Schweitzer Engineering Laboratories SEL-351A, Manual

Page: 221 / 666

6.23
Date Code 20080213
Instruction Manual SEL-351A Relay
Close and Reclose Logic
Reclosing Relay
Skip Shot and Stall
Open Interval Timing
Settings (79SKP and
79STL, respectively)
The skip shot setting 79SKP causes a reclose shot to be skipped. Thus, an
open interval time is skipped, and the next open interval time is used instead.
If 79SKP = logical 1 at the instant of successful reclose initiation (see
preceding discussion on settings 79RI and 79RIS), the relay increments the
shot counter to the next shot and then loads the open interval time
corresponding to the new shot (see
Table 6.3 ). If the new shot is the “last
shot,” no open interval timing takes place, and the relay goes to the Lockout
State if the circuit breaker is open (see
Lockout State on page 6.13 ).
After successful reclose initiation, open interval timing does not start until
allowed by the stall open interval timing setting 79STL. If 79STL = logical 1,
open interval timing is stalled. If 79STL = logical 0, open interval timing can
proceed.
If an open interval time has not yet started timing (79STL = logical 1 still), the
79SKP setting is still processed. In such conditions (open interval timing has
not yet started timing), if 79SKP = logical 1, the relay increments the shot
counter to the next shot and then loads the open interval time corresponding to
the new shot (see
Table 6.3 ). If the new shot turns out to be the “last shot,” no
open interval timing takes place, and the relay goes to the Lockout State if the
circuit breaker is open (see
Lockout State ).
If the relay is in the middle of timing on an open interval and 79STL changes
state to 79STL = logical 1, open interval timing stops where it is. If 79STL
changes state back to 79STL = logical 0, open interval timing resumes where
it left off. Use the OPTMN Relay Word bit to monitor open interval timing
(see
Monitoring Open Interval and Reset Timing on page 6.17 ).
Factory Settings Example
The skip shot function is not enabled in the factory settings:
79SKP =
0
(numeral 0)
The stall open interval timing factory setting is:
79STL =
TRIP
After successful reclose initiation, open interval timing does not start as long
as the trip condition is present (Relay Word bit TRIP = logical 1). As
discussed previously, if an open interval time has not yet started timing
(79STL = logical 1 still), the 79SKP setting is still processed. Once the trip
condition goes away (Relay Word bit TRIP = logical 0), open interval timing
can proceed.
Additional Settings Example 1
With skip shot setting:
79SKP =
50P2 * SH0
if shot = 0 (Relay Word bit SH0 = logical 1) and phase current is above the
phase instantaneous overcurrent element 50P2 threshold (Relay Word bit
50P2 = logical 1), at the instant of successful reclose initiation, the shot
counter is incremented from shot = 0 to shot = 1. Then, open interval 1 time
(setting 79OI1) is skipped, and the relay times on the open interval 2 time
(setting 79OI2) instead.
Courtesy of NationalSwitchgear.com