4. ccccccnnococcnnconcnnnononononnnnnnnnnnnnnnnnonnnnnnnnnnanannnnnns 18 4 1 7 SDECITICATIONS airis a a E N E e Ee TE E EE ai 19 4 2 Variable Frequency Drive cacesevcctazs dolida lena ci d iden did dela condon td denaia 3 dida 3d al asian 20 4 2 1 OPEN ii A A AA a ee ree 20 4 2 2 Specifications ir a E E E iia 23 4 3 Toshiba MOtO Fetal fe aeaea E e ei EE E Raa EERE 24 4 3 1 Speciation oie 24 4 4 Leroy Somer MOTOT iiec oieri rE EEEE EEE AEE EA EE EE 25 4 4 1 SpPecIICA MON ane a EE E E E E E R 25 5 System Des Nina caer ola hie haat tle aie 27 5 1 NA aaraa a e eared cc ea aeaea t Sea eea d aaaea Ee 27 5 2 Australian Wiring Standards ccccccccccccssssssssececececesseneaecececseseesaeaeeesecesseseuaeaeeeessessessnaeess 30 6 Resultando 33 6 1 TOSHIBA MOTOR ieee issic coc AE EE sveas a ida ida its 33 6 1 1 Calculations tii cel nasi acne ai aed ot ee el eee 35 6 1 2 Torque Speed Characteristics onions iaaii a e e ia ei Ea 38 6 2 Leroy Somer MOtOF ic cc aa ar aa aas raaa Eea aaa A E Aa E aLaaa a AAAA EAE aA naes a aa iaa RaRa 38 6 2 1 Calcula ti t ar e taa 40 6 2 2 Torque speed characteristics ui 42 A E OETA E 43 FULUTS Workers di it 44 8 1 A Fier RN 44 8 2 Calibration of the Power Analyser ccccecssssccecececsssesssaecesecscesseeaaeceeeessessesauaeseeeessessesaaees 46 8 3 DYNAMOMETE Poses cote o 46 APENAS idas 47 9 1 Appendix 1 Matlab Program for Torque Speed Characteristic Curve cooonoococccncnnnanannnnnnss 47 9 2
5. These wiring configurations allow any wye or delta connected motor to be attached to the system provided it operates within the specified ratings of the other connected equipment Note that where HI and LO are written these points correspond to the input and output terminals of each channel on the back of the Voltech PM6000 5 1 System Schematics Figures 10 to 12 indicate where leads are connected between each piece of equipment and Figure 13 provides a close up view of the connections that are made to and from the Power Analyser so that phase currents voltages and power drawn by the motor of interest can be measured Internal circuitry of the equipment itself has not been provided but can be found in the relevant user manuals if necessary 27 DC Analysis VoltechPM6000 Power Analyser Wye connected stator DC CH1 HI A Lo eS Ry HI R 1 CH1 To Ry Figure 10 Wiring Configuration for DC test AC Voltech PM6000 Power Analyser PHI HI ny Lo PHL A7 PH2 HI CRN Lo PH2 l D MOTOR PH3 H PH3 A A Lo f H Neutral i i PE HI HI HI Y CHL Lo Lo Lo LabVolt 3 Phase Power Supply i 0 415V f Figure 11 Wiring Configuration for no load test 28 AC Line Mains Connection Earth Neutral Single Phase Power Supply 240V Power Analyser Connection Voltech PM6000 Power Analyser PHL MO
6. basically a transformer operation the equivalent circuit of the motor ends up looking like a transformer equivalent circuit Chapman 2003 The equivalent circuit is a useful tool for determining the response of an induction motor to changes in load If the circuit is to be used to model a real machine the parameters of the model need to be determined These parameters are derived from test data measured during the three tests described in Section 3 The equivalent circuit as shown in Figure 1 is a single phase representation of a three phase wye connected motor but can be also be used to represent a delta connected machine Chapman 2003 In order to simplify the analysis of the circuit the impedances on the rotor side are all referred to the stator side so that the effective turns ratio between the stator and rotor windings does not need to be taken into consideration As a result the calculated impedances are not the true impedance values of the motor but can be used throughout this report where rotor parameters have been specified Figure 1 has been adapted from the circuit diagram provided in Section 5 9 of the IEEE Standard 112 IEEE Power Engineering Society 2004 IX2 VV l2 R2 Vo Z Ro 1 5 5 Figure 1 Per phase equivalent circuit With reference to Figure 1 the quantities that are associated with the equivalent circuit and the equations which are used in Section 3 are described below V input phase voltage V
7. be used in a variety of applications ranging from power supplies operating in standby mode to high frequency power converters Its accuracy and bandwidth allows it to take measurements of all power quantities on any piece of electrical equipment Voltech Instruments Inc 2009 Another advantage of using this unit is that it eliminates the problem of needing several multimeters to take readings on multiple phases This report provides an introduction to the setup and operation of the Power Analyser specifically for the types of experiments that have been undertaken during this project In Section 5 a series of wiring configurations have been proposed that future students could use as a guide for performing each of the three parameter tests which are discussed in Section 3 In addition alternative tests methods recommended by the IEEE Power Engineering Society are given in Appendix 4 These are provided for information purposes only and were not directly used at any stage during this project however they should yield similar results to the methods that have been used For the benefit of the reader some background theory has also been given on the design and operation of induction motors as well as the other equipment that has been used throughout this project Also clauses from the AS NZ 3000 Wiring Rules have been listed which provide important information about safety wiring and operation of electrical systems which should be taken into considerati
8. clean up the waveforms Another cause for concern is that the voltages recorded in Table 10 are different from the voltages that were measured using a UNI T Multimeter and yet both the Power Analyser and the multimeter were measuring the same RMS values When the output voltage of the VFD was increased to the maximum possible value using the speed control knob on the unit the reading given by the multimeter was 240V the rated value of the drive and the reading given by the PM6000 was less than this This might suggest the PM6000 has difficulty measuring the PWM signal from the motor drive because if a sinusoidal power supply is used instead of the VFD the measurements from both devices match exactly In conclusion the data in Table 10 is probably not reliable When the motor parameters were calculated using this data the magnetizing reactance Xm was negative Because of this and based on the observations above it is likely that the voltages measured by the Power Analyser were in error Table 11 shows that when the motor was run unloaded the power factor on the first phase was about 30 lower than the power factor on the other two phases suggesting that the inductance was higher on the first phase and that perhaps the rotor is not uniformly wound If necessary capacitors could be used to correct this and improve the overall efficiency of the machine The only cause for concern would be if the voltages on each phase were unbalanced which could c
9. higher than before since the inductive reactance is lower This is because X is proportional to f In this case the harmonic distortion on the current waveforms exceeds the recommended 5 maximum but the distortion on the voltage waveforms is exceptionally large greater than 100 as shown in Table 10 Table 10 Data from the locked rotor test performed at reduced frequency using the VFD Locked Rotor Test Trial2 Ch1 Ch2 Ch3 Average Vims V 216 84 216 38 216 80 216 6733 Arms A 1 0948 1 0643 1 0794 1 0795 33 Real Power W 31 317 29 459 30 320 30 36533 Complex Power VA 237 39 230 29 234 01 233 8967 Frequency Hz 4 8228 4 8228 4 8228 4 8228 Power Factor 0 1318 0 1279 0 1295 0 129733 Vino 100 18 105 02 106 76 103 9867 Arno 15 986 15 988 17 357 16 44367 At first glance the large THD does not make much sense but it is likely that this value is determined by comparing the voltage and current signals using current as a reference phasor Since the voltage is not sinusoidal in nature like the current but instead exhibits square wave properties the Power Analyser decides that the voltage is highly distorted Conversely using the voltage as the reference phasor Vryp becomes quite small and Ayyp exceeds 100 The results suggest that the quality of the power coming from the motor drive is quite poor and a filter might be needed to
10. in the standard as the inverse of the core loss conductance Ge which is a function of the total core loss P described in Section 5 5 5 of the standard the no load phase voltage V o and the X Xy ratio It can be calculated based on the following equation Eh xy Ge x 1 62 Hence 1 Rc E 63 To find R2 R2 is first calculated at the locked rotor test frequency 2 2 Pr X2 X2 2 R2 Rit Xx 1 7 2 x X Gc 64 Ri is equal to half of the line to line stator resistance at the test temperature Ry and R2 are then corrected to the required temperature as per Section 5 2 1 of the standard IEEE Power Engineering Society 2004 9 4 3 Method 2 Summary The second method involves performing a no load test and then a locked rotor test at multiple frequencies The first one is performed at the rated frequency the second at 50 rated frequency and the third one at 25 of the rated frequency All locked rotor tests are conducted at the rated current IEEE Power Engineering Society 2004 Calculation Procedure The same calculation procedure used in Method 1 is used to determine the total leakage reactance X11 X2 and the rotor resistance R at each test point Curves of rotor resistance vs frequency and total leakage reactance vs frequency are then plotted in order to determine these resistance and reactance values at the required reduced frequency These values are then used to find the other par
11. parameters If the data points match up well with the simulated curve this should be a good indication that the calculated parameters are correct Dynamometers from the Lab Volt equipment could be used for this however they are designed to operate together with less powerful machines and may not be suitable for the motors used in this project Either they would have to be removed from the Lab Volt system or the motors would have to be housed inside the system The shaft of each motor would have to be modified so that a belt can be attached and the height of the dynamometers would need to be adjusted to match up with the shaft height of the motors which is not ideal Hence a permanent solution should be found 46 9 Appendices The following appendices include Matlab scripts for generating the torque speed characteristic curve of the motors used in this project the frequency response of an RC filter and also the PWM output of a VFD Also included are the alternative calculation methods recommended by IEEE for accurately determining the equivalent circuit parameters of a polyphase induction motor 9 1 Appendix 1 Matlab Program for Torque Speed Characteristic Curve The following code has been adapted from the Matlab script provided by Chapman in his textbook Electric Machinery Fundamentals 4 Edition Chapman 2003 oe M file torque speed curve m M file create a plot of the torque speed curve of the induction motor of Example 7 5
