Lab4_handout - DalTech — Dalhensie University Department...

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Unformatted text preview: DalTech — Dalhensie University Department ef Electrical «it Cempnter Engineering Electrical Machines Laheratery ECED 31th} — Lab 4 — Three Phase Inductien Meter m Te snidy the principle ef eperatien and perfermance characteristics ef a 3-phase, weund— reter inductien meter. W Operating Principles: It has been peinted eut previeusly that ene- ef the advantages ef a pelyphase sysmm (3th in particular) is that it can preduce a retating magnetic field. This retating field prevides the basis ef eperatien fer all an machines. It is ebtained by distributing a set ef three phase windings abeut the periphery ef the meter cere. When three phase currents flew in these windings, the time and space phase shifts resulting in an mini" wave which has the appearance ef retating at a censtant angular velecity in the air gap between the reter and stater. Having ebtained this, there are twe basic means ef using this retating wave te preduce retatienal metien. Dec methed is te have the reter travelling at the same speed as the retating field. This results in a “synchreneus” meter where the reter is lucked inte step. er synchreniaed, with the field. Since the speed ef the retating field is determined seler by the input frequency and the geemetry ef the machine (Le. number ef peles}, this predeces a eeestant speed meter. The ether methed is te allew the reter speed te be less than the speed ef the retating field te preduce a flux cutting. er transfermer actien. This results in an “asynchrcncus” (er inductien) meter where the reter eperates at a “slip” speed. Slip i‘s'defined as the difference between reter and field speeds divided by thefield specdflhe field speed is called the synchreneus speed]. The inductien meter is an 'asynchreneus meter which has a speed which decreases slightly as mere lead is applied. r r fr 5; Construction Details for Induction Motors: _ “if E? Tho induction motor comos in two forms: W 3 _ .cr i 1} tho wound rotor yorslon and .5; r a 2) tho cast, squirrol cago rotor Tho wound rotor yorsion has 3:1; coppor windings omhoddod in tho rotor with tho sarno polo structure. as tho stator. Tho winding torminals aro accossihlo through sliding contacts on ono cud of tho rotor (callod slip rings} Wound rotor motors arc primarily usod for spood control applications whoro tho rotor rosistanco is ostornally controllod, thus controlling tho spood rs. torquo charactoristic. Squirrol cago motors aro by for tho most common induction motor hocauso of thoir mggodnoss and constructional simplicity A ring of short circuitod bars parallol to tho rotor axis is made out of cast aluminum. (Thoso bars look yory much liko tho osorciso whool usod for small pot squirrols, hamstors, otc.; honco its nauto]. This cago will tako on whatoyor polo structuro tho stator windings prosonL Most squin'ol cago motors hayo a singlo fiaod spood and oporato undor full load at approximaton 95% of synchronous spood. W Machino Undor Tost: Tho LahVolt Wound Rotor Induction Motor may ho startod diroot-on-liuo from a 200 V, 60 Ha supply proyidod that you short-circuit tho ammotor and curront coil of tho wattmotor to protoct thom against tho yory high starting curront. Orton-Circuit Tost: With tho rotor winding opon—circuitod, connoot tho stator to a 200 V, 60 Ha, 3-phaso supply as shown in Figuro 1. Tako roadings of tho stator input cuggut and in ut o or, and tho stand-still rotor o.m.f.!phaso E2. Lookodvflotor Tost: Uso tho locking doyico on tho Induction Motor to lock tho rotor. Short circuit tho rotor windings and incroaso V. yory slowly until II = 1.3 A, rocord if“ 1,. and input powor (W11: 3) .II'_-"-\. Relationship of Rotor e.m.f. and Frequencyr to Rotor Speed: Remove the locking device and open circuit rotor windings. At an}r siip S, the induced rotor e.m.f.lphse is sE2 and its frequencyr is sf where f is the supply,r frequency. To verify this. use the D.C. Motoo'Generator as a DC. shunt motor to drive the rotor, as shown in Figure 2, over the speed range D — 1800 r.p.m. and measure the amplitude and frequencyr of the induced rotor e.m.f. at D, 150i} and 1300 r.p.m., when the stator is connected to a 3-phase, it] v. 60 Hz supply. Reverse the direction of rotation of the rotating magnetic field (by reversing any two of the stator temiioals connected to the supplyF and notice the amplitude and frequency of the rotor e.m.f. at the same three speeds. Load Test: Replace the DAB. Moton’Generator with the Dynamometer to load the Induction Motor as shown in Figure 3. Run the motor at its rated voltage of 20H V. Load the motor in steps from no load to full load {1.3 A}. For each step. talte readings of VI, I], input power (WI it 3}, slip S. and shaft torque T. ' Stator and Rotor Resistance: Measurement of stator resistance per phase R, and rotor resistance per phase R1 should he made using A [3W1 Miro—uh * i 5 '5' . % t. Y _ '3’ F . 'i ‘J. L 54 I: {E} l? I '11 1' f : “1.15.1 J; a W as _ waits P fl]; 4... a fill _ _. . - “L “I n 1} Frcm the cpen circuit test, determinegithe effective turns ratic NIB)? _ H N! ' U3 IUE . I Mfg—en U. N -. ——._- it arts) and small/statcr 2} Obtain the ccg_e;lns lav subtracting the rctaticnal lessee. cc er lcssés {31’ 1@nm the in ut cwer at ric-lcad. ,. _ lilP was i. P_F’ Tear Rfi-LQct, :Coééggfi 3] Dhtain— E‘s-1 “U31 a) the infp_hase component cf the nc-lcad current which supplies the lcsses as P. I : I'H I. P b} the magnetizing ccrupcnent cf the nc—lcad current is I," = till: — I F1 . c] the magnetizing reactance X - i n: _- £1,” ' d} the resistance R: in the equivalent circuit which represents the ccre lcsses is V '- carelesses . calculated as R = ‘ , where It = —~— is that ccm cnent cf which = at «J51»: P It at: if“; /-i— «am supplies the ccre .lcsses cniv. Why are I: and 1', different? "ab 4) Frcm the lccked-rctcr test determinfl = 11% 1 Calculate X: J21 fist =(x, +X1). *s—r T) Frcm the results cf the lead test, plct the ingut pcwer, ut que, speed, pcwer n cne grap P- H“ factcr and efficiency tc a base cf mctcr current, W l_,__—_.__'_ .H 55"“ "a _ 3} Using the apprcitimate equivalent circuit cf the meter cbtained in ti}, ccmpute the fellcwing at rated vclta e, and at Sm as measured during the lead test: . Isi'lrlitug‘Jl ILL and ratifl IsLflfl. Tu, Tu“, Tm and the ratics rfi {L and TMII‘LL and 31m. II II The meter pcwer factcr and efficiencyr at full lcatL I Campare the ccmputed values at full iced with these chtained frcm the lead [ESL t .p: 5“ '-"‘ l’U .- xJ-‘h': fl A; Hf- H£,flfi zjlfi I R (1—0 , L: [3“ g: ififib‘r‘ wwla-Ifi '* “w M 5:; mm m: '1’?" qa‘o 1U: J 11.! 1 fl: ’2) In. T: P ...
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Lab4_handout - DalTech — Dalhensie University Department...

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