Installation and Operating Instructions - Crompton Instruments

Time over current characteristics
The response time of the relay when operating in Time Over Current mode may determined
using the relationship:
Time-Current Characteristic k1 k2 k3
Standard Inverse 0.01414 0.02 0.1
Very Inverse 1.3636 1 0.1
Extremely Inverse 8.0808 2 0.1
Long time standby Earth Fault 12.121 1 0.1
The curves describing these characteristics may be found on the following pages (Figs 4 to 7).
Limits of operation
The maximum “Multiple of trip setting” applicable for a trip setting at “nominal input” (e.g. Trip
point at 5 Amps on a 5 Amp unit) is 5. “Multiple of trip setting” values of greater than 5 are only
valid for trip levels of less than “nominal input”. This parameter is limited by the dynamic range
of the current input circuits which start to limit above 5 times “nominal” input.
The maximum time delay introduced by the Time-Current characteristics is limited by the
resolution of the current input in the region of the trip point. This limits the “Multiple of trip
setting” to approximately 1.007.
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