Installation and Operating Instructions - Crompton Instruments

TYPE 51 — AC TIME OVER CURRENT
Brief details
The relay will operate (trip) when the signal level on any of the “generator” current inputs is
greater than the selected value. The response time of the relay will be a function of how far
above the selected value the current value is. The relay will return to the “not tripped”
condition (provided that latched operation has not been selected) when all “generator” current
inputs fall below the selected trip.
Parameters
You must specify the following parameters for operation of the time over current relay:
●
The maximum permitted current on any of the current inputs from the “generator”.
●
The required time characteristic (digit identifying the level VS time curve required).
●
The “Time Dial Setting”.
Parameter details
Range of Current Trip point (Trip Point) 5 — 120% of nominal input
Time Curve (Time Curve)
1 (Standard Inverse)
2 (Very Inverse)
3 (Extremely Inverse)
Time Dial Setting Range (Time Dial) 0.1 to 9.9
Time Dial Setting Resolution 0.1
Resolution of curve timebase
100 milliseconds
Accuracy of timing (relative to the ± 5% of ideal + 2 loop times
characteristics described below)
Maximum Input current for which 25 Amps for 5 Amp nominal unit
Time-Current characteristics are valid 5 Amps for 1 Amp nominal unit
Response Time
NOTE: The time-over current function involves many
calculations, which are computationally intensive.
Worst case example: With all 12 relays defined as timeover
current trips, the product loop time can be up
to 150ms.
Note: Measurement accuracy should also be considered when operating at very small over
current levels since the slope of the curve could introduce additional timing errors.
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