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IPD1V03 USER MANUAL
6.2. Dependent time protection
There are two types of dependent time 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 C - Additional Information on Current Protection” for information regarding compliance to IEC 60255
6.2.1.
Over-Current Characteristics
See “vInv” Curves, Drawing IPDB018 and Overcurrent Functional Block Diagram, Drawing IPDB032 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:
t (sec) 
180  m
I 1
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 setpoint,
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 overcurrent 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:
tR (I ) 
1440  m
I 1
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.
IPDB014 IPD User Manual (1)
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