Note:
A minimum value of 8% negativ
e 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 autor
eclose cy
cle). 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
full load
= 500A
I
2
= 50A
therefore the quiescent I
2
/I
1
ratio = 0.1
To allow for tolerances and load variations a setting of 20% of this value may be typical: Therefore set:
I
2
/I
1
= 0.2
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
2
/I
1
Time Delay = 60 s to allow adequate time for short circuit fault clearance by time delayed protections.
P14x Chapter 6 - Current Protection Functions
P14xEd1-TM-EN-1 145
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