4.70
SEL-751A Relay Instruction Manual Date Code 20100129
Protection and Logic Functions
Reclose Logic
EXAMPLE 4.11 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.
EXAMPLE 4.12 Additional Settings Example 1
With skip shot setting:
79SKP := 50P2P AND 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 50P2P = 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.
In Tab le 4.2 9, note that the open interval 1 time (setting 79OI1) is a
short time, while the following open interval 2 time (setting 79OI2) is
significantly longer. For a high magnitude fault (greater than the
phase instantaneous overcurrent element 50P2 threshold), open
interval 1 time is skipped, and open interval timing proceeds on the
following open interval 2 time.
Once the shot is incremented to shot = 1, Relay Word bit SH0 = logical
0 and then setting 79SKP = logical 0, regardless of Relay Word bit
50P2P.
EXAMPLE 4.13 Additional Settings Example 2
If the SEL-751A Relay is used on a feeder with a line-side independent
power producer (cogenerator), the utility should not reclose into a
line still energized by an islanded generator. To monitor line voltage
and block reclosing, connect a line-side single-phase potential
transformer to channel VS on the SEL-751A as shown in Figure 4.36.
Table 4.29 Open Interval Time Example Settings
Shot
Corresponding
Relay Word Bit
Corresponding
Open Interval
Open Interval Time
Example Setting
(seconds
)
0 SH0 79OI1 0.50
1 SH1 79OI2 10
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