Alstom MiCOM P54 Series - 1.23.6 Distance scheme BLOCKING (Distance option only)

Operation P54x/EN OP/La4
MiCOM P543, P544, P545 & P546 (OP) 5-67
OP
System condition
Permissive
channel
received
Loss of guard
Permissive
trip allowed
Alarm
generated
Healthy Line No No No No
Internal Line Fault Yes Yes Yes No
Unblock No Yes
Yes, during a
150 ms window
Yes, delayed on
pickup by 150 ms
Signaling Anomaly Yes No No
Yes, delayed on
pickup by 150 ms
The window of time during which the unblocking logic is enabled starts 10 ms after the guard
signal is lost, and continues for 150 ms. The 10 ms delay gives time for the signaling
equipment to change frequency as in normal operation. For the duration of any alarm
condition, zone 1 extension logic will be invoked if the option Z1 Ext on Chan. Fail has been
Enabled.
1.23.6 Distance scheme BLOCKING (Distance option only)
The si
gnaling channel is keyed from operation of the reverse zone 4 elements of the relay. If
the remote relay has picked up in zone 2, then it will operate after the trip delay if no block is
received. Listed below are some of the main features/requirements for a BLOCKING
scheme:
 BLOCKING schemes require only a simplex signaling channel
 Reverse looking Zone 4 is used to send a blocking signal to the remote end to prevent
unwanted tripping
 When a simplex channel is used, a BLOCKING scheme can easily be applied to a
 multi-terminal line provided that outfeed does not occur for any internal faults
 The blocking signal is transmitted over a healthy line, and so there are no problems
associated with power line carrier signaling equipment
 BLOCKING schemes provides similar resistive coverage to the permissive overreach
schemes
 Fast tripping will occur at a strong source line end, for faults along the protected line
section, even if there is weak or zero infeed at the other end of the protected line
 If a line terminal is open, fast tripping will still occur for faults along the whole of the
protected line length
 If the signaling channel fails to send a blocking signal during a fault, fast tripping will
occur for faults along the whole of the protected line, but also for some faults within the
next line section
 If the signaling channel is taken out of service, the relay will operate in the conventional
basic mode
 A current reversal guard timer is included in the signal send logic to prevent unwanted
trips of the relay on the healthy circuit, during current reversal situations on a parallel
circuit
Figure 40 shows the simplified scheme logic.
Send logi
c: Reverse Zone 4
Trip logic: Zone 2, plus Channel NOT Received, delayed by Tp