ashishsoniwifistudy

1. If the speed of rotation of a dynamo is doubled, then

the induced emf will: [LMRC 2015]

a) become half

b) become double

c) become four times

d) remain unchanged

2. An exciter for a turbo generator is a: [LMRC 2015]

a) separately excited generator

b) shunt generator

c) series generator

d) compound generator

3. On which of the following parameters does the

power factor of an alternator depend? [UPRVUNL 2014]

a) Load

b) Speed or rotor

c) Core losses

d) Armature losses

4. Consider the following figure for a 4-pole, 3-phase,

24-slots double layer winding. Find the pole pitch and

the slot pitch angle. [UPRVUNL 2014]

a) 4 and 40 electrical degrees

b) 5 and 50 electrical degrees

c) 6 and 30 electrical degrees

d) 6 and 60 electrical degrees

5. If the excitation of an alternator operating in parallel

with other alternator is increased above the normal

value of excitation, its [SSCJE 2014]

a) Power factor becomes more lagging

b) Power factor becomes more leading

c) Output current decreases

d) output k W decreases

6. In an alternator, the effect of armature reaction is

minimum at power factor of [SSCJE 2014]

a) 0.5 lagging

b) 0.866 lagging

c) 0.866 leading

d) unity

7. Direction of the alternating e.m.f. produced in the

stator conductors of an alternator is given by [BSNL TTA

2016]

a) Lenz’s law

b) Flemings left hand rule

c) Fleming’s right hand rule

d) Kirchhoff’s Law

8. In a synchronous machine when the rotor speed

becomes more than the synchronous speed during

hunting, the damping bars develop [BSNL TTA 2016]

a) Synchronous motor torque

b) D.C. motor torque

c) Induction motor torque

d) Induction generator torque

9. The disadvantages of hunting in synchronous

machines is [ESE 2019]

a) fault occurs in the supply system.

b) causes sudden change in inertia.

c) causes large mechanical stresses and fatigue in the

rotor shaft.

d) causes harmonics.

10. A synchronous motor has 12-poles and operates

from 440V, 50Hz supply. If it takes a line current of 100A

at 0.8 power factor leading, its speed and torque are

nearly [ESE 2019]

a) 500 rpm and 1165N-m

b) 1000 rpm and 2330 N-m

c) 500 rpm and 2330 N-m

d) 1000 rpm and 1165 N-m

11. Which of the following is NOT an application of

synchronous motors? [ESIC 2019]

a) Reciprocating compressor drivers

b) Variable speed applications

c) Voltage regulation

d) Power factor correction

12. Identify the INCORRECT statement from below with

regard to synchronous motors [ESIC 2019]

a) Synchronous motors are inherently not self-starting

b) for a given frequency a synchronous motor will run

at constant average speed regardless of load

c) DC excitation is not required by synchronous motors

but required by induction motors

d) Synchronous motors can be operated over wide

range of power factors (both lagging and leading)

13. The maximum torque which the motor can develop

without pulling out of step or synchronism is called:

[ESIC 2019]

a) Starting torque

b) Pull out torque

c) Running torque

d) Pull in torque

14. Which of the following statements is true? [ESIC

2019]

a) The motoring machine draw a lagging power factor

current when over-excited

b) The generating machine supplies a lagging power

factor current when over-excited.

c) The generating machine supplies a lagging power

factor current when under-excited.

d) The motoring machine draws a leading power

factor current when under-excited.

15. Apart from the ability to operate under both

leading and lagging power factors, which among the

following is an advantage of a Synchronous motor?

