4.149
Date Code 20170927 Instruction Manual SEL-751 Relay
Protection and Logic Functions
Group Settings (SET Command)
Other Settings Considerations
If no special skip shot or stall open interval timing conditions are desired,
make the following settings:
79SKP := 0 (numeral 0)
79STL := 0 (numeral 0)
Block Reset Timing Setting (79BRS)
The block reset timing setting 79BRS keeps the reset timer from timing.
Depending on the reclosing relay state, the reset timer can be loaded with
either reset time:
79RSD (Reset Time from Reclose Cycle)
or
79RSLD (Reset Time from Lockout)
Depending on how setting 79BRS is set, none, one, or both of these reset
times can be controlled. If the reset timer is timing and then 79BRS asserts to:
79BRS = logical 1
reset timing is stopped and does not begin timing again until 79BRS deasserts
to:
79BRS = logical 0
When reset timing starts again, the reset timer is fully loaded. Thus, successful
reset timing has to be continuous. Use the RSTMN Relay Word bit to monitor
reset timing (see Monitoring Open Interval and Reset Timing on page 4.143).
EXAMPLE 4.27 Factory Settings Example
The reset timing is blocked if Relay Word bit TRIP is asserted, regardless of
the reclosing relay state:
79BRS := TRIP
EXAMPLE 4.28 Additional Settings Example 1
The block reset timing setting is:
79BRS := (51P1P OR 51G1P) AND 79CY
Relay Word bit 79CY corresponds to the reclose cycle state. The reclosing
relay is in one of the three reclosing relay states at any one time (see
Figure 4.84 and Table 4.53).
When the relay is in the reset or lockout states, Relay Word bit 79CY is
deasserted to logical 0. Thus, the 79BRS setting has no effect when the
relay is in the reset or lockout states. When a circuit breaker is closed from
lockout, there could be cold load inrush current that momentarily picks up a
time-overcurrent element [e.g., phase time-overcurrent element 51P1 pickup
(51P1P) asserts momentarily]. But, this assertion has no effect on reset
timing because the relay is in the lockout state (79CY = logical 0). The relay
times immediately on reset time 79RSLD and takes the relay from the
lockout state to the Reset State with no additional delay because 79BRS is
deasserted to logical 0.
When the relay is in the Reclose Cycle State, Relay Word bit 79CY is
asserted to logical 1. Thus, the example 79BRS setting can function to block
reset timing if time-overcurrent pickup 51P1P or 51G1P is picked up while the
relay is in the Reclose Cycle State. This helps prevent repetitive “trip-
reclose” cycling.
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