EXPERIMENT NO : EM I/1

Transcription

1 EE 491 ELECTRCL MCHE LB. MUL EXPERMET O : EM /1 TTLE STUDY THE CHRCTERSTCS OF SEPRTELY EXCTED DC GEERTOR OBJECTE : T plt the fllwing characteristics f a separately excited DC generatr. lad characteristics r magnetizing curve.. Lad characteristics.. External characteristics. PPRTUS: Type Range Makers Serial 1 Mtr Generatr 3 mmeter 1 4 mmeter 5 ltmeter 6 Rhestat 7 Lad Bx 8 Tachmeter THEORY : 1. O-LOD CHRCTERSTCS OR MGETZG CURE. We knw that Eg and fr separately excited D.C. generatr f. S the generated emf Eg f. By increasing r decreasing the generated field current f we can vary the generated emf E g with speed cnstant by varying the mtr field current. This characteristic, drawn between the generated emf E g and field current f knwn as n-lad characteristic which is shwn in Fig. E g t t rmature Resistance Drp rmature Reactin Drp f f L FG. 1. O-LOD CHRCTERSTC FG.. LOD CHRCTERSTC FG. 3. EXTERL CHRCTERSTC. LOD CHRCTERSTCS. We knw that fr separately excited D.C. generatr terminal vltage t Eg ara and als the generated emf Eg f. S by varying the generated field current f we can vary the terminal vltage t keeping the speed cnstant by varying the mtr field current fr a cnstant lad current a. This Prepare By: Partha Ray Page 1

2 DC Supply DC Supply ELECTRCL MCHE LB. MUL EE 491 characteristic, drawn between the terminal vltage t and field current f knwn as lad characteristic which is shwn in Fig. 3. EXTERL CHRCTERSTCS We knw that fr separately excited D.C. generatr terminal vltage t Eg ara and als the generated e.m.f. Eg f. S by varying the lad current a we can vary the terminal vltage t keeping the speed cnstant by varying the mtr field current fr a cnstant generated field current f. This characteristic, drawn between the terminal vltage t and lad current a knwn as external characteristic which is shwn in Fig. CRCUT DGRM : L F S 1 R fm F1 F M 1 G 1 F1 F R fg L O D PROCEDURE : 1) Cnnect the circuit as shwn in Fig. ) Keep the switch S1 in OFF psitin. 3) Switch O dc supply and start the mtr with the help f three pint starter. 4) Run the mtr at its rated speed by varying the rhestat R fm t adjust the speed. 5) te dwn the vltmeter reading ( E g ). Thugh the generatr field is pen the vltmeter will read few vlts induced due t residual magnetism. 6) Excite the generatr field with full resistance R fg frm the 0 dc surce. 7) ncrease the generatr field f by reducing the field resistance R fg in step. te dwn at least five reading f E g and f. G up t 10 % f rated generatr vltage. 8) w make the switch S1 O. 9) By varying the field rhestat R fg vary the field current f keeping the lad current a cnstant. 10) te dwn the vltmeter reading t and generated field current f. 11) gain make the switch S1 OFF. 1) w adjust the generatr field current f by varying the rhestat R fg t btain the rated induced emf n generatr. 13) w make the switch S1 O and vary the lad current a step by step. Fr each step adjust the mtr field rhestat R fm t keep the speed cnstant. 14) te dwn the vltmeter reading t and lad current a. 15) Discnnect the circuit frm the supply. 16) Draw the three characteristics f separately excited generatr. Page Prepare By: Partha Ray

3 EE 491 ELECTRCL MCHE LB. MUL OBSERTO TBLE : 1. O-LOD CHRCTERSTCS : Field Current f (amp). LOD CHRCTERSRCS : Field Current f (amp) Generated emf E g (vlt) Lad = 3. EXTERL CHRCTERSTCS : RESULT Lad 1 1 amp. amp. 3 3 amp. 4 4 amp. 5 5 amp. DSCUSSO : Terminal ltage t (vlt) amp. Terminal ltage t (vlt) Lad Current L (amp) Speed (rpm) Speed (rpm) Field Current f (amp) Speed (rpm) : Draw the n-lad characteristic, lad characteristic and external characteristic f separately excited dc generatr. 1. What is residual magnetism?. Why lad characteristics have similar nature with n-lad characteristics? 3. Draw the n-lad characteristic, lad characteristic and external characteristic f series and shunt dc generatr. 4. n external characteristics, what are the armature resistance drp and armature reactance drp? Prepare By: Partha Ray Page 3

