Electronics and Communication Engineering - Power Electronics

26. 

Which of these commutation methods uses an auxiliary SCR?

A. Class A
B. Class B
C. Class C
D. Class D

Answer: Option C

Explanation:

Class C commutation uses an auxiliary SCR and it is also called auxiliary commutation.


27. 

A thyristor needs protection against

A. high
B. high
C. both high and high
D. either high or high

Answer: Option C

Explanation:

Both high and high can destroy SCR.


28. 

Two semiconverters are connected in series to form a single phase series converter. The input v = Vm sin ωt and a1 = a2 are the firing angles of the two converters. If a1 = a2 = 0, the dc output voltage is

A.
B.
C.
D.

Answer: Option C

Explanation:

Output voltage is for each.


29. 

In integral cycle control the period of on-off control should be more than mechanical time constant of load.

A. True
B. False

Answer: Option B

Explanation:

It should be less than mechanical time constant.


30. 

A single phase half wave converter is feeding a resistive load. Just before triggering, the voltage across thyristor is

A. zero
B. about 1 V
C. same as input voltage
D. twice the input voltage

Answer: Option C

Explanation:

Before triggering the whole of applied voltage is across SCR and load current is zero.