Protective Relay Settings: toc_curve
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 | alpha const | curve designation | curve name | curve standard | formula | k const | notes | time dial range max | time dial range min |
|---|---|---|---|---|---|---|---|---|---|---|
| toc_curve | iec_c1 | 0.02 | C1 | Standard Inverse | IEC 60255-151 | t=TMS*(k/(M^alpha-1)) | 0.14 | IEC 60255-151 Standard Inverse (SI); also called IDMT; widely used in UK and European systems | 1 | 0.05 |
| toc_curve | iec_c2 | 1 | C2 | Very Inverse | IEC 60255-151 | t=TMS*(k/(M^alpha-1)) | 13.5 | IEC 60255-151 Very Inverse (VI); steep characteristic suitable for graded systems | 1 | 0.05 |
| toc_curve | iec_c3 | 2 | C3 | Extremely Inverse | IEC 60255-151 | t=TMS*(k/(M^alpha-1)) | 80 | IEC 60255-151 Extremely Inverse (EI); matches fuse characteristics; best for feeder circuits with heavy motor loads | 1 | 0.05 |
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