2 Functions
138
7SD5 Manual
C53000-G1176-C169-1
Figure 2-41 Polygonal characteristic (setting values are marked by dots)
Determination of
Direction
For each loop an impedance vector is also used to determine the direction of the short-
circuit. Usually similar to the distance calculation, Z
L
is used. However, depending on
the „quality“ of the measured values, different computation techniques are used. Im-
mediately after fault inception, the short-circuit voltage is disturbed by transients. The
voltage memorized prior to fault inception is therefore used in this situation. If the
steady-state short-circuit voltage (during a close-in fault) is even too small for direction
determination, an unfaulted voltage is used. This voltage is in theory quadrilateral to
the actual short-circuit voltage for both phase-earth loops as well as for phase-phase
loops (refer to Figure 2-42). This is taken into account when computing the direction
vector by means of a 90° rotation. In Table 2-11 the allocation of the measured values
to the six fault loops for the determination of the fault direction is shown.
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