IDMT Relay Calculator
Inverse Definite Minimum Time protection coordination
🔌 Phase 3 Calculator
Inputs
Range: 0.05 to 1.0
Format: Primary:Secondary
Results
Operating Time
1133.7
milliseconds
Plug Setting Multiple (PSM)20.00
CT Secondary Current5.00 A
Protection Curvestandard inverse
Time Dial0.5
✓ Relay will operate within configured time
Important: These results are indicative only. Relay coordination must be verified by a qualified electrical engineer. Do not use for final design without independent verification.
IDMT Relay Guide
IDMT (Inverse Definite Minimum Time) relays are widely used in electrical protection systems to provide selective protection coordination. The operating time decreases as the fault current increases, allowing protective devices closer to the fault to operate faster while permitting upstream devices more time to clear.
Protection Curves
- Standard Inverse: General purpose protection with moderate speed gradation.
- Very Inverse: Faster operation at high currents, used for backup protection.
- Extremely Inverse: Most sensitive to current changes, fastest at high faults.
- Long Time Inverse: Slow response at low multiples, for thermal protection.
- Definite Time: Fixed time delay regardless of current magnitude.
Disclaimer: This calculator is provided as a guide only and must be verified by a qualified electrical engineer before use in design or installation.