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6.66
SEL-421 Relay
Instruction Manual
Date Code 20171021
Protection Applications Examples
345 kV Tapped Overhead Transmission Line Example
ments cause the relay to trip when the SOTF scheme is active. Assertion of the
protection elements assigned to TRSOTF during the SOTFD time causes the
relay to trip instantaneously.
Apply SOTF when using line-side potentials for relaying. Use nondirectional
overcurrent protection to clear close-in faults. Also use instantaneous overreach-
ing distance protection to clear faults along the line. Assign instantaneous Zone 2
mho phase and ground-distance protection plus Level 1 phase overcurrent ele-
ment to TRSOTF.
TRSOTF :=
Z2P OR Z2G OR 50P1
.
Switch-Onto-Fault Trip (SEL
OGIC
Equa-
tion)
Single-Pole SOTF
This is a three-pole tripping application example; confirm that the SOTF protec-
tion is for three-pole tripping.
ESPSTF :=
N
.
Single-Pole Switch-Onto-Fault (Y, N)
Voltage Reset
You can configure the logic so the SOTF enable duration resets within at least 5
cycles after it first asserted, but before the SOTFD timer expires. To quickly reset
the SOTF period, the relay must sense that the positive-sequence voltage is
greater than the VRSTPU setting times the nominal voltage.
Use setting EVRST (Switch-Onto-Fault Voltage Reset) to enable fast reset. The
advantage of resetting SOTF protection quickly is that unwanted tripping does
not occur for subsequent faults external to the remote terminals during the SOTF
period; these trips can occur if you set instantaneous Zone 2 distance protection
elements in the TRSOTF SEL
OGIC
control equation. Enable the voltage reset
option, and leave VRSTPU = 0.8.
EVRST :=
Y
.
Switch-Onto-Fault Voltage Reset (Y, N)
SOTF Initiation
The SOTF logic asserts via one or both of the following methods:
➤
A change in the normally open auxiliary contact 52A status showing
that the circuit breaker has just opened
➤
Assertion of the relay control input assigned to the circuit breaker
close bus
The 52A method works well for both single and multiple circuit breaker applica-
tions and does not require an input from the close bus. However, the close bus
method only enables SOTF protection immediately following the close command
to the circuit breaker. For more information, see
.
Turn off 52AEND, 52A Pole-Open Time Delay, because the 52A method is not
used.
52AEND :=
OFF
.
52A Pole-Open Time Delay (OFF, 0.000–16000 cycles)
Select the close bus option for this application and set the close enable delay
(CLOEND) shorter than the shortest reclose open interval.
CLOEND :=
10.000
.
CLSMON or Single-Pole Open Delay
(OFF, 0.000–16000 cycles)
Содержание SEL-421-4
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