Question

Calculate the De-rating factor if the string efficiency is 20 %.

(a) .8

(b) .4

(c) .5

(d) .6

The question was posed to me in an interview.

My question is taken from Solid-State Devices topic in section Introduction to Solid-State Devices of Electric Drives

Answer 1

Right choice is (a) .8

To explain: De-rating factor is used to measure the reliability of a string. The value of the De-rating factor is 1-(string efficiency) = 1-.2 = .8.