What is IDMT Relay? Applications, Use, Function


What is IDMT Relay?


IDMT relay is a protection type relay whose operating time is inversely proportional to the magnitude of the fault current. The full form of the IDMT Relay is Inverse Definite Minimum Time Relay. So, when the amount of fault current is more it will operate quickly and when the amount of fault current is less it will take a long time to operate.

The IDMT relay is generally used with a circuit breaker, so when the relay senses a fault it will send a signal to the circuit breaker and the circuit breaker will break the circuit. The IDMT relay comes under the category of Overcurrent Relay. In fact, most of the overcurrent relays are works on the IDMT principle.

For example, if an IDMT Relay takes 2 seconds to operate for 25Kilo Ampere Current, it will take 1.5 seconds to operate for 30Killo Ampere Current. So you can understand more current means less time and less current means more time. Here, you can see the graph for IDMT Relay operating time with respect to fault current.

IDMT Relay Operating Characteristics


Generally, a Current Transformer or CT is used with the IDMT relay to sense the fault current. So when the secondary of the CT sends an actuating signal in form of an electrical current to the relay coil, it may be got saturated. So sometimes further amplification of the actuating signal is not possible. That is why a minimum time is required by the relay that can not be practically eliminated. Although the sensitivity of the IDMT relays is very high.

There are some types of IDMT relays are available such as,
  1. Inverse Relay
  2. Very Inverse Relay
  3. Extreme Inverse Relay


How does an IDMT Relay Work?


The working principle of an IDMT Relay is very simple. Basically, a current transformer placed with the line is to be protected and the output of the current transformer is connected to the relay coil. The output of the relay is connected to a circuit breaker. Now, the current transformer or CT continuously measures the flow of current through the line. Modern IDMT relays have digital displays also where you can see the value of the current flow. Now when the current flow exceeds the limit, the IDMT relay starts its work. As we know the operation time of the IDMT really depends upon the magnitude of the current. So, according to the magnitude of the current, the relay actuates. Once the relay is actuated the circuit breaker got a signal from the relay and it will break the circuit to turn off the power supply.


Applications and Uses of IDMT Relay


1. You can see the application of IDMT Relay in transmission lines or substations to observe the current flow and keep it at a safe level.

2. IDMT relay is used in continuous current flowing circuits.

3. IDMT relays are used in electrical power circuits, load circuits, safety circuits, etc


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What is IDMT Relay? Applications, Use, Function What is IDMT Relay? Applications, Use, Function Reviewed by Author on 1/30/2022 Rating: 5

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