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6.42
SEL-421 Relay
Instruction Manual
Date Code 20171021
Protection Applications Examples
500 kV Parallel Transmission Lines With Mutual Coupling Example
Select the third option if a 52A contact is available because the relay uses both
open-phase detection and status information from the circuit breaker(s). For
information on the pole-open logic, see
Switch-Onto-Fault Logic on page 5.117
.
TULO :=
3
.
Trip Unlatch Option (1, 2, 3, 4)
Single-Pole Trip Options
You can program the SEL-421 to single-pole trip for Zone 2 ground-distance
operations. Employ this method if you want single-pole tripping during ground
faults within the last 20 percent of the protected line when the communications
channel is not available. Do not enable this option.
Z2GTSP :=
N
.
Zone 2 Ground-Distance Time Delay SPT (Y, N)
The SEL-421 can assert a single-pole trip during high resistance ground faults
such that the fault impedance lies outside of the ground-distance protection char-
acteristics; the FIDS logic selects the faulted phase when residual directional
overcurrent elements provide communications-assisted tripping. Do not enable
this option.
67QGSP :=
N
.
Zone 2 Dir. Negative-Sequence/Residual Ground Overcurrent
SPT (Y, N)
Trip Timers
The SEL-421 provides dedicated timers for minimum trip durations and open-
pole time delays.
Minimum Trip Duration
The minimum trip duration timer settings, TDUR1D and TDUR3D, determine
the minimum length of time that Relay Word bits TPA1, TPA2, TPB1, TPB2,
TPC1, TPC2, and 3PT assert. Use these timers to control the designated trip con-
trol outputs. The control outputs programmed for tripping close for the greater of
the TDUR
n
D time, or the duration of the trip condition.
TDUR1D is the minimum trip duration following a single-pole trip. TDUR3D is
the minimum trip duration following a three-pole trip. If another trip occurs
during the single-pole open dead time following a single-pole trip, TDUR3D
replaces TDUR1D.
A typical setting for both of these timers is 9 cycles.
TDUR1D :=
9.000
.
SPT Min Trip Duration Time Delay (2.000–8000 cycles)
TDUR3D :=
9.000
.
3PT Min Trip Duration Time Delay (2.000–8000 cycles)
Table 6.12
Trip Unlatch Options
Option
Description
1
Unlatch the trip when the relay has detected that one or more poles of the
line terminal are open, and Relay Word bit 3PT has deasserted.
2
Unlatch the trip when the relay has detected that the corresponding 52A
contact(s) from both circuit breakers (e.g., 52AA1 and 52AA2) are deas-
serted.
3
Unlatch the trip when the relay has detected that the conditions for the first
two options are satisfied.
4
Do not run this logic.
Summary of Contents for SEL-421-4
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