[BSPHCL JE 2019]

a) Lower cost

b) Constant speed

c) Self-starting

d) Can be used for high speed drives

16. A salient pole synchronous motor is running at no

load. Its excitation is reduced to zero? [SAIL (RSP) OCTT

2019]

a) It will stop

b) It will remain running at synchronous speed

c) It will loose synchronism

d) It is uncertain

17. The mechanical power developed by synchronous

motor is independent of? [HPCL A.M.T. 2019]

a) speed

b) field excitation

c) applied stator voltage

d) torque angle

18. In which of the following conditions will a 3-phase

synchronous machine works as a capacitor? [UPPCL

J.E. 2018, SSC-JE 2018, DMRC, 2018, DMRC JE Electrical

2017, UPURVUNL 2014, MP JE 2016, SSC JE 2014, MPJE

2016]

a) None of these

b) Critically Excited

c) Under Excited

d) Over Excited

19. In a three phase synchronous motor, if one of the

winding is short circuited then the motor will [SSC-JE

2018, IOF 2014, SSC JE Electrical 2017]

a) run at ¼ of synchronous speed

b) not start

c) run with excessive vibrations

d) rotate at less than the rated load

20. Synchronous motor will stop when [SSC-JE 2018]

a) load in motor varies

b) supply voltage fluctuates

c) excitation winding gets disconnected

d) supply voltage frequency changes

21. While starting a synchronous motor as induction

motor, field winding is [SSC-JE 2018]

a) kept open-circuited

b) short-circuited by low resistance

c) connected to D.C. supply

d) None of these

22. In a synchronous motor, the negative phase

sequence exists when the motor is [SSC-JE 2018, SSCJE

2009]

a) under-loaded

b) supplied with unbalanced voltage

c) over-loaded

d) None of these

23. If the synchronous motor, properly synchronized to

the supply is running on no load and is having

negligible loss then [SSC-JE 2018]

a) the stator current will be very small

b) the stator current will be zero

c) the stator current will be very high

d) the back e.m.f. will be more than the supply voltage

24. A synchronous motor operates at rated voltage

and frequency and has a load torque angle of 30°. If

both the terminal voltage and frequency are reduce

by 10%, then [ESE 2015]

a) the load torque angle remains the same

b) the load torque angle increases

c) the load torque angle decreases

d) nothing can be said about the torque angle

25. The synchronous reactance of a 500 V, 50 kVA

alternator having an effective resistance of 0.2 Ω, if an

excitation current of 10 A produces 200 A armature

current on short circuit and an emf of 450 volts on

open circuit, is [ESE 2014]

a) 2.6 Ω

b) 5.2 Ω

c) 2.24 Ω

d) 4.5 Ω

26. A 3-phase synchronous motor with constant

excitation is driving a certain load drawing electric

power from infinite bus at leading power factor. If the

shaft load decreases [ESE 2012]

a) the power angle decreases while power factor

increases.

b) the power angle increases while power factor

decreases.

c) both power angle and power factor increase.

d) both power angle and power factor decrease.

27. A synchronous generator connected to an infinite

bus is supplying electrical power at unity power factor

to the bus. If the field current is increased [ESE 2012]

a) both the active and reactive power output of the

machine will remain unchanged.

b) the active power of the machine will remain

unchanged but the machine will also supply lagging

reactive power.

c) the active power output of the machine will

increase and the machine will draw leading reactive

power from the bus.

d) the active power output of the machine will remain

unchanged but the machine will also supply leading

reactive power.

28. Assertion (A): In a certain case of load change, an

alternator became unstable and pulled-out. [ESE 2011]

Reason (R): In an alternator, damper winding is

present.

a) Both A and R are true and R is the correct

explanation of A

b) Both A and R are true but R is NOT the correct

explanation of A

c) A is true but R is false

d) A is false but R is true

29. Assertion (A): A synchronous motor is not inherently

self starting. [ESE 2010]

Reason (R): At standstill the rotor of a synchronous

motor is subjected to alternate forces of repulsion and

attraction.

a) Both A and R are true and R is the correct

explanation of A

b) Both A and R are true but R is NOT the correct

explanation of A

c) A is true but R is false

d) A is false but R is true

30. Consider the following: [ESE 2010]

1. EMF

2. Reversal

3. MMF

4. Direct

Which methods among these are for the determination

of voltage regulation of an alternator?

