P74x/EN OP/N
(OP) 5-
The requirements for the three channel types are represented pictorially in the following
figure:
FIGURE 15: PICTORIAL COMPARISON OF OPERATING MODES
This diagram shows that a blocking signal should be fast and dependable; a direct intertrip
signal should be very secure and a permissive signal is an intermediate compromise of
speed, security and dependability. In MODEM applications, all three modes can be applied
to selected signaling bits within each message.
When InterMiCOM
64
is used for teleprotection, only two modes are available: Direct trip and
Permissive. Since the full and uncorrupted message has to be received by the relay over
fiber, there would be no difference between received Blocking, Permissive and Direct
commands in terms of speed, dependability or security, were just one message used. The
only difference would be the need for extra security when Intertripping is required and for
that reason a Direct trip command will be considered valid and executed only after 2
consecutive received commands (two consecutive messages in agreement instead of just
one).
1.5.7 EIA(RS)232 InterMiCOM (“MODEM InterMiCOM”)
1.5.7.1 Communications media
InterMiCOM is capable of transferring up to 8 commands over one communication channel.
Due to recent expansions in communication networks, most signaling channels are now
digital schemes utilizing multiplexed fiber optics and for this reason, InterMiCOM provides a
standard EIA(RS)232 output using digital signaling techniques. This digital signal can then
be converted using suitable devices to any communications media as required. The
EIA(RS)232 output may alternatively be connected to a MODEM link.
Regardless of whether analog or digital systems are being used, all the requirements of
teleprotection commands are governed by an international standard IEC60834-1:1999 and
InterMiCOM is compliant with the essential requirements of this standard. This standard
governs the speed requirements of the commands as well as the probability of unwanted
commands being received (security) and the probability of missing commands
(dependability).
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