Question

Plug setting Multiplier (P.S.M) of relay is the ratio:
1. pick up current to normal current
2. rated secondary current of CT to rated current of CT
3. fault current in circuit breaker to normal current
4. fault current in relay coil to pick up current

Answer 1

Correct Answer - Option 4 : fault current in relay coil to pick up current

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 = (Rated secondary current in CT) x (Current setting)

Important Point:

Time Multiplier Setting (TMS) is the ratio \(\frac{T}{{{T_m}}}\)

Where, for a given plug setting multiplier T is the desired relay operating time and Tm is the corresponding operating time.