Schweitzer Engineering Laboratories SEL-421-4 - Table 5.70 DCB Settings; Table 5.71 DCB Relay Word Bits

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 SELOGIC control
equation BT as follows:
BT := IN105 OR IN106. Block Trip Received (SELOGIC 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. Figure 5.92 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 (SELOGIC 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
Ta b l e 5 .7 1 DC B R e l ay Wo r d B i ts
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