Siemens siprotec 7SD5

2.5 Distance Protection
117
7SD5 Manual
C53000-G1176-C169-1
A precondition for measuring the phase-phase angles is that the associated phase
currents as well as the current difference relevant for the loop have exceeded a setta-
ble minimum value Iph>. The angle is determined by the phase–to–phase voltage
and its corresponding current difference.
A precondition for measuring the phase-earth angle is that the associated phase
current has exceeded a settable minimum value Iph> and that an earth fault has been
detected or only phase-to-earth measurements have been stipulated by setting pa-
rameters. The angle is determined by the phase-to-earth voltage and its correspond-
ing phase current without considering the earth current.
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 pickup can be seen from the current–voltage
characteristic shown in Figure 2-32. Initially it is shaped like the U/I pickup character-
istic (Figure 2-31).
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 2-32 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 2-32, can either be set to affect in forward direction (in direction of line) or in
both directions.
Figure 2-32 U/I/ϕ characteristic
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 fault detection represents an extension of the U/I fault detection, the same
program options apply. Tables 2-5 to 2-8 also apply for single-phase pickup.
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