4 ELECTRCL MCHE LB. MUL EE 491 EXPERMET O : EM / TLLE STUDY THE CHRCTERSTCS OF DC SHUT MOTOR OBJECTE : T draw the fllwing characteristics f a D.C. shunt mtr PPRTUS:. Speed vs. rmature Current. Trque vs. rmature Current. Speed vs. Trque 1 Mtr mmeter 3 ltmeter 4 Tachmeter Type Range Makers Serial THEORY : 1. TORQUE CURRET CHRCTERSTC : We knw that fr a dc mtrt a. f the effect f armature reactin is neglected, is nearly cnstant in dc shunt mtr and we can writet a. Thus, fr shunt mtr, the trque is directly prprtinal t the armature current. The trque-speed characteristic is a straight line passing thrugh rigin as shwn in Fig. 1. T Trque With rmature Reactin eglected Speed With rmature Reactin eglected Trque Speed Speed With rmature Reactin eglected Speed a a FG. 1. TORQUE CURRET CHRCTERSTC FG.. SPEED CURRET CHRCTERSTC FG. 3. TORQUE SPEED CHRCTERSTC. SPEED CURRET CHRCTERSTC : n a shunt mtr, sh / Rsh. f is cnstant sh will als remain cnstant. Hence the flux is cnstant at n lad. The flux decrease slightly due t armature reactin. f the effect f armature reactin is neglected, flux will remain cnstant. The mtr speed being given by ara Eb K Fr remain cnstant, the speed can be written as ara This is an equatin f a straight line with a negative slpe. Fr this reasn, the speed f shunt mtr decrease linearly with the increase in armature current as shwn in Fig.. T Page 4 Prepare By: Partha Ray

5 DC Supply EE 491 ELECTRCL MCHE LB. MUL 3. SPEED TORQUE CHRCTERSTC : Since the trque is prprtinal t armature current in a dc shunt mtr the speed trque characteristic f such a mtr will be identical t speed-current characteristic. The speed-trque characteristic f dc shunt mtr is shwn in Fig. 3. CRCUT DGRM : L F F1 1 F1 F M F PROCEDURE : 1) Cnnect the circuit diagram as shwn in Fig. ) Switch O the pwer supply and start the mtr with help f 3 pint starter. 3) Gradually increase the lad (mechanical r break lad) step by step. 4) te dwn the vltage, current, tensin F 1 and F, speed fr every step. 5) Discnnect the mtr frm pwer supply. 6) Calculate the efficiency f mtr. 7) Draw the three characteristics f dc shunt mtr. OBSERTO TBLE : ltage (vlt) CLCULTO : Current (amp) Frce (Kgf) F 1 F F = F 1 - F Diameter f pulley, d = m. nput t the mtr = Output f the mtr = Trque Where trque d = F 9.81 and f, f Efficiency = Output/nput 60 Speed (rpm) Prepare By: Partha Ray Page 5

6 ELECTRCL MCHE LB. MUL EE 491 SL O RESULT nput Pwer P in DSCUSSO : Ttal Frce F (Kgf) ngular Speed ω (rad/sec) Output Trque T (w-m) Output Pwer P Efficiency (%) : Draw the trque-current, speed-current and speed trque characteristic f d.c. shunt mtr. 1. Hw armature reactin affect the three characteristics f dc shunt mtr?. Explain the nature f efficiency vs. lad curve? 3. f the supply vltage is drpped by half, what is the effect n three characteristics? 4. What happen if suddenly lad is remved frm the mtr? Page 6 Prepare By: Partha Ray

7 EE 491 ELECTRCL MCHE LB. MUL EXPERMET O : EM /3 TTLE SPEED COTROL OF DC MOTOR OBJECTE : T study the speed cntrl f a DC shunt mtr using. Field current cntrl B. rmature vltage cntrl PPRTUS: 1 DC Mtr mmeter 1 3 mmeter 4 ltmeter 5 Rhestat 6 Tachmeter Type Range Makers Serial THEORY : The equatin gverning the speed f a dc shunt mtr is ar Where = speed f the mtr = armature vltage = armature current a R a = armature resistance = field flux n the abve equatin Ra is cnstant. S we can cntrl the speed f mtr in tw ways. Firstly by changing the field flux and secndly by changing the armature vltage. n the bth case we vary the speed f mtr by intrducing a rhestat in the field circuit and armature circuit respectively. The expected graph fr speed cntrl f dc shunt mtr by armature cntrl methd and field cntrl methd is shwn in belw. a Rated Speed Rated Speed Rated Field Current f Rated rmature ltage a Prepare By: Partha Ray Page 7

8 DC Supply DC Supply ELECTRCL MCHE LB. MUL EE 491 CRCUT DGRM : 1. FELD COTROL METHOD. RMTURE COTROL METHOD L F L F R 1 F1 R1 F1 M F 1 M F PROCEDURE: 1) Cnnect the circuit as shwn in Fig. ) Keep the armature rhestat t its maximum value and the field rhestat t its minimum value. 3) Switch O the DC supply and start the mtr by 3 pint starter. 4) Gradually decrease the armature resistance R 1 t zer keeping field resistance R cnstant. 5) te dwn the vltmeter reading a, armature reading a and speed. 6) Gradually increase the field resistance R t maximum keeping armature resistance R 1 cnstant. 7) te dwn the vltmeter reading a, armature reading f and speed. 8) Switch OFF the pwer supply. 9) Draw the graph vs. f and vs. a OBSERTO TBLE: Field Cntrl Methd Field Current Speed f (amp) (rpm) rmature Cntrl Methd rmature ltage Speed a (vlt) (rpm) rmature Resistance = Ω Field Resistance = Ω RESULT: Draw the speed vs. field current and speed vs. armature vltage curve f d.c. shunt mtr. DSCUSSO : 1. T cntrl the speed abve and belw the rated speed, which methd shuld have t use and why?. What are the methds fr speed cntrl f dc series mtr? 3. f the vltmeter is cnnected at pint f starter instead f acrss armature, what des it read? Page 8 Prepare By: Partha Ray

