// multi-utility computation suite · offline · instant · precise
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│ computation suite │
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eng.protective-relay-coordination Calculator
Calculates protective relay operating time and checks time-grading margins for overcurrent relay coordination in a power system. Relay grading margin of 0.3–0.4 seconds accounts for circuit breaker operating time, relay overshoot, and CT error.
Inputs
I Fault A
Rate of charge flow (A). I = V/R. Above ~100 mA through the body can be lethal. Fuses protect against overcurrent.
Ctr
Rate of charge flow (A). I = V/R. Above ~100 mA through the body can be lethal. Fuses protect against overcurrent.
Tds
Duration of the process. Make sure units match the rate inputs (seconds, minutes, or hours).
Pickup A
Rate of charge flow (A). I = V/R. Above ~100 mA through the body can be lethal. Fuses protect against overcurrent.
Results
relay current (secondary A)
Electric charge flow rate (A). Governs wire sizing — too much current causes dangerous heating. Fuses protect circuits from overcurrent.
multiple of pickup M = I/Ipu
Gratuity amount — the suggested amount to add to the bill as a service tip.
IEC 60255 inverse time (s)
The computed duration or time value.
ANSI time (IEEE C37.112) (s)
The computed duration or time value.
t = TDS × 0.14/(M^0.02 - 1)
Reference formula or conversion factor shown for context.