6.41
Date Code 20171021 Instruction Manual SEL-421 Relay
Protection Applications Examples
500 kV Parallel Transmission Lines With Mutual Coupling Example
DTA := RMB3A. Direct Transfer Trip A-Phase (SELOGIC Equation)
DTB := RMB4A. Direct Transfer Trip B-Phase (SELOGIC Equation)
DTC := RMB5A. Direct Transfer Trip C-Phase (SELOGIC Equation)
Trip Unlatch Options
Unlatch the control output programmed for tripping after the circuit breaker aux-
iliary a contacts break the dc current. The SEL-421 provides three methods for
unlatching control outputs programmed for tripping after occurrence of a protec-
tion trip:
➤ ULTR—following a protection trip, all three poles
➤ TOPD—Unlatch single-pole trip if another protection trip occurs
during single-pole dead time
➤ TULO—following a protection trip, phase selective
ULTR
Use ULTR, the unlatch trip SELOGIC control equation, to unlatch all three poles.
Use the default setting, to assert ULTR when you push the front-panel TARGET
RESET pushbutton.
ULTR := TRGTR. Unlatch Trip (SELOGIC Equation)
TOPD
It is common practice to trip the two remaining phases after the single-pole open
dead time, or if the single-pole autoreclose cycle does not reset, following the
original single-pole trip. If the SEL-421 internal reclosing relay is being used, the
E3PT, E3PT1, and E3PT2 settings in the trip logic should be set as shown in
Internal Recloser on page 6.9 and Internal Recloser on page 6.25 in the SEL-400
Series Relays Instruction Manual. See Autoreclose Example on page 6.137 for
information on using the SEL-421 reclosing relay.
To illustrate another way of using an external reclosing relay, this example will
not use the SEL-421 Relay’s autoreclose logic, rather, it uses the TOP (Trip
During Open Pole) Relay Word bit to control the trip logic.
The timer setting TOPD determines the length of time for converting any subse-
quent single-pole trips to a three-pole trip following the original single-pole trip.
Set this timer to the single-pole open dead time (30 cycles) and the reset time
(three seconds) for the recloser plus a 5-cycle safety margin. See Trip During
Open-Pole Time Delay on page 5.139 in this manual and External Recloser on
page 6.10 and External Recloser on page 6.26 in the SEL-400 Series Relays
Instruction Manual for additional information.
TOPD := 215.00. Trip During Open Pole Time Delay (2.000–8000 cycles)
TULO
Use TULO (Trip Unlatch Option) to select the conditions that cause the SEL-421
to unlatch the control outputs that you programmed for tripping. You can select
from among the four trip unlatch options in Table 6.12.
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