Operating Principle - ABB ETL600 Instruction Manual

ETL600
3.6.7.

Operating principle

The NSD600 uses the pilot signal of the ETL600 as a guard signal. It
is continuously evaluated on the receive side. In case of insufficient
signal quality (signal-to-noise ratio or signal level) the NSD600 initiates
an alarm.
For special purpose, e.g. transit relaying of NSD600 signals in a
repeater station, a separate guard signal for the teleprotection may be
programmed. It is then located above the chosen speech frequency
band (2.0, 2.2 or 2.4 kHz).
In the command state, the NSD600 interrupts the guard signal (ETL-
pilot or NSD-own guard) and transmits the tripping signal -
representing the command(s) injected at the G4AI input(s) - within the
ETL600 speech frequency band. The tripping signal can be boosted to
the maximum available transmitter power. Speech and selected data
signals (set as 'disconnectable') on all PLC channels are interrupted
during the short time of command transmission.
A start criterion from the protection relay may be used to prepare the
channel for transmission of protection signals by switching off speech
in advance.
If the duration of a command transmission exceeds five seconds
(default setting), an alarm will be given at the transmit end and the
guard signal as well as speech and superimposed data channels are
switched on again. As an option, also the trip duration on the receive
side can be monitored. If monitoring is enabled and the command
reception exceeds the configured duration, alarm is given and the
corresponding output(s) are set to the guard state.
Commands of long duration (e.g. between 5 s and 60 s) shall only be
allowed (via the HMI600) when the own guard signal is used, the ETL
pilot signal will not be switched off whilst these commands are
transmitted. Therefore all the services assigned to the pilot channel
(EOC, frequency synchronization (if needed), AGC, E&M signaling)
are still available.
As soon as the receiver recognizes the missing guard signal and
simultaneously detects a valid tripping signal of adequate quality, the
command is relayed to the designated output(s). Simultaneous
reception or simultaneous loss of a tripping signal and the guard signal
leads to an alarm. In the latter case, the output(s) programmed for
unblocking function are activated for the preset duration (default
setting: 200 ms).
At the receiver side speech is interrupted as long as a command is
given to the outputs. This prevent the command tones to be relayed for
an unduly long time to other line sections, e.g. via a switchboard.
Seven preset frequencies corresponding to the various commands or
command combinations are provided in the PLC speech frequency
band. All commands or their combinations are represented by dual-
tone tripping signals for obtaining short command transmission time in
the PLC channel at almost the best practical signal-to-noise ratio.
Structure and Function
1KHW001489-EN
November 2005
ABB Switzerland Ltd
3-71