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5.123
Date Code 20171021
Instruction Manual
SEL-421 Relay
Protection Functions
Directional Comparison Blocking Scheme
Three-Terminal Line
If you apply the DCB scheme to a three-terminal line, program SEL
OGIC
control
equation BT as follows:
BT :=
IN105 OR IN106
.
Block Trip Received (SEL
OGIC
Equation)
Relay inputs IN105 or IN106 assert when the relay receives a blocking signal
from either of the two other terminals. The relay cannot high-speed trip if either
control input asserts. These two control inputs were chosen for this particular
example. Use appropriate control inputs for your application.
Stopping Elements
Zone 2 distance and Level 2 directional overcurrent elements detect that the fault
is in the tripping direction and stop the starting elements from transmitting the
blocking signal to the remote terminal. Program an output contact to stop carrier
by energizing an input of the communications equipment transmitter.
The stopping elements must have priority over the nondirectional starting ele-
ments; however, directional starting elements must have priority over the stop-
ping elements.
shows that the directional starting elements have
internal priority over the stopping elements. Use SEL
OGIC
control equations to
make sure that the stopping elements have priority over the nondirectional start-
ing elements:
OUT101 :=
NSTRT AND NOT STOP OR DSTRT
.
Output (SEL
OGIC
Equation)
Table 5.70
DCB Settings
Setting
Prompt
Range
Default
(5 A)
Z3XPU
Zone 3 Reverse Pickup Delay (cycles)
0.000–16000
1.000
Z3XD
Zone 3 Reverse Dropout Time Delay (cycles)
0.000–16000
6.000
BTXD
Block Trip Receive Extension Time (cycles)
0.000–16000
1.000
21SD
Zone 2 Distance Short Delay (cycles)
0.000–16000
2.000
67SD
Level 2 Overcurrent Short Delay (cycles)
0.000–16000
2.000
BT
Block Trip Received
SEL
OGIC
Equation
NA
Table 5.71
DCB Relay Word Bits
Name
Description
Z3XT
Current reversal guard timer
Z2PGS
Zone 2 phase and ground short delay element
67QG2S
Negative-sequence and residual directional overcurrent short delay element
DSTRT
Directional start element
NSTRT
Nondirectional start element
STOP
Stop element
BTX
Blocking signal extended
Summary of Contents for SEL-421-4
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