Question

A step-down delta-star transformer, with per-phase turns ratio of 5 is fed from a 3-phase 1100 V, 50 Hz source.  The secondary of this transformer is connected through a 3-pulse type rectifier, which is feeding feeding an R load. Find the average value of output voltage.

(a) 220 V

(b) 257 V

(c) 1100/√3 V

(d) 206 V

This question was posed to me in semester exam.

The origin of the question is 3P-Diode Rectifiers-2 topic in chapter Diode Rectifiers of Power Electronics

Answer 1

The correct answer is (b) 257 V

Easiest explanation: Vph = 1100/5 = 220 V (Transformer ratio = 5)

Vmp = √2 x 220 V

Vo = 3√3/2π x Vmp = (√2 x √3 x 3 x 220)/(2 x π).