1. a) Explain the working principle of transformer and derive the emf equation. b) A single phase 50 Hz transformer has 100 turns on the primary and 400 turns on the secondary winding. The net cross-sectional area of core is 250 cm
2
. If the primary winding is connected to a 230 V 50 Hz supply, determine i. The EMF induced in the secondary winding ii. The maximum value of flux density in the core. ( Aug/Sep 2007 Set 1,Apr/May 2006 Set 1,
Nov/Dec-2004 Set 1)
2. a) Prove that the EMF induced in the windings of the transformer will lag behind the flux by 90
0
.
b) Explain how equivalent circuit of transformer can be obtained?(Aug/Sept 2007 Set 2, Apr/May 2006 Set 1, Apr/May 2007 Set
1, Nov/Dec 2005 Set 2, Apr/May 2005 Set 1, 2)
3. Explain the principle of operation of transformer. Deduce its equivalent circuit.(Aug/Sept 2007 Set 3, Apr/May 2007 Set 2, 3, Sept
2006 Set 1, 3)
4. a) Give the constructional differences between a core type and shell type transformers. How the iron losses are minimized.
b) A single phase transformer has turns ratio of 144/432 and operates at maximum flux of 7.5 x 10−3 wb at 50 Hz. When on no load the transformer takes 0.24 KVA at a power factor of 0.26 lagging from the supply. If the transformer supplies a load of 1.2 KVA at a power factor of 0.8 lagging, determine
i. Magnetizing current.
ii. Primary current
iii. Primary power factor (Aug/Sept 2007 Set 4, Nov/Dec 2005 Set 3)
5. a) What are the various methods to reduce the leakage flux in transformer.
b) Draw the phasor diagram of a single phase transformer with load having a leading power factor and explain. ( Apr/May 2006 Set
2, Nov/Dec 2004 Set 3)
6. a) Explain why hysterisis and eddy current losses occur in a transformer.
b) A transformer on load takes 1.5 amps at a power factor of 0.2 lagging when connected across 50 Hz 230 V supply. The ratio between primary and secondary number of turns is 3. Calculate the value of primary current when secondary is supplying a current of
40A at a power factor of 0.8 lagging. Neglect the voltage drop in the windings. Draw the relevant phasor diagram.(Apr/May 2006 Set
4, Apr/May 2007 Set 4, Apr/May 2005 Set 3)
7. a) Draw the phasor diagram of a transformer on no load and explain the function of active and reactive components of no load current of transformer.
b) Explain why transformer rating will be given in KVA but not in KW. (Sept 2006 Set 2,
Nov/Dec 2005 Set 1,Apr/May 2005 Set 4)
8. a) Explain the functions of the following in a transformer
i. Breather
ii. Conservator
iii. Oil
b) Draw and explain phasor diagram of transformer on lagging load. (Sept 2006 Set 4, Nov/Dec 2004 Set 2)
9 a) Explain how equivalent circuit of transformer can be obtained
b) The constants of a single phase 50HZ 2200/220V transformer are as follows
H.V side:r1=0.21
Ω ,x1=3.84
Rc1 =4800 Ω .xm1=3500 Ω
L.V side:r2=0.006
Ω ,x2=0.002
Ω

i) ii) iii) iv)
(i)
(ii)
Find the equivalent circuit parameters referred to
H.V side and
L.V side
10 a) Discuss how will you perform O.C and S.C test on a single phase transformer in the laboratory
(b) the maximum efficiency of a 500Kva ,3300/500V 50Hz,single phase transformer is 97% and 3/4 th full load and unity power factor
. if the impedance drop is 10% calculate the regulation at full load and 0.8pf lagging (set 1 April 09)
11 a) what precaution should be observed during the operation on load tap changer
b) Explain the function of centre tapped reactor in on-load tap changer
c) Describe one type of on-load tape changer with proper sequence of operation for changing the voltage
12 explain the following with respect to single phase transformer
Core
Winding
Methods of cooling
Conservator and bushing
b) a single phase transformer is connected to a230V ,50Hz supply the net cross –sectional area of the core is 50cm2 the number of turns of the primary is 460 and the secondary is 80.detrmine i)transformation ratio ii)peak value of the flux density in the core iii)e.m.f in the secondary winding (set2-april-2009)
13) a)derive EMF equation of a1-phase transformer
b) a transformer has a primary windings of800 turns and a secondary of 200turns .when load current on the secondary is 80A at
0.8 p.f lagging .determine the no-load current of the transformer and the phase angle with respect to the voltage (set-3 april-2009)
14 a) explain how do you minimize the hystresis and eddy current losses in a sigle phase transformer b)when asingle phase transformer is supplied at 400v ,50Hz ,the hysteresis losses found to be 320watts and eddy current losses is found to be 250watts .determine the hysteresis loss and eddy current losses when the transformer is supplied at 800v,100Hz (set-4
April-2009)
1. a) Explain various losses and derive the condition for maximum efficiency of a transformer
b) The efficiency at unity power factor of 6600/384 volts 100 KVA 50 Hz single phase transformer is 98% both at full load and at half full load. The power factor on no load is 0.2 and the full load regulation at a lagging power factor of 0.8 is 4 %. Draw the equivalent circuit referred to L.V. side and insert all the values. ( Aug/Sep 2007 Set 1, 2, April 2009/set-4 Sept 2006 Set 1, 2 ,
Nov/Dec 2005 Set 4 )
2. a) Define efficiency and regulation of a transformer. Show how the power factor affects both of them.
