Pilot Wire Comparison - Siemens siprotec 7SA6 User Manual

Functions
6.4.1.8

Pilot Wire Comparison

6-92
As soon as the distance protection has detected a fault in reverse direction, the
blocking signal is sent (e.g. "'LV76(1'", FNo ). The send signal can be
prolonged in address . If the fault is in forward direction, the blocking signal is
stopped (e.g. „'LV7%/ 6723", FNo ). To achieve a very fast-reacting blocking
scheme include the output signal of the jump detector for the send signal. Therefore
allocate the output "'LV-XPS%ORFNLQJ" (FNo ) also to the output relay to the
signal transmitting equipment during configuration. Since this jump signal usually
appears when a measured value suddenly changes, the latter should only be applied,
if guaranteed that the transmission channel has a fast response to the reset of the
send signal.
If there is a disturbance in the signal transmission path the overreaching zone can be
blocked via a binary input. The distance protection operates with the usual time
grading characteristic (non delayed trip in Z1). The overreaching zone Z1B can then
be activated by an automatic reclose function via the binary input "!(QDEOH
$5]RQHV" and address  "VW $5 ! =%" set to "Yes" (refer also to Figure 6-
38 bottom).
The influence of signals resulting from transients during clearance of external faults or
from direction reversal during the clearance of faults on parallel lines, is neutralized by
the "Transient Blocking". It prolongs the blocking signal by the transient blocking time
7U%ON %ORFN7LPH (address ), if it has been present for the minimum duration
equal to the waiting time 7U%ON :DLW 7LPH (address  ).
It lies in the nature of the blocking scheme that single end fed short circuits can also
be tripped rapidly without any special measures, as the non feeding end cannot
generate a blocking signal.
In the pilot wire comparison the overreaching zone Z1B functions as instantaneous
zone at both ends of the protected line. Zone Z1B is set to reach beyond the next
station. The pilot wire comparison avoids non-selective tripping.
The information exchange between both line ends is carried out via a closed quiescent
current loop (Figure 6-56) that is fed by a substation battery. One NC contact must be
allocated for each signal output, the receiving input must be configured to "low-active".
Alternatively two auxiliary relay combinations (e.g. 7PA5210–2A) can be used for
inverting the contact.
In the quiescent state the pilot wires carry direct current that, at the same time,
monitors the healthy state of the connection.
If the distance protection picks up, the following signal appears: "'LV76(1'". The
NC contact is opened and the pilot wire loop is initially interrupted. A trip by Z1B is
blocked via the receiving input „!'LV7HO 5HF&K". If the protection system then
detects a fault within the overreaching zone Z1B, the send signal resets. The NC
contact returns to its quiescent state (closed). If the loop in the remote station is also
closed after the same sequence, the loop is energized again: the tripping is again
released at both ends.
In case the short-circuit occurred outside the protected line the pilot wire loop is also
interrupted by the pickup of both devices (both NC contacts "Dis.T.SEND" are
opened). Since the send signal will not reset at least one of the line ends (fault is not
in line direction in zone Z1B), the loop at that end will remain open. Both receiving
inputs are deenergized and block the tripping (because of "L-active"). The other
distance stages including Z1, however, operate independently so that the back-up
protection function is not affected.
7SA6 Manual
C53000-G1176-C133-1