9 EE 491 ELECTRCL MCHE LB. MUL EXPERMET O : EM /5 TTLE MESUREMET OF SPEED OF DC SERES MOTOR S FUCTO OF LOD TORQUE. OBJECTE : T draw the fllwing characteristics f series mtr i. Speed vs. current. ii. Trque vs. current. iii. Speed vs. trque. PPRTUS : 1 DC Series Mtr mmeter 3 ltmeter 4 Tachmeter Type Range Makers Serial THEORY : 1. TORQUE CURRET CHRCTERSTC : We knw that fr a dc mtr T a.n series mtr, befre saturatin a and hence at rated lad T a The abve equatin shws that the trque-current characteristics f a series mtr will be parablic. When the irn cre becmes magnetically saturated, becme almst cnstant, s that at heavy lads T a The abve equatin is a straight line. Thus trque-current characteristic f a dc series mtr is initially parablic and finally becmes linear when lad becme large as shwn in Fig. 1. T Trque Speed With rmature Reactin eglected Speed With rmature Reactin eglected a Speed a Speed T FG. 1. TORQUE CURRET CHRCTERSTC FG.. SPEED CURRET CHRCTERSTC FG. 3. TORQUE SPEED CHRCTERSTC. SPEED CURRET CHRCTERSTC : The mtr speed fr a series mtr is given by Prepare By: Partha Ray Page 9

10 DC Supply ELECTRCL MCHE LB. MUL EE 491 a( Ra Rse ) Eb K t the lw value f a the vltage drp [ a( Ra Rse )] is negligibly small in cmparisn with. 1 Since is cnstant n series mtr the field flux is prduced by the armature current flwing in the field winding s that. Hence the series mtr is variable flux machine. S a 1 a Thus, fr series mtr, the speed is inversely prprtinal t the armature (lad) current. The speed-trque characteristic is a rectangular hyperbla as shwn in Fig.. 3. SPEED TORQUE CHRCTERSTC : The mtr speed fr a series mtr is given by [ a( Ra Rse )] nd the trque equatin is T a and field flux a characteristic f dc mtr is a rectangular hyperbla as shwn in Fig. 3. CRCUT DGRM :. S T. Thus speed-trque L F1 F 1 F1 F M PROCEDURE : 1) Cnnect the circuit diagram as shwn in Fig. ) Switch O the pwer supply and start the mtr with help f 3 pint starter. 3) pply rated vltage t mtr and gradually increase lad (mechanical r break lad) step by step. 4) te dwn the vltage, current, tensin T 1 and T, speed fr every step. 5) Discnnect the mtr frm pwer supply. 6) Calculate the efficiency f mtr and draw the abve mentin curves. Page 10 Prepare By: Partha Ray

11 EE 491 ELECTRCL MCHE LB. MUL OBSERTO TBLE : ltage (vlt) CLCULTO : Current (mp) Frce (Kgf) F 1 F F = F 1 - F Diameter f pulley, d = m. nput t the mtr = Output f the mtr = Trque Where trque d = F 9.81 and f, f Efficiency = Output/nput SL O RESULT nput Pwer P in DSCUSSO : Ttal Frce F (Kgf) ngular Speed ω (rad/sec) Output Trque T (w-m) Output Pwer P 60 Speed (rpm) Efficiency (%) : Draw the trque-current, speed-current and speed trque characteristic f dc series mtr. 1. Hw armature reactin affect the three characteristics f dc series mtr?. Explain the nature f efficiency vs. lad curve? 3. f the supply vltage is drpped by half, what is the effect n three characteristics? 4. What happen if suddenly lad is remved frm the mtr? Prepare By: Partha Ray Page 11