b) The maximum efficiency of 50 KVA transformer is 97.4 % and occurs at 90 % of the full load. Calculate the efficiency of transformer at
i.) Full load 0.8 power factor lagging
ii.) Half full load 0.9 power factor (Aug/Sep 2007 Set 3, Apr/May 2006 Set 1,2, Apr/May 2007 Set 3 , 4,Sept 2006 Set 3, Nov/Dec
2005 Set 1, 2, 3, Nov 2004 Set 3)
3. a) Write a short note on All day efficiency of the transformer.
b) Find the All day efficiency of single phase transformer having maximum efficiency of 98 % at 15 KVA at UPF and loaded as follows.
12 hours — 2 KW at 0.5 power factor lagging
6 hours — 12 KW at 0.8 power factor lagging
6 hours — no load (Aug/Sep 2007 Set 4, Apr/May 2006 Set 3, Apr/May 2007 Set 1)

4. A 40 KVA single phase transformer has got maximum efficiency of 97 % at 80 % of full load at UPF. During the day, the load on the transformer is as follows.
No. of hours Load Power factor
9 6 KW 0.6 lag
8 25 KW 0.8 lag
7 30 KW 0.9 lag
Determine the All day efficiency of the transformer. (Apr/May 2006 Set 4, Sept 2006 Set 4,
April/ May 2005 Set 1)
5. a) Derive the condition for zero voltage regulation. Also show that the magnitude of maximum voltage regulation equals to per unit value of leakage impedance.
b) A 20 KVA 2000/200 V single phase transformer has the following parameters.
H. V. Winding: R1 = 3 , X1 = 5.3, L. V. Winding: R2 = 0.05 , X2 = 0.1
Find the voltage regulation at i.) At a power factor of 0.8 lagging ii.) UPF iii.) 0.707 power factor leading (Apr/May 2007 Set 2, April/ May 2005 Set 2, 4, Nov 2004 Set 2)
6. a) Explain how the iron losses and copper losses are affected with change in load on the transformer.
b) Find the All Day efficiency of 1500 KVA transformer whose copper and iron losses at full load are 4.5 KW and 3.2 KW respectively. During a day of 24 hours it is loaded as follows:
No. of hours Load Power factor
6 1200 KW 0.8 lag
10 900 KW 0.75 lag
4 300 KW 0.8 lag
4 0 0 (April/May -2005 Set 3)
7. a) Derive the expression for voltage regulation of a transformer from the simplified approximate equivalent circuit and obtain condition for zero regulation.
b) The primary and secondary windings of 30 KVA,6000/230V transformer have resistances of 10 Ω and 0.016 Ω respectively.
The total reactance of transformer referred to primary is 23 Ω . Calculate the percentage regulation of transformer when supplying full load current at a power factor of 0.8 lagging. (Nov/Dec-2004 Set 1)
8. a) A single phase 120 KVA 2000/200 V 50 Hz transformer has impedance drop of 9% and resistance drop of 4.5 %. Find i) The regulation at 0.8 power factor lagging on full load. ii) At what power factor is the regulation zero.

b) The efficiency of 1000 KVA, 110/220 V,50 Hz single phase transformer is 98.5 % at half full load at 0.8 power factor leading and 98% at full load, UPF. Determine i) Iron loss ii) Copper loss iii) Maximum efficiency at UPF (Nov 2004 Set 4)
9 a) Explain how equivalent circuit of transformer can be obtained
b) The constants of a single phase 50HZ 2200/220V transformer are as follows
H.V side:r1=0.21
Ω ,x1=3.84
Rc1 =4800 Ω .xm1=3500 Ω
L.V side:r2=0.006
Ω ,x2=0.002
Ω
Find the equivalent circuit parameters referred to
(i) H.V side and
(ii) L.V side
10 give the equivalent circuit of a transformer and its parameter clearly state the assumption made in the applicability of the equivalent circuit (set-3,2 april-2009)
1. a) Explain the following characteristics of an auto transformer with two winding transformer: i.) Rating ii.) Losses iii.) Impedance drop iv.) Voltage regulation
b) The primary and secondary voltages of an auto transformer are 500V and 400V respectively. Show with the aid of a diagram, the current distribution in the winding when the secondary current is 100A and calculate the economy of Cu in this particular case.