12. 2 44 1552 Ry R Ri 44 155 12 340 31 815 Ry Xx Qian xix _ R2 jX21 XjXm 45 46 47 48 49 50 51 41 as R2XjXf Rx oi R2 jX2 XjXM 52 Ry Ry x 2 53 30 308 a i x ia 241 919 40 2862 In Summary the per phase resistance and reactance in the motor is Xm 241 9192 X 20 2062 X 30 3082 Ry 12 3402 R 40 2862 6 2 2 Torque speed characteristics Figure 16 is indicative of a squirrel cage motor that has a high rotor resistance The starting torque and breakdown torque appear to be quite similar at around 7 5Nm Induction Motor Torque Speed Characteristic 8 E F Tok 0 ln 0 500 1000 1500 n m Figure 16 Simulated torque speed curve for the Leroy Somer induction motor 42 7 Conclusion This project involved measuring the input currents and voltages of three phase induction motors under different operating conditions The measurements were taken using the Voltech PM6000 Power Analyser which was configured to take readings on all three phases of the motor stator simultaneously The data taken from this analysis was used to calculate circuit parameters so that the motors could be approximated by a per phase equivalent circuit which further enables their performance characteristics to be investigated A system design was proposed which allows any similar motor to be connected so that its parameters can also b
13. 20f p 22 Where N is in rpm and p is the number of poles in the stator winding Also known as frequency inverters or variable speed drives VSDs VFDs generally work by first rectifying the incoming AC voltage into DC and then generating a series of pulses from the DC voltage to simulate a sinusoidal waveform at the desired frequency see Figure 6 The most common method for doing this is to run a sine wave and a triangle wave through a comparator generating a pulse when the value of the triangle wave is less than the value of the sine wave This is achieved by using insulated gate bipolar transistors IGBTs however silicon controlled rectifiers SCRs can be used as well Novak 2009 20 Message Signal 5r F p F j E FI E l F E J E LAA 1 A NTN TTT PAN HY Sy fh Al Pl K A 3 IA Lo Sol J ty J 0 ER E J el Lae PA Y AE AY Y AN Pl PoP KS ULY L H f E Jo t fo It dl t H tl t 0 1 0 2 0 3 0 4 0 5 0 6 0 7 0 8 0 9 1 Time PWM Signal 2r F F E E T F E F E 1 oO jo 30 1 2G r r c c r im r r r my 0 0 1 0 2 0 3 0 4 0 5 0 6 0 7 0 8 0 9 1 Time Figure 6 Diagram showing triangle and sine waves placed through a comparator to generate the pulse width modula
14. 33 The data in Table 14 is for a locked rotor test performed at a reduced frequency using the VFD Again we find that the power factor decreases and the reactive power drawn by the motor increases substantially compared to when the 50Hz Lab Volt supplies is used Table 14 Data from the locked rotor test performed at reduced frequency using the VFD Locked Rotor Test Trial2 Channel 1 Channel 2 Channel3 Average Vims V 216 45 216 04 216 40 216 2967 Ams A 1 0945 1 0934 1 0922 1 093367 Real Power W 45 902 45 640 45 818 45 78667 Complex Power VA 236 89 236 23 236 36 236 4933 Frequency H2 6 5010 6 5010 6 5010 6 501 Power Factor 0 1937 0 1932 0 1938 0 193567 Vrun 190 75 167 26 144 77 167 5933 Asno 0 8773 0 8875 0 7962 0 853667 In Table 15 it can be seen that even when the motor is run unloaded a large amount of current is drawn The real power drawn on the first phase Channel 1 is also less than that of the other two phases resulting in a slightly smaller power factor on phase one Table 15 No load test data No Load Test Channel 1 Channel2 Channel3 Average Vims V 240 78 239 56 238 71 239 6833 Ams A 0 899 0 882 0 906 0 895667 Real Power W 40 268 43 015 45 256 42 84633 Complex Power VA 216 58 211 28 216 27 214 71 Frequency H2 50 000 50 000 50 000 50 000 Power Factor 0 1859 0 2036 0 2093 0 1996
15. Appendix 2 Matlab Program for Frequency Response of Proposed RC Filter 48 9 3 Appendix 3 Matlab Program for PWM Output of the Variable Frequency Drive 49 9 4 Appendix 4 Test Methods Recommended by IEEE occcccconononocnnonononanononanononcnncnannnonanons 50 9 4 1 ThE NO Load t st Teronen Ta E A E TE began tenis te a n 50 9 4 2 Method Li A tdi 50 9 4 3 MCU 2 esses ch sees cade ca cells rd ta 52 9 4 4 Method Bici 52 9 4 5 Method A ca ia Mis ie ie Ai ea ee eas aA ae ees chaos 54 BIN OSTIAS A A A A ba 55 Tables Table 1 Rules of thumb for separating the stator and rotor circuit reactances coconcococccncnnnanonannnnnns 14 Table 2 Menu and submenu items which can be accessed via the keypad cccconocccoocconononanonannnnnos 16 Table 3 Maximum voltage and current that can be measured continuously and over one second 19 Table 4 Maximum and minimum ratings for power that can be supplied to PM6000 006 19 Table 5 Dielectric strength of inputs and OUTPUTS ccocococccnccncnonononannnnnonnnanonononnnnnnnnnanonononnnnnnananannnonanoss 19 Table 6 Electrical and temperature specifications for the Movitrac 07 Unit ccccononococccnncnnnanenannnnnns 24 Table 7 Nameplate information for the Toshiba motor ccccconococcnnnononanononannnnnonnnanonononncnncnnnnnnnnononons 24 Table 8 Nameplate information for the Leroy Somer motor cocoocccccncnononononnnocnnonnnanonanonnnnncnna
16. ENG460 Engineering Thesis Measurement of Induction Motor Parameters Using the Voltech PM6000 Power Analyser AA Y Murdoch UNIVERSITY Ashley Van Niekerk Supervisor Dr Sujeewa Hettiwatte Co supervisor Assoc Prof Graeme Cole 22 12 2014 Acknowledgements I d like to thank Dr Sujeewa Hettiwatte Mr lafeta Laava and Mr John Boulton for their ongoing support throughout this project Table of Contents Tables ieiuna a a a a a vs Laded este ersten hi Gales 4 eA AE E E EE E E E E E E AE 4 T trod Gt ON siiin a a a E aaa a E ENa E LEa aE 5 1 1 OVEN VIGW estes ns taa 5 1 2 APPO CN scsi indi 6 2 Induction MOtOrS cia dt 7 2 1 OPEN ii A A A A 7 2 2 Squirrel Cage vs Wound Rotor Design cccccccecssssssssececececessenseaececececeeseaeseeeceeesseseaeaeeeeeess 8 2 3 Equivalent Circuit alain 8 3 Test AN 10 3 1 DE ts 10 3 2 NO Load Testi ilatina peau Eaa e aaae AA EEE AEEA 10 3 3 Locked ROTON tE Stroem anenai aae aaie aa aea aaa aea a aae eee 12 A Systemi COMPONENTS siinne aeaa aa a aa EE E EEEE E EEEE 15 4 1 PM6000 Power AnalySel ccccccccccsssssssscecececessesssaeseceesceesessaeseceescessesaeaeseeeseseeseaeaeeeeeesseseees 15 4 1 1 OPS ATION aeeie ade eevee ee eae a e ee EE aE eE vane ene REEE 15 4 1 2 Menu temis niert osas anen Eiane EEEE ENAA sachet AEE AAE ER Ri 15 4 1 3 ON 16 4 1 4 A r acta vied cases cae ees aE eaa gan sees aa 17 4 1 5 Display aa da 18 4 1 6 Establishing a connection to a Computer
17. VITRAC 07 lt 4 PH2 cH Internal Circuitry MOTOR PH3 Braking Resistor Connection Not Used Figure 12 Wiring Configuration for the locked rotor test Voltech Back Panel He a eLo He A elo He Aa elo PE Banana plugs are needed for inputs and outputs of Voltech PE PE renos To VFD To Motor PE PE L1 L1 L1 L1 L2 L2 L2 L2 13 13 13 13 Terminal Box Terminal Box Figure 13 Connections to Power Analyser 29 5 2 Australian Wiring Standards When building and testing the system proposed in this report it is important that the equipment and wiring conforms to the guidelines laid out in AS NZS 3000 Wiring Rules 2007 Electrical Installations Appropriate safety measures should be in place to protect persons working on or near the equipment at all times Standards Australia 2007 The following information is a paraphrased summary of some of the key wiring and safety information provided in this particular standard which can be accessed via the SAI Global Database AS NZS 3000 1 5 3 Protection against Electric Shock The system must be provided with protection against electric shock which may arise from touching parts that become live during fault conditions indirect contact o
18. actance X Hence X and R can be ignored and the equivalent circuit reduces approximately to Figure 2 Under these conditions the impedance of the motor is essentially a series combination of R jX and jXm as shown in Figure 2 Chapman 2003 R IX V V V a i I 2 V 2 H gt R as jX M S friction windage amp core gt gt Xm Figure 2 Approximation of the equivalent circuit under no load conditions Under no load conditions the power supplied to the motor is equal to the sum of the motor s individual losses Rotor copper losses are negligible since the rotor current l is extremely small and can be ignored Hence the input power P is equal to Pin Pscr Peore Praw Prise 5 where Psc is the stator copper losses P ore is the core losses Prgy represents the friction and windage losses and Pisc is the miscellaneous losses Chapman 2003 Copper losses occur due to the current flowing through the stator and rotor windings core losses occur due to hysteresis and eddy currents and frictional losses occur primarily in wound rotor motors when the rotor speed changes Miscellaneous losses can be caused by a non uniform current distribution in the motor and can also include additional core losses developed due to a distortion in the magnetic flux caused by the load current as well as losses due to harmonic fields Gonen 2011 The stator copper losses are given by Psc 317 Ry 6 The rotational loss
19. ameters in the motor s equivalent circuit as per Method 1 IEEE Power Engineering Society 2004 9 4 4 Method 3 Summary The third method involves performing an impedance test at a slip speed approximating the desired reduced rotor frequency The motor is allowed to run unloaded or with a reduced load and the voltage is reduced to give the full load slip point IEEE Power Engineering Society 2004 Calculation Procedure From the reduced voltage slip test the rotor resistance R and the leakage reactance X are obtained at a reduced frequency A no load saturation test described in Section 5 5 of the IEEE Standard is also performed Using the measurements from this test the reactance X on each phase 52 is determined at each test point and a plot of reactance vs phase voltage is created see Figure 20 The highest point on the curve gives the total no load reactance for each phase X4 Xm which is used in the calculations for the reduced voltage slip test IEEE Power Engineering Society 2004 Total reactance X per phase Volts per phase Figure 20 The total reactance from the no load test see text for description of labels In relation to Figure 20 A is the rated voltage B is the voltage measured during the reduced voltage slip test CDE is the total no load reactance determined from the no load test points Fis the reactance which corresponds to D the highest point on the curve CDE This value is used in calculation
20. ample motors should be fully enclosed so that fingers cannot be caught inside the rotor etc Standards Australia 2007 AS NZS 3000 1 5 14 Protection against external influences All parts of the system should be sufficiently protected against damage that could arise from environmental and other external influences that the system could be exposed to during normal operation Standards Australia 2007 AS NZS 3000 1 6 Design of an Electrical Installation Characteristics of the electrical installation shall be determined as per Section 1 6 of AS NZ 3000 Standards Australia 2007 AS NZS 3000 1 7 Selection and Installation of Electrical Equipment Electrical equipment which forms part of the system must be selected and installed to Operate safely during normal operating conditions and Not cause a danger from electric shock physical injury high temperature or fire in the event of reasonably expected conditions of abnormal operation overload fault or external influences that may apply in the electrical installation and Be installed in accordance with the manufacturer s instructions Standards Australia 2007 Further information on the General Arrangement of Electrical Equipment Control and Protection AS NZS 3000 2 2 1 2 Common Neutral 31 Each three phase and single phase part of the system which requires a neutral conductor in order to operate must have one A neutral conductor can be used for multiple circuits origi