12 ELECTRCL MCHE LB. MUL EE 491 EXPERMET O : EM /6 TTLE STUDY OF THE EQULET CRCUT OF SGLE-PHSE TRSFORMER. OBJECTE : T determine the parameter f the equivalent circuit f a single phase transfrmer PPRTUS : 1 Transfrmer mmeter 1 3 mmeter 4 ltmeter 1 5 ltmeter 6 Wattmeter Type Range Makers Serial THEORY : 1. OPE CRCUT (OC) OR O-LOD TEST The purpse f this test is t determine the shunt branches parameter f the equivalent circuit f the transfrmer. This test is perfrmed in L side which is cnnected t rated supply vltage at rated frequency and H side is kept pen as shwn in fig. The exciting current being abut t 6 % f full lad current and the hmic lss in the primary i.e. L side varies frm 0.04 % t 0.36 % f full lad hmic lss. n view f this hmic lss during pen circuit test is negligible in cmparisn with the cre lss. Hence the wattmeter reading can taken as equal t transfrmer cre lss. Let cnsider = pplied vltage n lw vltage side = Exciting current r -lad current P = Cre lss Then P cs P Therefre n lad pwer factr cs The energy cmpnent f n lad current The magnetizing cmpnent f n lad current Therefre cre lss resistance R e nd magnetizing reactance X. SHORT CRCUT (SC) TEST m cs e sin m This test is perfrmed t determine the series parameter f equivalent circuit f transfrmer as well as t btain the full lad cpper lss f a single phase transfrmer. The L side f the transfrmer is shrt circuited and the instruments are placed in H side. The applied vltage is varied by variac t supply the rated current n H side. s the primary mmf is almst equal t the secndary mmf in Page 1 Prepare By: Partha Ray

13 1 Φ C Supply 1 Φ C Supply EE 491 ELECTRCL MCHE LB. MUL transfrmer, therefre rated current in high vltage winding cause the flw f rated current in lw vltage winding. The wattmeter, in shrt circuit test, recrds the cre lss and hmic lss in bth the winding. Since the cre lss has been als negligible in cmparisn with rated vltage cre lss, wattmeter reading can taken as equal t transfrmer hmic lss in bth winding. Let cnsider sc = pplied vltage n high vltage side = Shrt circuit current n high vltage side sc P = Ttal hmic lss sc Psc Then the ttal equivalent resistance referred t high vltage side Req sc sc The ttal equivalent impedance referred t high vltage side Zeq Therefre the ttal equivalent reactance referred t high vltage side sc X Z R eq eq eq CRCUT DGRM : 1. OPE CRCUT TEST M L C W. SHORT CRCUT TEST Fig. (a) L H M L C W Fig. (b) H L PROCEDURE : 1) Cnnect the circuit as shwn in Fig (a) ) Set the variac at zer utput vltage. 3) Switch O the supply and by varying the applied vltage in step frm zer t rated vltage f lw vltage (L) side. 4) te dwn the ammeter, vltmeter and wattmeter reading. 5) Discnnect the circuit frm supply and again cnnect the circuit as shwn in Fig (b) 6) Set the variac at zer utput vltage. Prepare By: Partha Ray Page 13

14 ELECTRCL MCHE LB. MUL EE 491 7) Switch O the supply and increase the input vltage f transfrmer starting frm zer in varying small step till ammeter indicates the full lad current f high vltage (H) side. 8) te dwn the ammeter, vltmeter and wattmeter reading. 9) Discnnect the circuit frm supply. 10) Calculate the different parameter f transfrmer frm the recrd data. 11) Draw the equivalent circuit f single phase transfrmer. OBSERTO TBLE : ltage (vlt) Open Circuit Test Current (mp) Pwer nput W ltage sc (vlt) Shrt Circuit Test Current sc (mp) Pwer nput W sc RESULT : Cre lss resistance, R = hm Magnetizing reactance, X = hm Ttal equivalent resistance referred t high vltage side, R eq = Ttal equivalent reactance referred t high vltage side, X eq = hm hm DSCUSSO : Draw the equivalent circuit f single phase transfrmer. 1. Why OC and SC test is perfrmed n H and L side respectively?. Why irn lss and cpper lss is neglected in SC and OC test respectively? 3. Hw these tests are perfrmed in case f three phase transfrmer? Page 14 Prepare By: Partha Ray

15 EE 491 ELECTRCL MCHE LB. MUL EXPERMET O : EM /7 TTLE POLRTY TEST OF SGLE-PHSE TRSFORMER D STUDY OF THE DFFERET COECTOS OF THREE-PHSE TRSFORMER. OBJECTE : T check the plarity f a single-phase transfrmer and t study the different vectr grup f a three-phase transfrmer PPRTUS : 1 Transfrmer 1 Transfrmer 3 Transfrmer 3 4 ltmeter Type Range Makers Serial THEORY : 1. POLRTY TEST : Plarity testing f transfrmer is vital befre cnnecting them in parallel. Otherwise, with incrrect plarity, it is nt pssible t cnnect them in parallel. The tw terminals f primary are marked as 1 and and ther tw terminals f secndary are marked as a 1 and a respectively as shwn in fig. T determine the relative plarity f tw-winding transfrmer, the tw winding are cnnected in series acrss a vltmeter, while ne f the winding is excited frm a suitable vltage surce as shwn in fig. f the plarities f the windings are as marked n the diagram, vltmeter shuld read = 1 ~ and if it reads ( 1 + ) the plarity marking f ne f the winding must be interchanged. 1 a1 1 a. ECTOR GROUPG : Basically three-phase transfrmer has tw types f winding, namely (a) star and (b) delta. ccrdingly three-phase transfrmer is named Yd, Yy, Dy, Dd etc. n these varius cnnectins H line vltage and L line vltage f same transfrmer may have a phase displacement. Depending upn this phase difference, transfrmer are classified in different grups i. Grup (0º Displacement) : Yy0, Dd0. ii. Grup (180º Displacement) : Yy6, Dd6. iii. Grup (-30º Displacement) : Yd11, Dy11. iv. Grup (30º Displacement) : Yd1, Dy1. Prepare By: Partha Ray Page 15

