Control system mcq part -1

1. In an open loop control system
(a) Output is independent of control input
(b) Output is dependent on control input
(c) Only system parameters have effect on the control output
(d) None of the above

Ans: a

2. For open control system which of the following statements is incorrect ?
(a) Less expensive
(b) Recalibration is not required for maintaining the required quality of the
output
(c) Construction is simple and maintenance easy
(d) Errors are caused by disturbances

Ans: b

3. A control system in which the control action is somehow dependent on the output is known as
(a) Closed loop system
(b) Semiclosed loop system
(c) Open system
(d) None of the above

Ans: a

4. In closed loop control system, with positive value of feedback gain the overall gain of the system will
(a) decrease
(b) increase
(c) be unaffected
(d) any of the above

Ans: a

5. Which of the following is an open loop control system ?
(a) Field controlled D.C. motor
(b) Ward leonard control
(c) Metadyne
(d) Stroboscope

Ans: a

6. Which of the following statements is not necessarily correct for open control system ?
(a) Input command is the sole factor responsible for providing the control
action
(b) Presence of non-linearities causes malfunctioning
(c) Less expensive
(d) Generally free from problems of non-linearities

Ans: b

7. In open loop system
(a) the control action depends on the size of the system
(b) the control action depends on system variables
(c) the control action depends on the input signal
(d) the control action is independent of the output

Ans: d

8.----has tendency to oscillate.
(a) Open loop system
(b) Closed loop system
(c) Both (a) and (b)
(d) Neither (a) nor (b)

Ans: b

9. A good control system has all the following features except
(a) good stability
(b) slow response
(c) good accuracy
(d) sufficient power handling capacity

Ans: b

10. A car is raining at a constant speed of 50 km/h, which of the following is the feedback element for the driver ?
(a) Clutch
(b) Eyes
(c) Needle of the speedometer
(d) Steering wheel
(e) None of the above

Ans: c

11. The initial response when tne output is not equal to input is called
(a) Transient response
(b) Error response
(c) Dynamic response
(d) Either of the above

Ans: a

12. A control system working under unknown random actions is called
(a) computer control system
(b) digital data system
(c) stochastic control system
(d) adaptive control system

Ans: c

13. An automatic toaster is a ______ loop control system.
(a) open
(b) closed
(c) partially closed
(d) any of the above

Ans: a

14. Any externally introduced signal affecting the controlled output is called a
(a) feedback
(b) stimulus
(c) signal
(d) gain control

Ans: b

15. A closed loop system is distinguished from open loop system by which
of the following ?
(a) Servomechanism
(b) Feedback
(c) Output pattern
(d) Input pattern

Ans: b

16. ----is a part of the human temperature control system.
(a) Digestive system
(b) Rerspiration system
(c) Ear
(d) Leg movement

Ans: b

17. By which of the following the control action is determined when a man walks along a path ?
(a) Brain
(b) Hands
(c) Legs
(d) Eyes

Ans: d

18.--- is a closed loop system.
(a) Auto-pilot for an aircraft
(6) Direct current generator
(c) Car starter
(d) Electric switch

Ans: a

19. Which of the following devices are commonly used as error detectors in instruments ?
(a) Vernistats
(b) Microsyns
(c) Resolvers
(d) Any of the above

Ans: d

20. Which of the following should be done to make an unstable system stable ?
(a) The gain of the system should be decreased
(b) The gain of the system should be increased
(c) The number of poles to the loop transfer function should be increased
(d) The number of zeros to the loop transfer function should be increased

Ans: b

Power Electronics mcq Part One

Power Electronics Part One

1.An SCR is considered to be semi controlled device. Because
(A) It can be turned OFF but not turned ON with gate pulse
(B) It conducts during only one half cycle of an alternating current wave
(C) It can be turned ON but not turned OFF with a gate pulse
(D) It can be turned ON only during only one half cycle of an alternating voltage wave

Answer-C

2.SCR can be turned on by
1. Applying anode voltage at a sufficiently fast rate
2. Applying sufficiently large anode voltage
3. Increasing SCR temperature to a sufficiently large value
4. Applying adequately large gate current with SCR forward biased
From these, the correct statement
(A) 2, 4 (B) 4 only (C) 1, 2 4 (D) All