21. are should be taken when obtaining measurements from these tests After performing the test the machine s impedance values are calculated as follows Chapman 2003 The per phase input power is given by Pin Vy X I cos 10 Where V and I are the average phase voltage and current respectively and O is the power PF angle Rearranging the locked rotor power factor is equal to PF in 11 vxl 0 cos 1 PF 12 The magnitude of the per phase impedance of the motor during this test is given by v Ziel 2 13 1 Z p consists of both resistive and reactive components which can be found using trigonometry where Zin Rint jX ie 14 Z p X cos 0 j Z g X sin 0 15 Rig 1Z p X cos 16 X r 1Z p X sin 17 The locked rotor resistance Rg is equal to Rip Ri R gt 18 Hence the rotor resistance can be found as R gt Rip Ri 19 13 Where R was determined in the DC test The locked rotor reactance X g at the test frequency frest is equal to the sum of the rotor and the stator reactances X ir Xy XxX 20 Since the reactance and the frequency are proportional to each other the total equivalent reactance at the normal operating frequency frateg is equal to Xie Hi Xip X Xp 21 test In order to separate the contributions of the rotor and stator reactances from each other Table 1 can be used This table specifies the proportions between X and X
22. as the voltage level of the AC line feeding into the drive any unbalance on the three input phases filters on the drive and so on Amick Avery and Amer 2010 The third and final primary section of the main power circuit is the inverter This section is comprised of the IGBTs which are triggered to switch on and off in such a way that the output phases are lagging each other by 120 degrees The rate at which the transistors are gated or turned on usually ranges between 2 to 15kHz Higher carrier frequencies yield smoother current waveforms but also greater VFD losses Amick Avery and Amer 2010 It should be noted that there is a phase shift between current and voltage waveforms due to the inductance in the connected motor Harmonic distortion in the current is reduced using a line reactor inductor which is essentially a conductor coiled around a magnetic core When current flows through the core a magnetic field is established and sudden changes in current amplitude or direction are opposed by the magnetic field which could be caused by the harmonic content The 22 inductance in the attached system is what causes the current to appear sinusoidal in nature due to its power filtering characteristics Amick Avery and Amer 2010 Figure 8 shows additional features such as the V f control circuitry and a speed reference In most cases the speed reference is just a set point In more complex situations the speed reference might
23. ause overheating and affect performance characteristics such as the locked rotor torque Table 11 No load test data No Load Test Channel1 Channel2 Channel3 Average Vms V 240 42 241 79 240 22 240 81 Ams A 0 694 0 689 0 714 0 699 Real Power W 13 648 20 591 18 023 17 42067 Complex Power VA 166 82 166 70 171 58 168 3667 Frequency Hz 50 020 50 020 50 020 50 02 Power Factor 0 0818 0 1235 0 1050 0 103433 In Table 12 the readings from Channel 1 and Channel 2 are quite similar One of the disadvantages of doing the DC analysis across only two stator terminals is that we ignore the stator resistance on phase three so if the test had been done on the third stator terminal as well this would have led to a 34 slightly more accurate approximation of the average per phase stator resistance One of the limitations of the test is that unless we can pull apart the motor and measure the stator test temperature it is not possible to correct R to what it would be during normal operation Table 12 DC test data DC Test Channel 1 Channel2 Average Vims V 15 234 15 088 15 161 Arms A 1 1293 1 1326 1 13095 Real Power W 16 779 16 768 16 7735 Complex Power VA 17 218 17 104 17 161 Frequency H2 0 0000 0 0000 0 0000 Power Factor 0 9745 0 9803 0 9774 It seems a little odd that the measured power factor is not exactly one because a DC voltage does n
24. be marginally lower than 1500rpm i e closer to the value stated on the motor s nameplate The shape of this curve is typical of a motor with a high stator resistance Induction Motor Torque Speed Characteristic 10 Tind a 0 es r r 0 500 1000 1500 n m Figure 15 Simulated torque speed curve for the Toshiba induction motor 6 2 Leroy Somer Motor Again a locked rotor test was performed at full rated frequency see Table 13 and at a reduced frequency and the same problem arose where the calculated value for Xm was negative when values from Trial 2 see Table 14 were used As such this data in this table is probably not reliable Table 13 shows that by using the Lab Volt equipment to power the motor the harmonic distortions in the voltage and current waveforms are well below the 5 limit specified by IEEE There does not seem to be any anomalies in the data 38 Table 13 Data from the locked rotor test performed using the 50Hz Lab Volt power supply Locked Rotor Test Trial 1 Channel 1 Channel2 Channel3 Average Vims V 61 940 60 172 61 615 61 24233 Ams A 1 0422 1 0018 1 0231 1 022367 Real Power W 48 165 44 739 45 454 46 11933 Complex Power VA 64 553 60 279 63 035 62 62233 Frequency H2 49 982 49 982 49 982 49 982 Power Factor 0 7461 0 7422 0 7211 0 736467 Vino 1 7649 1 7542 2 0272 1 848767 Asno 0 4901 0 4725 0 5522 0 5049
25. bient temperature before performing another test 6 1 Toshiba Motor The locked rotor test has been performed at full rated frequency and at a reduced frequency because of certain issues that arose when the VFD was used These issues are described in detail below All currents and voltages are RMS values unless otherwise specified The data in Table 9 is for the locked rotor test performed at the full rated frequency The measured values look fairly consistent across all phases The total harmonic distortion THD in the current and voltage waveforms is well within the 5 limit recommended by IEEE in Section 3 1 2 of Standard 112 The power drawn by the motor is quite low much lower than the 370W rating so there is little chance that the windings would overheat during the experiment Table 9 Data from the locked rotor test performed using the 50Hz Lab Volt power supply Locked Rotor Test Trial1 Ch1 Ch2 Ch3 Average Vims V 59 709 59 828 58 179 59 23867 Ams A 1 1067 1 1333 1 1240 1 121333 Real Power W 40 298 41 174 40 511 40 661 Complex Power VA 66 082 67 802 65 395 66 42633 Frequency Hz 49 969 49 969 49 969 49 969 Power Factor 0 6098 0 6073 0 6195 0 6122 Vino 1 8770 1 7413 1 6668 1 7617 Arno 1 6080 1 4015 1 5921 1 533867 When performing the test at the reduced rotor frequency the amount of reactive power drawn by the motor is significantly
26. can be used to find individual losses in the machine which can be useful to know when looking at how well the machine converts electricity into mechanical energy To do this IEEE recommends running the test at 125 of the rated voltage down to the point where a further reduction in voltage increases the current For determining windage and frictional losses the stator 1 R losses are subtracted from the total no load loss the measured input power at each test point and the resulting values are graphed against the voltage with the curve extending down to zero voltage The intercept with the zero voltage axis is the winding and friction loss The core loss is obtained by subtracting the friction and windage loss and the stator losses from the input power A plot can then be constructed for finding the core loss at any desired voltage 9 4 2 Method 1 Summary The first method involves the no load test described above and a three phase locked rotor test performed at no more than 25 of the rated frequency that can be supplied to the motor During the locked rotor test several readings of the voltage the current and the input power are taken on all phases at different levels of voltage The voltage on each phase should be balanced The stator winding resistance or temperature is also recorded quickly so that the windings do not overheat The temperature can be equalized by taking the higher readings first and then the lower readings IEEE Power Eng
27. come from a process controller such as a tachometer or a PLC Amick Avery and Amer 2010 AC Line Diode LYYY Bridge Filter Rectifier Speed Reference gt Figure 8 Block diagram for a typical Variable Frequency Drive 4 2 2 Specifications The motor drive used in this project was developed by SEW Eurodrive and is a OS model from the Voltage amp Frequency Control Inverter Movitrac 07 series see Figure 9 OS indicates the size of this unit in terms of its power rating and is one of the smallest available Figure 9 Isometric view of the unit which is rated for 0 37kW AC machines Table 6 contains information about the operating specifications of the VFD Most importantly it gives the voltage current and frequency of the power that must be supplied to the drive in order for 23 it to properly function Also given in this table is the voltage current and power produced by the unit Table 6 Electrical and temperature specifications for the Movitrac 07 unit SEW Eurodrive 2003 Model MC07A004 2B1 4 00 Input Voltage V 200 240 Single Phase Current A 6 1 Frequency Hz 50 60 Output Voltage V O Vin Three Phase Current A 2 5 Power kW 0 37 IP Rating 20 Temp C 10 50 4 3 Toshiba Motor This section contains technical information about the Toshiba motor
28. d X are within 0 1 of their previous iterations Then Zz Va l 71 Ry sy Z2 X2 72 Using the value for total no load reactance X Xy obtained from the no load test point C the magnetizing reactance Xy is then determined by subtracting X from X Xy The rotor and stator resistances are corrected to the normal operating temperature IEEE Power Engineering Society 2004 9 4 5 Method 4 If no other method is practical a full load slip test can be used to determine R followed by a no load and locked rotor test to determine the remaining impedances as per Method 1 IEEE Power Engineering Society 2004 54 10 Bibliography Amick Christopher Paul Avery and Yaskawa Amer Machine Design 1 December 2010 http machinedesign com motorsdrives abcs and 1 2 3s variable frequency drives accessed November 2 2014 Bhatia A Understanding Motor Nameplate Information NEMA v s IEC Standards Fairfax Virginia n d British Standards Institution Degrees of Protection Provided by Enclosures for Electrical Equipment Against Mechanical Impacts IK Code 15 October 1995 Chan Tze Fun and Keli Shi Appendix H Experiment 1 Measuring the Electrical Parameters of Motor 3 In Applied Intelligent Control of Induction Motor Drives by Tze Fun Chan and Keli Shi 397 401 John Wiley amp Sons Pte Ltd 2011 Chapman Stephen Electric Machinery Fundamentals New York McGraw Hill 2003 Daware Kiran Three Phase Inducti
