Siemens siprotec 7SD5

2.5 Distance Protection
141
7SD5 Manual
C53000-G1176-C169-1
Figure 2-44 Directional characteristic with quadrature or memorized voltages
Determination of
Direction in Case of
Series-compensat-
ed Lines
The directional characteristics and their displacement by the source impedance apply
also for lines with series capacitors. If a short-circuit occurs behind the local series ca-
pacitors, the short-circuit voltage however reverses its direction until the protective
spark gap has picked up (see Figure 2-45).
Figure 2-45 Voltage characteristic while a fault occurs after a series capacitor.
a) without pickup of the protective spark gap
b) with pickup of the protective spark gap
The distance protection function would thus detect a wrong fault direction. The use of
memorized voltages however ensures that the direction is correctly detected (see
Figure 2-46a).
Since the voltage prior to the fault is used for determining the direction, the zeniths of
the directional characteristics in dependence of the source impedance and infeed con-
ditions before the fault are thus far displaced that the capacitor reactance — which is
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