16 1 Φ C Supply ELECTRCL MCHE LB. MUL EE 491 CRCUT DGRM : 1. POLRTY TEST : 1 3. COECTO Yy0 D Yy6: B Y R B Y R 1 B1 C1 1 B1 C1 B C B C a1 b1 c1 b y r a1 b1 c1 a b c a b c b y r 3. COECTO Yd1 D Yd11: B Y R B Y R 1 B1 C1 1 B1 C1 B C B C a1 b1 c1 b y r a1 b1 c1 b y r a b c a b c PROCEDURE : 1. POLRTY TEST 1) Cnnect the circuit as shwn in Fig. ) Excite the primary frm single phase C supply. Page 16 Prepare By: Partha Ray

17 EE 491 ELECTRCL MCHE LB. MUL 3) Take the ltmeter reading 1, and 3. 4) Marked the plarity n the basis f the vltmeter reading. 5) Discnnect the supply and this test is perfrmed n ther tw transfrmers.. ECTOR GROUPG 1) Cnnect the circuit as shwn in Fig. ) Excite the primary frm 30, 50 Hz single phase C supply. 3) Take the vltmeter reading Ph1, L1, Ph and L. 4) Discnnect the circuit frm the supply. 5) This test is dne fr different vectr grups as shwn in Fig. OBSERTO TBLE : Terminal Srted ltmeter 1 (vlt) TBLE - ltmeter (vlt) ltmeter 3 (vlt) Plarity RESULT DSCUSSO: Cnnectin Yy0 Yy6 Yd1 Yd11 Primary Winding Line ltage L1 (vlt) TBLE Phase ltage Ph1 (vlt) : Draw the vectr diagram f Dd0, Dd6, Dy1, Dy11. Secndary Winding Line ltage L (vlt) Draw the cnnecting diagram f Yd5, Yd7, Dy5, Dy7. Phase ltage Ph (vlt) 1. Why marking f plarity is essential?. Hw can yu change the vectr grup frm Dy1 t Dy11 fr an existing transfrmer bank? 3. Draw the cnnecting diagram f Dd, Dd4. Prepare By: Partha Ray Page 17

18 ELECTRCL MCHE LB. MUL EE 491 EXPERMET O : EM /8 TTLE STUDY OF EQULET CRCUT OF THREE-PHSE DUCTO MOTOR BY O-LOD TEST D BLOCKED-ROTOR TEST. OBJECTE : T determine the parameter f equivalent circuit f three phase inductin mtr. PPRTUS : 1 nductin Mtr ltmeter 3 mmeter 4 Wattmeter 1 5 Wattmeter 6 ariac Type Range Makers Serial THEORY : 1. O-LOD TEST : This test is similar t pen circuit test n a transfrmer. three-phase aut-transfrmer is used t supply rated vltage at the rated frequency. The mtr is runs at n lad. The pwer input is measured by tw wattmeter methd. The pwer factr under n-lad cnditin is generally less than 0.5. Therefre ne f the wattmeter will shw negative reading. t is therefre necessary t reverse the directin f current cil terminal t take the reading. Let cnsider = pplied per phase vltage n statr side = Exciting per phase current r -lad current W = Cre lss and Mechanical lss. Therefre n lad pwer factr cs nd per phase impedance Z 3 nd per phase resistance W R 3 Therefre the per phase reactance. BLOCK ROTOR TEST : 0 W 3 X Z R 0 0 n this test mtin f the rtr is blcked by a brake r belt. This test is analgus t the shrtcircuit test f a transfrmer because the rtr winding is shrt-circuited. Only a reduced vltage needs t be applied t the statr at rated frequency. This vltage shuld be such that the ammeter reads rated current f mtr. The ttal pwer input W sc is equal t the algebraic sum f the tw wattmeter reading i.e equal t cpper lss f statr and rtr. Page 18 Prepare By: Partha Ray