29. d rotor torque to start in a number of different industrial applications Bhatia n d 24 Insulation Class The Insulation Class is an industry standard that refers to the thermal tolerance of a motor s windings It is based on adding the operational heat and the ambient temperature of the motor together Class F indicates the motor has an operating life of approximately 20 000 hours at 155 C Bhatia n d Frame Most motor dimensions are standardized and are usually associated with a specific number and letter designation The letter usually indicates the type of mounting and the number is the height from the centre of the shaft to the base of the motor The motor s dimensions can be found by looking up the number letter designation from an IEC NEMA motor dimensions chart Pontiac Electric Motors and Drives n d For example using the IEC system D71 indicates a flange mount with a shaft height of 71mm Bhatia n d IEC uses IP Ratings to indicate the level of protection provided by the motor s enclosure An IP56 rating indicates complete protection from dust and flooding of water Bhatia n d Duty Cycle Rating The IEC uses eight duty cycle designations to describe the operating conditions of an electrical motor S1 refers to Continuous duty which means the motor operates at a fixed load long enough for it to reach temperature equilibrium The Engineering Toolbox 2014 4 4 Leroy Somer Motor This section contains technica
30. e calculated providing the system can provide sufficient power to the motor in question and that it operates within the specified ratings of the connected equipment Special care should be taken when analysing motors with a wound rotor design because the impedance of the rotor can vary depending on its position relative to the stator This is not the case with squirrel cage designs Most of the data that was gathered during this project was assumed to be reliable because the tests that were conducted could be replicated easily and with each trial there was minimal variation in the results This was not the case when the locked rotor test conducted at a reduced frequency because of the significant amount of noise present in the power being supplied to the motor One of the drawbacks of this investigation is that it did not take into account the effects of resistance changes due to temperature increases and variations in the impedance due to the skin effect which means the calculated parameter values may not be a completely accurate representation of the motors under normal operating conditions Regardless the equivalent circuit is still only an approximation due to various assumptions that are made in the calculation procedure The only way to properly verify that the calculations are correct would be through further investigation and by implementing the suggested recommendations in the following section of this report entitled Future Work 43 8 Fut
31. e phase voltage V y phase current 1 y and the input power Pp using the following equation Qo MV1 o 0 p 58 The magnetizing reactance Xy and the stator reactance X can then be calculated using an iterative procedure where _ m 1 An Qo MIf 9X1 d ar 59 QL X mi 44 Xq Xm x X1 X2 X1 Xy 60 Where X is the stator reactance at the locked rotor test frequency The stator reactance at the rated frequency is given by X ees oe 61 fL Where f is equal to 50Hz and f is the reduced locked rotor test frequency Firstly Xj is estimated by assuming values for Xy Xm and X4 Xy is estimated using the same value of X Xy The value for X X gt is selected based on the motor design as explained in the previous section Using the value obtained for X4 the value for X at the rated frequency is calculated Values obtained for X and Xm are then used to calculate new values for X and Xy The process is repeated until Xy and X are within 0 1 of their previous iterations Then using the selected X X gt ratio X is calculated at the rated frequency If convergence is not reached after 10 iterations it is likely that the initial guesses for the parameters are not good approximations of the final values and new values should be chosen 51 The final stage of this method involves determining the core loss resistance R and the resistance of the rotor R referred to the stator side R is defined
32. ed In the following calculation procedure Xy is taken into consideration and the two parallel branches in the circuit containing jXm and R jX respectively are combined producing Ry and Xy as shown in Figure 14 R IX IX R IX 5 jXx 3 Xv SR Y Ry Figure 14 Circuit diagram showing parallel branches combined to produce a simplified series circuit Qi y M h i Pf 28 59 239 x 1 121 40 6612 52 503VAr X r 29 _ 52 503 1 1212 36 41 780 For a Class B motor X 0 4X_R 0 4 x 41 780 16 7120 Xz 0 6X1R 0 6 x 41 780 25 0682 From the no load test Xn 342 6562 Hence Xm Xn 41 342 656 16 712 325 9440 B R P _ 40 661 1 1212 32 357 Ry R Ri 32 357 8 573 23 7840 _ R2 jX21 XjXm et Pee R2 jX21 XjXm Ry R2xiXm R2 jX2 xjXm Ry Ry X pan M 25 068 ta r x as 325 944 27 582 30 31 32 33 34 35 36 37 37 In Summary the per phase resistance and reactance in the motor is Xy 325 9440 X 16 7120 X 25 0682 R 8 5730 R 27 5820 6 1 2 Torque speed characteristics Figure 15 was generated using a Matlab script see Appendix 1 and is based on the calculated parameter values One of the limitations of the program is that it does not take into account the mechanical losses of the motor Taking these losses into account the maximum rotor speed would
33. ed for maintenance activities such as firmware upgrades Voltech Instruments Inc 2009 Connecting directly to a PC as opposed to the local network should avoid conflicts with the IT department A crossover cable can be used for making this connection Steps are given below 1 The cord should be plugged in to the correct socket and the Power Analyser should then be turned on 2 ADOS window must then be opened on the PC After the DOS prompt appears type ipconfig release and then wait for it to return Once the DOS prompt comes back the IP address displayed should be 0 0 0 0 Next type ipconfig renew and again wait for the DOS prompt to appear 5 To view the connection simply type ipconfig and the computer s IP address will appear Add a value of one to the fourth number of the address unless the last number is 255 If this is the case then subtract one from the number This new address will become the IP address of the Power Analyser 6 Take note of the subnet mask which in most cases is 255 255 0 0 7 Using the Power Analyser s interface navigate to the Ethernet menu and select Fix Settings 18 8 After this enter the Fix Settings submenu and set the IP address to the Power Analyser s new IP address determined in step 5 Also ensure that the subnet mask is the same as the computer s subnet mask for example 255 255 0 0 9 After this leave the menu If necessary turn off the computer s f
34. ed to prevent the rotor from locking and to increase the effective transformation ratio between the rotor and the stator Also the increased length of the conductors increases the resistance of the rotor which can improve the starting torque and the acceleration time Daware n d An advantage of the squirrel cage design is that there are no slip rings so sparking will not occur and the cost of these motors is relatively low since less conductive material is needed On the downside they have a lower starting torque a high starting current and are quite sensitive to supply voltage fluctuations Teja Squirrel Cage Induction Motors Advantages Disadvantages and Applications 2011 Wound rotor motors have a group of coils forming windings which are carried by the rotor As a result they are more expensive to build but have the advantage of being able to develop a higher starting torque and lesser starting current as compared to a squirrel cage motor Also the total resistance of these motors is not constant but can be varied by adjusting the external resistors connected to the rotor circuit at start up A fair amount of the heat generated during start up is dissipated in the resistors The Institution of Electrical Engineers 1997 2 3 Equivalent Circuit For an induction motor to work it relies upon the induction of voltages and currents in the rotor circuit from the stator circuit Since the induction of voltages and currents in the rotor circuit is
35. eristics of a machine over time such as an appliance which would draw a varying amount of power This feature is not useful for this project and will not be needed Voltech Instruments Inc 2009 Datalog Data logging allows the user to record a set of results to the Power Analyser 6MB of non volatile flash memory is available for this and floppy disks can be inserted for additional storage The user should take into consideration the amount of data they wish to store and also the rate at which measurements are taken Voltech Instruments Inc 2009 4 15 Display Features in the Display menu allow the user to display certain information on the screen which by default isn t shown such as peak voltage and current values and the total harmonic distortion on a particular signal Voltech Instruments Inc 2009 Using the Math feature measured parameters can also be used and manipulated to create new measurements This is achieved by selecting the required measurements and using the Edit Function option to create a new equation using the available operators For more information on this feature refer to the user manual Voltech Instruments Inc 2009 4 1 6 Establishing a connection to a Computer Using the data logging capability measurements can be saved and accessed either using the menu or by establishing a connection with a computer or a network and downloading the data using Internet Explorer An Ethernet connection can also be us
36. ersely proportional to f as per the following equation 1 C aft 55 R e e 2 Vin E Vout Figure 17 Circuit diagram for a first order low pass RC filter As the frequency is increased Xc becomes much smaller than R so most of the current flow is through the capacitor Consequently the voltage drop across the output terminals becomes quite low Storr 2014 Depending on the values of R and X there will also be a certain voltage drop across the entire filter In order to minimize this voltage drop components must be selected such that the output input voltage ratio is close to one where 44 V X out C 56 Vin R2 x2 Storr 2014 For this project a filter that allows anything with a frequency equal to or below the maximum 12 5Hz needed for the locked rotor test would be desirable since the circuit would not be used for other tests where the motor is required to operate at the 50Hz line frequency A cut off frequency of 12 6Hz could be achieved with 2000 resistors and 63uH capacitors connected on each phase as per Figure 18 Using these components there would be a voltage drop of around 28 9 when fouppiy iS equal to 12 6Hz which is quite significant Using these resistance values the VFD can supply 1 2A of phase current to the motor at 240V PH1 2000 63uH PH2 2000 63uH PH3 2000 63uH Figure 18 Schematic for the proposed three phase RC filter A higher order fil
37. es are given by Prot Peore Praw Pmisc 7 Hence 11 Pin 317 Ry Prot 8 Chapman 2003 The current needed to establish a magnetic field in an induction motor is large because of the air gap so the magnetizing reactance Xy will be much smaller than the resistances in parallel and the power factor will also be small Since the current is lagging most of the voltage drop will be across the inductive components of the motor and the equivalent impedance will be approximately equal to Zea X1 Xm 9 linl Chapman 2003 3 3 Locked Rotor test Combining the results from the previous two tests with the data from a locked rotor test shortly to be explained allows X X2 R and Xm to be found The locked rotor test corresponds to a short circuit test on a transformer To perform it the motor is connected as per Figure 12 see Section 5 Then the rotor is locked so that rotation is not possible and an AC voltage is supplied to the motor The voltage is increased until the current reaches the full load value Then resulting values for power phase current and phase voltage are quickly measured using the power analyser taking care not to overheat the windings Generally this is not an issue for small motors such as the ones used in this project since the current drawn isn t large enough to cause a significant temperature rise Chapman 2003 Since the rotor is stationary the slip is equal to one so the resistance i
