Electrical Machines Objective Questions
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Voltage regulation of transformer is given by
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A three phase 400 V, 6 pole, 50 Hz, squirrel cage induction motor is running at a slip of 5%. The speed of stator magnetic field with respect to rotor magnetic field and speed of rotor w.r.t stator magnetic field are
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A single phase transformer has specifications as 250 KVA, 11000 V/415 V, 50 Hz. What are the values of primary and secondary currents?
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A synchronous motor is supplying a load at unity power factor. If the load on the motor is increased keeping its excitation and terminal voltage constant, the power factor
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The frequency of a voltage at the secondary is
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R_{1} is the resistance of the primary winding of the transformer. The turn ratio in terms of primary to secondary is K. Then the equivalent resistance of the primary referred to secondary is
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A 5 KVA transformer has a turns ratio of N1/N2 = 10. The impedance of primary winding is 3+j5 ohms while that of secondary winding is 0.5+j0.8 ohms. The impedance of transformer when referred to primary will be
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Synchronous capacitor is
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A 400 V, 50 Hz, 30 Hp, three phase IM is drawing 50 A current at 0.8 p.f lagging. The stator and rotor copper losses are 1.5 KW and 900 W respectively. The friction and windage losses are 1050 W and core losses are 1200 W. The air gap power of the motor will be
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Which of the following statements is/are correct statements?
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The breakdown torque of a synchronous motor varies as
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An inverted Vcurve of synchronous motor shows the variation of
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The basic function of a transformer is to change
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A DC Motor is driving a constant load torque having armature resistance of 0.15 Î© and armature current of 0.25 A having connected to a voltage of 230 V. Now a resistance of 1 ohm is added into the armature circuit. The ratio of their speed will be
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Transformer action requires a
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The core flux in transformer depends mainly on
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Which of the following is not a necessary condition to be satisfied for synchronising an incoming alternator to an already operating alternator?
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The low voltage winding of a 400/230 V single phase 50 Hz transformer is to be connected to keep the magnetization current at the same level in both the cases the voltage at 25 Hz should be
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An alternator is feeding an infinite busbar. Its prime mover suddenly shutdown. The alternator will
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If the applied voltage of a certain transformer is increased by 50% and the frequency is reduced by 50%, the maximum flux density will (assuming that the magnetic circuit remains unsaturated)
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In a synchronous motor electromagnetic power varies
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Which of the following is/are not a self starting motor?
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For an ideal transformer the winding should have
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When the excitation of normally operating unloaded, salient pole synchronous motor suddenly gets disconnected, it continues to run as a
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What is the frequency of rotor current of 50 Hz induction motor operating at 4% slip?
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If the applied voltage of a DC motor is 230 V, then back emf, for maximum power developed is
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A 3phase 6 pole 50 Hz induction motor is running at 5% slip.What is the speed of the motor?
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When a synchronous motor is running at synchronous speed, the damper winding produces
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A 3 phase synchronous motor can operate over a wide range of power factors i.e. from lagging to leading power factor. This is achieved by
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For power factor improvement the synchronous motor is to be
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