CM
6.3.2 Phase Overcurrent Protection (P742 and P743)
If the overcurrent protection function is being used, both Ι>1 and I>2 elements should be
tested.
To avoid spurious operation of any current differential, earth fault, breaker fail or CT
supervision elements, these should be disabled for the duration of the overcurrent tests. This
is done in the relay’s CONFIGURATION column. Make a note of which elements need to be
re-enabled after testing.
6.3.2.1
Connect the test circuit
Determine which output relay has been selected to operate when an Ι>1 trip and an I>2
occur by viewing the relay’s programmable scheme logic.
The programmable scheme logic can only be changed using the appropriate software. If this
software has not been available then the default output relay allocations will still be
applicable.
If the trip outputs are phase-segregated (i.e. a different output relay allocated for each
phase), the relay assigned for tripping on ‘A’ phase faults should be used.
If stage 1 is not mapped directly to an output relay in the programmable scheme logic, output
relay 1,2 or 3 could be used for the test as it operates for trip condition (phase A, B and C).
The associated terminal numbers can be found in the external connection diagrams.
Connect the output relay so that its operation will trip the test set and stop the timer.
Connect the current output of the test set to the ‘A’ phase current transformer input of the
relay.
Ensure that the timer will start when the current is applied to the relay.
6.3.2.1.1
Perform the test
Ensure that the timer is reset.
Apply a current of twice the setting in cell [GROUP 1 OVERCURRENT, Ι>1 Current Set] to
the relay and note the time displayed when the timer stops.
Check that the red trip LED has illuminated.
6.3.2.1.2
Check the operating time
Check that the operating time recorded by the timer is within the range shown in Table 6.
Note: Except for the definite time characteristic, the operating times given in
Table 6 are for a time multiplier or time dial setting of 1. Therefore, to
obtain the operating time at other time multiplier or time dial settings,
the time given in Table 6 must be multiplied by the setting of cell
[GROUP 1 OVERCURRENT, Ι>1 TMS] for IEC and UK characteristics
or cell [GROUP 1 OVERCURRENT, Time Dial] for IEEE and US
characteristics.
In addition, for definite time and inverse characteristics there is an additional delay of up to
0.02 second and 0.08 second respectively that may need to be added to the relay’s
acceptable range of operating times.
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