38. for different rotor designs which are defined in NEMA MG 1 a standard published by the National Electrical Manufacturers Association NEMA in the United States Chapman 2003 Table 1 Rules of thumb for separating the stator and rotor circuit reactances X and X as functions of Xz Rotor Design X X Wound Rotor 0 5 Xir 0 5 X r Design A 0 5 Xin 0 5 Xip Design B 0 4 Xin 0 6 Xip Design C 0 3 Xin 0 7 Xin Design D 0 5 Xin 0 5 Xi Note In clause 5 5 1 of IEEE Standard 112 it is recommended that the machine is run for some time before taking measurements to ensure the input power to the motor is stable especially if the motor has grease lubricated bearings The reason for this is that the friction losses in the motor will change and will not stabilise until there is no excess grease on the moving parts Stability is considered to have been reached when the input power under no load conditions does not change by more than 3 between two consecutive readings taken half an hour apart at the same voltage level IEEE Power Engineering Society 2004 14 4 System Components 4 1 PM6000 Power Analyser The Voltech PM6000 is a versatile measurement tool with six configurable channels for AC and DC analysis It can be used in a variety of applications ranging from power supplies operating in standby mode to high frequency power converters Its accuracy and bandwidth allows it to take measurements of all power q
39. gning channels to groups For three phase measurements Channel 1 Channel 2 and Channel 3 can be assigned to a single group for precise measurement of each phase Using this setting Channel 1 becomes the reference phase for the other two phases A wiring configuration is also selected for the system being analysed Since there is a neutral wire in our system see Section 5 the Three Phase Four Wire mode is selected For the DC measurement the Single Phase Two Wire mode can be selected Only Channel 1 is required and can be assigned to its own group if desired Voltech Instruments Inc 2009 Y i n Seuges eee 8eges a see SSSES2 uu has SEEEES es Seegcea W Valtech Figure 5 Front view showing digital display with green and red sine waves indicating channel 1 current and voltage respectively Range Range settings are also applied to each group A range is determined by the highest signal that can be measured For instance with a voltage range of 200V a maximum voltage of 200V can be measured The range selected will depend on the type of shunt fitted With Voltech shunts 16 connected the Power Analyser will select the correct setting automatically when switched on Voltech Instruments Inc 2009 Coupling By default the PM6000 is set to AC DC coupling allowing it to measure both AC and DC signals simultaneously An AC only mode can be selected but is not necessary for this project
40. h can be used to model a real world machine if its parameters are known 2 1 Operation Induction motors work by supplying a balanced three phase voltage to the stator windings The current flowing through the windings produces a magnetic field which rotates at synchronous speed N Indian Institute of Technology 2006 The flux lines of the magnetic field cut through the rotor which is stationary at start An electromotive force EMF is then induced in the rotor at the supply frequency This causes current to flow in the rotor creating a magnetic field The rotor magnetic field interacts with the stator field to produce a turning force This torque causes the rotor to turn in the same direction as the rotating magnetic field and the relative speed between the two decreases Indian Institute of Technology 2006 The rotor speed N will however never reach the speed of the magnetic field synchronous speed because torque which is proportional to N N is needed to keep the rotor spinning At synchronous speed the induced EMF and the current in the rotor would reduce to zero and there would be no torque produced For this reason the rotor speed will always be less than N The rotor speed will vary depending on the size of the mechanical load connected to the shaft and the rotor losses which comprises mainly of copper losses Indian Institute of Technology 2006 The difference between synchronous speed and the rotor speed is termed as the
41. h the details of these tests are quite complex a simplified approach can be undertaken and is described below Note that Rc is not included in these tests R is added to the equivalent circuit model to account for hysteresis and eddy current losses in the motor However because these losses are a function of the rotor frequency the term is only an approximation Missouri University of Science and Technology n d In addition if the supply frequency is 50Hz the slip of the motor will be small hence the rotor frequency will be quite low and core losses will be negligible 3 1 DCtest The DC test is performed so that the stator per phase resistance R can be determined see Figure 1 It can be completed using the system proposed in Section 5 see Figure 10 With the variable DC source from the Lab Volt power supply connected to the motor the supply voltage is gradually increased from zero to the point where the measured stator current is equal to the motor s rated current The purpose of this test is to heat the windings to the normal operating temperature since resistance is a function of temperature Since the current flowing through the stator is DC no voltage will be induced in the rotor circuit and so no current will flow in the rotor As a result if Reis ignored the only parameter limiting current flow is the resistance in the stator windings Since the DC source is connected to two of the three stator terminals see Figure 10 the c
42. in particular its electrical specifications and other important design information Also provided are notes on what the numbers and letters on the motor s nameplate actually mean and what these indicate about its performance characteristics 4 3 1 Specifications Nameplate Data Table 7 Nameplate information for the Toshiba motor Toshiba International Corporation n d The following information was taken directly from the induction motor itself Because of the age of this particular model it was not possible to find further technical details in the catalogue available on Toshiba s website Rated Power kW 0 37kW Model TSHO1 Rated Voltage V 415 Compliance AS1359 Rated Current A 1 1 Design Class N Power Factor 100 Load 0 65 Insulation Class F Frequency 50Hz Frame D71 No of Poles 4 IP Rating 56 Stator Connection Wye Duty Cycle Rating S1 Rated Speed rpm 1410 Mass kg 16 Notes on Specifications Design Class The performance characteristics of a motor will depend on the motor windings and the rotor design The International Electrotechnical Commission IEC and the National Electrical Manufacturers Association NEMA have designated specific designs of general purpose motors using letters IEC Design Class N is equivalent to NEMA Design Class B and is the most common industrial motor design These motors have normal starting torques and low starting currents They have adequate locke
43. ineering Society 2004 It should be noted that a wound rotor s impedance will change with the position of the rotor relative to the stator As a result it is necessary to know the position of the rotor that results in an average impedance when performing this test This issue does not apply to squirrel cage motors as their impedance is always the same regardless of the position of the rotor IEEE Power Engineering Society 2004 After completing the locked rotor test IV and PV curves are plotted and values of voltage and input power are derived from the curves in order to find the resistance and reactance of the machine at the desired level of current These values are calculated using the procedure described below The calculations assume a relationship between X and X based on the rotor design For example X1 a 1 0 for Type A Type D motors and wound rotor induction motors 2 0 67 for Type B motors 2 50 2 0 43 for Type C motors 2 IEEE Power Engineering Society 2004 These values can be derived from Table 1 Calculation Procedure Using the test data from the locked rotor test described above the reactive power Q is determined as a function of the phase voltage V the phase current J and the input power P is given by Q mV 111 1 Pf 57 Where m is the number of phases Then using results gathered from the no load test the reactive power Qv is calculated under no load conditions as a function of th
44. irewall to allow file transfer 10 An Ethernet connection between the PC and the Power Analyser should now be established To test this type ping followed by the designated IP address at a DOS prompt You should get several responses 11 To open files and directories simply open an internet browser and type the designated IP address in the address bar and then press enter 12 If an Ethernet port was used that is usually used to connect to the local network the user should connect to the network open a new DOS prompt and type ipconfig renew After this you should be back on the University network Voltech Instruments Inc 2009 4 1 7 Specifications The following tables contain information about the electrical ratings of the Power Analyser In particular the maximum voltages and currents that can be measured directly by the unit are given Table 3 as well as the voltage frequency and magnitude of the power that must be supplied to the unit in order for it to properly function Table 4 In addition information is given about the dielectric strength of the inlets and outlets to the PM6000 Table 5 Electrical Table 3 Maximum voltage and current that can be measured continuously and over one second Voltech Instruments Inc 2009 Measurement Max Voltage Max voltage Max Channel for Continuous for 1 Second Frequency Measurements Measurements MHz V V Voltage 2000 4000 10 Connections Curren
45. l information about the Leroy Somer motor used in this project In particular its electrical specifications and other important design information is given 4 4 1 Specifications Table 8 Nameplate information for the Leroy Somer motor Leroy Somer n d From Table s 7 and 8 we find that the electrical characteristics of both motors are quite similar in comparison In particular both have a power and voltage rating of 0 37kW and 415V respectively a similar rated current and rated speed and both feature a wye connected stator Rated Power kW 0 37 Model Mot3 AS712 4 Rated Voltage V 415 Compliance AS1359 Rated Current A 1 02 Design Class A Power Factor 100 Load 0 75 Insulation Class F Frequency 50Hz IK Rating 08 No of Poles 4 IP Rating 55 Stator Connection Wye Duty Cycle Rating S1 Rated Speed rpm 1375 Mass kg 6 4 Notes on Specifications IK Rating The IK rating comes from the European standard EN62262 It defines the type of protection that is provided by enclosures of electrical equipment against dust moisture solid objects and other 25 external mechanical impacts Specifically an IK rating of 08 indicates the motor enclosure is made of steel has a mass of approximately 0 5kg and has undergone a variety of impact tests British Standards Institution 1995 26 5 System Design Section 5 contains wiring diagrams for each of the three parameter tests conducted
