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Define co-ordination in protection

Short answer

Protection coordination is the selection of pickup current and time settings of series-connected devices so that only the nearest device trips first, with upstream devices providing time-delayed backup. It uses time, current or IDMT grading with intervals of about 0.3–0.5 s.

Define co-ordination with reference to protection system.

Coordination (discrimination) in a protection system is the selection of settings (pick-up current and operating time) of all protective devices connected in series, so that for any fault only the device nearest to the fault operates first, and the upstream devices operate only as time-delayed back-up if it fails.

  • It is achieved by time grading, current grading or both (IDMT relays).
  • A coordination time interval of about 0.3–0.5 s is kept between successive relays.
  • Example: for a fault on a distribution feeder, the feeder relay (0.2 s) trips before the transformer relay (0.6 s).

✓ Answer checked by Claude Opus 5.5 (high effort)

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