Schweitzer Engineering Laboratories SEL-751 - Table 4.56 Open Interval Time Example Settings; Figure 4.86 Reclose Blocking for Islanded Generator

4.148
SEL-751 Relay Instruction Manual Date Code 20170927
Protection and Logic Functions
Group Settings (SET Command)
EXAMPLE 4.24 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 greater than
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 Table 4.56, 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 4.25 Additional Settings Example 2
If you use the SEL-751 Relay 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-751 as shown in Figure 4.86.
Figure 4.86 Reclose Blocking for Islanded Generator
If the line is energized, channel VS overvoltage element 59S1 can be
set to assert. Make the following setting:
79STL := 59S1 OR
…
If line voltage is present, Relay Word bit 59S1 asserts, stalling open interval
timing (reclose block). If line voltage is not present, Relay Word bit 59S1
deasserts, allowing open interval timing to proceed (unless some other set
condition stalls open interval timing).
EXAMPLE 4.26 Additional Settings Example 3
Refer to Figure 4.83 and accompanying setting example, showing an
application for setting 79STL.
Table 4.56 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
SEL-751
Bus 1
52
IA, IB, IC
VA, VB, VC VS
3-Phase
1-Phase
Generator