Q.1 The two windings of a transformer is
(A) conductively linked. (B) inductively linked.
(C) not linked at all. (D) electrically linked.
Ans : B
Q.2 A salient pole synchronous motor is running at no load. Its field current is switched off.
The motor will
(A) come to stop.
(B) continue to run at synchronous speed.
(C) continue to run at a speed slightly more than the synchronous speed.
(D) continue to run at a speed slightly less than the synchronous speed.
Q.3 The d.c. series motor should always be started with load because
(A) at no load, it will rotate at dangerously high speed.
(B) it will fail to start.
(C) it will not develop high starting torque.
(D) all are true.
Q.4 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.
Q.5 In a stepper motor the angular displacement
(A) can be precisely controlled.
(B) it cannot be readily interfaced with micro computer based controller.
(C) the angular displacement cannot be precisely controlled.
(D) it cannot be used for positioning of work tables and tools in NC machines.
Q.6 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.
Q.7 The generation voltage is usually
(A) between 11 KV and 33 KV.
(B) between 132 KV and 400 KV.
(C) between 400 KV and 700 KV.
(D) None of the above.
Q.8 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.
Q.9 If a transformer primary is energised from a square wave voltage source, its output
voltage will be
(A) A square wave.
(B) A sine wave.
(C) A triangular wave.
(D) A pulse wave.
Q.10 In a d.c. series motor the electromagnetic torque developed is proportional to
(A) Ia . (B) I2a .
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Q.11 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/(1 - s)
(C) (1− s) Pg .
(D) s × Pg .
Q.12 In a 3 – phase induction motor the maximum torque
(A) is proportional to rotor resistance r .
(B) does not depend on r .
(C) is proportional tosqrt( r ).
(D) is proportional to r2 .
Q.13 In a d.c. machine, the armature mmf is
(A) stationary w.r.t. armature.
(B) rotating w.r.t. field.
(C) stationary w.r.t. field.
(D) rotating w.r.t. brushes.
Q.14 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.
Q.15 The maximum power in cylindrical and salient pole machines is obtained respectively at load angles of
(D) 90'0 ,< 90'0 .
Q.16 The primary winding of a 220/6 V, 50 Hz transformer is energised from 110 V, 60 Hz supply. The secondary output voltage will be
(A) 3.6 V.
(B) 2.5 V.
(C) 3.0 V.
(D) 6.0 V.
Q.17 The emf induced in the primary of a transformer
(A) is in phase with the flux.
(B) lags behind the flux by 90 degree.
(C) leads the flux by 90 degree.
(D) is in phase opposition to that of flux.
Q.18 The relative speed between the magnetic fields of stator and rotor under steady state operation is zero for a
(A) dc machine.
(B) 3 phase induction machine.
(C) synchronous machine.
(D) single phase induction machine.
Ans: all options are correct
Q.19 The current from the stator of an alternator is taken out to the external load circuit through
(A) slip rings.
(B) commutator segments.
(C) solid connections.
(D) carbon brushes.
Q.20 A motor which can conveniently be operated at lagging as well as leading powerfactors is the
(A) squirrel cage induction motor.
(B) wound rotor induction motor.
(C) synchronous motor.
(D) DC shunt motor.
Q.21 A hysteresis motor
(A) is not a self-starting motor.
(B) is a constant speed motor.
(C) needs dc excitation.
(D) can not be run in reverse speed.
Q.22 The most suitable servomotor for low power applications is
(A) a dc series motor.
(B) a dc shunt motor.
(C) an ac two-phase induction motor.
(D) an ac series motor.
Q.23 The size of a conductor used in power cables depends on the
(A) operating voltage.
(B) power factor.
(C) current to be carried.
(D) type of insulation used.
Q.24 Out of the following methods of heating the one which is independent of supply
(A) electric arc heating
(B) induction heating
(C) electric resistance heating
(D) dielectric heating
Q.25 A balanced three-phase, 50 Hz voltage is applied to a 3 phase, 4 pole, induction motor. When the motor is delivering rated output, the slip is found to be 0.05. The
speed of the rotor m.m.f. relative to the rotor structure is
(A) 1500 r.p.m.
(B) 1425 r.p.m.
(C) 25 r.p.m.
(D) 75 r.p.m.