19 3 Φ C Supply EE 491 ELECTRCL MCHE LB. MUL Let cnsider sc = pplied per phase SC vltage n statr side. = Shrt circuit per phase current. sc W = Ttal hmic lss. sc Then the ttal equivalent per phase resistance Wsc Req 3sc The ttal equivalent per phase impedance sc Zeq 3 Therefre ttal equivalent per phase reactance CRCUT DGRM : PROCEDURE : sc X Z R eq eq eq 1) Cnnect the circuit as shwn in Fig. ) Switch O the pwer supply and apply the vltage in statr with the help f three-phase variac at rated vltage. 3) te dwn the vltmeter, ammeter and wattmeter reading. 4) ncrease the supply vltage gradually t rated the vltage. 5) te dwn the vltmeter, ammeter and wattmeter reading. 6) Discnnect the pwer supply and blck the rtr with the help f clamp as such a way that it cannt rtate. 7) pply very lw vltage by gradually increase until the rated full lad current will flw. 8) te dwn the vltmeter, ammeter and wattmeter reading. 9) Discnnect the circuit frm the supplies. 10) Calculate the different parameter f three-phase inductin mtr. OBSERTO TBLE : 3 Φ R C M C C M W1 W L L 3 Φ M Lad Test Blcked Rtr Test ltage (vlt) Current (amp) W 1 Wattmeter Reading W W = W 1 + W ltage SC (vlt) Current SC (amp) W 1 Wattmeter Reading W W = W 1 + W Prepare By: Partha Ray Page 19

20 ELECTRCL MCHE LB. MUL EE 491 Statr resistance per phase = Ω CLCULTO : Let x 1 = Per phase leakage reactance f statr winding. x = Per phase leakage reactance f rtr winding. r = Per phase statr resistance. 1 1 Per phase leakage reactance, x1 x X eq Therefre per phase magnetizing reactance X m X x1 nd per phase rtr self-reactance X X m x X Per phase rtr resistance r ( Req r1) X m -lad r irn lss Pirn W Full-lad cupper lss PcuFL Wsc RESULT : Statr resistance = Ω Rtr resistance = Ω Magnetic leakage reactance = Ω Statr and rtr leakage reactance = Ω Ttal lss P = P + x P lss irn cufl x P lss Efficiency f nductin Mtr x HP 746 h = x HP + P + x P 746 irn cufl 100% x η Draw the equivalent circuit f three phase nductin Mtr. DSCUSSO: 1. Hw the mechanical lad is incrprate in equivalent circuit? Page 0 Prepare By: Partha Ray

21 EE 491 ELECTRCL MCHE LB. MUL EXPERMET O : EM /9 TTLE : Perfrm Sumpner's test f single phase transfrmer OBJECTE : T determine efficiency and regulatin f single phase transfrmer. PPRTUS : Type Range Makers Serial 1 Transfrmer ltmeter 1 3 ltmeter 4 mmeter 1 5 mmeter 6 Wattmeter 1 7 Wattmeter THEORY : The Sumpner's test is anther methd f determining efficiency, regulatin and heating under lad cnditins. The O.C. and S.C. tests give us the equivalent circuit parameters but cannt give heating infrmatin under varius lad cnditins. The Sumpner's test gives heating infrmatin als. n O.C. test, there is n lad n the transfrmer while in S.C. circuit test als nly fractinal lad gets applied. n all in O.C. and S.C. tests, the lading cnditins are absent. Hence the results are inaccurate. n Sumpner's test, actual lading cnditins are simulated hence the results btained are much mre accurate. Thus Sumpner's test is much imprved methd f predetermining regulatin and efficiency than O.C. and S.C. tests. The Sumpner's test requires tw identical transfrmers. Bth the transfrmers are cnnected t the supply such that ne transfrmer is laded n the ther. Thus pwer taken frm the supply is that much necessary fr supplying the lsses f bth the transfrmers and there is very small lss in the cntrl circuit. The cnnectin diagram is shwn in the Fig. 1. While cnducting this test, the primaries f the tw identical transfrmers are cnnected in parallel acrss the supply 1. While the secndary are cnnected in series ppsitin s that induced e.m.f in the tw secndary ppse each ther. The secndary are supplied frm anther lw vltage supply are cnnected in each circuit t get the readings. Prepare By: Partha Ray Page 1

