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QUESTION BANK 2016
SIDDHARTH GROUP OF INSTITUTIONS :: PUTTUR
Siddharth Nagar, Narayanavanam Road – 517583
QUESTION BANK (DESCRIPTIVE)
Subject with Code : ET(15A02306)
Course & Branch: B.Tech - ECE
Year & Sem: II-B.Tech & I-Sem
Regulation: R15
UNIT –I
DC GENERATORS
1. Explain the constructional details of a D.C generator?
[L2][CO1][10M]
2. Explain principle of operation of D.C generator?
[L2][CO1][10M]
3. The resistance of the field circuit of a shunt wound D.C generator is 200 ohms. When the
output of the generator is 100 KW.The terminal voltage is 500V and the generated E.M.f is
525V.Caluculate 1)Armature resistance 2)The value of generated E.M.f when the output is
60KW with a terminal voltage of 520V.
[L4] [CO1][10M]
4. Short shunt compound generator delivers a load current of 30 A at 220 V and has armature,
series–field and shunt–field resistances of 0.05 Ω, 0.030 Ω and 200 Ω respectively. Calculate
the induced e.m.f and the armature current. Allow 1.0 V per brush for contact drop.
[L4][CO1][10M]
5. a) Describe the different types of generator.
b) Explain how voltage builds up in D.C shunt generator.
6. Explain the characteristics of D.C generator?
[L1][CO1][5M]
[L2][CO1][5M]
[L2][CO1][10M]
7. An 8-pole, lap-connected dc generator has 12 coils with 8 turns per coil. It is driven at 1500
rpm. If the flux per pole is 30 mWb, calculate the emf generated. If the machine is waveconnected, find the speed at which it is to be driven to generate the same emf as calculated with
lap connection.
[L4][CO1][10M]
8. The armature of a 4 pole, lap-wound D.c shunt generator has 120 slots with 4 conductors per
slot.The flux per pole is 0.05 wb. the armature resistance is 0.05ohm .and shunt field resistance
is 50 ohm.Find the speed of the machine when supplying 45A at a terminal voltage of 250V.
[L4][CO1][10M]
9. a) Derive expression for generated E.M.f of a D.C generator?
b) Explain about applications of D.C generators.
10. a) How will you find the direction of emf using Fleming’s Right hand rule
b) Define critical resistance of a D.C shunt generator?
ELECTRICAL TECHNOLOGY
[L4][CO1][5M]
[L2][CO1][5M]
[L1][CO1][2M]
[L1][CO1][2M]
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QUESTION BANK 2016
c) Why does saturation curve starts from some value higher than zero?
[L1][CO1][2M]
d) Define armature reaction in D.C machines
[L1][CO1][2M]
e) Write down the E.M.F equation of D.C generator?
[L1][CO1][2M]
Prepared by: J.YUGANDHAR / V.VAISHNAVI.
UNIT –II
DC MOTORS
1. a) Explain the working principle of D.C motor.
[L2][CO2][5M]
b) State the voltage and power equation of D.C motor explaining each term.
[L1, L2][5M]
2. a) Derive the expression for electro magnetic torque.
[L4][CO2][5M]
b) Why a series motor cannot be started on no load?
[L1][CO2][5M]
3. Explain the characteristics of D.C motor.
[L2][CO2][10M]
4. a) A 250 VD.C series motor has armature and series field resistance of 0.25and 0.15 ohms
respectively. a) caluculate the current for developing a torque of 80Nm at 1200 r.p.m
b) Caluculate the percentage reduction in flux when the motor runs at 1800 r.p.m at
half the current obtained in part (a).
5. a) Explain types of D.C motor.
[L4][CO2][10M]
[L2][CO2][5M]
b) A 250V,4 pole D.C shunt motor has two circuit armature winding with 500 conductors.
The armature circuit resistance is 0.25 ohms, field resistance is 125 ohm and the flux per pole is
0.02Wb.Find the speed and torque developed if the motor draws 14A from the mains.
[L1, L4][CO2][5M]
6. Explain the operation of starter with neat sketch.
[L2][CO2][10M]
7. Explain any two methods of speed control of D.C shunt motor.
[L2][CO2][10M]
8. Explain swinburne’s test for finding the efficiency of D.C machine.
[L2][CO2][10M]
9. Explain various losses in D.c machine.
[L2][CO2][10M]
10.a) Why swinburne’s test is also called no load test?
[L1][CO2][2M]
b) Write the condition for maximum efficiency.
[L1][CO2][2M]
c) Which method is preferred when speed of D.C shunt motor is to be controlled above rated value.
[L1][CO2][2M]
d) What is back E.M.F?Explain the significance of back E.M.F?
e) State and explain Flemings left hand rule.
[L1][CO2][2M]
[L1,L2][CO2][2M]
Prepared by: J.YUGANDHAR / V.VAISHNAVI.
ELECTRICAL TECHNOLOGY
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QUESTION BANK 2016
UNIT –III
SINGLE PHASE TRANSFORMERS
1. a) Explain the working principle of operation of single-phase transformer.
[L2][CO3][5M]
b) Explain why transformer rating will be given in KVA but not in KW.
2. a) Derive the emf equation of a single-phase transformer.
[L2][CO3][5M]
[L4][CO3][5M]
b) A transformer with an output voltage of 4000V is supplied at 220V. If the secondary has
2000 turns, calculate the no. of primary turns.
[L4][CO3][5M]
3. Explain the constructional details and types of single-phase transformers.
[L2][CO3][10M]
4. Draw the equivalent circuit parameters of a single-phase transformer.
[L1][CO3][10M]
5. a) Define efficiency and voltage regulation of a transformer. Show how the power factor
affects both of them.
b) Draw the phasor diagram for R and L load.
[L1, L2][CO3][5M]
[L1][CO3][5M]
6. a) Explain the various losses and derive the condition for maximum efficiency of a transformer.
