1. Single phase ac motors are used in largest number. This is due to (a) their great variety of useful services in the home, office, the factory, in business establishment and on the farm. (b) their wide applications in automatic control devices of various types. (c) lower cost. (d) both (a) and (b). 2. A […]
1. The speed of a slip-ring induction motor cannot be controlled by (a) rotor resistance control. (b) pole changing method. (c) concatenation or cascade operation. (d) rotor slip power control. 2. Consequent pole technique employed for speed control of induction motors involves changing of the (a) slip. (b) supply frequency. (c) number of poles. (d)
1. Presence of 5th harmonics in induction motor causes (a) cogging. (b) crawling. (c) small reverse braking torque. (d) hunting. 2. The cogging occurs in induction motors due to (a) harmonic induction torques. (b) harmonic synchronous torques. (c) vibration torques. (d) both (a) and (b). 3. Cogging of induction motors occurs at (a) high voltage
1. In a 3-phase induction motor, the variable mechanical load is represented electrically by a variable ………… only. (a) inductance (b) capacitance (c) resistance (d) any of these 2. The stator referred resistance in the equivalent circuit of an induction motor, representing mechanical output is (a) r2/s (b) r’2(1/s – 1) (c) r2/s (d) r22(1/s
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