Alstom MiCOM P546 - 1.23.8 Permissive overreach schemes current reversal guard (Distance option only); 1.23.9 Blocking scheme 1 and 2 current reversal guard (Distance option only)

Operation P54x/EN OP/La4
MiCOM P543, P544, P545 & P546 (OP) 5-69
OP
A
L1
B
Fault
C
L2
D
Strong
source
Weak
source
t2(C)
A
L1
B
Fault
C
L2
D
t2(D)
Note how after circuit breaker B on line L1 opens
the direction of current flow in line L2 is reversed.
P1157ENa
P1134ENa
Figure 41 Example of fault current reverse of direction
1.23.8 Permissive overreach schemes current reversal guard (Distance option only)
The
current reversal guard incorporated in the POR scheme logic is initiated when the
reverse looking Zone 4 elements operate on a healthy line. Once the reverse looking Zone 4
elements have operated, the relay’s permissive trip logic and signal send logic are inhibited
at substation D. The reset of the current reversal guard timer is initiated when the reverse
looking Zone 4 resets. A time delay tREVERSAL GUARD is required in case the
overreaching trip element at end D operates before the signal send from the relay at end C
has reset. Otherwise this would cause the relay at D to over trip. Permissive tripping for the
relays at D and C substations is enabled again, once the faulted line is isolated and the
current reversal guard time has expired.
1.23.9 Blocking scheme 1 and 2 current reversal guard (Distance option only)
The
current reversal guard incorporated in the BLOCKING scheme logic is initiated when a
blocking element picks-up to inhibit the channel-aided trip. When the current reverses and
the reverse looking Zone 4 elements reset, the blocking signal is maintained by the timer
tREVERSAL GUARD. Therefore, the relays in the healthy line are prevented from over
tripping due to the sequential opening of the circuit breakers in the faulted line. After the
faulted line is isolated, the reverse-looking Zone 4 elements at substation C and the forward
looking elements at substation D will reset.
Two variants of Blocking scheme exist, BLOCKING 1, and BLOCKING 2. The only
difference in functionality is:
 BLOCKING 1 - The Reversal Guard is applied to the Signal Send
 BLOCKING 2 - The Reversal Guard is applied to the Signal Receive
The difference in the receive logic is shown in Logic Diagrams, Figure 42 and Figure 43
belo
w:
1
DDB: CTx (498,514)
DDB: CRx Int (494,508)
1
DDB: COS/LGS Alarm (492,506)
DDB: Aided Trip En (501,517)
P1584ENc
Figure 42 Blocking 1 (Distance option only)