[L2][CO3][5M]
b) The efficiency at unity power factor of 6600/384 V, 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 LV side
and insert all the values.
[L4][CO3][5M]
7. a) Define regulation of transformer and also derive the condition for zero voltage regulation.
[L1][CO3][5M]
b) At 400V and 50 Hz the core loss of a transformer was found to be 2400W when the transformer
is supplied at 200V, and 25 Hz, core loss is 800W. Calculate the hysteresis and eddy current
losses at 400V 50Hz.
[L4][CO3][5M]
8. Explain the O.C & S.C tests on single-phase transformer? Explain with neat circuit
diagrams.
[L2][CO3][10M]
9. 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.
10. a)Why transformer rating is kva?
[L4][CO3][10M]
[L1][CO3][2M]
b) Define regulation of transformer?
[L1][CO3][2M]
c) What are properties of an ideal transformer?
[L1][CO3][2M]
d) By which test iron loss and copper loss are measured?
[L1][CO3][2M]
ELECTRICAL TECHNOLOGY
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QUESTION BANK 2016
e) Why Dc-supply is not given to transformer?
[L1][CO3][2M]
Prepared by: J.YUGANDHAR / V.VAISHNAVI.
UNIT –IV
3-PHASE INDUCTION MOTORS
1. Explain how rotating magnetic field produced in 3-phase induction motor.
[L2][CO4][10M]
2. a) Derive torque equation of 3-phase induction motor under running condition.
[L4][CO4][5M]
b) Derive condition for maximum torque under running condition
[L4][CO4][5M]
3. a)The stator of a 3-phase,4 pole induction motor is connected to a 50 HZ supply.The rotor runs 5M
at 1455 r.p.m at full load. Determine i)synchronous speed ii) slip at full Load speed
b) Derive condition for maximum torque under running condition.
4. a) Explain the constructional details of 3phase induction motor.
[L4][CO4][5M]
[L2][CO4][5M]
b) If three phase induction motor with 6-poles runs at 970 r.p.m when connected to a 50HZ supply
calculate i)percentage slip ii)frequency of rotor currents
5. a) Explain the torque slip characteristics of 3-phase induction motor.
[L4][CO4][5M]
[L2][CO4][5M]
b) A 3-phase induction motor is wound for 4 poles and is supplied from 50 Hz system.
Calculate: (i) the synchronous speed. (ii) the speed of the motor when slip is 4% and
(iii) The rotor current frequency when the motor runs at 600 r.p.m.
6. Explain the difference between slip ring and squirrel cage induction motor.
7. a) Explain the principle of operation of 3-phase induction motor
[L4][CO4][5M]
[L2][CO4][10M]
[L2][CO4][5M]
b) A 3-phase 50HZ,4 pole induction motor has a slip of 4% calculate
a)speed of the motor
b)frequency of rotor emf
[L4][CO4][5M]
8. a) Derive the expression for the rotor e.m.f and rotor current of an induction motor [L4][CO4][5M]
b) A 5 h.p,230V,50 HZ induction motor has a rated full load speed of 950 r.p.m.The induced voltage
per phase of rotor at stand still is 100V.calculate,i)number of poles and % full load speed ii)rotor
induced voltage and its frequency at full load.
[L4][CO4][5M]
9. a) Explain why the rotor of 3-phase induction motor can never attain synchronous speed
[L2][CO4][5M]
b) Explain the terms slip, slip speed, rotor frequency, rotor emf
10. a)Define slip and write its formula
[L2][CO4][5M]
[L1][CO4][2M]
b) Write the expression for maximum torque and starting torque
[L1][CO4][2M]
c) Define synchronous speed.
[L1][CO4][2M]
d) List the advantages of wound rotor induction motor.
ELECTRICAL TECHNOLOGY
[L1][CO4][2M]
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QUESTION BANK 2016
e) Why rotor bars are kept skewed.
[L1][CO4][2M]
Prepared by: J.YUGANDHAR / V.VAISHNAVI.
UNIT –V
SYNCHRONOUS MACHINES
1. (a) Explain the constructional features of 3-Ø alternators with the help of neat diagrams.
[L2][CO5]
(b) A 16 pole, 3-Φ, alternator is coupled to a engine running at 375 rpm. It supplies an IM that
has a full load speed of 1450 rpm. Find the slip & number of poles of the alternator.
2. (a) Explain the working principle of a three-phase alternator.
[L4][CO5][10M]
[L2][CO5]
(b) Calculate the EMF of a 4 pole, 3-Φ, star connected alternator running at 1500 rpm from the
following data:
flux per pole = 0.1 wb,
total number of slots =48,
conductors per slot (in two layers) = 4,
coil span = 1500.
[L4][CO5][10M]
3. Explain the Synchronous impedance method for calculating the regulation of a three phase
alternator.
[L2][CO5][10M]
4. Explain the theory of operation of a synchronous motor.
[L2][CO5][10M]
5.
[L4][CO5][10M]
Obtain the expression of EMF induced in an alternator.
4. (a) Explain the difference between salient pole and round rotor machines.
[L2][CO5]
(b) An alternator is operating at no load has an induced EMF of 346.4 V/ph and a frequency of
60Hz. If the pole flux is decreased by 15% & the speed is increased by 6.8%; determine i. the
induced EMF
ii. frequency.
[L4][CO5][10M]
7. (a) A 550 V, 55 KVA single phase alternator has an effective resistance of 0.2Ω. A field current
of 10A produces an armature current of short circuit and an emf of 450 V of open circuit. calculate
i)synchronous impedance and reactance ii) full load regulation when the power factor is 0.8 lagging.
(b) A three phase star connected alternator driven at 900 rpm is required to generate a line
voltage of 460V at 60 Hz on open circuit. The slots has 2 slots/pole/phase and 4 conductors/slot.
Calculate i) no. of poles ii) the useful flux per pole.