( Aug/Sep 2007 Set 1,Apr/May 2006 Set 4, Sept 2006 Set 2 ,April/May 2005 Set 4, Nov/Dec 2004 Set 2)
2. a) What are the conditions required for the parallel operation of two transformers.
b) Derive the equations for the currents supplied by each transformer when two transformers are operating in parallel with equal voltage ratios. (Aug/Sep 2007 Set 1, 2, 3, 4 ,
Apr/May 2006 Set 1, Apr/May 2007 Set 1, Apr/May 2007 Set 2, Sept 2006 Set 1,2, 4, Nov/Dec 2005 Set 2, 4, April/May 2005 Set
1)
3. a) Explain the procedure to predetermine the efficiency and regulation of a transformer with all necessary equations.
b) The iron losses in a transformer core at normal flux density were measured at frequencies of 30 and 50Hz and the results being
34W and 55W respectively. Calculate the hysteresis and eddy current losses at 50Hz. (Aug/Sep 2007 Set 2 ,Nov/Dec 2004 Set 4)
4. a) Two similar 250KVA similar transformers gave the following results when tested by back-to-back method: Mains wattmeter, W
1
= 5.0 KW, Primary series circuit wattmeter, W
2
= 7.5KW (at full load current). Find out the individual transformer efficiencies at
75% full load and 0.8 power factor lead.
b) A 10KVA, 440/3300V, 1-phase transformer, when tested on open circuit, gave the following figures on the primary side : 440V,
1.3A, 115W. When tested on short circuit with full load current flowing, the power input was 140W.Calculate the efficiency of the

transformer at (i.) full load unity power factor (ii.) one quarter full load 0.8p.f. ( Aug/Sept 2007 Set 3, Apr/May 2006 Set 2, Sept
2006 Set 3)
5. Explain the test procedure to separate the iron losses of a transformer with neat circuit diagram, Tabulation and Model graph.
(Aug/Sept 2007 Set 4 ,Nov/Dec 2005 Set 4)
6. A 4KVA, 200/400V, 50Hz, single phase transformer gave the following test results:
No-load : low voltage data, 200V, 0.7A, 60W.,
Short-circuit : High voltage data, 9V, 6A, 21.6W. Calculate a) The magnetizing current and the component corresponding to iron loss at normal voltage and frequency, b) The efficiency on full load at unity power factor, c) The secondary terminal voltage on full-load at power factors of unity, 0.8 lagging and 0.8 leading (Apr/May 2006 Set 1, Apr/May
2007 Set 3)
7. A 20KVA, 2300/230V, two winding transformer is to be used as an auto transformer, with constant source voltage of 2300V. At full load of unity power factor, calculate the power output, power transformed and conducted. If the efficiency of the two winding transformer at 0.6p.f.is 96%, find the auto transformer efficiency at the same power factor. (Apr/May 2006 Set 3, Nov/Dec 2005 Set
3, April/May 2005 Set 3 , Nov/Dec 2004 Set 3 )
8. a) Explain the procedure for conducting Sumpner’s test along with all precautions to be taken while conducting the test with neat diagram.
b) The corrected instrument readings obtained from short circuit test on 10 KVA,450/125V, 50Hz transformer are 9.65V, 22.2A,
120W, with low voltage winding short circuited. Compute voltage regulation for an 85% lagging load at 50% load. (Apr/May 2007
Set 1, Apr/May 2007 Set 3, Nov/Dec 2005 Set 2)
9. a) Explain the procedure for conducting OC and SC tests with neat diagrams.
b) A 20 KVA, 2500/250V, 50Hz, Single phase transformer gave the following test results: OC test (LV side): 250V, 1.6A, 110W;
SC test (HV side): 90V, 7A, 300W.
Compute the parameters of the approximate equivalent circuit referred to LV side. (Apr/May 2007 Apr/May 2009 Set 2 set3, Sept
2006 Set 4, Nov/Dec 2005 Set 1)
10. a) Derive the equation for saving in copper in using Auto transformer when compared to two winding transformer.
b) Obtain the equivalent circuit of an auto transformer. (Sept 2006 Set 1, April/May 2005 Set 1, April/May 2005 Set 2, Nov/Dec
2004 Set 1)
11 a)Discuss how will you perform O.C and S.C test on a single phase transformer in the laboratory
(b)the maximum efficiency of a 500Kva ,3300/500V 50Hz,single phase transformer is 97% and 3/4 th full load and unity power factor
. if the impedance drop is 10% calculate the regulation at full load and 0.8pf lagging (set 1 april 09)
12 a) show that one transformer may have slightly less temperature rise than the other in sumpner,s test
b)a 50Kva ,2200/1100v,single phase ,50Hz transformer has a full load efficiency of 95% and iron losses of 500W the transformer is connected as an auto transformer to3300v supply .whenit dlivers a load of 50Kw at unity power factor at 1100v calculate the currents in the winding .find also the increase in out put as auto transformer .also calculate the copper loss of two winding transformer(set2 april-09)

13 a)in sumpner,s test the reading of the wattmeter recording the core losses ,remains unaffected when low voltage is injected in the secondary series circuit .explain
b) discuss the relative merits and demerits of an auto transformer
c) a11000/2200v ,100KVA,single phase two winding transformer is to be used as an auto –transformer by connecting the two windings in series .give the possible values of voltage ratio and KVA outputs (set-3 april-2009)
14) a)state the essential and desiradle conditions which should be satisfied before two single phase transformers may be operated parallel
b)Two single phase 500KVA and400kva transformers connected in parallel to supply aload of 800KVA at 0.8 p.f lagging .the resistance and leakage reactance of the first transformers are 2.5 percent and 6 percent respectively and of the second transformer 1.6 percent and 7 percent respectively.calculate the KVA loading and power factor at which each transformer operate (set-4 april-2009)
1. a) Describe the principle of regulating the voltage with the help of tap-changers.
