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Chapter 9 - Current Protection Functions
Note:
A minimum value of 8% negative phase sequence current is required for successful operation.
Since sensitive settings have been employed, we can expect that the element will operate for any unbalanced
condition occurring on the system (for example, during a single pole autoreclose cycle). For this reason, a long time
delay is necessary to ensure co-ordination with other protection devices. A 60 second time delay setting may be
typical.
The following example was recorded by an IED during commissioning:
I
= 500A
full load
I
= 50A
2
therefore the quiescent I
To allow for tolerances and load variations a setting of 20% of this value may be typical: Therefore set:
I
/I
= 0.2
2
1
In a double circuit (parallel line) application, using a 40% setting will ensure that the broken conductor protection
will operate only for the circuit that is affected. A setting of 0.4 results in no pick-up for the parallel healthy circuit.
Set I
/I
Time Delay = 60 s to allow adequate time for short circuit fault clearance by time delayed protections.
2
1
220
/I
ratio = 0.1
2
1
P54A/B/C/E
P54xMED-TM-EN-1
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