[L4][CO5][10M]
8. The stator of a three phase 16 pole alternator has 214 slots and there are 4 conductors per slot
connected in 2 layers and the conductors of each phase are connected in series. If the speed of the
ELECTRICAL TECHNOLOGY
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QUESTION BANK 2016
alternator is375 rpm, calculate induced Emf per phase. Resultant flux in the air gap is 5 mWb per pole
sinusoidally distributed. Assume the coil span as 1500 electrical
[L4][CO5][10M]
9. (a) A 4pole alternator has an armature with 25 slots and 8 conductors per slot and rotates at
1500 rpm and the flux per pole is 0.05 wb. Calculate the EMF generated, if winding factor is
0.96 and all the conductors in a phase are in series.
[L4][CO5]
(b) Sketch and explain the open circuit and short circuit characteristics of a synchronous
machine. How voltage regulation can be calculated by the use of their results.
10. (a) Define voltage regulation of a alternator.
[L4][CO5][10M]
[L1][CO5][2M]
(b) Define winding factor.
[L1][CO5][2M]
(c) Write down the formula for distribution factor and pitch factor.
[L1][CO5][2M]
(d) Define synchronous reactance.
[L1][CO5][2M]
(e) Define leakage reactance in an alternator.
[L1][CO5][2M]
Prepared by: J.YUGANDHAR / V.VAISHNAVI.
ELECTRICAL TECHNOLOGY
Page 1
QUESTION BANK 2016
SIDDHARTH GROUP OF INSTITUTIONS :: PUTTUR
Siddharth Nagar, Narayanavanam Road – 517583
QUESTION BANK (OBJECTIVE)
Subject with Code : ET(15A02306)
Course & Branch: B.Tech -ECE
Year & Sem: II-B.Tech & I-Sem
Regulation: R15
UNIT – I
DC GENERATORS
1. The D.C. Generator works on the principle of
[
]
A) Flemings left hand rule
B) Ampere’s law
C) Lenz’s law
D)Faradays laws of Electromagnetic induction
2. Laminated yoke in a dc generator reduces
[
]
A) Iron losses
B) Temperature rise
C) Speed regulation
D) Sparking on load
3. The EMF generated in a D.C. Generator depends on
[
]
A) No. of turns in the armature
B) Flux / pole
C) Speed
D) All
4. The load current and field current of a DC shunt generator are 50A and5A respectively.
Its armature current is________
[
]
A) 50A
B) 55A
C) 45A
D) 40A
5. In a d.c shunt generator the field winding is connected in................. to the armature. [
]
A) parallel
B)series
C) both A & B
D) none of the above
6. The current relation in dc separately excited generator is
A) If= Ia
B) IL=Ia
C) Ia=-IL
D) Ia=0
7. A D.C. Generator is a machine that converts
[
]
[
]
A) Electrical energy into Mechanical energy
B) Electrical energy into Electrical energy
C) Mechanical energy into Mechanical energy
D)Mechanical energy into Electrical energy
8. The brush voltage drop in d.c machine is about …….
A) 0.1V
B) 2V
C) 10V
D) 20V
9. The purpose of commutator in a d.c. generator is to_______
A) reduce sparking at brushes
ELECTRICAL TECHNOLOGY
[
]
[
]
B) convert the induced a.c. into d.c.
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QUESTION BANK 2016
C) increase output voltage
D) provide smoother output
10. Which of the following DC Generators is suitable for charging Batteries?
A) Shunt generator
B) Series Generator
C) Differentially compounded Generator
D) None
11. The current relation in dc compound generator is
A) Ia=Ish+IL
B) Ia=Ish
C) Ia=IL
D) Ia=0
[
]
[
]
[
]
[
]
[
]
[
]
12. Residual magnetism is essential in the field electromagnets for building up of voltage
of all types of d.c generators except.................
A) shunt
B) compound
C) separately excited
D) series
13. The critical resistance of the D.C. generator is the resistance of
A) armature
B) field
C) load
D) brushes
14. The armature of a d.c. machine is made of________
A) wrought iron
B) silicon steel
C) cast steel
D) soft iron
15. A separately excited d.c generator is normally not used because
A) It is costly
B) Separate d.c source is required for field circuit
C) Terminal voltage rises with increase in load D) None of these
16. The purpose of brush in a d.c. machine is to________
A) prevent sparking
B) clean the commutator
C) collect current from the commutator
D) none of these
17. For short shunt compound generator, which of the following equation is correct?
A) IA=ISH+IL
B) IL=IA+ISH
C) IA=ISE
D) All
18. The induced emf in the armature of d.c generator is ………
A) Statically induced emf
B) Dynamically induced emf
C) Self induced emf`
D) None
19. If residual magnetism is present in a dc generator ,the induced emf at zero will be
A) zero
B)small
C)the same as rated voltage
D)high
20. Function of yoke is
A) To provide mechanical support to the poles
B) Reduce losses
C) carry current
D) All
ELECTRICAL TECHNOLOGY
[
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[
]
[
]
[
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[
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QUESTION BANK 2016
21. For a given d.c generator, the magnitude of generated voltage depends on ______
[
]
22. A 200V DC Generator has a shunt field resistance of 200ohms. Its field current is___ [
]
A) Flux only
B) Speed only
C) No. of poles only
D) All
A) 1A
B) 2A
C) 3A
D) 4A
23. Which of the following machine converts mechanical energy into electrical energy
A)Motor
B)Generator
C)Both
D)None
24. Classification of D.C. Generators are depending on the method in which
[
]
[
]
[
]
A) field windings are connected to the armature circuit
B) the armature circuit is connected to the load
C) the field windings are connected to the load
D) none of the above
25. The current relation in dc series generator is
A) Ise= Ia +IL
B) Il=Ise- Ia
C) Ia=IL
D) All
26. The Commutator segments of a D.C. Machine are insulated from each other by a thin layer
0f _________
A) Bakelite
B) PVC
C) Hard rubber
D) Mica
27. Copper brushes in D.C. machine are used
[
]
[
]
[
]
[
]
[
]
A) where low voltage and high currents are involved
B) where high voltage and low currents are involved
C) in both of the above cases
D) none of the above cases
28. Brushes in D.C machines are made of
A) Carbon
B) Soft Copper
C) Hard Copper
D) all the above
29. Magnetic field in a D.C generator is produced by
A) Electro magnets
B) Permanent magnets
C) both (a) and (b)