46. ment used must be installed and operated so that the temperature characteristics of the equipment do not cause damage to the installation or any other installation either electrical or otherwise In particular equipment should not be operated outside its specified operating region unless advised otherwise to prevent overheating Where heat is generated during normal operation equipment should be adequately ventilated in order to maintain an operating temperature below the specified or rated limit of the equipment Standards Australia 2007 30 AS NZS 3000 1 5 9 Protection against Overcurrent Overcurrent protection must be in place which either disconnects the supply before the overcurrent reaches a dangerous value or which limits the maximum overcurrent to a safe value and duration Standards Australia 2007 AS NZS 3000 1 5 10 Protection against Earth Faults Parts of the system intended to carry an earth fault current such as protective earthing conductors must be capable of carrying the current without overheating Standards Australia 2007 AS NZS 3000 1 5 11 Protection against abnormal voltages Protection must be provided against harmful voltages which may arise from a fault between live parts of circuits and so on Standards Australia 2007 AS NZS 3000 1 5 13 Protection against injury from moving mechanical parts Protection must be provided against injury from mechanical movement of electrically actuated equipment for ex
47. n the rotor becomes close to Ra which happens to be quite small Since R and X are small most of the current will flow through them rather than the magnetizing reactance Xm which is much larger in comparison Under this condition the equivalent circuit can be approximated by a series combination of R1 X R2 and X2 as shown in Figure 3 Chapman 2003 R IX JX gt NNN LEN YY li l2 Ic Im 5 Ps A ERRIN AA E X lt Pe N Figure 3 Approximation of the equivalent circuit for the locked rotor test 12 When the rotor is stationary the rotor frequency f is equal to the supply frequency However during normal operation the slip of the motor is quite small Typically for most motors it is between 2 and 4 for the Toshiba and Leroy Somer motors their slip at full rated speed is 6 and 8 33 respectively Therefore the resulting rotor frequency is much less than the supply frequency 1 to 3Hz For this reason it is important to conduct the experiment at a reduced frequency typically 25 or less of the rated value in order to get accurate results since the effective rotor resistance is a strong function of f This can be achieved using a variable frequency drive VFD Chapman 2003 This procedure is generally acceptable for motors with a constant rotor resistance design Classes A and D however it could give misleading results when trying to find the resistance of a variable resistance rotor As such special c
48. nanannnonons 25 Table 9 Data from the locked rotor test performed using the 50Hz Lab Volt power supply 33 Table 10 Data from the locked rotor test performed at reduced frequency using the VFD 33 Table 11 N load testidatd iii ida eddie caida dada cid 34 Table 12 DCteSt daa decada iaa iaa 35 Table 13 Data from the locked rotor test performed using the 50Hz Lab Volt power supply 39 Table 14 Data from the locked rotor test performed at reduced frequency using the VFD 39 Table 15 No load test data sssrinin nirna ai O ETAO NORE 39 Table 16 DCs d annn E E E 39 Figures Figure 1 Per phase equivalent circuit ccccccccccecessesssseceeeeecessesssaeeeceeecesseeaaeseceescesseaaaeeeeeesesssessaaeess 9 Figure 2 Approximation of the equivalent circuit under no load conditions coccocococcnncnonanonannnnnss 11 Figure 3 Approximation of the equivalent circuit for the locked rotor test cocononoccccccncnonanonannnnnns 12 Figure 4 Rear view showing connections to Lab Volt equipment cccononococncononononononnnnconcnnnananannnnnns 15 Figure 5 Front view showing digital display cccsssscccccsssssesssceeeeeceseeseaeseeeeeceeseseaaeaeeseseessesssaees 16 Figure 6 Diagram showing triangle and sine waves placed through a comparator ceseeseseeees 21 Figure 7 Circuit diagram for a PWM VED c cccccccscsssssssaececececeeseseaeeeeecesseesaeaeeeeeces
49. nating from the same supply subject to the following conditions The continuity of the common neutral conductor must not depend on connections at the terminals of electrical equipment including control switches Sub circuits that have a common neutral must be controlled and protected by linked switches or linked circuit breakers The neutral conductor must be marked at switchboards to identify the associated active conductors Standards Australia 2007 AS NZS 3000 2 2 3 Selection and installation of conductors AS NZS 3000 2 2 4 2 Voltage The voltage rating of electrical equipment must be adequate for the nominal voltage of the system to which it is connected Standards Australia 2007 AS NZS 3000 2 2 4 3 Current Each item of electrical equipment must be selected and installed to be suitable for The design current taking into consideration any inductive capacitive and harmonic effects and The current likely to flow through the system during abnormal conditions for such periods of time as are determined by the characteristics of the protective devices concerned Standards Australia 2007 AS NZS 3000 2 2 4 4 Frequency If frequency has an effect on the characteristics of electrical equipment the rated frequency of electrical equipment must correspond to the nominal frequency of the power supply to which the system is connected Standards Australia 2007 AS NZS 3000 2 2 4 5 Power Each item of electrical equipme
50. nce sine wave amplitude c 1 SPWM output amplitude sDefines sine wave and sawtooth signals being compared inside the Scomparator ve a sawtooth 2 pi fc t 0 5 vm b sin 2 pi fm t Creates the pulse width modulated output voltage by generating a pulse Swhen the absolute value of vm is equal or greater than the absolute value Sof vc SThe pusle is negative when vc is negative n length vc for i l n if vm i vm i abs vm i gt ve 1 vm i abs vm i pwm i c vm i abs vm i else pwm i 0 end end sCreates subplot for comparator waveforms subplot 2 1 1 plot t vm t vc xlabel Time ylabel Amplitude title Message Signal grid on Creates subplot for PWM waveform subplot 2 1 2 plot t pwm xlabel Time ylabel Amplitude title PWM Signal axis 0 1 2 c 2 c grid on 49 9 4 Appendix 4 Test Methods Recommended by IEEE IEEE recommends a number of different methods for finding the parameters of an induction machine in Standard 112 Test Procedure for Polyphase Induction Motors and Generators All of these methods are similar in nature to the method described in Section 3 and should yield the same if not more accurate results They are summarised below 9 4 1 The No Load test The no load test is performed by running the motor at the rated voltage and frequency with no connected load It
51. nse of Proposed RC Filter SFirst need to define filter parameters for the single phase equivalent circuit R 200 C 6 3 10 5 RC R C fo 1 2 pi RC sCreating the transfer function for the Bode plot num 1 RC den 1 1 RC sys tf num den sGenerates the curves for Magnitude vs Frequency and Phase Angle vs SFrequency bode sys Converts the x axis units from rad s to Hz Mag Phase W bode sys Freq Hz W 2 pi Mag dB 20 logl1l0 Mag sCreates a label for the data point at the cutt off frequency labels fc num2str fc Hz SAdds labels to the first curve subplot 2 1 1 semilogx Freq Hz Mag dB title Bode Diagram xlabel Frequency Hz ylabel Magnitude dB hold on plot fc 3 rx text fc 3 labels VerticalAlignment top HorizontalAlignment right hold off SAdds labels to the second curve subplot 2 1 2 semilogx Freq Hz Phase xlabel Frequency Hz ylabel Phase deg hold on plet te 45 TIRT text fc 45 labels VerticalAlignment top HorizontalAlignment right hold off 48 9 3 Appendix 3 Matlab Program for PWM Output of the Variable Frequency Drive cle clear all t 0 0 000001 1 fc 15 5 Ssawtooth frequency fm 1 sreference sine wave frequency a 5 Ssawtooth amplitude b 4 srefere
52. nt selected on the basis of its power characteristics shall be suitable for the duty demanded of the electrical equipment Standards Australia 2007 AS NZS 3000 2 2 4 6 Effects on operator or other equipment Each item of electrical equipment shall be selected and installed so that providing it is maintained it will not cause harm to an operator or harmful effects to other equipment or impair the supply during normal service including switching operations Standards Australia 2007 32 6 Results This section discusses the results from the three tests performed on each induction motor as per Section 3 From this data the motor parameters were determined and then used to generate a torque speed curve in Matlab which can then be compared with measured torque values to verify that the calculated motor parameters are correct It should be noted that these results cannot be 100 accurate Certain factors which could influence the accuracy of the data can include calibration error of the instruments in particular the Power Analyser and also the internal resistance of the cables was not taken into consideration although this was thought to be negligible and thus shouldn t have a significant impact on the end results Something which may have a more noticeable impact on the end results is a temperature increase in the motor windings although care was taken to run the motor for as short a time as possible and to allow it to cool down to the am
53. oO oe oe First values needed in this program are initialised 1 12 340 Stator resistance 1 20 206 Stator reactance r2 40 286 Rotor resistance x2 30 308 Rotor reactance xm 241 919 Magnetization branch reactance v_phase 415 sqrt 3 Phase voltage ae o Je oO oe oO n sync 1500 Synchronous speed r min w_ sync 157 08 Synchronous speed rad s Thevenin voltages and impedances are calculated v_th v_phase xm sqrt r1 2 xl xm 2 z th 3 xm rl 3 x1 r1 3 x1 xm r th real z th x th imag z th Now the torque speed characteristic for many slips between 0 and 1 are calculated Note that the first slip value is set to 0 001 instead of exactly 0 to avoid divide by zero problens s 01 50 50 Slip s 1 0 001 nm 1 s n sync Mechanical speed o The torque for the original rotor resistance is calculated for ii 1 51 t indl ii 3 y th 2 ref s ii Y wee w_sync r th r2 s ii 2 x th x2 2 end Plot the torque speed curve plot nm t_indl Color k LineWidth 2 0 hold on label ita fm Fontweight Bold ylabel tau ind Pontweight Bold title Induction Motor Torque Speed Characteristic Fontweight Bold grid on hold off 47 9 2 Appendix 2 Matlab Program for Frequency Respo
54. on Motors n d http www electricaleasy com 2014 02 three phase induction motor html accessed October 17 2014 Energy Management Corporation VFDs com 20 March 2014 http www vfds com accessed October 11 2014 Gonen Turan Electrical Machines with MATLAB Second Edition London CRC Press 2011 IEEE Power Engineering Society IEEE Standard Test Procedure for Polyphase Induction Motors and Generators New York 4 November 2004 Indian Institute of Technology Lesson 30 Construction and Operation of Induction Motors Kharagpur 25 August 2006 Kothari D P and I J Nagrath Modern Power System Analysis New Dehli McGraw Hill 2003 Leroy Somer Nameplate Data for 3 Phase Induction Motor n d Missouri University of Science and Technology Induction Motor Parameter Measurement Electrical and Computer Engineering n d http ece mst edu media academic ece documents classexp ee208labs 09_ _Induction_Motor_Parameter_Measurement pdf accessed December 22 2014 Natural Resources Canada Principles of Operation AC VFD Drives 6 June 2014 http www nrcan gc ca energy products reference 15433 accessed October 3 2014 Novak Peter EC amp M Electrical Construction and Maintenence 1 May 2009 http ecmweb com power quality basics variable frequency drives accessed October 25 2014 Polka Dave Variable Speed Drives and Controls 2001 http www joliettech com what_is_a_variable_frequency_drive how_vfd_w
