Relay Tripping Time Calculator

Theory and Formula

The IDMT (Inverse Definite Minimum Time) curve plays a key role in the coordination of protective relays. It ensures that faults closer to the source trip faster, improving fault discrimination and minimizing disruption.

This calculator uses the standard IEC 60255 formula for calculating relay operating time:

t(I) = (K / ((I / Is)^p - 1)) * TMS
          

Where:

• I = Fault current
• Is = Relay pickup current
• K = Curve constant (standard values: 0.14 for Standard Inverse)
• p = Exponent (e.g. 0.02 for IEC standard)
• TMS = Time Multiplier Setting

Adjust the parameters based on the protection relay's settings and the type of inverse curve selected (standard, very inverse, extreme inverse, etc.).