The messages received on each channel are individually assessed for quality to ensure the IM64 signalling scheme
is av
ailable for use. If no messages are received for a period equal to the Channel Timeout setting or the signal
quality falls below a defined value, DDB signals are activated as shown in the IM64 channel fail and scheme fail
logic diagram.
Poor quality is indicated if the percentage of incomplete messages exceeds the IM Msg Alarm Lvl setting in a
100 ms period (rolling window), or if the communications propagation time of the IM64 message exceeds the Max
Ch PropDelay (assuming the Prop Delay Stats setting is Enabled), or if (in IEEE C37.94 configuration only, and not
shown on the diagram) the Ch Mux Clk flag has been raised to indicate an incorrect baud rate.
If either the Ch Timeout or the Ch Degraded signal persists in the alarmed state for more than the duration of the
Comm Fail Timer setting, according to the conditions set in the Comm Fail Mode setting, the Signalling Fail signal
is raised.
For two-ended schemes (including dual redundant schemes), the IM64 SchemeFail signal is generated at the same
time as the Signalling Fail signal. However, for three-terminal applications, the IM64 SchemeFail signal indicates
that the full set of signalling bits cannot be processed by the scheme. Due to the self-healing nature of the three-
terminal application, this occurs when both channels at any one terminal are not receiving valid signals. This
condition generates a flag in the IM64 message structure which is passed to both remote ends, as well as
generating the local IM64 SchemeFail signal. Using this method, in three-terminal applications the scheme fail
indication is raised at all three ends.
The scheme fail signalling is generated by the inability of a device to receive messages through communication
failure. The transmitting device only knows that communication to a remote device has failed if it receives
notification from the remote device. If a device in the scheme is put into test mode, the communication failure
information is not passed on to the remote ends. If the communications failure is bidirectional, there will be no
indication at the remote device. If this causes operational issues, it may be necessary to include other signals to
enable more precise indication of scheme failure.
In addition to the main IM64 channel fail and scheme fail conceptual logic, there are number of additional alarm
DDB signals associated with test modes, reconfiguration for 3-terminal schemes, and the communication mode
(‘Standard’ or ‘IEEE C37.94’) shown in the logic diagrams.
The majority of signals are associated with the ‘IEEE C37.94’ communications mode and are not activated if the
Standard communication mode is selected. The Comms Changed DDB logic is to show that switching between
the different communication modes requires a power cycle to be performed before the change is activated.
5.4 TWO-ENDED SCHEME EXTENDED SUPERVISION
For two-terminal applications, the Signalling Fail and IM64 SchemeFail signals operate together. As such, the
basic indications available on each device should be considered as local-terminal indications only. If remote
indication is needed to assure scheme functionality, it is necessary to use additional signals to communicate the
status to the remote end. One method of performing this is shown below:
Chapter 15 - Fibre Teleprotection P54A/B/C/E
326 P54xMED-TM-EN-1
To Next Page
Loading...
Need help?
General
