Question

For the below shown circuit, a motor load (RLE) is connected to the SCR through supply Vs. The minimum value of the firing angle to turn on the SCR would be

(a) Sin^-1(E/Vm)

(b) Sin^-1(Vm/E)

(c) Cos^-1(E/Vm)

(d) Cos^-1(E/Vm)

The question was asked in examination.

I'm obligated to ask this question of Single-Phase HW AC-DC-4 in section Converters of Power Electronics

Answer 1

Right answer is (a) Sin^-1(E/Vm)

To elaborate: The firing angle should be such that the value of V exceeds E. So SCR turns on at excatlly Vm sinωt = E

Therefore ωt  = min. angle = Sin^-1(E/Vm).