Ampcontrol Pty Ltd
– ABN 28 000 915 542
IPD USER MANUAL
IPDB014 Version 14
– SEP/2020
Uncontrolled Copy - Refer to Ampcontrol Website for Latest Version
Page 47 of 96
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10.2 Time Dependent Current Protection
There are two types of time dependent protection implemented in the IPD:
Over-Current (per IEC 60255-151)
Motor Overload (per IEC 60255-8)
One of these two techniques may be selected, at Level 9, Position 5: “vInv” for over-current or “m-OL” for
motor overload.
See “Appendix B - Additional Information on Current Protection” for information regarding compliance to
IEC 60255
10.2.1 Over-Current Characteristics
) and Overcurrent Functional Block Diagram (Drawing
in Appendix A
– Drawings.
If the selected current protection type is “vInv”, then a very inverse over-current characteristic set of
curves are available for selection. The Very Inverse curve implemented in the IPD is equivalent to
Curve B in Annex A of IEC 60255-151:
Where:
t(sec) is the trip time,
m is the selected time multiplier, and
I is the input current ratio relative to the full load current set point.
The three phase currents are compared and the highest current is used to calculate the trip time. If the
current exceeds the selected full load current an “over-current trip accumulator” increases at a rate
determined by the above function. The accumulated value can be displayed on the RDM (Level 5,
Position 2). If the over-current condition persists so that the trip accumulator reaches 100% then a trip
occurs. If viewed during start up the trip accumulator can help determine if over-current settings are
correct.
When a trip occurs the “OC” LED on the Remote Display Module is illuminated and the open collector
output on the relay is switched on to provide remote monitoring if required.
If the current falls below the selected full load current the trip accumulator reduces towards zero. The
reset time is determined by the following function:
Where:
tR(I) is the time to completely empty the accumulator from 100%, and all other
metrics are as above.
The reset ratio of the IPD is 96%, nominal.
To reset the relay following an over-current trip, operate the reset button.