b) Discuss whether the winding should be tapped on HV side or LV side. (Nov/Dec 2004
Set 2)
2. a) Describe the principle of regulating the voltage with the help of tap changers.
b) Explain why the transformer winding should be tapped in the middle.( Nov/Dec 2004 Set 3)
3. a) Why should the tap-changer be connected near the neutral? What about delta connected transformer.
b) Describe the no load tap changer with a suitable diagram.( April 2009 set-4,Nov/Dec 2004 Set 4)
4.
A 3-phase 50KVA, 6.6/0.4 Kv, 50Hz transformer is ▲ /Y connected. It yielded the following test results:
OC test SC test
Po = 520 W Psc = 610 W
Io = 4.21A Isc = 4.35 A
Vo = 400V Vsc = 340 V
Calculate the pu circuit parameters of the transformer. Determine its efficiency and voltage regulation at full load 0.8 p.f. lagging.
Calculate also the maximum efficiency and the load (0.8 p.f) at which it will occur.( April/May -2005 Set 2)
5. a) List out the advantages and disadvantages of a bank of 3, 1-phase transformers to single 3-phase transformers.
b) A ▲ /Y connected 3-phase transformer has a voltage ratio of 22Kv ( ▲ )/345Kv (Y) (line-to-line). The transformer is feeding 500
MWAR to the grid (345Kv). Determine the VA and voltage rating of each unit (I-Phase).Compute all currents and voltages to both magnitude and phase angle in all the windings. ( April/May -2005 Set 3, Apr/May 2007 Set 3 )
6. a) What precautions should be observed during the operation of on-load tap changer.
b) Explain the function of center-tapped reactor in on load tap changer.( April/May 2005
Set 4)
7. a) Discuss in detail the effect of i.) current harmonics, ii.) voltage harmonics on the performance of three phase transformers.
b) Explain how the harmonics can be suppressed using Star/Delta earthing transformer. Draw the relevant connection diagram.
(Nov/Dec 2005 Set 3)

8. a) Why is it preferable to operate a bank of transformers rather than 3 independent 1phase transformers.
b) A 3 phase transformer bank consisting of three 1-phase transformers is used to step down the voltage of a 3-phase, 6600v transmission line. If primary line-current is 10A, Calculate the secondary line voltage, line current and output KVA for the following connections. i. Y/ ▲ and ii. ▲ /Y. The turn’s ratio is 12 neglect losses (Apr/May 2007 Set 4)
9. A ▲ /Y connected bank of 3 identical 60 KVA, 2000/100V, 50Hz transformers is fed with power through a feeder whose impedance is 0.75 + j0.25 per phase. The voltage at the sending end of the feeder is held fixed at 2 KV line-to-line. The short circuit test when conducted on one of the transformers with its L.V. terminals short circuited gave the following results:
V hv
= 40 V, f = 50Hz , I hv
= 35 A, P = 800 W a) Find the secondary line-to-line voltage when the bank delivers rated current 2A balanced 3-phase u.p.f. load. b) Calculate the currents in the transformer in the primary and secondary windings and in the feeder wires on the occurrence of a solid
3-phase short circuit at the secondary line terminals. (Apr/May 2006 Set 2, 4)
10. Two transformers each rated 250 KVA, 11/2 KV and 50 Hz are connected in open delta on both primary and secondary. a) Find the load KV A that can be supplied from this transformer connection. b) A delta connected 3-phase load of 250 KVA, 0.8 p.f., 2 KV is connected to the low voltage terminal of this open voltage transformers. Determine the transformer currents on the 11 Kv side of this connection.( Apr/May 2006 Set 3)
11 a) what precaution should be observed during the operation on load tap changer
b) explain the fuction of centre tapped reactor in on-load tap changer
c) describe one type of on-load tape changer with proper sequence of operation for changing the voltage (set1april o9)
12 a) describe four possible ways of connection of 3-phase transformer with relevant relation amongst voltage and current on both
\
H.V,L.V sides
b)a bank of three single phase transformer has its H.V terminals connected to 3-wire ,3-phase,11Kv system .it,s L.V terminals are connected to a3 wire 3 phase load rated at 1500KVA ,2200v specify the voltage ,current and kva ratings of each transformer for both
H.V,L.V windings for the following connection i) Y▲ ii) ▲ - Y ii) Y- Y (set-2 april -2009)
13 a) explain the advantages of using a tertiary winding in abank of star-star transformers
b)two T-connected transformers are used to supply a440v,33Kvbalanced load form a3-phase supply of 3.3Kv .calculate i)voltage and current rating of each coil ii)kva rating of the main and teaser transformer (set-3 april-2009)

1.a) With the help of neat sketch, explain the constructional features of a three phase induction motors.
