Functional Assignment; Intermicom Settings - GE MiCOM P40 Agile Technical Manual

Application Notes
MiCOM P40 Agile P442, P444
5.6.2

Functional Assignment

Even though settings are made on the relay to control the mode of the intertrip signals, it is
necessary to assign interMiCOM input and output signals in the relay Programmable
Scheme Logic (PSL) if InterMiCOM is to be successfully implemented. Two icons are
provided on the PSL editor of MiCOM S1 Agile for "Integral tripping In" and "Integral tripping
out" which can be used to assign the 8 intertripping commands.
It should be noted that when an InterMiCOM signal is sent from the local relay, only the
remote end relay will react to this command. The local end relay will only react to
InterMiCOM commands initiated at the remote end.
5.6.3

InterMiCOM Settings

The settings necessary for the implementation of InterMiCOM are contained within two
columns of the relay menu structure. The first column entitled "INTERMICOM COMMS"
contains all the information to configure the communication channel and also contains the
channel statistics and diagnostic facilities. The second column entitled "INTERMICOM
CONF" selects the format of each signal and its fallback operation mode. The following
tables show the relay menus including the available setting ranges and factory defaults.
Once the relay operation has been confirmed using the loopback test facilities, it will be
necessary to ensure that the communications between the two relays in the scheme are
reliable. To facilitate this, a list of channel statistics and diagnostics are available in the
InterMiCOM COMMS column:
5.6.3.1 Setting Guidelines
The settings required for the InterMiCOM signalling are largely dependant upon whether a
direct or indirect (modem/multiplexed) connection between the scheme ends is used.
Direct connections will either be short metallic or dedicated fiber optic (using CILI204) based
and hence can be set to have the highest signalling speed of 19200 b/s. Due to this high
signalling rate, the difference in operating speed between the direct, permissive and blocking
type signals is so small that the most secure signalling (direct intertrip) can be selected
without any significant loss of speed. In turn, since the direct intertrip signalling requires the
full checking of the message frame structure and CRC checks, it would seem prudent that
the "IM# Fallback Mode" be set to "Default" with a minimal intentional delay by setting "IM#
FrameSyncTim" to 10 msecs. In other words, whenever two consecutive messages have an
invalid structure, the relay will immediately revert to the default value until a new valid
message is received.
For indirect connections, the settings that should be applied will become more application
and communication media dependent. As for the direct connections, it may be appealing to
consider only the fastest baud rate but this will usually increase the cost of the necessary
modem/multiplexer.
In addition, devices operating at these high baud rates may suffer from "data jams" during
periods of interference and in the event of communication interruptions, may require longer
re-synchronization periods.
Both of these factors will reduce the effective communication speed thereby leading to a
recommended baud rate setting of 9600 b/s. It should be noted that as the baud rate
decreases, the communications become more robust with fewer interruptions, but that
overall signalling times will increase.
Since it is likely that slower baud rates will be selected, the choice of signalling mode
becomes significant. However, once the signalling mode has been chosen it is necessary to
consider what should happen during periods of noise when message structure and content
can be lost.
If "Blocking" mode is selected, only a small amount of the total message is actually used to
provide the signal, which means that in a noisy environment there is still a good likelihood of
receiving a valid message. In this case, it is recommended that the "IM# Fallback Mode" is
set to "Default" with a reasonably long "IM# FrameSyncTim".
If "Direct Intertrip" mode is selected, the whole message structure must be valid and checked
to provide the signal, which means that in a very noisy environment the chances of receiving
P44x/EN AP/Hb6
(AP) 5-133