MCQs on Power Electronics | All student world

1). The typical value of SCR formodern alternator is
a)    1.5
b)    0.5
c)    1.0
d)    1.2

2). An SCR is considered to be a semi controlled device because
a)    it can be turned OFF but not ON with a gate pulse
b)    it conducts only during one half cycle of an alternating current wave
c)    it can be turned ON but NOT with a gate pulse   
d)    it can be turned ON only during one half cycle of an AC  

3). An SCR has half cycle surge current rating of 3000 A for 50 Hz supply. one cycle surge current will be
a)    1500 A    
b)    6000 A
c)    2121.32 A
d)    4242.64

4). A single phase one pulse controlled circuit has a resistance R and counter EMF E load 400 sin(314 t) as the source voltage . For a load counter emf of 200 v, the range of firing angle control is
a)    30° to 150°   
b)    30° to 180°
c)    60° to 120°
d)    60° to 180°

5). A single phase full bridge Inverter can operated in load communication mode in case load consist of
a)    RL  
b)    RLC underdamped
c)    RLC overdamped
d)    RLC critically damped.

6). The latching current of SCR is 20 mA its holding current will be
a)    23mA
b)    40mA
c)    10mA
d)    60mA

4). Thyristor can be protected from over voltages by using
a)    Voltage clamping device  
b)    fuse
c)    heat sink
d)    snubber circuit

8). Example of a voltage clamping device
a)    fast acting fude
b)    snubber circuit
c)    metal oxide varistor
d)    aluminium block

9). Under over voltage condition impedance offered by the voltage clamping device is
a)    high
b)    low
c)    moderate    
d)    infinity

10). Under normal operating condition voltage clamping device offers impedance of
a)    high value
b)    low value
c)    zero value
d)    moderate value