b) A 3-phase, 4-pole, 415 V, 50 Hz, delta connected induction motor running at a slip of 4%. The stator winding is delta connected with 240 conductors per phase, and the rotor winding is star connected with 48 conductors per phase. The per phase rotor winding resistance is 0.013 ohms and a leakage reactance of 0.048 ohms at standstill. Calculate the following: i.) The per phase rotor emf at standstill with the rotor open circuit, ii). The rotor emf and current at 4% slip, iii.) The phase difference between the rotor emf and rotor current at 4% slip.( Aug/Sep 2007 Set 1, 2, 4, Apr/May 2006 Set 1, 3 ,
Nov/Dec 2005 Set 2)
2. a) Explain how torque is produced in the rotor of an induction motor?
b) i. Show that the relative speed between resultant rotor field and resultant stator field of a 3-phase induction motor is zero,
ii. Derive the expression for the rotor e.m.f and rotor current of an induction motor. (Aug/Sep 2007 Set 3, April/May 2005 Set 4,
Nov/Dec 2004 Set 2)
3. a) Discuss the points of similarities between a transformer and an induction machine. Hence, explain why an induction machine is called a generalized transformer.
b) Explain why an induction motor, at no load, operates at a very low power factor. (Apr/May 2006 Set 2, Apr/May 2007 Set 3,
Sept 2006 Set 2, Nov/Dec 2005 Set 1, Nov/Dec 2005 Set 3)
4. a) Explain why the rotor of poly phase induction motor can never attain synchronous speed
b) The rotor of a slip ring induction motor is connected to an AC source, where as its stator winding is short circuited. If rotating magnetic field produced by rotor winding’ rotates clock wise, Explain the direction in which rotor must revolve. (Apr/May 2006 Set
4, Apr/May 2007
Set 1, 2 , Nov/Dec 2005 Set 4, April/May 2005 Set 1, 2, 3 )
5. a) Does the induction motor have any similarities with the transformer? Compare the similarities and differences between them.
b) Show that a rotating magnetic field is produced in the air-gap, when a balanced three-phase ac supply is given to the stator of a
3-phase induction motor. Justify your claim with necessary mathematical equations. (Apr/May 2007 Set 4, Sept 2006 Set 4, Nov/Dec
2004
Set 1)
6. a) Explain why an induction motor cannot develop torque when running at synchronous speed. Define the slip speed of an induction motor and deduce how the frequency of rotor currents and magnitude of rotor emf are related to slip.
b) A 4-pole induction motor is energized from a 50 Hz supply. If the machine runs on full load at 2% slip, determine the i.) Rotor speed with respect to resultant rotor field, ii.) Stator resultant field speed with respect to rotor structure, and iii.) Frequency of rotor currents. ( Sept 2006 Set 1, 3, Nov/Dec-2004 Set 3)
7. a) Explain the principle of operation of a three-phase induction motor and the meaning of the term slip. How does slip vary with the load?
b) Most induction motors have a full load slip of 0.05 or less. The measured speed of a 60Hz motor at rated load is 575 rpm. i) How many poles does the motor have and what is its synchronous speed?

v) ii) What is the full-load slip? iii) If no-load slip is 0.01, what is the percentage speed regulation?
What is the frequency of rotor voltage at no-load, full-load and the instant of starting?
8 a)describe the constructional feature of both squirrel cage induction motor and slip ring induction motor discus the merits of one over the other
b)a 4-pole 50Hz induction motor runs with slip of 0.01 p.u on no load. Calculate the frequency of the rotor current
i)at standstill and
ii) on full load
9) a)explain the principle of operation of 3-phase induction motor with neat sketch
b)a 4-pole ,3-phase induction motor operates from a supply whose frequency is 50Hz calculate i)the speed at which the magnetic field of the stator rotating ii)the speed of the rotor current when the slip is0.04 iii) the frequency of the rotor current when the slip is 0.04 iv)the frequency of the rotor current at stand still (set-2 april-2009)
10) )explain the principle of operation of 3-phase induction motor. explain why the rotor is forced to rotate in the direction of rotating magnetic field?
