[foberecr-310113-01.tif, 1, en_US]
EXAMPLE
For the 5 A transformer as above
Desired pickup value I
pick
= 0.1 A (corresponds to 16 A primary)
[fober5aw-310113-01.tif, 1, en_US]
For the 1 A transformer as above
Desired pickup value I
pick
= 0.05 A (corresponds to 40 A primary)
[fober1aw-310113-01.tif, 1, en_US]
The series resistor R must be designed for a minimum continuous load P
continuous
.
[fopdau5a-310113-01.tif, 1, en_US]
[fopdau1a-310113-01.tif, 1, en_US]
Further, the series resistor R must be designed for a fault current lasting approximately 0.5 s. This time is
usually sufficient for fault clearing through backup protection.
The thermal stress of the series resistor depends on the voltage V
RMS,stab
that is present during an internal fault.
It is calculated according to the following equations:
[fousta5a-310113-01.tif, 1, en_US]
[fousta1a-310113-01.tif, 1, en_US]
I
K,max,int
corresponds to the maximum fault current here in the case of an internal fault.
5-A current transformer 800/5 with 40 kA primary corresponds to I
K,max,int
= 250 A secondary.
1-A current transformer 800/1 with 40 kA primary corresponds to I
K,max,int
= 50 A secondary.
This results in a temporary load for the series resistor over 0.5 s of:
[fop05s5a-310113-01.tif, 1, en_US]
[fop05s1a-310113-01.tif, 1, en_US]
Protection and Automation Functions
6.12 Overcurrent Protection, 1-Phase
540 SIPROTEC 5, Overcurrent Protection, Manual
C53000-G5040-C017-8, Edition 07.2017
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