Test: Power Electronics - 1 - Electrical Engineering (EE) MCQ

Two thyristor of same rating and same specifications

The amount of dielectric heating is inversely proportional to frequency.

A semiconverter feeding an RLE load operates in

The phenomenon of overlap in converter operation due to

A thyristor has a maximum allowable junction temperature of 120ºC and the ambient temperature is 40ºC. If thermal resistance is 1.6º C/W, the maximum allowable internal power dissipation is

For a 12 pulse operation, the two 6 pulse units are fed by

In a single phase full wave converter (M - 2 connection) feeding a highly inductive load, the firing angle for each thyristor is a in the respective half cycle. The period of conduction of each thyristor is

An SCR is triggered at 40ºin the positive half cycle only. The average anode current is 50 A. If the firing angle is changed to 80º, the average anode current is likely to be

The characteristics of a non-linear resistance is i = kv⁴. If i becomes 100 times, v becomes

In a step down chopper using pulse width modulation, T_on = 3 x 10^-3 and T_off = 1 x 10^-3 s. The chopping frequency is

Thyristors are suitable for dc circuit breakers but not for ac circuit breakers.

Assertion (A): Inverters and choppers use fast switching thyristors

Reason (R): Fast switching SCR has low turn off time.

The value of capacitor C for dynamic equalising circuit of series connected thyristors is determined by

A chopper

Assertion (A): If the duty cycle of chopper is low the current would not become discontinuous

Reason (R): If the time constant L/R of the load in chopper is low the current may become discontinuous.

An electric heater is controlled by thyristors through on-off control. If a = 0.4, the heating is

A two winding transformer is feeding a single phase half wave rectifier circuit. The load is purely resistive. The rms value of transformer secondary current is I_s and rms value of load current in I_rms. Then

The terminals of a power BJT are called

In single phase half wave regulator, the average current over one full cycle

The dynamic equalising circuit consists of a series combination of capacitor C and resistor R_C across each thyristor. This resistance R_C (along with parallel connected diode)

A single phase semiconverter is feeding a highly inductive load and has freewheeling diode across the load. The waveshapes of output voltage and output current

A full-wave rectifier uses 2 diodes. The internal resistance of each diode is 20 Ω. The transformer RMS secondary voltage from centre tap to each end of the secondary is 50 V and the load resistance is 980 Ω. Mean load current will be