22 ELECTRCL MCHE LB. MUL EE 491 T 1 and T are tw identical transfrmers. The secndary f T 1 and T are cnnected in series ppsitin. S E EF = E GH i.e. induced in tw secndary are equal but the secndary are cnnected such that E is cnnected t G and F is cnnected t H. Due t such series ppsitin, tw e.m.f act in ppsite directin t each ther and cancel each ther. S net vltage in the lcal circuit f secndary is zer, when primaries are excited by supply 1 f rated vltage and frequency. S there is n current flwing in the lp frmed by tw secndary. The series ppsitin can be checked by anther vltmeter cnnected in the secndary circuit as per plarity test. f it reads zer, the secndary are in series ppsitin and if it reads duble the induced e.m.f. in each secndary, it is necessary t reverse the cnnectins f ne f the secndary. s per superpsitin therem, if is assumed zer then due t phase ppsitin t current flws thrugh secndary and bth the transfrmers T 1, T are as gd as n n lad. S O.C. test gets simulated. The current drawn frm surce 1 in such case is where is n lad current f each transfrmer. The input pwer as measured by wattmeter W 1 thus reads the irn lsses f bth the transfrmers. s T 1, T are identical -lad lss per transfrmer, P i = P / Then a small vltage is injected int the secndary with the help f lw vltage transfrmer, by clsing the switch S. With regulatin mechanism, the vltage is adjusted s that the rated secndary current flws thrugh the secndary as shwn. flws frm E t F and then frm H t G. The flw f 1 is restricted t the lp BJCDLKB and it des nt pass thrugh W 1. Hence W 1 cntinues t read cre lsses. Bth primaries and secndary carry rated current s S.C. test cnditin gets simulated. Thus the wattmeter W reads the ttal full lad cpper lsses f bth the transfrmers. Full-lad lss per transfrmer, P cu = P sc / Thus in the Sumpner's test withut supplying the lad, full irn lss ccurs in the cre while full cpper lss ccurs in the windings simultaneusly. Hence heat run test can be cnducted n the tw transfrmers. n O.C. and S.C. test, bth the lsses d nt ccur simultaneusly hence heat run test cannt be cnducted. This is the advantage f Sumpner's test. Frm the test results the full lad efficiency f each transfrmer can be calculated as, where utput = rating x cs Φ h = Out put 100% P P sc Out put + + s all the vltage, currents and pwers are measured during the test, the equivalent circuit parameters als can be determined. Hence the regulatin at any lad and lad pwer factr cnditin can be predetermined. The nly limitatin is that tw identical transfrmers are required. n practice exact identical transfrmers cannt be btained. s tw transfrmers are required, the test is nt ecnmical. Let cnsider = pplied vltage n lw vltage side = Exciting current r -lad current P = Cre lss Then P cs Page Prepare By: Partha Ray

23 1 Φ C Supply 1 Φ C Supply EE 491 ELECTRCL MCHE LB. MUL Let cnsider P Therefre n lad pwer factr cs The energy cmpnent f n lad current The magnetizing cmpnent f n lad current Therefre cre lss resistance R nd magnetizing reactance X sc m e cs e = pplied vltage n high vltage side = Shrt circuit current n high vltage side sc P = Ttal hmic lss sc sin m Psc Then the ttal equivalent resistance referred t high vltage side Req sc sc The ttal equivalent impedance referred t high vltage side Zeq Therefre the ttal equivalent reactance referred t high vltage side sc X Z R eq eq eq CRCUT DGRM : M L L M sc C W 1 a1 Wsc C sc a STDP1 STDP 1 a1 a PROCEDURE : 1) Cnnect the circuit as shwn in Fig. ) Switch O STDP 1 with kept pen STDP. Set primary input vltage t rated vltage f high vltage (H) side. 3) te dwn the ammeter, vltmeter and wattmeter reading. Prepare By: Partha Ray Page 3

24 ELECTRCL MCHE LB. MUL EE 491 4) Switch O STDP with kept pen STDP 1. Set the secndary input vltage f transfrmer at a lw value when ammeter indicates the full lad current f lw vltage (L) side. 5) te dwn the ammeter, vltmeter and wattmeter reading. 6) Discnnect the circuit frm supply. 7) Draw the equivalent circuit f single phase transfrmer. OBSERTO TBLE : ltage (vlt) Open Circuit Test Current (mp) Pwer nput W ltage sc (vlt) Shrt Circuit Test Current sc (mp) Pwer nput W sc RESULT : Ttal lss P = P + x P lss irn cufl x P lss x S cs f FL Efficiency f transfrmer h = x S cs f + P + x P FL irn cufl 100% x η (0.8 pf) η (unity pf) Z = cs q ± f 100% q = tan eq Regulatin f transfrmer reg x ( ) - 1 sc sc x lag unity lead φ (degree) Reg (x=0.8) Reg (x=1.0) Draw the equivalent circuit f single phase transfrmer Draw the lss curve, efficiency curve and regulatin f single phase transfrmer. DSCUSSO: X R eq eq Page 4 Prepare By: Partha Ray

25 Speed EE 491 ELECTRCL MCHE LB. MUL EXPERMET O : EM /10 TTLE SPEED COTROL OF THREE-PHSE SLP RG DUCTO MOTOR BY ROTOR RESSTCE COTROL. OBJECTE : Speed cntrl f three-phase slip ring inductin mtr by rtr resistance cntrl. PPRTUS : 1 nductin Mtr mmeter 3 ltmeter 4 Resistance Type Specificatin / Range Makers Serial THEORY : ip ring inductin mtrs are usually started by cnnecting starting resistance in the secndary circuit, which are shrted ut as the mtr speed up. f the hmic values f these resistances are prperly chsen and if the resistrs are designed fr cntinuus peratin, they can serve dual purpse i.e. starting and speed cntrl. This methd f speed cntrl has characteristics similar t thse f dc mtr speed cntrl by means f resistance in series with armature. ksre Trque develped by an inductin mtr is given byt R s X When the speed is very near t synchrnus speed term sx is very small and can be neglected as cmpared t s prprtinal t R s i.e. when sip is very lw the value f the R and trque develped becme. S it is bvius that fr a given trque, slip s can be increased r speeds can be reduced by increasing the rtr resistance. n this methd speed can be cntrl nly belw the rated speed. f step f external resistance is larger speed cntrl is smther. n this methd efficiency is largely reduced at lw speed. The curve f speed vs. resistance is shwn in Fig belw Resistance Prepare By: Partha Ray Page 5

