Areva MiCOM P441, Technical Manual

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P44x/EN AP/E33 Application Notes
Page 50/220 MiCOM P441/P442 & P444
Two types of carrier received signals are used:
•
Carrier received (INP_CR - binary input)
•
Carrier Out of Service (INP_COS - binary input for distance logic) and
(INP_COS_DEF - binary input for DEF logic)
2.9.4.1 None
The status of opto is copied directly :
UNB_ALARM = I INP_COS_DEF
UNB_CR = INP_CR
UNB_CR_DEF = INP_CR_DEF
2.9.4.2 Loss of Guard Mode
This mode is designed for use with frequency shift keyed (FSK) power line carrier
communications. When the protected line is healthy a guard frequency is sent between line
ends, to verify that the channel is in service. However, when a line fault occurs and a
permissive trip signal must be sent over the line, the power line carrier frequency is shifted to
a new (trip) frequency. Thus, distance relays should receive either the guard, or trip
frequency, but not both together. With any permissive scheme, the PLC communications
are transmitted over the power line which may contain a fault. So, for certain fault types the
line fault can attenuate the PLC signals, so that the permissive signal is lost and not received
at the other line end. To overcome this problem, when the guard is lost and no “trip”
frequency is received, the relay opens a window of time during which the permissive scheme
logic acts as though a “trip” signal had been received. Two opto inputs to the relay need to
be assigned, one is the Channel Receive opto, the second is designated Loss of Guard (the
inverse function to guard received). The function logic is summarised in Table 3.