D) None
30. In D.C. generator Lap winding is used for
A) high voltage , high current
ELECTRICAL TECHNOLOGY
B) low voltage , high current
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QUESTION BANK 2016
C) high voltage , low current
D) low voltage , low current
31. Which of the following D.C. generator cannot build up on open-circuit?
A) Shunt
B) Series
C) Short Shunt
D) Long Shunt
32. The External Characteristics of a D.C. generator gives the relation between
A) V and IL
B) E and Ia
C) Eo and If
D) V and If
33. The Internal Characteristics of a D.C. generator gives the relation between
A) V and IL
B) E and Ia
C) Eo and If
D) V and If
34. The O.C. Characteristics of a D.C. generator gives the relation between
A) V and IL
B) E and Ia
C) Eo and If
D) V and If
35. Which of the following D.C. generator is used for arc welding
A) Shunt
B) Series
C) cumulative compound
D) Differential compound
36. Which of the following D.C. generator is used as Boosters
A) Shunt
B) Series
C) cumulative compound
D) Differential compound
37. In D.C. generator Wave winding is used for
A) high voltage , high current
B) low voltage , high current
C) high voltage , low current
D) low voltage , low current
38. Bearings in a D.C. machine is used to
A) reduce the friction
B) carry current
C) reduce the losses
D) none
39. In cumulative compound D.C. generator the total flux ØT=
A) ØSh+ ØSe
B) ØSh- ØSe
C) ØSh= ØSe
D) none
40. In Differential compound D.C. generator the total flux ØT=
A) ØSh+ ØSe
B) ØSh- ØSe
C) ØSh= ØSe
D) none
[
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[
]
[
]
[
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[
]
[
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[
]
[
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[
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[
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Prepared by: J.YUGANDHAR / V.VAISHNAVI.
ELECTRICAL TECHNOLOGY
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QUESTION BANK 2016
UNIT –II
DC MOTORS
1.The purpose of commutator in a d.c.Motor is to________
A) convert the induced d.c. into a.c
B) reduce sparking at brushes
C) increase output voltage
D) provide smoother output
2. Which dc motor is generally preferred for cranes
A) differentially compound motor
B)shunt motor
C) cumulatively compound motor
D) series motor
3. For short shunt compound motor, which of the following equation is correct?
A) IA=ISH -IL
B) IL=IA+ISH
C) IA=ISE
D) All
4. Which motor should not be started on no-load
A) differentially compound motor
B)shunt motor
C)cumulatively compound motor
D) series motor
5. A D.C.Motor is a machine that converts
[
]
[
]
[
]
[
]
[
]
[
]
[
]
A) Electrical energy into Mechanical energy
B) Electrical energy into Electrical energy
C) Mechanical energy into Mechanical energy
D) Mechanicalenergy into Electrical energy
6. The load current and field current of a DC shunt motor are 40A and 4A respectively.
Its armature current is________
A) 44A
B)36A
C) 1A
D) 40A
7. In a d.c series motor the field winding is connected in................. to the armature.
A) series
B) parallel
C) both A & B
D) none of the above
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QUESTION BANK 2016
8. The EMF generated in a D.C. Motor is called as
A)Back emf
B) Generated emf
C) Both(A)&(B)
D) None
9. Which of the following DC Motor is used in traction
A) Shunt Motor
B) Series Motor
C) Differentially compounded Motor
D) None
10.The current relation in dc Series Motor is
[
]
[
]
[
A) Ise= Ia +IL
B) Il=Ise- Ia
C) Ia=IL= Ise
D) All
11. The condition for maximum power in case of dc motor is
A)backemf=2*supply voltage
B)back emf=1/2* supply voltage
C)Both
D)None
[
]
]
12. Which of the following rule/law can be used to determine the direction of rotation of dc motor
[
]
A) Lenz’s law
B) Faraday’s law
C) Coulomb’s law
D) Fleming’s left hand rule
13.Which of the following is a electrical machine
A)Motor
B)Generator
C)Both
D)None
14.The D.C.Motor works on the principle of
[
]
[
]
A) Flemings left hand rule
B) Ampere’s law
C) Lenz’s law
D) Faradays laws of Electromagnetic induction
15. A 100V DC Motor has a shunt field resistance of 100ohms. Its field current is_____ [
A) 1A
B) 2A
C) 3A
D) 4A
16.The current relation in dc compound Motor is
[
A) Ish= Ia +IL
B) Ish=IL- Ia
C) Ia=IL
D) Ia=0
ELECTRICAL TECHNOLOGY
]
]
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QUESTION BANK 2016
17.The speed of a dc motor can be controlled by varying
A) Its flux per pole
B) resistance of the armature circuit
C) applied voltage
D) all of the above
18. The direction of D.C.series motor can be changed by
A) interchanging the Supply terminals
B) interchanging the Field terminals
C) Either (a) & (b)
D) None
[
]
[
]
19. The current drawn by a 120V D.C. motor of armature resistance 0.5Ω and back emf 110V is
______ ampere
[
]
A) 20
B)240
C)220
D)5
20. The shaft torque of a D.C. motor is less than the armature torque because of __losses [
A) copper
B) mechanical
C) iron
D) rotational
21. Which of the following motor is used in centrifugal pumps, Blowers and fans
]
[
]
[
]
[
]
24. In D.C. series motor the electromagnetic torque developed is directly proportional to [
]
A) differentially compound motor
B)shunt motor
C)cumulatively compound motor
D) series motor
22. Which of the following motor is used in Traction, Trolley and cars
A) differentially compound motor
B)shunt motor
C)cumulatively compound motor
