3.33
Date Code 20110408 Instruction Manual SEL-551 Relay
Relay Elements and Logic
Reclosing Relay
When reset timing starts again, it will be with a fully-loaded reset time. Thus,
successful reset timing has to be continuous.
Factory Settings Example
The block reset timing setting is:
79BRS = (51P1 + 51G1) * (79RS + 79CY)
Relay Word bits 79RS and 79CY correspond to the Reset State and the
Reclose Cycle State, respectively. The reclosing relay is in one and only one
of the three reclosing relay states at any one time (see Figure 3.15 and
Table 3.5).
When the relay is in the Lockout State, Relay Word bits 79RS and 79CY are
deasserted to logical 0. Thus, the factory 79BRS setting has no effect when the
relay is in the Lockout State. When a circuit breaker is closed from lockout,
there is usually cold load inrush that would momentarily pick up a time-
overcurrent element [e.g., phase time-overcurrent element 51P1T pickup
(51P1) asserts momentarily]. But, this assertion of pickup 51P1 has no effect
on reset timing because the relay is in the Lockout State (79RS = logical 0,
79CY = logical 0). The relay will time immediately on reset time 79RSLD
and take 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 not in the Lockout State, either Relay Word bit 79RS or
79CY is asserted to logical 1. Thus, the factory 79BRS setting can function to
block reset timing if time-overcurrent pickup 51P1 or 51G1 is picked up. This
helps prevent repetitive “trip-reclose” cycling.
Additional Settings Example 1
The block reset timing setting can be set as:
79BRS = (51P1 + 51G1) * 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 3.15 and Table 3.5).
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 51P1T pickup
(51P1) asserts momentarily]. But, this assertion of pickup 51P1 has no effect
on reset timing because the relay is in the Lockout State (79CY = logical 0).
The relay will time immediately on reset time 79RSLD and take 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 factory 79BRS setting can function to block reset
timing if time-overcurrent pickup 51P1 or 51G1 is picked up while the relay is
in the Reclose Cycle State. This helps prevent repetitive “trip-reclose” cycling.
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