Determine operating current of the relay, for 5 A, 2.2-sec IDMT rating, and 125% relay setting?

Question

Question

Answer 1

Concept:

The plug setting multiplier of a relay is defined as the ratio of secondary fault current to the pick-up current.

PSM = Secondary fault current / Relay current setting

Pick up current or operating current = (Rated secondary current in CT) x (Current setting)

Calculation:

Given that,

Current setting = 125% = 1.25, Rated secondary current = 5 A

Therefore, operating current of relay = 5 x 1.25 = 6.25 A