Question

Below shown ideal circuit is triggered at a firing angle of α. The voltage across the SCR is zero from ωt =

(a) 0 to α

(b) 0 to π

(c) α to 2π

(d) α to π

I had been asked this question in an internship interview.

This intriguing question originated from Single-Phase HW AC-DC-1 in chapter Converters of Power Electronics

Answer 1

Correct choice is (d) α to π

The best explanation: Before the SCR is triggered all of the supply voltage appears across it that is from 0 to α, at α the device is gated and it starts to conduct acting like a S.C (ideally). Hence voltage across it is zero from α to π. At π the SCR is again naturally commutated due to the reversal of the AC supply & a negative voltage appears across it.