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Functions
2.8 Earth Fault Protection in Earthed Systems (optional)
The phase selector uses the phase angle between negative sequence current and zero-sequence current to
determine the fault type. The phase currents are evaluated - if necessary with load current compensation - to
distinguish between different fault types. This method relies on the fact that in the event of a single phase fault
the fault-free phases can conduct either no fault currents at all or only such fault currents that are almost com-
pletely in phase.
If this criterion does not allow to determine the fault type, e.g. because the zero-sequence current or negative
sequence current is too low, an additional check is carried out for considerable voltage drops or overcurrents
that would indicate a single-phase fault.
The phase selector has an action time of approximately 40 ms. If the phase selector has not made a decision
during this time, three-pole tripping is initiated. Three-pole tripping is initiated anyway as soon as a multi-pole
fault has been detected, as described above. Therefore the phase-selective transmit signals in teleprotection
schemes can have a delay of up to 40 ms as compared to the non phase-selective transmit signal 1384 „EF
Tele SEND" (see Section 2.9).
Figure 2-113 shows the logic diagram. The phase determined by the phase selector can be processed selec-
tively for each phase, for example the internal information „E/F PickupL1" etc. is used for phase-selective signal
transmission.
External indication of the phase-selective pickup is performed via the information „E/F L1 selec." etc. This
information appears only if the phase was clearly detected. Single-pole tripping requires of course the general
prerequisites to be fulfilled (device must be suited for single-pole tripping, single-pole tripping allowed).
230
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011
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