Sel SEL-421 - Stopping Elements; Three-Terminal Line; DCB Settings; DCB Relay Word Bits

R.1.90
SEL-421 Relay Reference Manual Date Code 20111215
Protection Functions
Directional Comparison Blocking Scheme
Timer BTXD (Block Trip Extension) delays dropout of the control input
assigned to Relay Word bit BT so that unwanted tripping does not occur
during momentary lapses of the blocking signal (carrier holes). This timer
maintains the blocking signal at the receiving relay by delaying the dropout of
Relay Word bit BT.
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
elements; however, directional starting elements must have priority over the
stopping elements. Figure 1.61 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 starting elements:
OUT101 := NSTRT AND NOT STOP OR DSTRT Output (SELOGIC Equation)
Table 1.64 DCB Settings
Setting Description 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
Tabl e 1 . 65 DCB Re lay Wo rd B it s
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