Protection Engineering Basics and Schemes Protection Engineering | Página 204
Relay works on below algorithm,
If I operating > KI restraint then relay will pick up, K is bias factor and ranges from 0.3 to 0.8( 30 to 80 %).
In case of external fault I operating = 0
slope = m = I differential
I restraint
Inrush current is due to high flow of current at energization of transformer, this inrush current causes harmonics in system, whenever we assign our values of pick up in relay we also includes harmonics block timing. If harmonics remains in system till passage of timing, relay issue trip signal to associated circuit breaker.