DC Motor viva qns

1) How can be the direction of rotation of motor be reversed?

2) If the direction of terminals of a dc series is reversed, what will happen?

3) What will happen if ac supply is given to: a) dc shunt motor b) dc series motor. Explain your answer

4) What is the need for starter for a dc motor?

5) What will happen if a shunt motor is connected to the supply line directly?

6) A dc motor is found to stop running after a short period of time.What do think could be the possible causes? How can you remedy each?

7) Comment on the running of a a)dc series b) shunt motor when supplied with only half the rated voltage

What will happen to the losses in a dc motor when its supply voltage is: a) doubled b) halved

9) Which is the most efficient method of increasing the speed of a 3.75kW dc shunt motor?

10) What is the main advantage of Ward-Leonard system used for speed control?

11) What are the various speed control methods used to bring down speed of a motor from rated?

12) Give three main applications of dc shunt and series motors

13) Where are dc compound motors used?

14) Which motor is preferred for traction purposes? Why?

15) What is meant by regenerative braking? What are its advantages? Give one of its main applications

16) What is the nature of the emf wave produced in the armature conductors of a dc motor?

17) Give the type of dc motor used in the following cases: a) lathes b) cranes and hoists c) shears and punches d) machine tools

18) Why is the shaft torque of a dc motor less than its armature torque?

19) Sketch the N-T characteristics of dc series and shunt motors

20) Explain the significance of the back emf in a dc motor

21)What is meant by the shaft torque of a motor?

22) In case of dc shunt motors, can flux control be used to reduce the speed below rated speed?

23) Where are differentially compounded shunt motors used?

24) What may be the causes of sparking in a motor?

25) Can a dc motor be made to work as a generator? Discuss the relative ratings in both cases(ie which will be greater etc)

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