Question

Calculate the circuit turn-off time for 3-Φ Fully controlled rectifier if the firing angle is 170° and supply frequency is 50.5 Hz.

(a) 32.4 msec

(b) 35.2 msec

(c) 39.3 msec

(d) 31.5 msec

I have been asked this question in examination.

This interesting question is from Solid-State Switching Circuits topic in portion Introduction to Solid-State Switching Circuits of Electric Drives

Answer 1

The correct choice is (d) 31.5 msec

To elaborate: The circuit turn-off time for 3-Φ Fully controlled rectifier is (180°-α)÷Ω. The value of circuit turn-off time for ∝ ≥ 60° is (180°-170°)÷6.28×50.5=31.5 msec.