Relay Settings
Test Results (seconds)
Comparison
Typical tolerance: ±5% for electronic relays, ±7.5% for electromechanical
A trip test out of tolerance points either at the relay or at settings that do not match the study. Checking the settings is part of a protection study. Protection studies →
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Related: Trip times for all four IEC curves
Curve Comparison
Frequently Asked Questions
How is the deviation calculated?
The expected trip time comes from the IEC 60255-151 formula t = TMS x k / ((I/Is)^alpha - 1) for the curve, I/Is and TMS entered. Each measured time is compared with it as a percentage: (measured / expected - 1) x 100.
What tolerance should a relay trip test meet?
The deviation shows green within 5 %, amber up to 7.5 % and red beyond. Those are typical figures for electronic and electromechanical relays respectively; the accuracy class the relay manufacturer declares is the one to test against.
Can I test all three phases?
Yes. Enter the measured trip time for L1, L2 and L3 and each is compared with the expected time and plotted against the curve.