a) 1, 2, 3 and 4

b) 1 and 2 only

c) 2 and 3 only

d) 1 and 3 only

1. Power factor of an alternator driven by constant

prime mover input can be changed by changing its

[ESE 2010]

a) Speed

b) Load

c) Field excitation

d) Phase sequence

2. What is the effect of the field failure of salient pole

synchronous motor connected with infinite bus? [ESE

2009]

a) Reduces motor torque and speed

b) Not change motor torque and speed

c) Stop the motor

d) Reduces motor torque but motor will continue to run

at synchronous speed

3. Consider the following:

1. L.P.F. method

2. E.M.F. method

3. Z.P.F. method

4. M.M.F. method

Which of the above methods are correct for

determination of voltage regulation of an alternator?

[ESE 2009]

a) 1, 2 and 3

b) 2, 3 and 4

c) 2 and 3 only

d) 3 and 4 only

4. Which of the following conditions are to be satisfied

for proper synchronization of alternators? [ESE 2008]

1. Equal terminal voltage

2. Same frequency

3. Same phase sequence

4. Same kVA rating

5. Same phase displacement

Select the correct answer using the code given below:

a) 1, 3 and 4

b) 1, 2, 4 and 5

c) 2, 3, 4 and 5

d) 1, 2, 3 and 5

5. If the excitation of a 3-phase alternator operating on

infinite bus bars is changed, which one of the following

shall alter? [ESE 2008]

a) Active power of machine

b) Reactive power of machine

c) Terminal voltage of machine

d) Frequency of machine

6. The stator of a 3-phase, 6-pole a.c. machine has 45

slots. The stator winding has 45 coils with a coil span of

6 slots. What type of winding will be selected for this

machine? [ESE 2008]

a) Double-layer, fractional slot, short-pitched winding

b) Single-layer, fractional slot, short-pitched winding

c) Single-layer, integral slot, full-pitch winding

d) Double-layer, fractional slot, full-pitch winding

7. A three phase 50 Hz, 11 kV and 37.5 MW at 0.9 p.f.

capacity synchronous generator has its stator core

diameter of 765 cm and an axial core length of 80 cm.

For which power plant this generator is suitable? [ESE

2009]

a) Thermal coal fired plant

b) Hydroelectric power plant

c) Nuclear power plant

d) Pumped storage power plant

8. Assertion (A): AC armature windings are short

chorded by selecting value of coil span more than the

pole pitch.

Reason (R): Short chording is done to eliminate

harmonics in the induced e.m.f. [ESE ]

a) Both A and R are true and R is the correct

explanation of A

b) Both A and R are true but R is NOT the correct

explanation of A

c) A is true but R is false

d) A is false but R is true

9. Assertion (A): For a 3-phase alternator operating on

leading p.f. at full load, the terminal voltage may be

more than the no-load induced e.m.f.

Reason (R): At leading power factor, the effect of

armature reaction is demagnetizing. [ESE 2008]

a) Both A and R are true and R is the correct

explanation of A

b) Both A and R are true but R is NOT the correct

explanation of A

c) A is true but R is false

d) A is false but R is true

10. Match List-I (Machine characteristic) with List-II

(Quantity) and select the correct answer using the

code given below the lists: [ESE 2008]

List-I List-IIA. Open-circuit characteristic 1. 𝐏. 𝐟. 𝐯𝐬. 𝐈𝐟B. V-curve 2. 𝐄𝐚 𝐯𝐬. 𝐈𝐚C. Internal characteristic 3. 𝐄𝐠 𝐯𝐬. 𝐈𝐟D. Inverted V-curve 4. 𝐈𝐚 𝐯𝐬. 𝐈𝐟Codes:

A B C D

a) 3 1 2 4

b) 2 4 3 1

c) 3 4 2 1

d) 2 1 3 4

11. A 10 pole, 25 Hg alternator is directly couple to and

is driven by 60 Hz synchronous motor. What is the

number of poles for the synchronous motor? [ESE 2007]

a) 48

b) 12

c) 24

d) 16

12. Consider the following statements:

Assertion (A): Large synchronous machines are

constructed with armature winding on stator.

