Schweitzer Engineering Laboratories SEL-421-4 - Table 6.20 Setting TULO Unlatch Trip Options

6.81
Date Code 20171021 Instruction Manual SEL-421 Relay
Protection Applications Examples
345 kV Tapped Overhead Transmission Line Example
Level 2 negative-sequence residual ground directional overcurrent element
(67QGS2) in the TRCOMM SEL
OGIC control equation. See Directional Com-
parison Blocking Scheme on page 5.121 for more information.
TRCOMM := Z2PGS OR 67QG2S. Communications-Assisted Trip
(SEL
OGIC Equation)
TRSOFT
The TRSOTF SELOGIC control equation defines which protection elements cause
the relay to trip when the SOTF scheme is active. Assertion of these protection
elements during the SOTFD time causes the relay to trip instantaneously (see
SOTF Scheme on page 6.8). Set instantaneous Zone 2 distance protection (Z2P
and Z2G) and Level 1 phase instantaneous overcurrent element (50P1) in the
TRSOTF SEL
OGIC control equation.
TRSOTF := Z2P OR Z2G OR 50P1. Switch-Onto-Fault Trip (SELOGIC Equation)
Trip Unlatch Options
Unlatch the control output you programmed for tripping (OUT101) after the cir-
cuit breaker auxiliary “a” contacts break the dc current. The SEL-421 provides
two methods for unlatching control outputs following a protection trip:
➤ ULTR—all three poles
➤ TULO—phase selective
ULTR
Use ULTR, the Unlatch Trip SELOGIC control equation, to unlatch all three
poles. Use the default setting, which asserts ULTR when you push the front-panel
target reset button.
ULTR := TRGTR. Unlatch Trip (SELOGIC Equation)
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. Table 6.20
shows the four trip unlatch options for setting TULO.
Select Option 3 because a 52A contact is available; the relay uses both open-
phase detection and status information from the circuit breaker to make the most
secure decision. For information on the pole-open logic, see Pole-Open Logic on
page 5.25.
TULO := 3. Trip Unlatch Option (1, 2, 3, 4)
Table 6.20 Setting TULO Unlatch Trip Options
Option Description
1 Unlatch the trip when the relay detects that one or more poles of the line termi-
nal are open and Relay Word bit 3PT has deasserted.
2 Unlatch the trip when the relay detects that the corresponding 52A contact(s)
from both circuit breakers (e.g., 52AA1 and 52AA2) are deasserted.
3 Unlatch the trip when the relay detects that the conditions for Options 1 and 2
are satisfied.
4 Do not run this logic.