1. The torque developed in an induction motor is nearly proportional to (a) 1/V (b) V (c) V2 (d) none of these. 2. If a 400 V, 50 Hz star-connected, 3-phase squirrel cage induction motor is operated from a 400 V, 75 Hz supply, the torque that the motor can now provide while drawing rated […]
1. The rotor of an induction motor never runs at synchronous speed, because then the relative speed between the rotating flux and rotor will be (a) maximum and hence, torque will he maximum. (b) maximum and hence, torque will be zero. (c) zero and hence, torque will be maximum. (d) zero and hence, torque will
1. The poly-phase induction motors are, by a very considerable margin, the most widely used ac motors as (a) these are cheaper in cost, simple and rugged in construction and require little maintenance. (b) they are capable of operation under a wide range of power factors both leading and lagging. (c) they have maximum efficiency
1. The alternators are operated is parallel because it (a) increases the reliability of supply. (b) makes the repairing economical and convenient. (c) is easy to install an additional unit as and when required. (d) all of the above. 2. Which of the following conditions are to be satisfied for proper synchronization of alternators? Equal
1. A synchronous motor is operating on no load at unity power factor. If the field current is increased, the power factor will become (a) leading and the current will decrease. (b) lagging and the current will increase. (c) lagging and the current will decrease. (d) leading and the current will increase. [I.E.S. E.E.-II, 1998]
1. Electromagnetic torque is present in rotating machines when (a) stator winding carries current. (b) rotor winding carries current. (c) both stator and rotor windings carry current. (d) none of the above. 2. In a synchronous motor electromagnetic power varies (a) directly as applied voltage. (b) directly as square of the applied voltage. (c) inversely
1. The mmf produced by single phase winding is (a) pulsating and rotating with constant speed. (b) pulsating and stationary. (c) constant in amplitude and stationary. (d) constant in amplitude and rotating. 2. A polyphase field is (a) pulsating and stationary. (b) pulsating and rotating. (c) constant in amplitude and rotating at synchronous speed. (d)
1. The zero power factor characteristic for the Potier diagram can be obtained by loading the alternator using (a) lamp load. (b) synchronous motor. (c) water load. (d) dc motor. [U.P.S.C. I.E.S. 1999] 2. Modern alternators are designed to have poor regulation as it (a) increases the value of short-circuit current. (b) limits the value
1. Leakage reactance of the armature of a salient pole synchronous machine which varies with the position of rotor is due to leakage flux (a) of end connections. (b) which comes out of slot teeth, crosses the air-gap and enters the pole faces. (c) which remains within the slot. (d) none of the above. 2.
1. Armature winding is one in which (a) emf is induced by the leakage flux. (b) emf is induced by the main or working flux. (c) working or main flux is created by the field current. (d) working or main flux is created by the armature current. 2. Armature winding in ac machines (a) is