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Pickup on earth faults is effectively suppressed in networks with non-earthed neutral points by means of the
measures described in Section „Earth Fault Detection".
The basic characteristics of the U/I/ϕ pick-up can be seen from the current–voltage characteristic shown in
Figure 2-42. Initially it is shaped like the U/I pickup characteristic (Figure 2-41).
For angles in the range of large phase difference, i.e. in the short-circuit angle area above the threshold angle
ϕ>, the characteristic between U(I>) and U(Iϕ>) also takes effect; it is cut off by the overcurrent stage Iϕ>. The
bold dots in Figure 2-42 mark the settings which determine the geometry of the current/voltage characteristic.
The angle-dependent area, i.e. the area within the short-circuit angle of the characteristic in Figure 2-42, can
either be set to affect in forward direction (in direction of line) or in both directions.
Figure 2-42
Loop pickup will drop out if the signal falls below 95% of the respective current value or exceeds approx. 105%
of the respective voltage value. A hysteresis of 5° applies to phase-angle measuring.
The adaptation to different network conditions is determined by pickup modes. As the U/I/ϕ pickup is an exten-
sion of the U/I pickup, the same program options are available. Table 2-5 to Table 2-8 also apply for single–
phase pickup.
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011
U/I/ϕ characteristic
Functions
2.5 Distance Protection
123
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