Answer-D

3.Which of the following does not cause permanent damage to SCR?
(A) high current (B) high rate of rise of current
(C) high temperature rise (D) high rate rise of voltage

Answer-A

4.Thyristors can be turned off by
1. reducing the current below the holding level
2. applying a negative voltage to the anode of the device
3. reducing gate current
from these, the correct statements are
(A) 1 and 3 (B) 1 and 2 (C) 1, 2 and 3 (D) 2 and 3

Answer-B

5.What is a TRIAC?
(A) Two thyristors connected in parallel mode
(B) Two thyristors connected in series mode
(C) Two thyristors connected in anti parallel mode
(D) Two transistors connected in anti parallel mode

Answer-C

6.TRIAC is
(A) Uncontrolled switch (B) Semi controlled switch
(C) Fully controlled switch (D) None of the above

Answer-B

7.For a TRIAC and SCR
(A) both are unidirectional devices
(B) TRIAC requires more current for turn on than SCR at a particular voltage
(C) TRIAC has less time for turn off than SCR
(D) Both are available with comparable voltage and current ratings

Answer-B

8.Which one of the following statements is TRUE for an ideal power diode?
(A) Forward voltage drop is zero and reverse saturation current is non zero
(B) Reverse recovery time is non zero and reverse saturation current is zero
(C) Forward voltage drop is zero and reverse recovery time is zero
(D) Forward voltage drop is non zero and reverse recovery time is zero

Answer-C

9.Surge current rating of an SCR specifies the maximum
(A) repetitive current with sine wave (B) non repetitive current with rectangular wave
(C) non repetitive current with sine wave (D) repetitive current with rectangular wave

Answer-C

10.Consider the following statements
1. IGBT has low input impedance compared to PMOSFET
2. IGBT and PMOSFET are both voltage controlled devices
3. IGBT can be designed for higher voltages as compared to PMOSFETs
4. IGBT converters are more costly and bigger in size compared to BJT converters
The correct statements are:
(A) 1 and 2 (B) 2 and 3 (C) 3 and 4 (D) 1 and 4

Answer-B

11.Thyristor A has rated gate current of 2 A and thyristor B has rated current of 100 mA
1. A is a GTO and B is a conventional SCR
2. B is a GTO and A is conventional SCR
3. A may operate as a transistor
4. B may operate as a thyristor
From the above the correct statements are
(A) 1, 4 (B) only 1 (C) 2, 3 (D) 2, 4

Answer-B

12.In a GTO, anode current begins to fall when gate current
(A) is negative peak at t = 0
(B) is negative peak at t = storage period ts
(C) just begins to become negative at t = 0
(D) is negative peak at t = (ts + fall time)

Answer-B

13.The snubber circuit is used in thyristor circuits for
(A) triggering (B) phase shifting
(C) di/dt protection (D) dv/dt protection

Answer-D

14.Snubber circuits are used to protect thyristor from which of the following?
(A) High di/dt and low dv/dt (B) High dv/dt and low di/dt
(C) High dv/dt and high di/dt (D) low di/dt and low dv/dt

Answer-C

15.Snubber circuit is used to limit the rate of
(A) Rise of current (B) Conduction period
(C) Rise of voltage across SCR (D) None of the above

Answer-C

16.For an SCR, dv/dt protection is achieved through
(A) RL in series with SCR (B) RC across SCR
(C) L in series with SCR (D) L across SCR

Answer-B

17.The snubber circuit used to shape the turn on switching trajectory of thyristor and/or to limit di/dt during turn on is
(A) L – R snubber polarized (B) R – C snubber polarized
(C) R – C snubber unpolarized (D) L – R snubber unpolarized

Answer-A

18.For an SCR, di/dt protection is achieved through
(A) R in series with SCR (B) RL in series with SCR
(C) L in series with SCR (D) L across SCR

Answer-C

19.Which one of the following statements is NOT true?
(A) For SCRs to be in conduction state, forward anode current must be greater than the
latching current
(B) For SCRs to be in blocking state, forward anode current must be lower than the holding
current
(C) When SCRs in conduction state, they can be turned off by applying suitable gate pulses
(D) When avalanche break down takes place, SCRs enter into the conduction state

