MCQs on Power Electronics | All Student World

1). what is used to protect the SCR from over current ?
a)    CB and fuse
b)    Heat sink
c)    Snubber circuit
d)    Voltage clamping device

2). CB used for over current protection of thyristor operates when the fault current is
a)    of long period
b)    of short period
c)    both (a) and (b)   
d)    neither (a) nor (b)  

3). when a large surge current of very short duration flows through a thyristor then which one of the following device will operate to protect the thyristor ?
a)    CB    
b)    Snubber circuit
c)    voltage clamping device
d)    Fast acting current limiting device (FACL fuse)

4). what is used to protect a thyristor from high di / dt condition ?
a)    fuse   
b)    Snubber circuit
c)    Inductor
d)    Voltage clamping device

5). What happen due to high di / dt ?
a)    Breakdown of junction  
b)    Local hot spot
c)    Insulation failure
d)    Non of these

6). Which of the following is used in SCR to protect from high dv / dt ?
a)    Snubber circuit
b)    fuse
c)    Equalizing circuit
d)    circuit breaker

7). What may happen high dv / dt ?
a)    Unwanted turn ON  
b)    Breakdown of J2 junction
c)    both a and b
d)    Anyone of these

8). why resistor is used in Snubber circuit ?
a)    To minimize the loss
b)    To minimize the charging current
c)    To minimize the discharging current
d)    All of these

9). Delay time is defined by the interval when
a)    gate current increased from 90 % to 100 % of its final value
b)    anode current reaches 10 % from forward leakage current
c)    anode voltage drop from 100 % to 90 % of its actual value    
d)    all of these.

10). Snubber circuit is used with SCR
a)    In series
b)    in parallel
c)    either series or parallel
d)    anti parallel