Control Devices for Industrial Motors Interview Questions and Answers:

1. What are the two main applications of a thyratron ?

Ans. Two main applications of thyratron are (i) switching and (ii) rectification.

2. Why is series compensating winding employed in amplidyne ?

Ans. Compensating winding is connected in series with the power output brush terminals of the amplidyne to neutralize the armature reaction set up by the load current and increase amplification factor.

3. Why are amplidynes provided with split-poles ?

Ans. Amplidynes are provided with split-poles to provide space for interpoles.

4. What is the effect of temperature on the reverse current of a P-N junction ?

Ans. Reverse current of a P-N junction increases with the increase in junction temperature. It has been found that reverse current of a P-N junction approximately doubles for each 10°C rise in temperature in case of germanium and for each 8°C in temperature in case of silicon.

5. What is Zener diode ?

Ans. Zener diode is a P-N junction diode specially designed for operation in its breakdown region in reverse bias condition.

6. How is current limited in conducting state of an SCR ?

Ans. The current in conducting state of an SCR is controlled by an external impedance.

7. What is false triggering ?

Ans. False triggering is unintended turn-on of an SCR either through gate due to noise pick-up or excessive anode voltage.

8. Why is it necessary to keep supply voltage much less than breakover voltage of an SCR ?

Ans. The supply voltage is kept much less than breakover voltage of an SCR otherwise the device will get damaged.

9. Where do you recommend the use of freewheeling diode ?

Ans. Use of freewheeling diode is recommended in motor control circuits to provide an alternate path for continuity of current in the inductive circuit following the switching-off of some power device between the motor and the supply source.

10. Where are float switches used ?

Ans. Float switches are used for opening or closing pipe valves for the control of fluids.