D) series motor
23. Which of the following motor is used in Elevators, Shears and Punches
A) differentially compound motor
B)shunt motor
C)cumulatively compound motor
D) series motor
A) Ia
B) Ia2
C) 1/Ia
D) 1/Ia2
25. In D.C. shunt motor the electromagnetic torque developed is directly proportional to [
A) Ia
B) Ia2
C) 1/Ia
D) 1/Ia2
ELECTRICAL TECHNOLOGY
]
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QUESTION BANK 2016
26. The Ta/Ia graph of a D.C. series motor is
[
]
A) parabola from no-load to over load B) straight line throughout
C) parabola throughout
D) parabola upto full-load and a straight line at over loads
27. Starters in D.C. motor is used to
[
A) to limit starting current to a safe value
B) to limit voltage
C) to limit speed
D) none
]
28. The most economical method of finding no-load losses of a large D.C.shunt motor is ---Test
A) Hopkinson’s test
B) Swinburne’s test
C) retardation
D) Field’s
29. Ward-Leonard system of speed control is not recommended for
A) wide speed range
B) constant speed operation
C) frequent motor reversals
D) very low speeds
30. In case of D.C. motor connected across A.C. mains
A) the motor will burn
[
]
[
]
[
]
B) the motor will run at rated speed
C) the motor will run at corresponding synchronous speed D) the motor will run at low speed
31. A three point starter is considered as suitable for
[
]
A) Shunt motors
B) Shunt as well as compound motors
C) Shunt, compound and series motors
D) all D.C. motors
32. A 220V shunt motor develops a torque of 54 N-m at armature current of 10A. The torque produced
when armature current is 20A,is
[
]
A) 54 N-m
B) 81 N-m
C) 108 N-m
D) None of the above
33. A D.C. motor develops a torque of 200 N-m at 25 rps. At 20 rps it will develop a torque of ----N-m
[
A) 200
B) 160
C) 250
D) 128
ELECTRICAL TECHNOLOGY
]
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QUESTION BANK 2016
34. The speed of a D.C motor is directly proportional to
A) Eb/Ø
B) Eb* Ø
C) Eb2
D) none
35. Which one is the Direct test of D.C motor
A) Brake test
B) Swinburne’s test
C) Hopkinson’s test
D) none
36. At noload condition of D.C motor the armature torque Ta =
A) TL
B) Tsh + TL
C) Tsh
D) none
37. Which one is the In - Direct test of D.C motor
A) Brake test
B) Swinburne’s test
C) Both a & b
D) none
38. The _____ torque which is used to do the useful work
A) shaft torque
B) Loss torque
C) armature torque
D) none
39. The _____ torque which is used to overcome the losses
A) shaft torque
B) Loss torque
C) armature torque
D) none
40. Turning or Twisting force about an axis is known as
A) shaft torque
B) Loss torque
C) torque
D) none
[
]
[
]
[
]
[
]
[
]
[
]
[
]
Prepared by: J.YUGANDHAR / V.VAISHNAVI
ELECTRICAL TECHNOLOGY
Page 1
QUESTION BANK 2016
UNIT –III
SINGLE PHASE TRANSFORMERS
1. The two windings of a transformer is
A) conductively linked
B) inductively linked
C) not linked at all
D) electrically linked.
2. The efficiency of a transformer is mainly dependent on
A) core losses.
B) copper losses.
C) stray losses.
D) dielectric losses.
3. In a transformer the voltage regulation will be zero when it operates at
A) unity p.f.
B) leading p.f.
C) lagging p.f.
D) Zero p.f. leading
4. An ideal transformer is one which
A) has more losses
C) has no losses and leakage reactance
B) 750
C) 7.5
D) 0.13
7. The main purpose of performing open-circuit test on a transformer is to measure its
A) Copper loss
B) total loss
C) core loss
D) heat loss
8. Transfer of electrical power from primary to secondary in a transformer takes place
A) Electrically
B) Electromagnetically
[
]
[
]
[
]
[
]
[
]
[
]
D) none of the above
9. The path of a magnetic flux in a transformer should have
A) high resistance
B) high reluctance
ELECTRICAL TECHNOLOGY
]
D) copper loss
A) 75
C) low resistance
[
D) All the above
6. To step 120 V ac up to 900 V ac, the turn’s ratio must be
C) magnetically
]
B) does not work
5. Which of the following is minimized by laminating the core of a transformer?
A) Eddy current loss
B) Hysteresis loss
C) Heat loss
[
[
]
D) low reluctance
Page 1
QUESTION BANK 2016
10. The efficiency of a transformer will be maximum when
[
A) copper losses = hysteresis losses
B) hysteresis losses = eddy current losses
C) eddy current losses = copper losses
D) copper losses = iron losses
]
11. Which of the following is not a part of transformer installation?
[
]
[
]
A) Conservator
B) Breather
C) Buchholz relay
D) Exciter
12. A transformer cannot raise or lower the voltage of a D.C. supply because
A) there is no need to change the D.C. voltage
B) a D.C. circuit has more losses
C) Faraday's laws of electromagnetic induction are not valid since the rate of change of flux is zero
D) none of the above
13. A transformer is so designed that primary and secondary have………………
A) high leakage reactance
B) tight magnetic coupling
C) large resistance
[
]
[
]
B) amperes
D) kVA
17. When load on a transformer is decreased ___________ loss is decreased
A) Eddy current
B) hysteresis
C) friction
D)Copper
18. Which of the following does not change in transformer
A) Voltage
B) Current
C) Power
D) Frequency
19. Silicon steel used for laminating the core to reduce
A) Hysteresis loss
B) Eddy current loss
C) Copper loss
D) All
ELECTRICAL TECHNOLOGY
]
D) 25 percent
16. The transformer ratings are usually expressed in terms of
A) volts
C) kW
[
D) Secondary winding
15. Efficiency of a power transformer is of the order of
A) 100 percent
B) 98 percent
C) 50 percent
]