Answer-C

20.During forward blocking state, a thyristor is associated with
(A) low current, large voltage (B) large current, low voltage
(C) medium current, large voltage (D) low current, medium voltage

Answer-A

Measurement mcq Part One

Measurement  Part One

1. Hot wire ammeters are used for measuring
(a) Only a.c.
(b) Only d.c
(c) Neither a.c nor d.c
(d) Both a.c. and d.c.

Answer-D

2. Which of the following meters is an integrating type instrument?
(a) Ammeter
(b) Voltmeter
(c) Wattmeter
(d) Energy meter

Answer-D

3. An electrodynamometer type of instruments finds its major use as
(a) Standard instrument only
(b) Transfer instrument only
(c) Both as or standard and transfer instruments
(d) An indicator type of instrument

Answer-C

4. Electrostatic instruments are used for measuring
(a) AC and DC voltage
(b) Ac voltage and current
(c) Dc voltage and current
(d) AC and DC currents

Answer-A

5. Rectifier type instrument can be use in
(a) a.c.
(b) d.c.
(c) Both (a) and (d)
(d) Pulsating

Answer-A

6. Dynamometer type of instrument can use in
(a) a.c.
(b) d.c.
(c) a.c. and d.c.
(d) Pulsating

Answer-c

7. Which one of the following instruments is equally accurate on ac as well as dc circuits?
(a) PMMC voltmeter
(b) Dynamometer wattmeter
(c) Moving iron ammeter
(d) Induction wattmeter

Answer-c

8. Which one of the following types of instruments does suffer from error due to magnetic hysteresis?
(a) Induction type
(b) Electrodynamics
(c) Moving Iron
(d) PMMC

Answer-C

9. A generated voltage is equally dependent on three resistance R1 , R2 , R3 and its value V= (R1 R2)/ (R3). If tolerance of each resistor is 0.1%, what will be the maximum error in voltage?
(a) 0.30%
(b)0.3%
(c) 0.10%
(d) 0.1%

Answer-B

10.Which one of the following statements correctly response the systematic error?
(a) These error can be calculated from the details of the instrument.
(b) These are the residual errors.
(c) These errors may occur controlled conditions.
(d) These are the error committed by the experiments.

Answer-A

11. Swamp resistance and condenser are used
(a) To reduce the error while measuring DC quantities in a moving iron instrument
(b) To reduce the error while measuring AC quantities in a moving iron instrument
(c) To reduce the error while measuring DC quantities in a moving coil instrument
(d) None of these

Answer-C

11. For accuracy of the instrument which is necessary
(a) Conformity
(b) Precision
(c) Both
(d) None of the above

Answer-C

12. Energy meter runs slowly even if power is not used. This error is called
(a) Speed error
(b) Phase error
(c) Creeping error
(d) None of these

Answer-C

13. A null type of instrument as compared to a deflecting type instrument has
(a) Higher accuracy
(b) Lower sensitivity
(c) Faster response
(d) All of the above

Answer-A

14.The efficiency of electrical machines should be calculated by measuring
(a) Output and input
(b) Losses and output
(c) Losses and input
(d) Losses

Answer-D

15. The ratio error in current transformer is due to
(a) Power factor of primary
(b) Wattles component of the current in the primary
(c) Exciting currents
(d) Leakage flux

Answer-C

16. To minimize the errors due to lead and contact resistance, low resistance used in electrical measurement work are provided with
(a) Guard rings
(b) Four terminals
(c) Thick insulation
(d) Metal shields

Answer-B

17. A 150 V moving iron voltmeter of accuracy class 1.0 reads 75 V when used in a circuit under standard condition. The mssimum possible percentage error in the reading is
(a) 4.0
(b) 2.0
(c) 1.0
(d) 0.5

Answer-B

18. In order to achieve accuracy, how should the slide wire of a potentiometer be?
(a) As long as possible
(b) As short as possible
(c) Very thin
(d) Very thick

Answer-A

19. Torque/weight ratio of an instrument indicates
(a) Selectivity
(b) Sensitivity
(c) Accuracy
(d) Fidelity

Answer-B

20. A 0-10 A ammeter has a guaranteed accuracy of 1% of full scale deflection, the limiting error while reading 2.5A will be
(a) 1%
(b) 2%
(c) 4%
(d) None of these

