Functions
2.5 Distance Protection
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011
118
The maximum asymmetry to be expected for a load current or a single earth fault can be set via the parameter
1523 Uph-ph unbal.. Furthermore, in these systems, a simple earth fault is assumed initially and the pickup
is suppressed in order to avoid erroneous pickup as a result of the earth fault inception transients. After a con-
figurable delay time T3I0 1PHAS, the pickup is released again; this is necessary to ensure that the distance
protection is still able to detect a double earth fault with one base point on a dead-end feeder. If the phase-to-
phase voltages are asymmetrical, this indicates a double earth fault and the pickup is released immediately.
Figure 2-39 Symmetry detection for phase-to-phase voltages
k= Setting value for parameter 1523
Figure 2-40 Earth fault detection in isolated or resonant-earthed systems
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