Power Electronics and Drives MCQ-2

1. The basic elements of a electric drive is(are)-

(A) Electric motor
(B) Control system
(C) Electric motor and Control system
(D) None of the above

2. Three phase converter are employed for :

(A) Large KW motors
(B) Small KW motors
(C) In all motors
(D) Never used

3. A cycloconverter is :

(A) One stage power converter
(B) One stage voltage converter
(C) One stage frequency converter
(D) None of the above

4. Which method of heating control has leading power factor ?

(A) Resistance heating
(B) Di-electric heating
(C) Arc heating
(D) Induction heating

5. When cells of storage battery are connected in parallel, then

(A) Voltage increases
(B) Voltage decreases
(C) Capacity increases
(D) Capacity decreases

6. A Thyristor is a :

(A) Four layer, three junction device
(B) Four layer, four junction device
(C) Four layer, two junction device
(D) Three layer, single junction device

7. If the cathode of an SCR is made positive with respect to anode and no gate current is applied, then :

(A) All junctions are reverse biased
(B) All junctions are forward baised
(C) Only the middle junction is forward baised
(D) Only the middle junction is reverse baised

8. Which of the following is the most suitable method to “Turn ON” thyristor :

(A) Gate triggering method
(B) dv/dt triggering method
(C) forward voltage triggering method
(D) Temperature triggering method

9. The sink to ambient thermal resistance of SCR

(A) Depends on the flatness of the device
(B) Depends on the length of the device
(C) Depends on the current carrying capabiliaties
(D) Is independent of SCR configuration

10. In a single-phase half-wave circuit with load RL and free-wheeling diode, the free-wheeling period is

(A) 0 to π
(B) α to π+α
(C) π to 2π+α
(D) π/2 to 2π-α

11. A fully controlled converter uses :

(A) Diodes only
(B) Thyristor only
(C) Both (a) and (b)
(D) None of the above

12. A three-phase full converter will require _______ number of SCRs

(A) 3
(B) 6
(C) 9
(D) 2

13. The cycloconverter requires forced or natural commutation as under :

(A) Forced commutation in step-up cycloconverter
(B) Forced commutation in step-down cycloconverter
(C) Forced commutation in both step-up and step-down cycloconverter
(D) Natural commutation in both step-up and step-down cycloconverter

14. A chopper is a :

(A) Time ratio controller
(B) AC to DC converter
(C) AC transformer
(D) High speed semiconductor switch

15. In case of variable frequency system of chopper which is varied ?

(A) T
(B) Ton
(C) Toff
(D) f

16. Type-C chopper consists of :

(A) Two diodes and two switches
(B) One diode and one switch
(C) One diode and three switches
(D) Three diode and two switches

17. Forced commutation requires :

(A) A pre-charged capacitor
(B) A pre-charged inductor
(C) An over damped RLC load
(D) A very high frequency AC source

18. The shape of the output voltage waveform in a single pulse width modulation is :

(A) Square wave
(B) Triangular wave
(C) Quasi-square wave
(D) Sine wave

19. Single phase half bridge inverters requires-

(A) Two wire AC supply
(B) Two wire DC supply
(C) Three wire AC supply
(D) Three wire DC supply

20. In the series inverter control method :

(A) Two inverter connected back to back
(B) The output from the inverter is taken serial
(C) Output voltage of two inverters are summed up with the help of a transformer
(D) Output voltage of two inverters are summed up the help of a third inverter.