Free Tool · IEC 60255-151

Protection Relay Coordination

Check selectivity between an upstream relay and downstream protective device. Computes the time-current coordination curve, selectivity ratio (I_up/I_down), coordination status, and backup protection confirmation per IEC 60255-151.

Upstream Protective Device

Device type

Pickup current I_s (A)

Time Dial / TMS

Curve type

Instantaneous I_set (A, 0=off)

0 = instantaneous disabled

Downstream Protective Device

Device type

Rating (A)

Pickup current I_s (A)

Time Dial / TMS

Curve type

Definite time t_s (s)

Coordination Criterion

Fault current upstream (kA)

Fault current downstream (kA)

Target selectivity ratio

Min time margin (s)

Free Tool · IEC 60255-151
Run a coordination check to see results.