Answer-C

Cable mcq part -1

1. The insulating material for a cable should have
(a) low cost
(b) high dielectric strength
(c) high mechanical strength
(d) all of the above

Ans: d

2. Which of the following protects a cable against mechanical injury ?
(a) Bedding
(b) Sheath
(c) Armouring
(d) None of the above

Ans: c

3. Which of the following insulation is used in cables ?
(a) Varnished cambric
(b) Rubber
(c) Paper
(d) Any of the above

Ans: d

4. Empire tape is
(a) varnished cambric
(b) vulcanised rubber
(c) impregnated paper
(d) none of the above

Ans: a

5. The thickness of the layer of insulation on the conductor, in cables, depends upon
(a) reactive power
(b) power factor
(c) voltage
(d) current carrying capacity

Ans: c

6. The bedding on a cable consists of
(a) hessian cloth
(b) jute
(c) any of the above
(d) none of the above

Ans: c

7. The insulating material for cables should
(a) be acid proof
(b) be non-inflammable
(c) be non-hygroscopic
(d) have all above properties

Ans: d

8. In a cable immediately above metallic sheath is provided.
(a) earthing connection
(b) bedding
(c) armouring
(d) none of the above

Ans: b

9. The current carrying capacity of cables in D.C. is more thanthat in A.C. mainly due to
(a) absence of harmonics
(b) non-existence of any stability limit
(c) smaller dielectric loss
(d) absence of ripples
(e) none of the above

Ans: c

10. In case of three core flexible cable the colour of the neutral is
(a) blue
(b) black
(c) brown
(d) none of the above

Ans: a

11 cables are used for 132 kV lines.
(a) High tension
(b) Super tension
(c) Extra high tension
(d) Extra super voltage

Ans: d

12. Conduit pipes are normally used to protect cables.
(a) unsheathed cables
(b) armoured
(c) PVC sheathed cables
(d) all of the above

Ans: a

13. The minimum dielectric stress in a cable is at
(a) armour
(b) bedding
(c) conductor surface
(d) lead sheath

Ans: d

14. In single core cables armouring is not done to
(a) avoid excessive sheath losses
(b) make it flexible
(c) either of the above
(d) none of the above

Ans: a

15. Dielectric strength of rubber is around
(a) 5 kV/mm
(b) 15 kV/mm
(c) 30 kV/mm
(d) 200 kV/mm

Ans: c

16. Low tension cables are generally used upto
(a) 200 V
(b) 500 V
(c) 700 V
(d) 1000 V

Ans: d

17. In a cable, the maximum stress under operating conditions is at
(a) insulation layer
(b) sheath
(c) armour
(d) conductor surface

Ans: d

18. High tension cables are generally used upto
(a) 11kV
(b) 33kV
(c) 66 kV
(d) 132 kV

Ans: a

19. The surge resistance of cable is
(a) 5 ohms
(b) 20 ohms
(c) 50 ohms
(d) 100 ohms

Ans: c

20. PVC stands for
(a) polyvinyl chloride
(b) post varnish conductor
(c) pressed and varnished cloth
(d) positive voltage conductor
(e) none of the above

Ans: a

Transmission and distribution mcq part -1

1. By which of the following systems electric power may be transmitted ?
(a) Overhead system
(b) Underground system
(c) Both (a) and (b)
(d) None of the above

Ans: c

2. ----Are the conductors, which connect the consumer's terminals to the distribution
(a) Distributors
(b) Service mains
(c) Feeders
(d) None of the above

Ans: b

3. The underground system cannot be operated above
(a) 440 V
(b) 11 kV
(c) 33 kV
(d) 66 kV

Ans: d

4. Overhead system can be designed for operation upto
(a) 11 kV
(b) 33 kV
(c) 66 kV
(d) 400 kV

Ans: c

5. If variable part of annual cost on account of interest and depreciation on the capital outlay is equal to the annual cost of electrical energy wasted in the conductors, the total annual cost will be minimum and the corresponding size of conductor will be most economical. This statement is known as
(a) Kelvin's law
(b) Ohm's law
(c) Kirchhoffs law
(d) Faraday's law
(e) none of the above

Ans: a

6. The wooden poles well impregnated with creosite oil or any preservative compound
have life
(a) from 2 to 5 years
(b) 10 to 15 years
(c) 25 to 30 years
(d) 60 to 70 years

