---
title: "Define co-ordination in protection"
subject: "Switchgear and Protection"
chapter: 1
key: "semester_6/switchgear_and_protection:define-coordination"
source: https://www.bctengineer.com/q/semester_6/switchgear_and_protection/define-coordination
site: BCT Engineering
---

# Define co-ordination in protection

Switchgear and Protection · Chapter 1: Principle of Power System Protection

- Asked in: 2071 Magh, 2 marks
- Video: [SELECTIVITY, DISCRIMINATION and CO-ORDINATION of electrical devices for protection](https://www.youtube.com/watch?v=lOcbVQgCSpM) — LEARN ELECTRICS
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/switchgear_and_protection/define-coordination
- Whole chapter: https://www.bctengineer.com/md/semester_6/switchgear_and_protection/chapter-1

## Question

Define co-ordination with reference to protection system.

## 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.

## Answer

**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).

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. In coordination, which device operates first for a fault?
   A. The device farthest upstream
   B. All devices at once
   C. The device nearest to the fault
   D. The transformer relay always
   Answer: C. Upstream devices act only as time-delayed back-up. (Key point: Coordination meaning)

2. How is coordination achieved?
   A. Time grading, current grading or both (IDMT)
   B. Using identical settings
   C. Removing time delays
   D. Using only fuses
   Answer: A. Settings of pick-up and time are graded. (Key point: Achieving coordination)

3. What coordination time interval is kept between successive relays?
   A. About 5 s
   B. About 0.3-0.5 s
   C. About 0.01 s
   D. None
   Answer: B. This covers breaker time and errors. (Key point: Time interval)

## Related in Switchgear and Protection

- [Protection requirements; protective system vs scheme](https://www.bctengineer.com/question.md?key=semester_6%2Fswitchgear_and_protection%3Aprotective-system-vs-scheme) — Switchgear and Protection, chapter 1
- [Basic requirements of a protection scheme](https://www.bctengineer.com/question.md?key=semester_6%2Fswitchgear_and_protection%3Abasic-requirements-protection-scheme) — Switchgear and Protection, chapter 1, asked 3×
- [Zones of protection and their rules](https://www.bctengineer.com/question.md?key=semester_6%2Fswitchgear_and_protection%3Azones-of-protection) — Switchgear and Protection, chapter 1, asked 2×
- [Need for protection and causes of faults](https://www.bctengineer.com/question.md?key=semester_6%2Fswitchgear_and_protection%3Aneed-protection-fault-causes) — Switchgear and Protection, chapter 1

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