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MCQs 1: The method used for starting synchronous motor is/are

Using pony motors Using damper windings As a slip ring induction motor All of the above
Answer Explanation

MCQs 2: A synchronous motor is started by using damper winding. When the motor runs at synchronous speed then the induced emf in the damper winding will be

Zero Maximum Half of the terminal voltage None of these
Answer Explanation

MCQs 3: With increase in load, the speed of synchronous motor

Increases Decreases Remains constant None of the above
Answer Explanation

MCQs 4: Back emf in case of synchronous motor depends on the

Excitation given to the field winding Speed Both (a) and (b) None of the above
Answer Explanation

MCQs 5: If the load on a synchronous motor increases then its

Current drawn by motor increases and load angle decreases Current drawn by motor decreases and load angle remains constant Current drawn by motor remains constant and load angle increases Current drawn by motor increases and load angle also increases
Answer Explanation

MCQs 6: In a synchronous motor the torque produced will be maximum when load angle is equal to

0° electrical 90° electrical 180° electrical 360° electrical
Answer Explanation

MCQs 7: Practically in a synchronous motor, the pull-out torque will occur when the torque angle is nearly equal to

30° electrical 45 ° electrical 60 ° electrical 75 ° electrical
Answer Explanation

MCQs 8: For a synchronous motor, as the load angle reaches up to 90 ° electrical i.e. half a pole pitch, then the magnetic locking between the stator and rotor

No longer exist Will be strongest Will be weakest None of these
Answer Explanation

MCQs 9: Under excitation occurs when the magnitude of induced emf of synchronous motor is less than the applied voltage. During under excitation the current drawn by the motor and power factor

Increases, decreases and will be lagging in nature Decreases, increases and will be leading in nature Increases, increases and will be leading in nature Decreases, decreases and will be lagging in nature
Answer Explanation

MCQs 10: If the field of the synchronous motor is overexcited then its power factor will be

Lagging Leading Unity Zero
Answer Explanation

MCQs 11: For critical excitation the power factor of the synchronous motor will be equal to

0 1 0.5 MΩ None of the above
Answer Explanation

MCQs 12: If graph of armature current drawn by synchronous motor is against field current is plotted then the resulted graph is known as

V-curves Inverted V-curves Both (a) and (b) None of these
Answer Explanation

MCQs 13: The plot of power factor against the field current of synchronous motor is known as

V-curves Inverted V-curves Both (a) and (b) None of these
Answer Explanation

MCQs 14: The value of load angle δ and the internal machine angle ∅ for maximum power developed in synchronous motor is equal to

0°electrical, 0° electrical 0° electrical, 90° electrical 90° electrical, 0° electrical 90° electrical, 90° electrical
Answer Explanation

MCQs 15: A synchronous motor is running at a load angle of 25 degree at rated frequency with negligible armature resistance. Now, if the supply frequency is increased by 15% keeping the other parameters constant, then the new load angle will be equal to

26.89 degree 29.07 degree 32.05 degree 38.20 degree
Answer Explanation

MCQs 16: Oscillations of the rotor about its new equilibrium position, due to sudden application or removal of load in synchronous motor is called

Hunting Galloping Swinging Both (a) and (c) None of the above
Answer Explanation

MCQs 17: Hunting in a synchronous motor results in

Loss of synchronism Mechanical and electrical stresses on motor Large current drawn by motor all of the above None of the above
Answer Explanation

MCQs 18: In a synchronous motor, the phenomenon of hunting caused by the sudden application or removal of load is prevented by

Using damper winding Using a capacitor Using an inductor All of the above None of the above
Answer Explanation

MCQs 19: An over excited synchronous motor operating on no load condition is called as

Synchronous capacitor Synchronous condenser Both (a) and (b) None of these
Answer Explanation

MCQs 20: The synchronous motor as a synchronous condenser is used to

Improve power factor Reduce hunting Both (a) and (b) None of these
Answer Explanation

MCQs 21: In a step-up transformer when the voltage delivered is higher than that received, the current delivered is

Higher than that received Lower than that received Equal to that received Equal to half of that received
Answer Explanation

MCQs 22: What happens if dc supply is given to the transformer?

Transformer will work more efficiently It will work less efficiently It will work same as with ac supply Not work at all
Answer Explanation

MCQs 23: For a transformer, permeability and hysteresis loss should be

Low, low Low, high High, low High, high
Answer Explanation

MCQs 24: During starting, the magnetic field produced in a transformer is

1.5 times the maximum Equal to the maximum 0.5 times of the maximum Equal to zero
Answer Explanation

MCQs 25: For transformers ratings are always given in kVA, not in kW because

It is conventional Power factor of load is not known For higher efficiency To make calculation simple
Answer Explanation

MCQs 26: In a 5 kV / 400V, 75 kVA single phase transformer, the current flowing in the primary winding of transformer is 10A. what will be the current flowing in the secondary winding?

100A 120A 125A 130A
Answer Explanation

MCQs 27: The hysteresis loss in a transformer is minimized by using

Laminated sheets of steel Special grade of heat treated grain oriented silicon steel Bracing of transformer assemblies Proper design of winding
Answer Explanation

MCQs 28: Laminations and varnish are used to reduce the eddy current losses. The laminations and varnish tends to present a

High resistance path to eddy current Low resistance path to eddy current Low reluctance magnetic path High reluctance magnetic path
Answer Explanation

MCQs 29: In a transformer sludging is principally due to

Moisture present in oil Dust particles present inside the tank Decomposition of oil Vaporization of oil
Answer Explanation

MCQs 30: Breather present in a transformer is used to

Absorb atmospheric moisture Prevent insulation failure Cooling All of these
Answer Explanation

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