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IDMT Earth Fault Relay Setting (50N/51N)

Earth-fault variant of the IDMT overcurrent relay — same IEC 60255-151 / IEEE C37.112 curve mathematics, applied to a residual/earth-fault CT circuit, plus an optional high-set instantaneous stage.

AAJappsEngineering Calculation Report

IDMT Earth Fault Relay Setting (50N/51N)

IEC 60255-151 / IEEE C37.112

Generated

For preliminary engineering use only — always verify results against project-specific standards and a qualified engineer's review before use in a real design.

Earth Fault Relay (50N/51N)

Curve standard

Curve type

Pickup current, Is (A)

TMS

CT ratio (primary : 1) — use 1 if fault current entered is already relay-side

Fault current & instantaneous stage

Earth fault current (primary)

Instantaneous pickup, Ie>> (primary)

Instantaneous time delay

Earth fault relay response

Relay (secondary) current7.50 A

Plug setting multiplier37.50×

IDMT operating time0.372 s

Instantaneous stageDoes not operate