(B) A 3phase 50 Hz induction motor has a full load speed of 1440 rpm.for this motor calculate the following
I) number of poles ii)full load slip and frequency iii)speed of motor field with respect to
a)stator structure and
b) also rotor structure iv) speed of rotor field with respect to
a)rotor structure and
b)stator field (set-3 april-2009)
1.a) With the help of rotor equivalent circuit of an induction motor, show that the power transferred magnetically from stator to rotor is given by I
2
2 r
2/ s per phase.
b) Explain the terms air gap power Pg, internal mechanical power developed Pm and shaft power Psh. How these terms are related with each other? Hence show that P g
: rotor ohmic loss : P m
= l : s : 1-s. (Nov/Dec 2004 Set 1, Sept 2006 Set 1, Apr/May 2007 Set 3,
Aug/Sep 2007 Set 1, 3, 4 set 1 Apr/May 2009)
2. a) Sketch & discuss the typical torque-speed characteristics of an induction motor.
b) A 3-phase wound rotor of induction motor develops a maximum torque of 4 times the full load torque at slip of 0.20. The per phase rotor resistance is 0.04
Ω . The stator resistance and rotational losses are negligible. Calculate the value of external resistance that must be inserted in the rotor circuit in order to minimize torque at starting. (Nov/Dec 2004 Set 2, Apr/May 2007 Set 2)

3. a) Sketch the torque-slip characteristics of an induction motor working at rated voltage and frequency. Explain and draw these characteristics with respect to the normal one, if the applied voltage and frequency are reduced to half.
b) For a 3-phase induction motor, the rotor ohmic loss at maximum torque is 16 times that at full load torque. The slip at full load torque is 0.03. If stator resistance and rotational losses are neglected, then calculate the starting torque in terms of full load torque.
(Nov/Dec 2004 Set 3)
4. a) Derive the condition of maximum torque developed in a 3-phase induction motor and hence prove that to increase the starting torque extra resistance must be added to the rotor circuit.
b) A 4-pole, 50Hz,3-phase induction motor develops a maximum torque at a speed of 1350 rpm and per phase rotor resistance is
0.2
Ω . Calculate the value of external resistance that must be inserted in series with each rotor phase to produce a starting torque equal to half the maximum torque. Neglect stator resistance.( Nov/Dec 2004 Set 4)
5 . a) In an induction motor deduce the condition P
2
: P m
: P c
: :l :1-s :s
b) A 4-pole wound rotor induction motor is used as a frequency changer. The starter is connected to a 50 Hz 3-phase supply. The load is connected to the rotor slip rings. What are the possible speeds at which the rotor can supply power to this load at 25Hz? What would be the ratio of voltages at load terminals at these speeds? Assume the rotor impedance to be negligible.( April/May -2005 Set
1, Sept 2006 Set 2, 4, Apr/May 2007 Set 4, Apr/May 2006
Set 1, 3)
6. A 4-pole, 3-phase slip ring induction motor is coupled mechanically with a synchronous motor having 2 poles. The synchronous motor and stator of the induction motor are fed from 50Hz voltage source. What will be the frequency of the emfs at the rotor terminals if the synchronous motor is driven? a) In a direction opposite to the induction motor stator rotating field. b) In a direction of the induction motor stator rotating field. If the frequency of the rotor voltage is required to be 300Hz, then calculate b) The number of poles that the induction motor must have.( April/May -2005 Set 2, 3, 4)
7. a) Describe the phenomenon of production of torque in an induction motor.
b) A 6 pole 50 Hz, 3-phase induction motor running on full load develops a useful torque of 160N-m and the rotor emf is absorbed to make 120 cycles/min.Calculate the net mechanical power developed. If the torque loss in windage and friction is 12 N-m, find the copper loss in the rotor windings, the input to the motor and efficiency.Given: starter losses = 200W (inclusive of core loss) (
Nov/Dec 2005 Set 1, 2, 4, Apr/May 2007 Set 1, Apr/May 2006 Set 2)
8. a) Derive the expression for torque in an induction motor.
b) Derive the condition for maximum torque.( Nov/Dec 2005 Set 3)
9 .a) Compare the construction and principle of an induction motor with that of a transformer.
b) An 8-pole, 3 phase, 50Hz induction motor runs at a sped of 710 rpm with an input power of 35Kw. The stator copper loss at this operating condition is 1200W while the rotational losses are 600W. Find i.) Rotor copper loss. ii.) Gross torque developed. iii). Gross mechanical power developed and iv.) Net torque and mechanical power output.
( Sept 2006 Set 3)

10. a) A 3-phase induction motor has operating p.f. of 0.85 at full load speed of 960 rpm and at 400V supply voltage. In case the supply voltage falls to 350V, find the operating p.f. at the same full load torque.
b) 3-phase induction motor has a rotor resistance of 0.5 per phase and rotor standstill leakage reactance of 5 per phase. If the ratio of maximum starting torque to full load torque is 2, find the ratio of actual starting torque to full load torque for direct starting.
