Power Electronics Questions

• Natural commutation can be used in :
• The gate lead, in a thyristor is welded to :
• Which chopper circuit operates in all the 4 quadrants?
• Which converter is used in HVDC transmission?
• A chopper cannot be line commutated.
• Assertion (A): Typical value of thermal resistance from source to sink of an SCR is about 0.3° C/W Reason (R): Heat sinks of thyristors are generally made of aluminium.
• In integral cycle control of ac regulators, the period of integral cycle control, i.e., (m + n) T should be
• In load commutated chopper, the commutating element
• Assertion (A): A transistor has lower voltage drop during conduction as compared to thyristor Reason (R): Transistors are manufactured in very high voltage and current ratings.
• The symbol in figure is for
• In the circuit of figure, the waveshape of load current when thyristor conducting is
• An n pulse rectifier is fed by a source having an inductance L. If load current is I0, the voltage drop due to overlap is
• In brushless excitation system of modern alternators, the main exciter is
• In a step down chopper using time ratio control, the input voltage is V and duty cycle is a. The load is purely resistive having resistance R. The average and rms load currents are
• If 4 quadrant operation is required we need
• A separately excited dc motor is run from a dc source through a chopper. At 600 rpm and rated torque, the duty cycle of chopper is 0.8. At 600 rpm and half the rated torque, the duty cycle is likely to be
• In a 3 phase full converter, the firing angle is less than 60°. The instantaneous output voltage
• As compared to BJT, MOSFET has
• In pulse width modulation of chopper
• All other parameters remaining the same, a 3 phase bridge inverter with 180° mode of operation