[ueb-einph-widerstand-021026-rei, 1, en_US]
Calculation Example:
For the 5 A CT as above
desired pickup value Ι
pu
= 0.1 A (equivalent to 16 A primary)
[ueb-einph-widerstand-5a-021026-rei, 1, en_US]
For the 1 A CT as above
desired pickup valueΙ
pu
= 0.05 A (equivalent to 40 A primary)
[ueb-einph-widerstand-1a-021026-rei, 1, en_US]
Series resistor R must be rated for a minimum permanent load P
permanent
:
[fohochimppcont5a-20120514, 1, en_US]
[fohochimppcont1a-20120514, 1, en_US]
Furthermore, series resistor R must be rated for a fault current applying for approx. 0.5 s. This time is usually
sufficient for the backup protection to clear the fault.
The thermal load of the series resistor depends on the voltage V
rms,stab
applying during an internal fault. It is
calculated according to the following formulas:
[fohochimpvrmsstab5a-20120514, 1, en_US]
[fohochimpvrmsstab1a-20120514, 1, en_US]
where I
k,max,int
corresponds to the maximum fault current during an internal fault.
For the 5 A current transformer 800/5 with 40 kA primary, Ι
k,max,int
equals 250 A secondary.
For the 1 A current transformer 800/1 with 40 kA primary Ι
k,max,int
50 A secondary.
This yields a short-time load over 0.5 s for the series resistor of:
[fohochimpp-5a-20120514, 1, en_US]
Functions
2.5 Single-Phase Overcurrent Protection
SIPROTEC 4, 7SJ80, Manual 119
E50417-G1140-C343-A8, Edition 12.2017
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