Sel 411L - Directional Comparison Unblocking Scheme Logic; Figure 3.153 POTT Cross-Country Logic Diagram

P.3.232
SEL-411L Relay Protection Manual Date Code 20151029
Protection Functions
Directional Comparison Unblocking Scheme Logic
Figure 3.153 POTT Cross-Country Logic Diagram
Directional Comparison Unblocking Scheme Logic
The directional comparison unblocking (DCUB) tripping scheme in the relay
provides a good combination of security and reliability, even when a
communications channel is less than perfect. Communications channel
failures are unlikely to occur during external faults. You can use the DCUB
trip scheme with conventional communications channels such as PLC (power
line carrier). Use improved methods such as M
IRRORED BITS communications
to implement the DCUB tripping scheme efficiently and economically.
M
IRRORED BITS communications and the DCUB tripping scheme give secure,
high-speed operation.
Through a control input programmed to the LOG (loss-of-guard) function, the
relay monitors the LOG output from the communications receiver. If LOG
asserts, and no trip permission is received, the relay can high-speed trip during
a short window using selected overreaching elements. The relay then asserts
permissive trip blocking signal UBB and locks out permissive trip Relay Word
bit PTRX. The typical DCUB application is a POTT scheme with the addition
of a frequency shift-keying (FSK) carrier as the communications medium.
Enable the DCUB logic by setting ECOMM to DCUB1 or DCUB2. You must
provide the relay all POTT settings plus the settings exclusive to the DCUB
scheme. The following is an explanation of the differences between setting
choices DCUB1 and DCUB2:
➤ DCUB1—directional comparison unblocking scheme for two-
terminal lines (i.e., communication from one remote terminal)
➤ DCUB2—directional comparison unblocking scheme for
three-terminal lines (i.e., communication from two remote
terminals)
The DCUB logic takes the loss-of-guard and permissive trip outputs from the
communications receivers and makes permissive trip (PTRX1 and PTRX2)
outputs and permissive trip (unblock) blocking (UBB1 and UBB2) outputs.
0
2
CYC
0
EDURD
ETDPU
0
KEY3
KEY1
Reset
3PT
Z2P
Z3RB
Z2G
APS
BPS
CPS
PT3
PT1
SPO
Relay
Word
Bits
Relay
Word
Bits