D)good electric coupling
14. Which winding in a transformer has more number of turns?
A) Low voltage winding
B) High voltage winding
C) Primary winding
[
[
]
[
]
[
]
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QUESTION BANK 2016
20. Eddy current loss will depend on
A) Frequency
B) flux density
C) thickness
D) All
21. Short circuit test on transformer is conducted to determine
A) Current loss
B) Copper loss
C) Voltage loss
D) Iron loss
22. Which of the following type transformer is wide in use
A) Shell type transformer
C) Both
A) Eddy current loss
B) Hysteresis loss
C) Windage loss
D) Copper loss
25. Sumpner’s test is conducted on transformers to determine
A) Temperature
B) Stray losses
C) All day efficiency
D) None
26. The highest level voltage of generation in india is
A) 33KV
B) 11KV
C) 132KV
D) All
27. Which of the following is step up transformer
A) If K<1
B) If K>1
C) If K=1
D) All
28. Which of the following is step down transformer
A) If K<1
B) If K>1
C) If K=1
D) All
29.Transformation ratio is denoted by a letter of
A) V
B) I
C) K
D) P
30. Hysteresis loss will depends on
ELECTRICAL TECHNOLOGY
]
[
]
[
]
[
]
[
]
[
]
[
]
[
]
[
]
[
]
B) Core type transformer
D)None
24. Which loss is not common between a transformer and rotating machine
A) f2
[
B) f3
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QUESTION BANK 2016
C) f
D) f1.6
31. Total core loss is also called as -------------?
A) Eddy current loss
B) Hysteresis loss
C) Magnetic loss
D) Copper loss
32. Which of the following are variable losses?
A) Eddy current loss
B) Hysteresis loss
C) shunt field loss
D) armature copper loss
33. The basic function of a transformer is to change
A) the power level
B) the power factor
C) the level of the voltage
D) the frequency
[
]
[
]
[
]
34. R1 is the resistance of the primary winding of the transformer. The turn ratio in terms of primary to
secondary is K. Then the equivalent resistance of the primary referred to secondary is
[
A) R1/K
B) K²R1
C) R1/K²
D) K*R1
35. Voltage regulation of transformer is given by
A) (E2 - V2) / V2
B) (E2 - V2) / E2
C) (V2 - E2) / V2
D) (V2 - E2) / E2
36. Transformer oil is used as
A) an insulator
B) a coolant
C) both 1 and 2
D) inert medium
37. Conservator tank is used
A) to take up the expansion of oil due to temperature rise
B) to act as an oil storage
C) for better cooling of transformer
D) none of the above
38. In a transformer which of the following losses are zero ?
A) iron loss
B) copper loss
C) mechanical loss
D) all of the above
39. Breather is provided in a transformer to
A) absorb moisture of air during breathing
]
[
]
[
]
[
]
[
]
[
]
B) provide cold air in transformer
C) absorb moisture from air entering in transformer D) filter the transformer oil
ELECTRICAL TECHNOLOGY
Page 1
QUESTION BANK 2016
40. The leakage flux in a transformer depends upon
[
A) the applied voltage
B) the load current
C) the frequency
D) the mutual flux
]
Prepared by: J.YUGANDHAR / V.VAISHNAVI.
UNIT –IV
3-PHASE INDUCTION MOTORS
1. The frequency of the rotor current in a 3 phase 50 Hz, 4 pole induction motor at full load
[
speed is about
A) 50 Hz.
B) 20 Hz.
C) 2 Hz.
D) Zero.
]
2. In a 3 – phase induction motor running at slip ‘s’ the mechanical power developed in terms of air
gap power Pg is
[
]
A) (s -1)Pg .
B) Pg/ (s -1).
C) (1-S) Pg.
D) s Pg .
3. The rotor frequency for a 3 phase 1000 RPM 6 pole induction motor with a slip of 0.04
is________Hz
[
]
A) 8
B) 4
C) 6
D) 2
4. The frame of an induction motor is usually made of
A) Silicon steel
B) cast iron
C) aluminum
D) bronze
5. The efficiency of an induction motor can be expected to be nearly
A) 60 to 90%
B) 80 to 90%
C) 95 to 98%
[
]
[
]
[
]
D) none
7. If any two phases for an induction motor are interchanged
ELECTRICAL TECHNOLOGY
]
D) 99%
6. The number of slip rings on a squirrel cage induction motor is usually
A) two
B) three
C) four
[
Page 1
QUESTION BANK 2016
A) The motor will run in reverse direction B) the motor will run at reduced speed
C) the motor will not run
D) the motor will burn
8. An induction motor is
[
]
[
]
10. In three-phase induction motors sometimes copper bars are placed deep in the rotor to [
]
A) Self-starting with zero torque
B) self-starting with high torque
C) Self-starting with low torque
D) non self-starting
9. A 3-phase slip ring motor has
A) double cage rotor
B) wound rotor
C) short-circuited rotor
D) any of the above
A)Improve starting torque
B)reduce copper losses
C)improve efficiency
D)improve power factor
11. The rotor of an induction motor runs at
A) Synchronous speed
B) below synchronous speed
C) above synchronous speed
D) any of the above
12. The shaft of an induction motor is made of
A) Stiff
B) flexible
C) hollow
D) any of the above
[
]
[
]
13. A 3-phase 440 V, 50 Hz induction motor has 4% slip. The frequency of rotor e.m.f will be
A) 200 Hz
B) 50 Hz
C) 2 Hz
D) 0.2 Hz
14. The starting torque of a squirrel-cage induction motor is
[
]
[
]