55. on when using the equipment An analysis of results has been provided which includes the theoretical calculations that were performed and a discussion of the reliability of the measured data Some recommendations have been made to further improve the project in Section 8 1 2 Approach This project began with preliminary research into the principles of operation of induction motors and the recommended test procedures After this a review of the Australian wiring standards was conducted and a series of circuit diagrams were developed for each parameter test Once these were approved the relevant equipment was acquired Some of the equipment that was used had to be modified In particular the motor shafts had to be fitted with detachable plates that were used to the lock the rotors in position for one of the tests Also some of the leads were not compatible Terminal boxes were made which replaced the three phase plugs that were fitted to the motors This allowed connections to be made to the Power Analyser After the modifications were completed testing could begin 2 Induction Motors Section 2 summarises the design and operation of induction motors It also highlights the differences between squirrel cage and wound rotor designs and compares each rotor type in terms of their performance characteristics The final part of this chapter introduces the equivalent circuit which is a single phase representation of a three phase induction motor whic
56. or and they are generally very efficient and low cost The other two major types are voltage source inversion VSI drives and current source inversion drives CSI which are known to cause motor cogging below 6Hz Energy Management Corporation 2014 21 As shown in Figure 7 a simple topology for a VFD includes a diode bridge converter a smoothing capacitor a filter and an inverter as well as additional control circuitry for achieving the desired frequency Polka 2001 YN A A K L K PH1 PHz MOTOR PH3 CL A Input Converter DC Bus Output Converter Diode Bridge Filter IGBTs Figure 7 Circuit diagram for a PWM VFD The convertor consists of six diodes connected in a full wave bridge configuration allowing current flow in one direction after the rectification When phase 1 s voltage is higher than the voltage on phases 2 and 3 the corresponding diode conducts a current When phase 2 becomes more positive than phase 1 then phase 1 s diode does not conduct This is also the case for the diodes on the negative side of the bus This results in a series of pulses as each diode opens and closes Amick Avery and Amer 2010 In order to smoothen the voltage waveform from the converter so that it is as close as possible to a DC voltage a capacitor is placed in parallel with the converter Typically this reduces the ripple to less than 3V but it can be affected by factors such
57. orks htm accessed October 16 2014 55 Pontiac Electric Motors and Drives Metric Dimensions Charts n d http www electric motor works com store metric dimensions charts php accessed September 19 2014 SEW Eurodrive Movitrac 07 System Manual Bruchsal Germany February 2003 Standards Australia AS NZS 3000 2007 Wiring Rules Sydney 2007 Storr Wayne Passive Low Pass Filter 2014 http www electronics tutorials ws filter filter_2 html accessed November 24 2014 Teja Dharma Harmonic Effects on Induction Motors 12 January 2012 http electricalquestionsguide blogspot com au 2012 01 harmonics effect induction motor impact html accessed October 26 2014 Squirrel Cage Induction Motors Advantages Disadvantages and Applications 15 November 2011 http electricalquestionsguide blogspot com au 2011 11 squirrel cage induction motor html accessed November 13 2014 The Engineering Toolbox IEC Duty Cycles 2014 http www engineeringtoolbox com iec duty cucles d_739 html accessed October 20 2014 The Institution of Electrical Engineers Power System Protection 3 Application London The Institution of Electrical Engineers 1997 Toshiba International Corporation Nameplate Data for 3 Phase Induction Motor n d Voltech Instruments Inc Voltech PM6000 User Manual Issue 19 Fort Myers FL 21 January 2009 56
58. ot vary with time so there can be no phase displacement in the current waveform and therefore the current could not be lagging the voltage This suggests that there must still be some AC signal flowing through the system which is very small and will not have much of an effect on the results 6 1 1 Calculations Note that the calculation procedure used below differs from the method presented in Section 3 This procedure has been used instead of the method proposed in Chapman 2003 because it assumes that the locked rotor test was performed at 50Hz and not at a reduced operating frequency although both approaches yield similar results The calculations below follow the procedure provided in Chan and Shi 2011 DC Test 2R 23 Ipc _ Voce 1 2Ipc _ 15 161 2x1 13095 8 573 No Load Test Q V 1 P 24 4 240 81 x 0 699 17 421 167 422VAr Xn Y 25 are 35 _ 167 422 0 6992 342 6560 Because s 0 Xn Xy Xu 26 Determining Losses Pin PscL Feore Pmisc 27 317R Prot 3 x 17 421 3 x 0 699 x 8 573 Prop 52 263 12 566 Prot Prot 39 697W Locked Rotor Test Performed at 50Hz Here two new quantities are introduced which were not mentioned previously in Section 3 3 namely Rx and Xx In Section 3 3 the calculations assume that under locked rotor conditions the equivalent circuit is essentially a series combination of R1 X R2 and X and Rc and Xyare ignor
59. r parts that are live during normal operation direct contact In section 1 5 4 2 of the Wiring Rules it is stated that methods of protection against electric shock arising from direct contact may include Insulation as per Section 1 5 4 3 Barriers or enclosures as per Section 1 5 4 4 Obstacles as per Section 1 5 4 5 Placing live parts out of reach as per Section 1 5 4 6 Protection against electric shock arising from indirect contact may include Devices that automatically disconnect the power supply when a fault occurs that is likely to cause a current flow through a person touching exposed conductive parts Devices that limit the amount of fault current that can pass through a person to a level that is safe Standards Australia 2007 AS NZS 3000 1 5 6 Residual Current Devices RCDs RCDs are designed to switch off the supply when current leaking to earth is detected at harmful levels and offer protection against electric shock Note that by themselves they are not recognized as an adequate method of protection against live parts but can be used in addition to the methods listed above RCDs should be installed in order to protect circuits power outlets lighting hand held equipment and other electrical installations as specified in AS NZS 3001 AS NZS 3002 AS NZS 3003 AS NZS 3004 AS NZS 3012 and AS NZS 4249 Standards Australia 2007 AS NZS 3000 1 5 8 Protection against Thermal Effects The electrical equip
60. re heavily distorted and the current waveforms are not This could be the case if a pulse width modulated PWM motor drive is used for speed control due to the harmonic content produced by the drive particularly at low rpms Voltech Instruments Inc 2009 This was found to be the case in this project when using a variable frequency drive VFD to control the motor under locked rotor conditions 4 1 4 Setup Mode This menu allows the user to select the best operating mode for the waveform being measured The default Normal mode is suitable for most measurement applications The Voltech continuously tries to detect the fundamental frequency of the voltage being supplied to the motor The PWM Output setting can also be chosen to analyse the output from motor drives when there is a fair amount of harmonic content Using this mode the data is sampled at high speed and the frequency of the motor is detected every few seconds using the voltage waveform The analysis of the harmonics will take longer at lower motor frequencies The PM6000 will analyse all of the requested harmonics before detecting the motor frequency Hence detection will be less frequent if the maximum number of harmonics to be analysed is increased Once completed the PM6000 will 17 attempt to show the modulated current and voltage waveforms at the motor frequency Voltech Instruments Inc 2009 Integrator The integrator feature can be used to determine the charact
61. s for the reduced voltage slip test as the total reactance X4 Xm G is the total reactance X Xy which is used for calculating Xy in the per phase equivalent circuit after X X and R are found from the reduced voltage slip test IEEE Power Engineering Society 2004 Using the data obtained from the reduced voltage slip test the total impedance per phase Z can be determined and then power factor can be calculated Using the power factor the phase angle of the input current can be calculated where 6 arccos PF 65 The total apparent reactance per phase X and the total apparent resistance per phase R can then calculated since both are a function of the impedance Z and the input current phase angle X Z x sin 6 66 R Z x cos 0 67 53 The value for X calculated is used as an initial estimate for the sum of the rotor and stator Xi reactances X4 X2 A value for a is determined based on the motor design Then the stator 2 reactance can then be found as follows X x X1 68 1 X1 X2 Using the value for X Xy obtained from Figure 20 the magnetizing reactance Xy is approximated by Xq X1 Xu Xi 69 Using the reduced voltage slip test data the induced rotor voltage V and current I referred to the stator are calculated and X is found Then Using the new value for X and the X X ratio that was previously determined the calculation process is repeated until X4 an
62. seseuaeeeecessessnsenaees 22 Figure 8 Block diagram for a typical Variable Frequency Drive ccccccononococnconononanononnnncnncnnnanonanonnnns 23 Figure 9 Isometric view of the unit which is rated for 0 37kW AC machines ccccccccesesssssseees 23 Figure 10 Wiring Configuration for DC test cccccssssscececeeseseseceeeeeceseeseaaeseeeescesseseaaeaeeeeseessesnaeens 28 Figure 11 Wiring Configuration for no load teSt ooocconcccccconocnncnononnncnononnncnononnncnonennnnnnnonnnnnnnrnnnnnnnns 28 Figure 12 Wiring Configuration for the locked rotor t St ccccsscccccecessesssseceeeeecessessaeeeeeeseessnseaeens 29 Figure 13 Connections to Power ANalySeT oooocccccononocoonnnnonononononnnonnnnnnnnnnnononnnnnnnnnnnnnn nn nnnnnnnnnnnnnnnnnons 29 Figure 14 Circuit diagram showing parallel branches cCoMbinNed ccccccccconoccnncnnnanonononncnnonnnanannnnnnons 36 Figure 15 Simulated torque speed curve for the Toshiba induction MoOtoF cccconccoococcnncnnnanonanonnnos 38 Figure 16 Simulated torque speed curve for the Leroy Somer induction MOtOF ooooooccccncnncanononnnnno 42 Figure 17 Circuit diagram for a first order low pass RC filter occcononococncnnononanononancnnonnnananannnnnns 44 Figure 18 Schematic for the proposed three phase RC filter ccoconccccccnncnonanononaancnnnnnnanrnnnnnnons 45 Figure 19 Frequency response of the proposed first order low pass filter
