Siemens siprotec 7SD5

2 Functions
214
7SD5 Manual
C53000-G1176-C169-1
Figure 2-92 Zero-sequence power protection
Phase Current
Stabilization
Non-symmetrical load conditions in multiple-earthed systems or different current
transformer errors can result in a zero sequence current. This zero sequence current
could cause faulty pickup of the earth current stages if low pickup thresholds are set.
To avoid this, the earth current stages are stabilized by the phase current: as the
phase currents increase, the pickup thresholds are increased (Figure 2-93). The sta-
bilization factor (= slope) may be changed by means of the parameter Iph-STAB.
Slope (address 3104). It applies to all stages.
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