7 APPLICATION NOTESElectrical InterMiCOM settings are contained within two columns; INTERMICOM COMMS and INTERMICOM CONF.The INTERMICOM COMMS column contains all the settings needed to configure the communications, as well as thechannel statistics and diagnostic facilities. The INTERMICOM CONF column sets the mode of each command signaland defines how they operate in case of signalling failure.Short metallic direct connections and connections using fire-optic converters will generally be set to have thehighest signalling speed of 19200b/s. Due to this high signalling rate, the difference in operating time between thedirect, permissive, and blocking type signals is small. This means you can select the most secure signallingcommand type (‘Direct’ intertrip) for all commands. You do this with the IM# Cmd Type settings. For theseapplications you should set the IM# Fallback Mode to Default. You should also set a minimal intentional delayby setting IM# FrameSyncTim to 10 msecs. This ensures that whenever two consecutive corrupt messages arereceived, the command will immediately revert to the default value until a new valid message is received.For applications that use Modem and/or multiplexed connections, the trade-off between speed, security, anddependability is more critical. Choosing the fastest baud rate (data rate) to achieve maximum speed may appearattractive, but this is likely to increase the cost of the telecommunications equipment. Also, telecommunicationservices operating at high data rates are more prone to interference and suffer from longer re-synchronisationtimes following periods of disruption. Taking into account these factors we recommend a maximum baud ratesetting of 9600 bps. As baud rates decrease, communications become more robust with fewer interruptions, butoverall signalling times increase.At slower baud rates, the choice of signalling mode becomes significant. You should also consider what happensduring periods of noise when message structure and content can be lost.● In ‘Blocking’ mode, the likelihood of receiving a command in a noisy environment is high. In this case, werecommend you set IM# Fallback Mode to Default, with a reasonably long IM# FrameSyncTim setting.Set IM# DefaultValue to ‘1’. This provides a substitute for a received blocking signal, applying a failsafe forblocking schemes.● In ‘Direct’ mode, the likelihood of receiving commands in a noisy environment is small. In this case, werecommend you set IM# Fallback Mode to Default with a short IM# FrameSyncTim setting. Set IM#DefaultValue to ‘0’. This means that if a corrupt message is received, InterMiCOM will use the default value.This provides a substitute for the intertrip signal not being received, applying a failsafe for directintertripping schemes.● In ‘Permissive’ mode, the likelihood of receiving a valid command under noisy communications conditions issomwhere between that of the ‘Blocking’ mode and the ‘Direct’ intertrip mode. In this case, werecommended you set IM# Fallback Mode to Latched.The table below presents recommended IM# FrameSyncTim settings for the different signalling modes and baudrates:Minimum Recommended "IM# FrameSyncTim" SettingBaud Rate Direct Intertrip Mode Blocking Mode Minimum Setting(ms)Maximum Setting(ms)600 100 250 100 15001200 50 130 50 15002400 30 70 30 15004800 20 40 20 15009600 10 20 10 150019200 10 10 10 1500Chapter 17 - Electrical Teleprotection P14x378 P14xEd1-TM-EN-1
