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5.139
Date Code 20171021
Instruction Manual
SEL-421 Relay
Protection Functions
Trip Logic
TULO
shows the four trip unlatch options for setting TULO.
ULTR
Use ULTR, the unlatch trip SEL
OGIC
control equation, to define the conditions
that unlatch the trip contact outputs. This method always unlatches all three
poles.
Timers
The SEL-421 provides dedicated timers (minimum trip duration, trip during open
pole, etc.) for the trip logic.
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 for the designated trip control out-
puts. The trip output occurs for the TDURD time or the duration of the trip condi-
tion, whichever is greater.
TDUR1D is the minimum trip duration time following a single-pole trip.
TDUR3D is the minimum trip duration time following a three-pole trip. If
another trip occurs during the single-pole open dead time following a single-pole
trip, TDUR3D replaces TDUR1D.
Trip During Open-Pole Time Delay
If another fault occurs, it is common to trip the two remaining phases for the fol-
lowing two periods:
➤
During the single-pole-open interval following the original single-
pole trip.
➤
During the reclosing relay reclaim (reset) time state following a
single-pole reclose.
To use the reclosing relay in the SEL-421 to reclose the breaker(s), see
Internal Recloser on page 6.25 in the SEL-400 Series
Relays Instruction Manual
. This section describes the E3PT, E3PT1, and E3PT2
settings necessary for autoreclose logic control of the single-pole and three-pole
tripping sequence. The TOPD (Trip during Open-Pole Time Delay) setting has no
relevance in this situation.
Table 5.77
Setting TULO Unlatch Trip Options
Option
Description
1
Unlatch the trip when the relay detects that one or more poles of the line terminal
are open and the 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.
Summary of Contents for SEL-421-4
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