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1) The method used for starting synchronous motor is/are a. Using pony motors b. Using damper windings c. As a slip ring induction motor d. All of the above
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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 a. Zero b. Maximum c. Half of the terminal voltage d. None of these
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3) With increase in load, the speed of synchronous motor a. Increases b. Decreases c. Remains constant d. None of the above
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4) Back emf in case of synchronous motor depends on the a. Excitation given to the field winding b. Speed c. Both (a) and (b) d. None of the above
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5) If the load on a synchronous motor increases then its a. Current drawn by motor increases and load angle decreases b. Current drawn by motor decreases and load angle remains constant c. Current drawn by motor remains constant and load angle increases d. Current drawn by motor increases and load angle also increases
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6) In a synchronous motor the torque produced will be maximum when load angle is equal to a. 0° electrical b. 90° electrical c. 180° electrical d. 360° electrical
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7) Practically in a synchronous motor, the pull-out torque will occur when the torque angle is nearly equal to a. 30° electrical b. 45 ° electrical c. 60 ° electrical d. 75 ° electrical
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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 a. No longer exist b. Will be strongest c. Will be weakest d. None of these
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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 a. Increases, decreases and will be lagging in nature b. Decreases, increases and will be leading in nature c. Increases, increases and will be leading in nature d. Decreases, decreases and will be lagging in nature
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10) If the field of the synchronous motor is overexcited then its power factor will be a. Lagging b. Leading c. Unity d. Zero
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11) For critical excitation the power factor of the synchronous motor will be equal to a. 0 b. 1 c. 0.5 MΩ d. None of the above
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12) If graph of armature current drawn by synchronous motor is against field current is plotted then the resulted graph is known as a. V-curves b. Inverted V-curves c. Both (a) and (b) d. None of these
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13) The plot of power factor against the field current of synchronous motor is known as a. V-curves b. Inverted V-curves c. Both (a) and (b) d. None of these
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14) The value of load angle δ and the internal machine angle ∅ for maximum power developed in synchronous motor is equal to a. 0°electrical, 0° electrical b. 0° electrical, 90° electrical c. 90° electrical, 0° electrical d. 90° electrical, 90° electrical
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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 a. 26.89 degree b. 29.07 degree c. 32.05 degree d. 38.20 degree
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16) Oscillations of the rotor about its new equilibrium position, due to sudden application or removal of load in synchronous motor is called a. Hunting b. Galloping c. Swinging d. Both (a) and (c) e. None of the above
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17) Hunting in a synchronous motor results in a. Loss of synchronism b. Mechanical and electrical stresses on motor c. Large current drawn by motor d. all of the above e. None of the above
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18) In a synchronous motor, the phenomenon of hunting caused by the sudden application or removal of load is prevented by a. Using damper winding b. Using a capacitor c. Using an inductor d. All of the above e. None of the above
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19) An over excited synchronous motor operating on no load condition is called as a. Synchronous capacitor b. Synchronous condenser c. Both (a) and (b) d. None of these
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20) The synchronous motor as a synchronous condenser is used to a. Improve power factor b. Reduce hunting c. Both (a) and (b) d. None of these
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21) In a step-up transformer when the voltage delivered is higher than that received, the current delivered is a. Higher than that received b. Lower than that received c. Equal to that received d. Equal to half of that received
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22) What happens if dc supply is given to the transformer? a. Transformer will work more efficiently b. It will work less efficiently c. It will work same as with ac supply d. Not work at all
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23) For a transformer, permeability and hysteresis loss should be a. Low, low b. Low, high c. High, low d. High, high
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24) During starting, the magnetic field produced in a transformer is a. 1.5 times the maximum b. Equal to the maximum c. 0.5 times of the maximum d. Equal to zero
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25) For transformers ratings are always given in kVA, not in kW because a. It is conventional b. Power factor of load is not known c. For higher efficiency d. To make calculation simple
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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? a. 100A b. 120A c. 125A d. 130A
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27) The hysteresis loss in a transformer is minimized by using a. Laminated sheets of steel b. Special grade of heat treated grain oriented silicon steel c. Bracing of transformer assemblies d. Proper design of winding
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28) Laminations and varnish are used to reduce the eddy current losses. The laminations and varnish tends to present a a. High resistance path to eddy current b. Low resistance path to eddy current c. Low reluctance magnetic path d. High reluctance magnetic path
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29) In a transformer sludging is principally due to a. Moisture present in oil b. Dust particles present inside the tank c. Decomposition of oil d. Vaporization of oil
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30) Breather present in a transformer is used to a. Absorb atmospheric moisture b. Prevent insulation failure c. Cooling d. All of these
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