# How is Idmt calculated?

## How is Idmt calculated?

IEEE Standard IDMT Calculation: t(s) = TD/7 ((A / (I(F)/Is)p – 1) + B) Hence, the formula in terms of TSM, T(s) = 0.143 * TSM * ((A / (I(F)/Is)p – 1) + B) As we said above the A, B, p are the curve constant and IF = Actual Fault current in Amps and Is = Relay Setting current in Amps.

## 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 IDMT Relay follows?

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.

What is TMS in IDMT relay?

Time Multiplier Setting used to change the value of operation of the relay. If it is more the relay will take more time to operate and vice versa. Changing the position of TMS setting, changes the distance between the contact of the rotating disk and the coil.

### How do you calculate relay time?

Operating Time of Relay for Very Inverse Curve (t) =13.5 / ((PSM)-1). Operating Time of Relay for Extreme Inverse Curve (t) =80/ ((PSM)2 -1). Operating Time of Relay for Long Time Inverse Curve (t) =120 / ((PSM) -1). Operating Time of Relay for Normal Inverse Curve (t) =0.14 / ((PSM) 0.02 -1).

### How do you calculate relay settings?

Calculation of Over Current Relay Setting:

1. Over Load Current (In) = Feeder Load Current X Relay setting = 384 X 125% =480 Amp.
2. Required Over Load Relay Plug Setting= Over Load Current (In) / CT Primary Current.
3. Required Over Load Relay Plug Setting = 480 / 600 = 0.8.

What is the use of IDMT relay?

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.

What is the IDMT relay?

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.

#### How is definite minimum time achieved in an IDMT relay?

Inverse Definite Minimum Time (IDMT) Relays: This is achieved by using a core of the electromagnet which gets saturated for currents slightly greater than the pick-up current.

What is minimum time in IDMT relay?

What is full form of Idmt?

## Why IDMT relays are widely used for?

IDMT relays are widely used for the protection of distribution lines or distribution feeders.

## What is IDMT earth fault relay?

Backup protection of electrical transformer is simple Over Current and Earth Fault protection are applied against external short circuit and excessive over loads. These over current and earth Fault relays may be of Inverse Definite Minimum Time (IDMT) or Definite Time type relays (DMT).

Why are Idmt relays used?