63. since we are interested in performing both alternating and direct current measurements Voltech Instruments Inc 2009 Scaling Scaling is applied to measurements to change the scaled output of transducers so that the true measured currents are shown on the screen of the PM6000 Since Voltech shunts are being used in this project a scaling factor of 12 5 is automatically applied to the measured current Voltech Instruments Inc 2009 Filter By default a 2MHz filter is applied to each channel in the group which prevents signals with a higher frequency from being measured A smaller bandwidth could be selected to help reduce noise in the measurements As a guideline the user manual suggests a filter setting of 10 times the frequency of interest 2kHz is the minimum setting available and because we are interested primarily in the fundamental frequency of the currents and voltages that are being measured this is the setting that was chosen Voltech Instruments Inc 2009 Frequency For the Power Analyser to accurately measure the RMS current RMS voltage power and so forth it needs to determine the fundamental frequency of the signal being measured This eliminates the problem of noise being included in the measurements By default Volts is the selected frequency source since the voltage waveform is not usually distorted during normal operation Voltech Instruments Inc 2009 The Amps setting can be chosen if the voltage waveforms a
64. slip of the motor and is usually expressed by the following ratio s Mr Ns 1 Where N and N are the synchronous and rotor speeds in rpm Indian Institute of Technology 2006 If the rotor speed is equal to the synchronous speed then the slip is zero With the rotor at rest the slip is equal to one With the torque varied from the no load to the full load value the slip is proportional to the torque At full load the slip will increase with the size of the motor usually between 1 and 5 As discussed before the frequency f of the EMF and also the current induced in the rotor at start up are equal to the supply frequency f The rotor frequency is a function of the slip where f pxNs N sxf 2 where N and N are given in rev s and p is the number of magnetic poles As the slip is generally small during normal operation f will only be a small fraction of the 50Hz supply frequency When stationary the N is equal to zero and f will be equal to f Indian Institute of Technology 2006 2 2 Squirrel Cage vs Wound Rotor Design Induction motors with squirrel cage rotors are robust in design and are used more commonly in industry than induction motors with wound rotors Squirrel cage rotors are made from a laminated core with parallel slits that support conductors The conductors are riveted to a short circuiting ring at each end to give the appearance of a cage The Institution of Electrical Engineers 1997 They are slightly skew
65. t 2 5 50 10 Connections Table 4 Maximum and minimum ratings for power that can be supplied to PM6000 Voltech Instruments Inc 2009 Line Input Min Max Voltage 90 264 VAC Frequency 47 63 Hz Power 170 170 VA Table 5 Dielectric strength of inputs and outputs Voltech Instruments Inc 2009 Dielectric Strength Voltage Mains Supply Inlet 2 9kV DC Live neutral to 19 earth Voltage 2kVpk Measurement Current 2kVpk Measurement Isolated supplies 2kVpk 30A Shunt 2kVpk 4 1 7 1 Measurement Accuracy The user manual lists formulas for calculating the error in each measurement The relevant formulas can be found in Section 8 6 of the User Manual Voltech Instruments Inc 2009 4 2 Variable Frequency Drive This chapter contains information about the design and operation of variable frequency drives VFDs and how they can be used for motor control Also included are the electrical specifications for the VFD that has been used in this project during the locked rotor test described in Section 3 3 4 2 1 Operation Essentially a variable frequency drive VFD is a motor controller that drives an AC machine by changing the frequency f of the current that is supplied to the motor Energy Management Corporation 2014 The synchronous speed N of the machine is directly proportional to f as per the following equation N 1
66. ted output signal The VFD also increases the output voltage in proportion to the supply frequency in order to maintain a fixed voltage to frequency V f ratio It is necessary to do this so that the motor can produce enough torque to keep running Voltage control is achieved by varying the duty cycle of the modulated voltage waveform Natural Resources Canada 2014 The frequency conversion process is not 100 efficient as 2 to 3 of the input power is converted to heat inside the VFD Furthermore the process can cause overvoltage spikes and harmonic distortion in the current Energy Management Corporation 2014 These distortions are significantly increased when operating from a single phase supply and particularly so on single wire earth return systems Fortunately there are several things that can be done to eliminate this problem The easiest method is to place a filter either side of the drive Another method is to connect capacitors to a common bus which act as a short circuit causing the harmonics to travel through the capacitors to ground If the harmonics are not removed on the line side of the drive overheating and crosstalk can occur where the distortion in one circuit interferes with other circuitry Energy Management Corporation 2014 Pulse width modulated VFDs are widely used in industry since they have a high input power factor due to a fixed DC bus voltage there is no motor cogging magnetic locking between the stator and the rot
67. ter could be used instead if a first order RC circuit is not sufficient One of the benefits of a higher order filter though is the narrower roll off region which prevents frequencies slightly larger than f from passing through the circuit Figure 19 is a bode plot which demonstrates that the proposed filter could potentially allow a fair bit of noise through because the roll off region is wide 45 Bode Diagram S 40 Magnitude dB 10 10 10 10 10 10 Frequency Hz Phase deg 10 10 10 10 10 10 Frequency Hz Figure 19 Frequency response of the proposed first order low pass filter Increasing the cut off frequency to 15Hz by using a 53uH capacitor instead would reduce the voltage drop to 23 2 It should be noted that the cut off of the filter does not need to match up exactly with the frequency of interest because at 12 5Hz the supply will likely produce harmonics of that frequency and these higher harmonics are the waveforms we are interested in removing 8 2 Calibration of the Power Analyser It appears as though the PM6000 has not been calibrated since 2009 It is recommended that the instrument is recalibrated to ensure any future measurements taken are as accurate as possible 8 3 Dynamometer A dynamometer should be used to take torque measurements This will allow students to compare the measured torque at various test points with a simulated torque speed curve based on their calculated motor
68. uantities on any piece of electrical equipment Voltech Instruments Inc 2009 4 11 Operation As specified in Table 3 a maximum voltage of 2000 V peak can be measured that can be connected directly into the yellow and black safety sockets at each channel refer to Figure 4 With the Voltech shunts fitted currents of up to 30A can be measured These shunts can be mounted directly onto the measurement channels without the need for additional wiring as shown in Figure 4 30A Voltech A which plug directly into the measurement channels y 7 Vf Yellow and black safety sockets which allow banana plugs to be connected Figure 4 Rear view showing connections to Lab Volt equipment 30A current shunts are fitted to each channel 4 1 2 Menu Items In order to configure the Power Analyser for AC and DC measurements the appropriate settings must be selected via the men using the front panel display of the unit see Figure 5 Menu items are organised as per Table 2 Voltech Instruments Inc 2009 15 Table 2 Menu and submenu items which can be accessed via the keypad Input Setup Display System Menus Other Functions Wiring Mode Measurement Config Menu Hold Range Integrator Format Interface Help Reset Clear Coupling Datalog Graph Printing User Integ Run Scaling Data Menu 1 Data Pump Filter Trigger Menu 2 Print Frequency Self Test Menu 3 Curve 4 1 3 Input Wiring The Power Analyser works by assi
69. ure Work It is advised that a permanent setup is built with equipment placed on a rack or housed inside an insulated box The VFD and the terminal boxes should be mounted inside the box so that the proposed system can be easily reconfigured for each of the tests This setup should be built in accordance with clauses referred to in Section 5 2 and other relevant guidelines from AS NZS 3000 In addition to this the following recommendations have been made 8 1 Low Pass Filter A passive RC filter is recommended for removing the harmonic content from the VFD s output The main reason for having this is because based on the observations in Section 6 1 the Power Analyser may have trouble taking accurate RMS measurements due to the large amount of distortion in the voltage waveform coming from the VFD Noise can also have a negative effect on the performance of the induction motor by increasing core losses increasing the skin effect causing electromagnetic interference EMI and a deviation from the motor s torque speed characteristics Teja Harmonic Effects on Induction Motors 2012 The RC filter works by only allowing currents through that are below a given cut off frequency fo which depends on the size of the capacitor and the resistor that are used in the filter circuit where fe 54 At low frequencies the capacitive reactance Xc becomes much larger than the resistance so most of the current does not flow through the capacitor Xc is inv
70. urrent only flows through two of the windings so the total resistance path is equal to 2R Hence R the per phase stator resistance can be found v O e 3 _ Voc i 2Ipc 4 The downside with this test is that it does not take into account the skin effect which is a tendency for AC current to flow mainly around the outer surface of a conductor This causes the effective stator resistance to be higher when AC power is supplied particularly at high frequencies Kothari and Nagrath 2003 Another issue is the effect of temperature Temperature corrections should be made to correct the calculated resistance value from the test temperature to the temperature the motor would be at during normal operation and this is not possible unless a thermal sensor can be placed inside the motor 3 2 No Load Test The no load test provides information about rotational losses and the magnetisation current of the motor The motor is connected to a variable AC supply as per Figure 11 see Section 5 and is allowed 10 to spin freely The only loads on the motor are the windage and frictional losses so all the power consumed by the motor is converted to mechanical losses in the form of heat The slip of the motor ends up being very small perhaps less than 0 001 As a result R 1 s s the resistance corresponding to the power that is converted is much larger than R the resistance corresponding to the rotor copper losses and much larger than the rotor re

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