Ans: c

7. Which of the following materials is not used for transmission and distribution of
electrical power ?
(a) Copper
(b) Aluminium
(c) Steel
(d) Tungsten

Ans: d

8. Galvanised steel wire is generally used as
(a) stay wire
(b) earth wire
(c) structural components
(d) all of the above

Ans: d

9. The usual spans with R.C.C. poles are
(a) 40—50 metres
(b) 60—100 metres
(c) 80—100 metres
(d) 300—500 metres

Ans: c

10. The corona is considerably affected by which of the following ?
(a) Size of the conductor
(b) Shape of the conductor
(c) Surface condition of the conductor
(d) All of the above

Ans: d

11. Which of the following are the constants of the transmission lines ?
(a) Resistance
(b) Inductance
(c) Capacitance
(d) All of the above

Ans: d

12. 310 km line is considered as
(a) a long line
(b) a medium line
(c) a short line
(d) any of the above

Ans: a

13. The phenomenon qf rise in voltage at the receiving end of the open-circuited or lightly
loaded line is called the
(a) Seeback effect
(b) Ferranti effect
(c) Raman effect
(d) none of the above

Ans: b

14. The square root of the ratio of line impedance and shunt admittance is called the
(a) surge impedance of the line
(b) conductance of the line
(c) regulation of the line
(d) none of the above

Ans: a

15. Which of the following is the demerit of a 'constant voltage transmission system' ?
(a) Increase of short-circuit current of the system
(b) Availability of steady voltage at all loads at the line terminals
(c) Possibility of better protection for the line due to possible use of higher terminal
reactances
(d) Improvement of power factor at times of moderate and heavy loads
(e) Possibility of carrying increased power for a given conductor size in case of longdistance
heavy power
transmission

Ans: a

16. Low voltage cables are meant for use up to
(a)l.lkV
(b)3.3kV
(c)6.6kV
(d)llkV

Ans: a

17. The operating voltage of high voltage cables is upto
(a)l.lkV
(b)3.3kV
(c)6.6kV
(d)llkV

Ans: d

18. The operating voltage of supertension cables is upto
(a) 3.3 kV
(b) 6.6 kV
(c) 11 kV
(d) 33 kV

Ans: d

19. The operating voltage of extra high tension cables is upto
(a) 6.6 kV
(b) 11 kV
(c) 33 kV
(d) 66 kV
(e) 132 kV

Ans: d

20. Which of the following methods is used for laying of underground cables ?
(a) Direct laying
(b) Draw-in-system
(c) Solid system
(d) All of the above

Ans: d

Synchronous motor mcq part -1

1. Synchronous motors are generally not self-starting because
(a) the direction of rotation is not fixed
(b) the direction of instantaneous torque reverses after half cycle
(c) startes cannot be used on these machines
(d) starting winding is not provided on the machines

Ans: b

2. In case one phase of a three-phase synchronous motor is short-circuited the motor will
(a) not start
(b) run at 2/3 of synchronous speed
(c) run with excessive vibrations
(d) take less than the rated load

Ans: a

3. A pony motor is basically a
(a) small induction motor
(b) D.C. series motor
(c) D.C. shunt motor
(d) double winding A.C./D.C. motor

Ans: a

4. A synchronous motor can develop synchronous torque
(a) when under loaded
(b) while over-excited
(c) only at synchronous speed
(d) below or above synchronous speed

Ans: c

5. A synchronous motor can be started by
(a) pony motor
(b) D.C. compound motor
(c) providing damper winding
(d) any of the above

Ans: d

6. A three-phase synchronous motor will have
(a) no slip-rings
(b) one slip-ring
(c) two slip-rings
(d) three slip-rings

Ans: c

7. Under which of the following conditions hunting of synchronous motor is likely to occur
?
(a) Periodic variation of load
(b) Over-excitation
(c) Over-loading for long periods
(d) Small and constant load

Ans: a

8. When the excitation of an unloaded salient pole synchronous motor suddenly gets disconnected
(a) the motor stops
(b) it runs as a reluctance motor at the same speed
(c) it runs as a reluctance motor at a lower speed
(d) none of the above