Neglect stator impedance and rotational losses.( Aug/Sep 2007 Set 2)
11 a) draw the torque-slip characteristics of an induction motor. Explain them briefly
b)a 3-phase squirrel induction motor has arotor strating current of6 times is full load value the motor has afull load slip of 5%.determine i)the strating torque in terms of full load torque ii)the slip atwhich maximum torque occurs and ii)max.torque in terms of full load torque (set-2aprill-2009)
12 a) explain the difference between the characteristics of slip-ring and squirrel cage,polyphase induction motors.sketch atypical characteristic for each c) a 20KW,6Pole,400v,50Hz,3-phase induction motor has a full load slip of0.02.if the torque ,lost in mechanical losses is 20N-m,find the rotor ohmic losses,motor input and efficiency.stator losses totals 900watts ( set-3aprill-2009)
1. a) Draw and explain the phasor diagram of 3-phase induction motor.
b) Discuss the phenomenon of crawling and cogging in an induction motor. (Aug/Sep 2007 Set 2, 3, 4, Apr/May 2006 Set 4,
Apr/May 2007 Set 2, 3, Sept 2006 Set 1, 2, Nov/Dec 2005 Set 3, April/May 2005 Set 1, Nov/Dec-2004 Set 1)
2. a) Explain the torque development process in an induction motor and its dependence on rotor slip.
b) A 12 pole, 3-phase, 50Hz induction motor draws 2.80A and 110Kw under the block rotor test. Find the starting torque when switched on direct to rated voltage and frequency supply. Assume the stator and rotor copper losses to be equal under the blocked rotor test.
( Aug/Sep 2007 Set 1, Apr/May 2007 Set 1, 4 , April/May 2005 Set 4 , Nov/Dec 2004 Set 4)
3. a) A 10KW, 420V.3-phase,4-pole, 50HZ delta connected squirrel cage induction motor gave the following data on blocked rotor test.210V, 20A, 5KW Stator core loss at rated voltage and frequency is 300 watts. The dc resistance measured between any two terminals of stator is 0.6 ohm. Determine the starting torque.
b) A 10KW, 400V, 4-pole delta connected squirrel cage induction motor gave the following test results.
No load test : 400V, 8A, 250W
Blocked rotor test : 90V, 35A, 1350 watts.
DC resistance per phase of stator is 0.6 calculate equivalent circuit parameters.( Apr/May 2006 Set 1)
4. A 4 KW, 400V, 3-phase, delta connected slip ring induction motor gave the following test results.
No load test : 210V, 16A, power factor = 0.45
Blocked rotor test : 400V, 3.3A, power factor =0.174
Draw circle diagram and final maximum torque and corresponding efficiency and line current. At stand still rotor and stator resistances are equal.( Apr/May 2006 Set 2, 3, Sept 2006 Set 4

5. a) Explain the no load and blocked rotor tests on 3-phase induction motor.
b) Explain how the equivalent circuit parameters 3-phase induction motors are obtained from the tests.( Sept 2006 Set 3, Nov/Dec
2004 Set 3)
6. A 4.5 KW, 400V, 50HZ, 3-phase delta connected induction motor gave the following test results.
No load test: 400V, 4.2A, 480W
Blocked rotor test: 215V, 15A, 1080W
The ratio of stator to rotor resistance referred to stator is 2:1 Calculate the torque, line current, power factor and efficiency at 125% of full load. (Nov/Dec 2005 Set 1)
7. A 400V, 3-phase, 8-pole, 50 Hz star connected induction motor gave the following test results.
No load test : 400V, 10A, 800 watt
Blocked rotor test : 160V, 30A, 1920 watt
Stator and rotor ohmic losses are equal. Calculate the efficiency line current, power factor at full load by drawing circle diagram.
(Nov/Dec 2005 Set 2, 4)
8. a) Draw the approximate equivalent circuit of an induction motor. Also explain the significance of each component.
b) A 7.5Kw, 440V, 3-phase star connected, 50Hz, 4 pole squirrel cage induction motor develops full load torque at a slip of 5% when operated at rated voltage and frequency. Rotational losses are to be neglected. Motor impedance data is as follows: r
1
=1.32
Ω , x
1
= x
2
=1.46 Ω ,x m
= 22.7 Ω
Determine the maximum motor torque at rated voltage and the slip at which it will occur. Also calculate the starting torque. (
April/May 2005 Set 2, 3)
9. a) Describe the methods to reduce the effect of crawling and cogging in an induction motor.
b) Write short notes on:
i) Double cage and ii) Deep bar Rotors. (Nov/Dec 2004 Set 2)
10) A 4Kw,400v ,50Hz,3 phase ,4 pole delta connected slip ring induction motor has startor
Resistance of 0.36
Ω per phase ,rotor resistance of 0.06
Ω per phase and per phase stator to rotor turns of 2. The following data pertains to the line values during light load testes
No load : 400V,3.3A,cosØ0=0.174
Locked rotor :210V,16A,cosØsc=0.45
Draw the circle diagram and compute
Line current,power factor,slip,torque and efficiency at full load (Nov/Dec 2004 Set 2)
11) a) what is the represented by the circle diagram of an induction motor .what information obtained from it
b)show that the diameter of current –locus circle of apoly phase induction motor is V1/x1+x2 where x1 is the per phase stator leakage reactance ,x2 is the stand still per phase rotor reactance referred to stator and v1 is the per phase stator voltage (april-
2009,set-2)
12) a 3-phase squirrei cage induction motor has a shortcircuit current of 5 times the full load current. It,s full load slip is 5%.