A) Low
B) negligible
C) same as full-load torque
D) slightly more than full-load torque
15. For which motor the speed can be controlled from rotor side?
A)Squirrel-cage induction motor
B) Slip-ring induction motor
C) Both A and B
D) None
16. The maximum torque in an induction motor depends on
ELECTRICAL TECHNOLOGY
[
]
[
]
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QUESTION BANK 2016
A) Frequency
B) rotor inductive reactance
C) square of supply voltage
D) all of the above
17. Which type of bearing is provided in small induction motors to support the rotor shaft[
A) Ball bearings
B) Cast iron bearings
C) Bush bearings
D) None of the above
]
18. The shape of the torque/slip curve of induction motor is
A) parabola
B) hyperbola
C) rectangular parabola
D) straight line
[
]
19. In an induction motor, no-load the slip is generally
A) less than 1%
B) 1.5%
[
]
C) 2%
D) 4%
20. In Ns is the synchronous speed and s the slip, then actual running speed of an induction motor will
be
[
]
A) Ns
B) S*Ns
C) (l-S)Ns
21. In case of the induction motors the torque is
A) inversely proportional to (slip) 2
C) Inversely proportional to slip
D) (Ns-l)S
B) directly proportional to (slip)
[
]
[
]
[
]
[
]
2
D) directly proportional to slip
22. Rotor rheostat control method of speed control is used for
A) squirrel-cage induction motors only
B) slip ring induction motors only
C) both A & B
D) none
23. In three-phase squirrel-cage induction motors
A) Rotor conductor ends are short-circuited through slip rings
B) rotor conductors are short-circuited through end rings
C) rotor conductors are kept open
D) rotor conductors are connected to insulation
24. If a 3-phase supply is given to the stator and rotor is short circuited rotor will move
A) In the opposite direction as the direction of the rotating field
B) in the same direction as the direction of the field
C) in any direction depending upon phase sequence of supply
D) none
ELECTRICAL TECHNOLOGY
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QUESTION BANK 2016
25. The stating torque of the slip ring induction motor can be increased by adding _____ to the rotor
[
]
A) external inductance
B) external resistance
C)external capacitance
D)both resistance and inductance
26. Slip ring motor is preferred over squirrel cage induction motor where
A) high starting torque is required
C) heavy pull out torque is required
[
]
B) load torque is heavy
D) all of the above
27. In squirrel cage induction motors, the rotor slots are usually given slight skew in order to
[
]
[
]
[
]
[
]
31. In a three-phase induction motor, the number of poles in the rotor winding is always [
]
A) Reduce windage losses
C) reduce accumulation of dirt and dust
28. Slip rings are usually made of
A) copper
C) phospor bronze
B) reduce eddy currents
D) reduce magnetic hum
B) carbon
D) aluminium
29. An induction motor with 1000 r.p.m. speed will have
A) 8 poles
B) 6 poles
C) 4 poles
D) 2 poles
30. An induction motor is identical to
A) D.C. compound motor
B) D.C. series motor
C) synchronous motor
D) asynchronous motor
A) zero
B) more than the number of poles in stator
C) less than number of poles in stator
D) equal to number of poles in stator
32. The speed of a squirrel-cage induction motor can be controlled by all of the following except
A) changing supply frequency
B) changing number of poles
C) changing winding resistance
D) reducing supply voltage
33. The low power factor of induction motor is due to
A) rotor leakage reactance
B) stator reactance
ELECTRICAL TECHNOLOGY
[
]
[
]
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QUESTION BANK 2016
C) the reactive lagging magnetizing current necessary to generate the magnetic flux
D) all of the above
34. A squirrel cage induction motor is not selected when
[
]
[
]
[
]
A) initial cost is the main consideration
B) maintenance cost is to be kept low
C) higher starting torque is the main consideration
D) all above considerations are involved
35. The power factor of a squirrel cage induction motor is
A) Low at light load only
B) Low at heavy load only
C) Low at light and heavy load both
D) Low at rated load only
36. The slip of an induction motor normally does not depend on
A) rotor speed
B) synchronous speed
C) shaft torque
D) core-loss component
37. Find the number of poles required, when the frequency is 50Hz and speed of the motor is 500 rpm?
[
]
A) 5
B) 10
C) 12
D) 24
38. Which of the following induction motor has the highest starting torque?
A) Squirrel cage induction motor
B) slip ring induction motor
C) same in both induction motors
D) none of the above
39. A 4 pole 50 Hz induction motor is running at 1470 rpm. What is the slip value?
A) 0.2
B) 0.02
C) 0.04
[
]
[
]
[
]
D) 0.4
40. Which of the following motors is /are widely used?
A) Squirrel cage induction motor
B) slip ring induction motor
C) either of these
D) none of the above
Prepared by: J.YUGANDHAR / V.VAISHNAVI.
UNIT –V
SYNCHRONOUS MACHINES
ELECTRICAL TECHNOLOGY
Page 1
QUESTION BANK 2016
1. The magnitude of the three voltage drops in an alternator due to armature resistance, leakage
reactance and armature reaction is solely determined by
[
A) load current, Ia
B) p.f of the load
C) Whether it is a lagging or leading p.f load
D) field construction of the alternator
2. The effect of armature reaction for an alternator for zero power factor lagging
[
A) cross magnetizing
B) wholly demagnetizing
C) non- effective
D) magnetizing
3. At leading p.f the armature flux in an alternator ____________ the rotor flux.
[
A) opposes
B) aids
C) distorts
D) does not affect
4. The power factor of an alternator is determined by its
[
A) speed
B) load
C) excitation
D) prime mover
5. What parameter of load influences the armature reaction of an alternator?
[
A) power
B) Voltage
6.
7.
8.
9.