Ans: a
 

9. When V is the applied voltage, then the breakdown torque of a synchronous motor varies as
(a) V
(b) V312
(c) V2
(d) 1/V

Ans: a

10. The power developed by a synchronous motor will be maximum when the load angle is
(a) zero
(b) 45°
(c) 90°                                                                                                                                (d) 120°

Ans: c

11. A synchronous motor can be used as a synchronous capacitor when it is
(a) under-loaded
(b) over-loaded
(c) under-excited
(d) over-excited

Ans: d

12. A synchronous motor is running on a load with normal excitation. Now if the load on the motor is increased
(a) power factor as well as armature current will decrease
(b) power factor as well as armature current will increase
(c) power factor will increase but armature current will decrease
(d) power factor will decrease and armature current will increase

Ans: d

13. Mostly, synchronous motors are of
(a) alternator type machines
(6) induction type machines
(c) salient pole type machines
(d) smooth cylindrical type machines

Ans: c

14. The synchronous motor is not inherently self-starting because
(a) the force required to accelerate the rotor to the synchronous speed in an instant is absent
(b) the starting device to accelerate the rotor to near synchronous speed is absent
(c) a rotating magnetic field does not have enough poles
(d) the rotating magnetic field is produced by only 50 Hz frequency currents

Ans: a

15. As the load is applied to a synchronous motor, the motor takes more armature current because
(a) the increased load has to take more current
(b) the rotor by shifting its phase backward causes motor to take more current
(c) the back e.m.f. decreases causing an increase in motor current
(d) the rotor strengthens the rotating field casuing more motor current

Ans: b

16. Synchronous motor always runs at
(a) the synchronous speed
(b) less than synchronous speed
(c) more than synchronous speed
(d) none of the above

Ans: a

17. An over-excited synchronous motor takes
(a) leading current
(b) lagging current
(c) both (a) and (b)
(d) none of the above

Ans: a

18. The working of a synchronous motor is similar to
(a) gear train arrangement
(b) transmission of mechancial power by shaft
(c) distribution transformer
(d) turbine
(e) none of the above

Ans: b

19. The minimum armature current of the synchronous motor corresponds to operation at
(a) zero power factor leading
(b) unity power factor
(c) 0.707 power factor lagging
(d) 0.707 power factor leading

Ans: b

20. In a synchronous motor, the magnitude of stator back e.m.f. & depends on
(a) d.c. excitation only
(b) speed of the motor
(c) load on the motor
(d) both the speed and rotor flux

Ans: a

Singal phase induction motor part -1

1. In a split phase motor, the running winding should have
(a) high resistance and low inductance
(b) low resistance and high inductance
(c) high resistance as well as high inductance
(d) low resistance as well as low inductiance

Ans: b

2. If the capacitor of a single-phase motor is short-circuited
(a) the motor will not start
(b) the motor will run
(c) the motor will run in reverse direction
(d) the motor will run in the same direction at reduced r.p.m.

Ans: a

3. In capacitor start single-phase motors
(a) current in the starting winding leads the voltage
(b) current in the starting winding lags the voltage
(c) current in the starting winding is in phase with voltage in running winding
(d) none of the above

Ans: a

4. In a capacitor start and run motors the function of the running capacitor in series with the auxiliary winding is to
(a) improve power factor
(b) increase overload capacity
(c) reduce fluctuations in torque
(d) to improve torque

Ans: a

5. In a capacitor start motor, the phase displacement between starting and running winding can be nearly
(a) 10°
(b) 30°
(c) 60°
(d) 90°

Ans: d

6. In a split phase motor
(a) the starting winding is connected through a centrifugal switch
(b) the running winding is connected through a centrifugal switch
(c) both starting and running windings are connected through a centrifugal switch
(d) centrifugal switch is used to control supply voltage

Ans: a

7. The rotor developed by a single-phase motor at starting is
(a) more than i.he rated torque
(b) rated torque
(c) less than the rated torque
(d) zero

Ans: d

8. Which of the following motor will give relatively high starting torque ?
(a) Capacitor start motor
(b) Capacitor run motor
(c) Split phase motor
(d) Shaded pole motor

Ans: a

9. Which of the following motor will have relatively higher power factor ?
(a) Capacitor run motor
(b) Shaded pole motor
(c) Capacitor start motor
(d) Split phase motor

