Top 250+ Solved Power Electronics MCQ Questions Answer
Q. A 3 phase induction motor is fed by a 3 phase ac regulator to change the stator voltage. The variation in speed will be more if
a. load torque is constant
b. load torque increases with increase in speed
c. load torque decreases with increase in speed
d. either (a) or (b)
Q. The waveshape of output voltage of half bridge inverter is
a. sinusoidal
b. square
c. triangular
d. either (a) or (b)
Q. The gate current required to turn on an SCR is
a. few amperes
b. a few mA
c. almost equal to anode current
d. about 50% of anode current
Q. In a 3 phase semiconverter, the firing frequency is
a. equal to line frequency
b. 3 times the line frequency
c. 6 times the line frequency
d. 12 times the line frequency
Q. A thyristor has its gate current zero. To start conduction the forward voltage must exceed
a. about 0.5 V
b. forward breakover voltage
c. on state voltage
d. peak working off state forward voltage
Q. On load tap changer using thyristors can have a maximum of twotaps.
a. True
b. False
c. none
d. all
Q. In a single phase full wave ac regulator, the firing angles in the two half cycles
a. are always equal
b. are sometimes equal
c. are never equal
d. may be equal or unequal
Q. As regards single phase dual converter
a. the change in operation from one quadrant to the other is faster in non-circulating current mode
b. the change in operation from one quadrant to the other is faster in circulating current mode
c. the time response to change in operation from one quadrant to other is the same in both the modes
d. the time response to change in operation from one quadrant to the other may be faster in any of the two modes
Q. To protect an SCR against high di/dt we connect
a. a capacitance in series with SCR
b. a capacitance in parallel with SCR
c. an inductance in parallel with SCR
d. an inductance in series with SCR
Q. In a parallel inverter
a. the commutating capacitor C is across the primary of transformer and the load is across the secondary
b. the commutating capacitor and load are connected across the secondary of transformer
c. the commutating capacitor C and load are connected in series and the combination is across the secondary of transformer
d. none of the above
Q. A single phase fully controlled bridge rectifier is fed by a source having inductance. The output voltage during overlap period is
a. Vm
b. 0.5 Vm
c. zero
d. 0.5 Vm - voltage drop across inductance
Q. Which of these commutation methods is used in AC-DC converters?
a. Class A
b. Class C
c. Class D
d. Class F
Q. When thyristors are connected in series and parallel, it may benecessary to have :
a. current derating
b. voltage derating
c. both current and voltage derating
d. none of the above
Q. A single phase half wave regulator uses
a. 2 diodes and 2 thyristors
b. 2 thyristors
c. 1 diode and 1 thyristor
d. 2 diodes
Q. A high frequency series inverter consists of
a. a number of series inverters in series
b. a number of series inverters in parallel
c. a number of parallel inverters in parallel
d. a number of parallel inverters in series