Phase Segregated Line Protection; Relaying Tripping Signals Through Intermediate Stations - ABB ETL600 Instruction Manual

ETL600
An especially high availability of the communications channel may be
specified at important power lines of the highest voltage range. A
second set of PLC and NSD600 equipment is recommended in these
situations. The command inputs and outputs of which are simply
connected in parallel.
3.6.5.7.

Phase Segregated Line Protection

An NSD600 with its four commands can also be used for phase-
segregated protection of a three-phase line. The permissive
commands A, B and C then mean 'permission to trip phase A, B, or C';
in the event of a 2-phase or 3-phase fault, the direct command D
means 'permission to trip all three phases'.
3.6.5.8.

Relaying Tripping Signals Through Intermediate Stations

In relatively seldom cases it is necessary for protection tripping signals
to be relayed through intermediate (repeater) stations. One possibility
in the repeater station is to connect two NSD600's via teleprotection
interfaces back-to-back, but this has the disadvantage that each
repeater station increases the end-to-end transmission time by the
standard channel transit time (the operating times are connected in
series).
Better performance from the transmission time point of view is
achieved by establishing a wide-band AF four-wire link between the
two PLC units in the repeater station. Pilot blocking filters have to be
installed because of system requirements to prevent the pilot signal
from passing through the repeater station. Each PLC link increases the
delay by 5 ... 6 ms.
The lack of pilot continuity is overcome by arranging for the NSD600
units at the two terminal stations to generate their own guard signals
using a frequency within the band which will pass through the repeater
station. The corresponding setting information for selecting an
independent guard signal is to be found in section 5.3.3. This
arrangement has the disadvantage that the ETL pilot signal and
superimposed data channels are only disconnected on the first line
section when a command is injected. Therefore the maximum boost
level has to be carefully calculated (adapted to the ETL600 link for the
second line section).
No teleprotection interfaces may be inserted into the PLC equipment in
the repeater station and the NSD600 has to be switched off as well in
this station when using the operating mode described in the paragraph
above! Speech in the TPE channel(s) of the ETL600 may only be
transferred between the end stations in this particular case.
Note:
Structure and Function
1KHW001489-EN
It is recommended to relay the commands in the
intermediate station on a contact basis at the
teleprotection interface(s), thus enabling the boosting
facility on each line section.
The drawback of a higher end-to-end transmission
time under noise-free conditions is compensated by
November 2005
ABB Switzerland Ltd
3-65