Ans: a

10. In a shaded pole motor, the shading coil usually consist of
(a) a single turn of heavy wire which is in parallel with running winding
(b) a single turn of heavy copper wire which is short-circuited and carries only induced current
(c) a multilayer fine gauge copper wire in parallel with running winding
(d) none of the above

Ans: b

11. In a shaded pole single-phase motor, the revolving field is produced by the use of
(a) inductor
(b) capacitor
(c) resistor
(d) shading coils

Ans: d

12. A centrifugal switch is used to dis- connect 'starting winding when motor has
(a) run for about 1 minute
(b) run for about 5 minutes
(c) picked up about 50 to 70 per cent of rated speed
(d) picked up about 10 to 25 per cent of rated speed

Ans: c

13. If a particular application needs high speed and high starting torque, then which of the following motor will be
preferred ?
(a) Universal motor
(b) Shaded pole type motor
(c) Capacitor start motor
(d) Capacitor start and run motor

Ans: a

14. The value of starting capacitor of a fractional horse power motor will be
(a) 100 uF
(6) 200 uF
(c) 300 uF
(d) 400 uF

Ans: c

15. In repulsion motor direction of rotation of motor
(a) is opposite to that of brush shift
(b) is the same as that of brush shift
(c) is independent of brush shift

Ans: b

16. In a single phase motor the centrifugal switch
(a) disconnects auxiliary winding of the motor
(b) disconnects main winding of the motor
(c) reconnects the main winding the motor
(d) reconnects the auxiliary winding of the motor

Ans: a

17. The running winding of a single phase motor on testing with meggar is found to be ground. Most probable location of the ground will be
(a) at the end connections
(b) at the end terminals
(c) anywhere on the winding inside a slot
(d) at the slot edge where coil enters or comes out of the slot

Ans: d

18. A capacitor-start single phase induction motor is switched on to supply with its capacitor replaced by an inductor of equivalent reactance value. It will
(a) start and then stop
(b) start and run slowly
(c) start and run at rated speed
(d) not start at all

Ans: d

19. Which of the following motors is used in mixies ?
(a) Repulsion motor
(b) Reluctance motor
(c) Hysteresis motor
(d) Universal motor

Ans: d

20. Which of the following motors is inherently self starting ?
(a) Split motor
(b) Shaded-pole motor
(c) Reluctance motor
(d) None of these

Ans: b

Three phase induction motor part -1

1. Which of the following component is usually fabricated out of silicon steel ?
(a) Bearings
(b) Shaft
(c) Statorcore
(d) None of the above

Ans: c

2. The frame of an induction motor is usually made of
(a) silicon steel
(b) cast iron
(c) aluminium
(d) bronze

Ans: b

3. The shaft of an induction motor is made of
(a) stiff
(b) flexible
(c) hollow
(d) any of the above

Ans: a

4. The shaft of an induction motor is made of
(a) high speed steel
(b) stainless steel
(c) carbon steel
(d) cast iron

Ans: c

5. In an induction motor, no-load the slip is generally
(a) less than 1% (b) 1.5%
(c) 2%
(d) 4%

Ans: a
 

6. In medium sized induction motors, the slip is generally around (a) 0.04%
(b) 0.4%
(c) 4%
(d) 14%

Ans: c

7. In squirrel cage induction motors, the rotor slots are usually given slight skew in order to
(a) reduce windage losses
(b) reduce eddy currents
(c) reduce accumulation of dirt and dust
(d) reduce magnetic hum

Ans: d

8. In case the air gap in an induction motor is increased
(a) the magnetising current of the rotor will decrease
(b) the power factor will decrease
(c) speed of motor will increase
(d) the windage losses will increase

Ans: b

9. Slip rings are usually made of
(a) copper
(b) carbon
(c) phospor bronze
(d) aluminium

Ans: c

10. 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

Ans: c

11. In Ns is the synchronous speed and s the slip, then actual running speed of an induction motor will be
(a) Ns
(b) s.N,
(c) (l-s)Ns
(d) (Ns-l)s