NS = 120f /P = 120 x 50 /4 =1500rpm
N = NS ( 1-s) = 1500 (1-0.05) = 1425
relative speed = 1500 – 1425 = 75 rpm
Q.26 An alternator is delivering rated current at rated voltage and 0.8 power-factor lagging case. If it is required to deliver rated current at rated voltage and 0.8 power-factor leading, the required excitation will be
(C) more or less.
(D) the same.
Q.27 Over excitation gives leading power factor and under excitation gives lagging p.f .
A ceiling fan uses
(A) split-phase motor.
(B) capacitor start and capacitor run motor.
(C) universal motor.
(D) capacitor start motor.
Q.28 A stepper motor is
(A) a dc motor.
(B) a single-phase ac motor.
(C) a multi-phase motor.
(D) a two phase motor.
Q.29 The ‘sheath’ is used in cable to
(A) provide strength to the cable.
(B) provide proper insulation.
(C) prevent the moisture from entering the cable.
(D) avoid chances of rust on strands.
Q.30 The drive motor used in a mixer-grinder is a
(A) dc motor.
(B) induction motor.
(C) synchronous motor.
(D) universal motor.
Q.31 A 1:5 step-up transformer has 120V across the primary and 600 ohms resistance
across the secondary. Assuming 100% efficiency, the primary current equals
(A) 0.2 Amp.
(B) 5 Amps.
(C) 10 Amps.
(D) 20 Amps.
Q.32 A 50 Hz, 3-phase induction motor has a full load speed of 1440 r.p.m. The number of
poles of the motor are
Q.33 In a 3-phase synchronous motor
(A) the speed of stator MMF is always more than that of rotor MMF.
(B) the speed of stator MMF is always less than that of rotor MMF.
(C) the speed of stator MMF is synchronous speed while that of rotor MMF is zero.
(D) rotor and stator MMF are stationary with respect to each other.
Q34.In a capacitor start single-phase induction motor, the capacitor is connected
(A) in series with main winding.
(B) in series with auxiliary winding.
(C) in series with both the windings.
(D) in parallel with auxiliary winding.
Q35.A synchro has
(A) a 3-phase winding on rotor and a single-phase winding on stator.
(B) a 3-phase winding on stator and a commutator winding on rotor.
(C) a 3-phase winding on stator and a single-phase winding on rotor.
(D) a single-phase winding on stator and a commutator winding on rotor.
Q.36 As the voltage of transmission increases, the volume of conductor
(B) does not change.
(D) increases proportionately.
Q.37 The size of the feeder is determined primarily by
(A) the current it is required to carry.
(B) the percent variation of voltage in the feeder.
(C) the voltage across the feeder.
(D) the distance of transmission.
Q. 38 The boundary of the protective zone is determined by the
(A) Location of CT
(B) sensitivity of relay used
(C) Location of PT
(D) None of these
Q.39 In a three phase transformer, if the primary side is connected in star and secondary side is connected in delta, what is the angle difference between phase voltage in the two cases.
(A) delta side lags by -30°.
(B) star side lags by -30°.
(C) delta side leads by 30°.
(D) star side leads by -30°.
Q.40 This is vector group and has +30° displacement. Therefore, delta side leads by +30°.
Q.43 To achieve low PT error, the burden value should be ____________.
(D) none of the above
Q.41 Slip of the induction machine is 0.02 and the stator supply frequency is 50 Hz. What will be the frequency of the rotor induced emf?
(A) 10 Hz.
(B) 50 Hz.
(D) 2500 Hz.
Q.42 A 4 pole lap wound dc shunt motor rotates at the speed of 1500 rpm, has a flux of 0.4
mWb and the total number of conductors are 1000. What is the value of emf?
(A) 100 Volts.
(B) 0.1 Volts.
(C) 1 Volts.
(D) 10 Volts.
Q.43 The synchronous reactance of the synchronous machine is ______________.
(A) Ratio between open circuit voltage and short circuit current at constant fieldcurrent
(B) Ratio between short circuit voltage and open circuit current at constant field current
(C) Ratio between open circuit voltage and short circuit current at different field current
(D) Ratio between short circuit voltage and open circuit current at different field current
Q.44 A 3 stack stepper motor with 12 numbers of rotor teeth has a step angle of ____________.
Q.45 In case of a universal motor, torque pulsation is minimized by _________.
(A) load inertia
(B) rotor inertia
(C) both rotor and load inertia
(D) none of the above
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