Protective Relay Settings: coordination
Protective relay settings and coordination parameters per IEEE C37 and IEEE 242. Covers IEEE C37.112-2018 inverse time-overcurrent curve constants (A, B, p, tr) for moderately/very/extremely inverse curves and SEL vendor extensions; IEC 60255-151 curve constants (k, alpha); CT accuracy classes C100/C200/C400/C800 per IEEE C57.13-2016 with burden limits; relay pickup guidance by ANSI device number (50, 51, 50N, 51N, 27, 59, 81U, 81O); coordination time intervals (CTI) per IEEE 242-2001; and CT saturation voltage thresholds.
| parameter type | record id | curve designation | curve name | curve standard | notes | time dial range max | time dial range min |
|---|---|---|---|---|---|---|---|
| coordination | cti_em_relay | CTI_EM | CTI Electromechanical Relay | IEEE 242 | Minimum CTI 0.30-0.40s between electromechanical OC relay pairs; accounts for relay overshoot and CB interrupting time; overshoot ~0.1s | 0.4 | 0.3 |
| coordination | cti_fuse_relay | CTI_FUSE | CTI Fuse to Relay | IEEE 242 | Minimum CTI 0.10-0.20s between upstream relay and downstream current-limiting fuse; fuse characteristic overlap must be checked | 0.2 | 0.1 |
| coordination | cti_relay_cb | CTI_CB | CTI Relay to Circuit Breaker | IEEE 242 | CB interrupt time: 3-8 cycles (0.05-0.133s); total CTI = CB time + relay overtravel + safety margin = 0.25-0.40s | 0.4 | 0.25 |
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