Ans: c

12.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) 99%

Ans: b

13. The number of slip rings on a squirrel cage induction motor is usually
(a) two
(b) three
(c) four
(d) none

Ans: d

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

Ans: a

15. A double squirrel-cage induction motor has
(a) two rotors moving in oppsite direction
(b) two parallel windings in stator
(c) two parallel windings in rotor
(d) two series windings in stator

Ans: c

16. Star-delta starting of motors is not possible in case of
(a) single phase motors
(b) variable speed motors
(c) low horse power motors
(d) high speed motors

Ans: a

17. The term 'cogging' is associated with
(a) three phase transformers
(b) compound generators
(c) D.C. series motors
(d) induction motors

Ans: d

18. In case of the induction motors the torque is
(a) inversely proportional to (Vslip)
(b) directly proportional to (slip)2
(c) inversely proportional to slip
(d) directly proportional to slip

Ans: d

19. An induction motor with 1000 r.p.m. speed will have
(a) 8 poles
(b) 6 poles
(c) 4 poles
(d) 2 poles

Ans: b

20. The good power factor of an induction motor can be achieved if the average flux density in the air gap is
(a) absent
(b) small
(c) large
(d) infinity

Ans: b

Transformer mcqs part-1

1. Which of the following does not change in a transformer ?
(a) Current
(b) Voltage
(c) Frequency
(d) All of the above

Ans: c

2. In a transformer the energy is conveyed from primary to secondary
(a) through cooling coil
(b) through air
(c) by the flux
(d) none of the above

Ans: c

3. A transformer core is laminated to
(a) reduce hysteresis loss
(b) reduce eddy current losses
(c) reduce copper losses
(d) reduce all above losses

Ans: b

4. The degree of mechanical vibrations produced by the laminations of a transformer depends on
(a) tightness of clamping
(b) gauge of laminations
(c) size of laminations
(d) all of the above
Ans: d

5. The no-load current drawn by transformer is usually what per cent of the full-load current ?
(a) 0.2 to 0.5 per cent
(b) 2 to 5 per cent
(c) 12 to 15 per cent
(d) 20 to 30 per cent

Ans: b

6. The path of a magnetic flux in a transformer should have
(a) high resistance
(b) high reluctance
(c) low resistance
(d) low reluctance

Ans: d

7. No-load on a transformer is carried out to determine
(a) copper loss
(b) magnetising current
(c) magnetising current and loss
(d) efficiency of the transformer

Ans: c

8. The dielectric strength of transformer oil is expected to be
(a) lkV
(b) 33 kV
(c) 100 kV
(d) 330 kV

Ans: b

9. Sumpner's test is conducted on trans-formers to determine
(a) temperature
(b) stray losses
(c) all-day efficiency
(d) none of the above

Ans: a

10. The permissible flux density in case of cold rolled grain oriented steel is around
(a) 1.7 Wb/m2
(b) 2.7 Wb/m2
(c) 3.7 Wb/m2
(d) 4.7 Wb/m2

Ans: a

11.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

Ans: d

12. No-load current in a transformer
(a) lags behind the voltage by about 75°
(b) leads the voltage by about 75°
(c) lags behind the voltage by about 15°
(d) leads the voltage by about 15°

Ans: a

13. The purpose of providing an iron core in a transformer is to
(a) provide support to windings
(b) reduce hysteresis loss
(c) decrease the reluctance of the magnetic path
(d) reduce eddy current losses

Ans: c

14. Which of the following is not a part of transformer installation ?
(a) Conservator
(b) Breather
(c) Buchholz relay
(d) Exciter

Ans: d

15. While conducting short-circuit test on a transformer the following side is short circuited
(a) High voltage side
(b) Low voltage side
(c) Primary side
(d) Secondary side

Ans: b

16. In the transformer following winding has got more cross-sectional area
(a) Low voltage winding
(b) High voltage winding
(c) Primary winding
(d) Secondary winding

Ans: a

17. A transformer transforms
(a) voltage
(b) current
(c) power
(d) frequency

Ans: c

18. 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

Ans: c

19. Primary winding of a transformer
(a) is always a low voltage winding
(b) is always a high voltage winding
(c) could either be a low voltage or high voltage winding
(d) none of the above

Ans: c

20. Which winding in a transformer has more number of turns ?
(a) Low voltage winding
(b) High voltage winding
(c) Primary winding
(d) Secondary winding

Ans: b