C) power factor of load
D)none
The effect of armature reaction for an alternator for power factor leading ____
A) magnetizing
B) wholly demagnetizing
C) non-effective
D) distorting
When the load on an alternator is varied, its terminal voltage is also vary due to
A) armature resistance
B) armature leakage reactance
C) on account of armature reaction vary
D) all of the above
Zero power factor method of an alternator is used to find its
A) efficiency
B) voltage regulation
C) armature resistance
D) synchronous impedance
Under no-load condition, power drawn by the prime mover of an alternator goes to
A) produce induced emf in armature winding
B) meet no- load losses
C) produce power in the armature
D) meet cu losses both in armature and rotor windings
]
]
]
]
]
[
]
[
]
[
]
[
]
10. As load p.f of an alternator becomes more leading, the value of generated voltage required to give
rated terminal voltage
[
]
A) increases
B) remains unchanged
C) decreases
D) varies with rotor speed
11. The voltage regulation of an alternator having 0.75 leading p.f load, no-load induced emf of 2400V
and rated terminal voltage of 3000V is __________ percent
[
]
A) 20
B) -20
C) 150
D) -26.7
ELECTRICAL TECHNOLOGY
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QUESTION BANK 2016
12. Synchronous impedance method is known as
A) MMF method
C) ASA method
[
]
[
]
[
]
B) EMF method
D) none
13. Zero power factor method another name is _____________
A) Potier method
B) MMF method
C) EMF method
D) ASA method
14. Ampere Turn method is also named as _____________
A) Potier method
B) MMF method
C) EMF method
D) ASA method
15. What are the characteristics required for potier method of computing voltage regulation
[
A) Open circuit characteristic
]
B) Short circuit characteristic
C) Zero power factor full load voltage characteristic
D) all of the above
16. Which quantities are usually determined using the zero-power factor characteristics of a
synchronous machine?
[
]
A) leakage reactance drop
B) voltage drop due to armature reaction
C) armature reaction ampere turns
D) all of the above
17. Which method of regulation is called pessimistic method?
A) EMF method
B) MMF method
C) Potier method
[
]
D) none
18. When a synchronous motor is running at synchronous speed, the damper winding
produces
[
]
A)damping torque
B) eddy current torque
C) torque aiding the developed torque
D) no torque
19. Which of the following relation is correct?
[
A) Xd = Xq
B) Xd < Xq
C) Xd > Xq
D) None
ELECTRICAL TECHNOLOGY
]
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QUESTION BANK 2016
20. If the excitation is increased, the power factor is
A) unity power factor
B) leading power factor
C) lagging power factor
D) none of the above
21. If the excitation is reduced, the power factor is
A) unity power factor
B) leading power factor
C) lagging power factor
D) none of the above
22. Maximum power developed is depends on
A) voltage
B) reactance
C) both 1and 2
D) load angle
23. Field winding of an alternator is
A) DC excited
B) AC excited
C) both(A) & (B)
D) none
24. Regulation of an alternator supplying resistive or inductive load is:
A) always positive
B) always negative
C) either of the above or zero
[
]
[
]
[
]
[
]
[
]
[
]
D) none
25. Regulation of an alternator supplying capacitive load is:
A) always positive
B) always negative
C) either of the above or zero
D) none
26. Which kind of rotor is most suitable for turbo alternators which are designed to run at high speed
[
]
A) Salient pole type
B) Non-salient pole type
C) Both (A) and (B) above
D) None of the above
27. The frequency of voltage generated by an alternator having 4 poles and rotating at 1800 rpm is
[
]
A) 60 Hz
B) 7200 Hz
C) 120 Hz
D) 450 Hz
28. The number of electrical degrees passed through in one revolution of a four pole alternator is
[
]
A) 360:
B) 720
C) 1080
ELECTRICAL TECHNOLOGY
D) 2160
Page 1
QUESTION BANK 2016
29. A 10 pole AC generator rotates at 1200 rpm. The frequency of AC voltage in cycles per second will
be
[
]
A)120
B)110
C) 100
D) 50
30. The rating of an alternator is usually expressed in terms of
A) full load current
B) rated voltage
C) KVA
D) KW
31. If an alternator is operating at leading P.F
A) alternator is over excited
B) alternator is under exciter
C) torque angle is negative
D) none
32. The salient pole type rotors have
A) larger diameter
B) smaller axial length
C) larger axial length
D) both A & B
[
]
[
]
[
]
33. The synchronous speed of an alternator having 2 poles and operating on a 50Hz supply is[
A) 1500rpm
B) 1800rpm
C) 3000rpm
D) 6000rpm
34. The power factor of an alternator depends on
[
A) Load
B) Speed of rotor
C) Core losses
D) Armature losses
]
]
35. The number of electrical degrees passed through in one revolution of a two pole alternator is [
A)3600
B)7200
C) 10800
D)21600
]
36. An electric motor in which the both the rotor and stator fields rotates with the same speed is called
a _____ motor
[
]
A) D.C
B) charge
C) synchronous
D) universal
37. The direction of rotation of a synchronous motor can be reversed by reversing
A) current to the field winding
B) supply phase sequence
C) polarity of rotor poles
D) none of the above
ELECTRICAL TECHNOLOGY
[
]
Page 1
QUESTION BANK 2016
38. In a synchronous motor,the magnitude of stator back e.m.f Eg depends on
A) speed of the motor
B) load on the motor
C) both the speed and rotor flux
D) D.C. excitation only
39. In a synchronous motor, the rotor Cu losses are met by
A) motor input
B) armature input
C) supply lines
D) D.C source
[
]
[
]
40. A synchronous motor running with normal excitation adjusts to load increases essentially by
increase in its
[
]
A) power factor
B) torque angle
C) back e.m.f
D) armature current
Prepared by: J.YUGANDHAR / V.VAISHNAVI.
ELECTRICAL TECHNOLOGY
Page 1