IG-150-EN version 04; 03/10/16
95
General instructions
ekor.rps
Protection functions. Description and settings
Figure 4.28. Directional unlocking
Additional pilot protection schemes
Reverse direction locking
It is used on double-circuit lines in order to prevent the
immediate tripping of a protection that is seeing a fault
backwards (and the carrier signal, which is sent to it by the
forward protection) when the power ow direction changes
(due to opening of the parallel line breaker). It delays the
pilot protection tripping for a few cycles in order to give
the remote terminal time to remove the permission (ETP)
signal after the change of ow direction due to the breaker
opening. The Z3 signal is used with a storage time (Z3(R)
MEM), thereby obtaining the Z3(R)MEM signal to be used
in the rest of the schemes, as shown in the following gure.
The gure shows a ow scheme when the fault occurs and
when the breaker is opened. If this scheme is not used, the
eect could be the following:
When the failure occurs, terminal C sees it in zone 1, D in
zone 1 or 2 according to the length, B backwards and A in
zone 2. In this situation, C opens the breaker and sends the
ETP signal to D. A likewise sends ETP to B.
When the breaker is opened and the ow changes, A would
see the fault backwards and B would see it in zone 2 or 3 (F),
whereby it could trip before A removes the RTP signal.
Figure 4.29. Reverse Directional Locking
Figure 4.30. Flow Change due to breaker opening
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