x/EN AP/Na7
-18 MiCOM P74
In this example a setting of 1305 A can be used for both phase and earth faults.
2.2.7 Setting guidelines
A spreadsheet tool called “FastExtThreshold” is available on request.
This feature has to be used when secondary maximum current is over 50A (IN = 1A) or 250A
(IN=5A) or the CT does not meet the CT requirements and if the maximum feeder
contribution is far less than the maximum external fault.
For each PU connected to a Circuit Breaker
2.2.7.1 CT features:
Only 5 values have to be known and entered:
1. Phase CT Primary current given by the manufacturer.
2. Phase CT secondary current (1 or 5 A) given by the manufacturer.
3. CT secondary resistance given by the manufacturer.
4. Secondary burdens to be measured.
5. Knee point Voltage (or Rated Burden and KSCC) given by the manufacturer.
2.2.7.2 Sub-station features
1. Maximum feeder load
2. Feeder contribution to internal fault
2.2.7.3 Please use FastExtThreshold Setting calculation spreadsheet
Put for I>2 the recommended value.
2.2.8 EIA(RS)232 InterMiCOM (“MODEM InterMiCOM”)
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 settings required for the InterMiCOM signaling 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 based and hence can
be set to have the highest signaling speed of 19200b/s. Due to this high signaling rate, the
difference in operating speed between the direct, permissive and blocking type signals is so
small that the most secure signaling (direct intertrip) can be selected without any significant
loss of speed. In turn, since the direct intertrip signaling 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
10msecs. 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 9.6 kbit/s. It
should be noted that as the baud rate decreases, the communications become more robust
with fewer interruptions, but that overall signaling times will increase.
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