Calculate the starting torque as percentage of full load torque if the motor is started by, a) Direct on-line starter b) Star-Delta starter c) Auto t/f starter, limiting the motor starting current to twice the full load current. Also, find the starting current to twice the full load current. Also, find the starting current drawn from the supply, in terms of motor full load current.
What is the percentage auto-transformer tapping in this case?

d) Auto-transformer starter limiting the supply line starting to twice the full load current. Find the auto transformer tapping in this case also.(set3, April 2009)
1. a) An Induction motor rated 3-phase, 400V, 50HZ, 4HP is running at full load slip of 5%. The rotation losses are 360 Watts and stator copper loss of 200 watts. What is the efficiency of the machine if it is run as induction generator at same slip. b) What are the modes of operation of 3 φ induction ? (Nov/Dec 2004 Set 4)
2. Explain briefly the methods of speed control from stator side and from rotor side for 3-phase induction motor. ( Nov/Dec 2004 Set
3, Sept 2006 Set 2 )
3. a) Describe static slip power recovery scheme of speed control with neat sketch.
b) What are the merits of this method over classical methods? (Nov/Dec 2004 Set 2)
4. Explain the following schemes of speed control with sketch.
a) Cascade method. b) Pole changing method. (Nov/Dec 2004 Set 1 set-3,april-2009 )
b)explain the principle of operation of induction generator
5. The rotor of 3-phase slip ring induction motor has an induced voltage of 100V and impedance of 0.2 + j1 ohm at stand still. The induction motor has full load slip of 0.04 driving constant torque load and running at 1440 rpm. Calculate the voltage to be injected if the motor is to be driven at
(a) 800 rpm
(b) 1000 rpm ( April/May 2005 Set 1, 2, 3, Nov/Dec 2005 Set 4, Sept 2006 Set 3, 4, Apr/May 2007 Set 2, 3, 4, Apr/May 2006 Set 1,
2, 4 )
6. a) A 3-phase, 4 pole, 50 Hz, squirrel cage Induction motor has rotor leakage impedance of 1 + j2 Ω /ph, stand still voltage of 100V per phase driving a constant torque load at 0.03 slip. What is speed of the motor, if i.) supply voltage in increased by 25% and frequently in constant. ii.) supply voltage in increased by 25% and frequency is decreased by 25%
b) A 3-phase, 400V, 6-pole, 50Hz, 960 rpm slip ring induction motor has rotor resistance of 0.1 ohm per phase and leakage reactance of 0.5 ohm per phase. The load torque is independent of the speed. i.) Calculate the speed of motor if 0.05 ohm is inserted in the rotor circuit. ii.) What is the maximum external resistance that can be inserted in the rotor and corresponding speed. (April/May 2005 Set 4,
Nov/Dec 2005 Set 3 )
7. a) Explain DOL starter with neat sketch and obtain the expression for starting torque in terms of full load torque.
b) A 3-phase induction motor rating 400V, 50Hz, 3-phase, 4KW draws staring current 5 times the full load current. What is the starting torque in terms of full load torque if applied voltage is rated voltage. Calculate the same if supply voltage is reduced to 90% of its rated value. The full load slip is 0.06.(Nov/Dec 2005 Set 1, 2 , Nov/Dec 2005 Set 1, 2 )
8. a) Explain the method of emf injection for controlling speed of slip ring induction motor with the help of necessary diagrams and above and below the synchronous speed.
b) Explain the principle of operation of induction generator. ( Sept 2006 Set 1, Aug/Sep 2007 Set 1 )
9. a) Explain the reactor starting method for 3-phase squirrel cage induction motors with neat sketch obtain the expression for starting torque in terms of full load torque.
b) A 400V, 3-phase, 50 Hz star connected squirrel cage induction motor has a total impedance of 11.5 ohm/phase at stand still if the starting current is to be limited to 10A what should be voltage applied and corresponding starting torque in terms of full load torque if the full load current is 4A and full load slip is 0.05. (Apr/May 2007 Set 1)
10. Explain the following methods of speed control with slip-torque characteristics.
a) Frequency control b) stator voltage control (Apr/May 2006 Set 3, Aug/Sep 2007 Set 2,3, 4 ).
8 explain briefly the various methods of speed control of 3-phase induction motor (set1 april-09)

11 a)explain pole –changing method of speed control of 3-phase induction motor
b)discuss the working of induction generator .mention its advantages and disadvantages (set1 april-09)