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
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
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
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
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Fault Loop Impedance Calculator
This fault loop impedance calculator is based on the Standards. Refer to our article “Understanding Earth Fault Loop Impedance“.
Protection Software
Discrimination studies for protective devices made easy.
