R.1.107
Date Code 20111215 Reference Manual SEL-421 Relay
Protection Functions
Trip Logic
ULTR
Use ULTR, the unlatch trip SELOGIC 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
outputs. The trip output occurs for the TDURD time or the duration of the trip
condition, 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
following 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 R.2.26. This section describes the E3PT, E3PT1,
and E3PT2 settings necessary for auto-reclose 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.
If an external reclosing relay is being used, control signals from the reclosing
relay will typically be used to control the SEL-421 single- and three-pole
tripping sequence. Another method is to use the TOP (Trip during Open-Pole)
Relay Word bit to select a three-pole trip after a single-pole trip in the
SEL-421 by making an appropriate setting for TOPD (Trip during Open-Pole
Time Delay), and then including the TOP Relay Word bit in the E3PT
Table 1.71 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 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.
To Next Page
Loading...
