Question

In the figure given below, for 180° mode of operation if T1 is fired at 0°. Then SCRs T3 and T5 should be fired at _________ and _________ respectively.

(a) 180°, 360°

(b) 90°, 180°

(c) 120°, 240°

(d) none of the mentioned

The question was asked in semester exam.

I want to ask this question from 3-Phase Bridge Inverters-1 topic in chapter Inverters of Power Electronics

Answer 1

Right option is (c) 120°, 240°

To elaborate: T1-T4 form the first pair. T3-T6 form the second pair, and like-wise. For the 180° mode, each SCR conducts for 180°, but the groups of SCRs lag the prior group by an angle of 120°. e.g. If T1 is fired at 0 then T3 must be fired at an angle of 0 + 120° and T5 at 120 + 120 = 240°.