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IDMT Relay Tripping Time Calculator

Home / Resources / Electrical Design Calculators / IDMT Relay Tripping Time Calculator

IDMT Relay Tripping Time Calculator

Inverse definite minimum time (IDMT) relays serve the purpose of interrupting the fault currents while ensuring safety and minimising damage to power system equipment. To achieve this, relays are supposed to trip in a short time therefore it is of great importance to know the tripping time.

For protection discrimination studies you can use our protection coordination software.

Time Current Curve Equations

The curve equations for different standards are given below:

IEC Curves

1 4 - IDMT Relay Tripping Time Calculator

TMS is Time Multiplier Setting,

I is the fault current in Amps,

Is is the relay pickup current in Amps,

I / Is  is the Plug Setting Multiplier,

td is the operating time of relay,

k and p are constants for the various characteristic curves given below:

Characteristic Curves k p
Standard Inverse
0.14
0.02
Very Inverse
13.5
1
Long Time Inverse
120
1
Extremely Inverse
80
2
Ultra Inverse
315.2
2.5

IEEE Curves

2 4 - IDMT Relay Tripping Time Calculator

Here TDS is Time Dial Setting,

A, B and p are constants and their values for various type of inverse curves are given below:

Characteristic Curves A B p
Moderately inverse
0.0515
0.1140
0.0200
Very inverse
19.61
0.4910
2.0000
Extremely inverse
28.2
0.1217
2.0000

IAC Curve

4 1 - IDMT Relay Tripping Time Calculator

The values of constants A, B, C, D and E for various type of inverse curves are given below:

Characteristic Curves A B C D E
IAC Inverse
0.208
0.863
0.8
-0.418
0.195
IAC Very Inverse
0.090
0.795
0.1
-1.288
7.958
IAC Extremely Inverse
0.004
0.638
0.620
1.787
0.246

Rapid Inverse (RI) Curve

3 3 - IDMT Relay Tripping Time Calculator

Related Resources:

elek calculator cable size - IDMT Relay Tripping Time Calculator

Cable Size Calculator

This calculator determines minimum cable size using the method described by the Standard AS/NZS 3008.1.1 and uses the accurate voltage drop method.

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elek calculator fault loop - IDMT Relay Tripping Time Calculator

Fault Loop Impedance Calculator

This fault loop impedance calculator is based on the Standards. Refer to our article “Understanding Earth Fault Loop Impedance“. 

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Protection Software
Cable Pro Web Protection Coordination Software module

Discrimination studies for protective devices made easy.

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Manufacturers:
ABB logo - IDMT Relay Tripping Time Calculator
Hager logo - IDMT Relay Tripping Time Calculator
NHP logo - IDMT Relay Tripping Time Calculator
Schneider logo - IDMT Relay Tripping Time Calculator

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