Synchronous motor mcq

1. Synchronous motors are generally not self-starting because

(a) the direction of rotation is not fixed

(b) the direction of instantaneous torque reverses after half cycle

(c) startes cannot be used on these machines

(d) starting winding is not provided on the machines

2. A pony motor is basically a

(a) small induction motor

(b) D.C. series motor

(c) D.C. shunt motor

(d) double winding A.C./D.C. motor

3. A synchronous motor can be started by

(a) pony motor

(b) D.C. compound motor

(c) providing damper winding

(d) any of the above

4. A three-phase synchronous motor will have

(a) no slip-rings

(b) one slip-ring

(c) two slip-rings

(d) three slip-rings

5. Synchronous motor always runs at

(a) the synchronous speed

(b) Gyu than synchronous speed

(c) more than synchronous speed

(d) none of the above

6. An over-excited synchronous motor takes

(a) leading current

(b) lagging current

(c) both (a) and (b)

(d) none of the above

7. For V-curves for a synchronous motor the graph is drawn between

(a) field current and armature current

(b) terminal voltage and load factor

(c) power factor and field current

(d) armature current and power factor

8. The back e.m.f. of a synchronous motor depends on

(a) speed

(b) load

(c) load angle

(d) all of the above

9. A synchronous motor can operate at

(a) lagging power factor only

(b) leading power factor only

(c) unity power factor only

all of the above

10. When the field of a synchronous motor is under-excited, the power factor will be

(a) leading

(b) lagging

(c) unity

(d) zero

11. The speed regulation of a synchronous motor is always

(a) 1%

(b) 0.5%

(c) positive

(d) zero

12. The percentage slip in case of a synchronous motor is

(a) 1%

(b) 100%

(c) 0.5%

(d) zero

13. Synchronous motors are

(a) not-self starting

(b) self-starting

(c) essentially self-starting

(d) none of the above

14. An over excited synchronous motor is used for

(a) fluctuating loads

(b) variable speed loads

(c) low torque loads

(d) power factor corrections

15. Slip-rings in a synchronous motor carry

(a) direct current

(b) alternating current

(c) no current

(d) all of the above

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