26 3 Φ Supply ELECTRCL MCHE LB. MUL EE 491 CRCUT DGRM : 3 Φ M 3 Φ External Rtr Resistance PROCEDURE : FG : EXPERMETL SET-UP FOR PERFORMG SPEED COTROL OF SLP-RG DUCTO MOTOR 1) Cnnect the circuit as shwn in Fig. ) Switch O the pwer supply. 3) With the help f external rtr resistance starts the inductin mtr. 4) ary the rtr resistance and nte dwn the varius speed. 5) Switch OFF the pwer supply and discnnect the mtr. 6) Measure the external rtr resistance in each step by multimeter. 7) Draw the speed vs. rtr resistance curve. OBSERTO TBLE : SL O RESULT ltage (vlt) DSCUSSO : Rtr Current (amp) External Rtr Resistance R (Ω) Speed (rpm) : Draw the speed vs. rtr resistance curve f slip ring inductin mtr. 1. State the different methd f speed cntrl f squirrel cage inductin mtr.. Cmpare the different methd f speed cntrl f squirrel cage inductin mtr 3. State any ther methd f speed cntrl f slip-ring inductin mtr. Page 6 Prepare By: Partha Ray

27 EE 491 ELECTRCL MCHE LB. MUL EXPERMET O : EM /11 TTLE : Study f the perfrmance f three-phase Squirrel-Cage inductin Mtr- Determinatin f rn-lss, Frictin & Windage Lsses OBJECTE : T determine the effect f varying applied vltage n speed, pf, input pwer and current etc. and determine the rn-lss, Frictin & Windage Lsses f three-phase squirrel-cage inductin mtr. PPRTUS : 1 nductin Mtr ltmeter 3 mmeter 4 Wattmeter 1 5 Wattmeter 6 ariac Type Range Makers Serial THEORY : This test is basically pen circuit test r n lad test. When the inductin mtr is decupled frm lad and the rated vltage is applied t the statr, the mtr runs at n lad then there exists tw types f lsses 1. rn lss and cre lss. Mechanical lss cnsisting f frictin lss and windage lss The cpper lss in primary is negligible as because n lad current is very small. nd as such the ttal input pwer is taken t be equal t the sum f irn lss and frictin and windage lss, as the mtr is run at n lad. The input current, input vltage, input pwer and speed f mtr are bserved frm the experiment and the perfrmance quantities that can be calculated are explained belw 1. ip Due t the three phase supply given t statr f an inductin mtr, a rtating field f cnstant magnitude is set up in the statr f mtr. The speed with which this rtating magnetic field rtates is knwn as synchrnus speed and is given by Where f = supply frequency s 10 f P P = n. f ples n the statr f the rtr The actual speed f rtr r is always less than the synchrnus speed. S the slip f the mtr is s r s 100% s Prepare By: Partha Ray Page 7

28 3 Φ C Supply ELECTRCL MCHE LB. MUL EE 491. Pwer Factr Pwer factr can be calculated frm the relatin CRCUT DGRM : P cs 3 M L Φ C R W1 3 Φ M C C M W L Mtr at Standstill Speed Rated ltage Pwer Factr nput Pwer nput Current Cre Lss Frictin and Windage Lsses ip PROCEDURE : nput ltage 1) Cnnect the circuit as shwn in Fig. ) Switch O pwer supply and apply rated vltage in statr with the help f variac. 3) te dwn the vltmeter, ammeter and wattmeter's reading. 4) Decrease the supply vltage in steps till mtr stps and take the meter readings in every step. 5) Discnnect the circuit frm the supplies. 6) Draw the input pwer vs. vltage curve. The difference between the input pwer at rated vltage and the intercept f frictin and windage lss gives the cre lss f the mtr. 7) Plt the speed, input pwer, current, p.f. and slip vs. statr vltage. Page 8 Prepare By: Partha Ray

29 EE 491 ELECTRCL MCHE LB. MUL OBSERTO TBLE : ltage L (vlt) Current L (amp) W 1 Wattmeter Reading W W = W 1 + W Speed (r.p.m.) RESULT : nput ltage (vlt) nput Current (amp) nput Pwer Speed (r.p.m.) ip (%) Pwer Factr Prepare By: Partha Ray Page 9

30 ELECTRCL MCHE LB. MUL EE 491 DSCUSSO: Cre Lss r rn Lsss = watt Frictin and Windage Lss = watt Draw the speed vs. statr vltage, input pwer vs. statr vltage, current vs. statr vltage, pf vs. statr vltage and slip vs. statr vltage. 1. Explain the nature f all abve curves. Page 30 Prepare By: Partha Ray