Table of Contents
Advertisement
74
Scheme communication logic (ZCOM)
6FKHPH FRPPXQLFDWLRQ ORJLF =&20
$SSOLFDWLRQ
To achieve fast fault clearing for a fault on the part of the line not covered by the instan-
taneous zone 1, the stepped distance protection function can be supported with logic,
that uses communication channels.
One communication channel in each direction, which can transmit an on/off signal is
required. The performance and security of this function is directly related to the trans-
mission channel speed, and security against false or lost signals. For this reason special
channels are used for this purpose. When power line carrier is used for communication,
these special channels are strongly recommended due to the communication distur-
bance caused by the primary fault.
The logic supports the following communications schemes; blocking scheme, permis-
sive schemes (overreach and underreach) and direct intertrip.
)XQFWLRQDOLW\
7KHRU\ RI RSHUDWLRQ
Depending on whether a reverse or forward directed impedance zone is used to issue
the send signal (ZCOM-CS), the communication schemes are divided into Blocking
and Permissive schemes, respectively.
%ORFNLQJ FRPPXQLFDWLRQ VFKHPH
In a blocking scheme, the received signal (ZCOM-CR) carries information about the
fault position, which specifies that it is outside the protected line, on the bus or on ad-
jacent lines. Do not prolong the sent signal, so set tSendMin to zero. The sending might
be interrupted by operation of a forward zone if it is connected to ZCOM-CSNBLK.
An overreaching zone is allowed to trip after a co-ordination time (tCoord), when no
signal is received from the remote terminal. The tCoord time must allow for the trans-
mission of the blocking signal with a certain margin.
In case of external faults, the blocking signal (ZCOM-CR) must be received before the
tCoord elapses, to prevent a false trip.
&KDSWHU
/LQH LPSHGDQFH
Advertisement
Table of Contents