Reason (R): Stationary armature winding would have

reduced armature reactance.

Of these statements [ESE 2007]

a) Both A and R are true and R is the correct

explanation of A

b) Both A and R are true but R is not the correct

explanation of A

c) A is true but R is false

d) A is false but R is true

13. The resultant flux density in the air gap of a

synchronous generator is the lowest during [ESE 2006]

a) Open circuit

b) Solid short circuit

c) Full load

d) Half load

14. A loss-less cylindrical rotor synchronous generator

is floating on the system bus-bar after being properly

synchronised and is running at no-load. Now, if the

prime mover is acting as a mechanical load on the

machine, then [ESE 2006]

a) the torque developed by the machine will act in the

same direction as the prime-mover torque.

b) the torque developed by the machine will act in the

opposite direction to that of the prime-mover torque.

c) the machine rotor would fall-back and the induced

emf would lag behind the terminal voltage.

d) the machine rotor would overspeed and the

induced emf would lead the terminal voltage

15. Which one of the following statement is not correct

in respect of synchronous machines? [ESE 2006]

a) In salient pole machines, the direct-axis

synchronous reactance is greater than the quadrature

axis synchronous reactance.

b) The damper bars help the motor to self-start.

c) Short circuit ratio is the ratio of field current required

to produce the rated voltage on open circuit to the

rated armature current.

d) The V-curve of a synchronous motor represents the

variation in the armature current with field excitation at

a given output power.

16. What is the value of the load angle when the power

output of a salient pole synchronous generator is

maximum? [ESE 2006]

a) 0°

b) 45°

c) 90°

d) None of these

17. In the measurement of 𝐗𝐝, 𝐗𝐪 (in ohms), following

data are obtained by the slip test on a salient pole

machine: [ESE 2005]

𝐈𝐝max = 10 A 𝐈𝐝 min = 6.5 A

𝐕𝐝 max = 30 V 𝐕𝐝 min = 25 V

Which one of the following is correct?a) 𝐗𝐝 = 𝟑, 𝐗𝐪 = 𝟑. 𝟖𝟔

b) 𝐗𝐝 = 𝟒. 𝟔𝟏𝟓, 𝐗𝐪 = 𝟐. 𝟓

c) 𝐗𝐝 = 𝟑, 𝐗𝐪 = 𝟐. 𝟓

d) 𝐗𝐝 = 𝟒. 𝟔𝟏, 𝐗𝐪 = 𝟑. 𝟖𝟔

18. A synchronous motor is operated from a bus

voltage of 1.0 p.u. and is drawing 1.0 p.u. zero power

factor leading current. Its synchronous reactance is 0.5

p.u. What is the excitation emf of the motor? [ESE 2005]

a) 2.0

b) 1.5

c) 1.0

d) 0.5

19. Assertion (A): If the load requirement of a

synchronous motor exceeds the pull-out torque, the

synchronous motor action is lost.

Reason (R): Rotor and stator fields are no longer

stationary with respect to each other. [ESE 2004]

a) Both A and R are true and R is the correct

explanation of A

b) Both A and R are true but R is NOT the correct

explanation of A

c) A is true but R is false

d) A is false but R is true

20. Assertion: A synchronous motor operating from

constant voltage and constant frequency source has a

substantially constant resultant air-gap flux.

Reason (R): If the d.c. field current in this motor can set

up the required resultant air-gap flux, the lagging

reactive volt-amperes drawn from a.c. source is zero.

[ESE 2004]

a) Both A and R are true and R is the correct

explanation of A

b) Both A and R are true but R is NOT the correct

explanation of A

c) A is true but R is false

d) A is false but R is true

SSC JE-2019

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(28) In a steam power plant…………heats the feed water on its way to the boiler by

delivering heat from the flue gases: -

(A) Superheater (B) Economizer

(B) Preheater (D) Turbine

(29) Power generation of thermal power plants is based on: -

(A) Rankine cycle

(B) Otto cycle

(C) Diesel cycle

(D) Carnot cycle