Idmt relay curve

1. What is IDMT curve?
2. Which curve does IDMT relay follow?
3. What are the different types of IDMT curves?
4. How does an IDMT relay work?

What is IDMT curve?

Inverse Definite Minimum Time (IDMT) curves are used in both mechanical and electronic protection devices. These curves define the amount of time which should pass at a given current, before initiating an action, usually the tripping of a circuit breaker.

Which curve does IDMT relay follow?

The 'EI' type IDMT relay curve operates at very fast at high short-circuit currents and very slow at low short-circuit currents. This type of IDMT curve is most suited for coordination with fuses. Ideally, the same type should be used throughout the system.

What are the different types of IDMT curves?

There are four curve types used in IEC 60255 which are: standard inverse, very inverse, extremely inverse and long time standard inverse.

How does an IDMT relay work?

IDMT relay is inverse definite minimum time relay. It is one in which Time of operation is inversely proportional to magnitude of fault current near pickup value and becomes substantially constant slightly above the pickup value of the Relay.