Siemens siprotec 7SA6 User Manual page 395

Distance protection

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6.14.2 Applying the Function Parameter Settings

C53000-G1176-C133-1

The resulting single–phase AC voltage is fed to the two threshold stages 8 and

8 (see Figure 6-109). Combined with the associated time delays 7 8 and 7

8 these stages form a two-stage undervoltage protection for the positive

sequence system.

Current can be used as an additional criterion for the undervoltage protection of the

positive sequence system (current supervision &855683). An undervoltage is only

detected if the current flow is detected in at least one phase together with the

undervoltage criterion.

The undervoltage protection for the positive sequence system can be blocked via the

binary input "!8 %/.". The stages of the undervoltage protection are

automatically blocked if voltage failure is detected ("Fuse–Failure–Monitor", also see

Section 6.19.1.3) or, if the trip of the mcb for the voltage transformer is indicated via

the binary input "!)$,/)HHGHU 97" (internal blocking).

Figure 6-109 Logic diagram of the undervoltage protection for positive sequence voltage

During single-pole dead time for automatic reclosure (using the internal automatic

reclosure function) the stages of the undervoltage protection are automatically

blocked in the positive sequence system so that they do not respond to the reduced

voltage cause by the disconnected phase in case the voltage transformers are located

on the outgoing side.

The voltage protection can only operate if it has been set to (QDEOHG during the

configuration of the device scope (see Section 5.1, address ).

The overvoltage and undervoltage stages can detect phase–to–earth voltages,

phase–to–phase voltages or the symmetrical positive sequence system of the

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