Sel 551 - Page 64

3.26
SEL-551 Relay Instruction Manual Date Code 20110408
Relay Elements and Logic
Reclosing Relay
Determination of Number of Reclosures (Last Shot)
The number of reclosures (last shot) is equal to the number of open interval
time settings that precede the first open interval time setting set equal to zero.
In the above factory settings, two set open interval times precede the third
open interval time, which is set to zero (79OI3 = 0.000):
79OI1 = 30.000
79OI2 = 600.000
79OI3 = 0.000
For this example:
Number of reclosures (last shot) = 2 = the number of set open interval
times that precede the first open interval set to zero.
Reset Timer
The reset timer qualifies breaker closure before taking the relay to the reset
state from the reclose cycle state or the lockout state. Breaker status is
determined by the SEL
OGIC control equation setting 52A (see preceding Close
Logic on page 3.20 and Optoisolated Inputs on page 3.3 for more discussion
on SEL
OGIC control equation setting 52A).
Setting 79RSD
Qualifies closures in the Reclose Cycle State. These closures would usually be
automatic reclosures resulting from open interval time-out.
It is also the reset time used in sequence coordination schemes [see Sequence
Coordination (79SEQ) on page 3.34].
Setting 79RSLD
Qualifies closures in the Lockout State. These closures would usually be
manual closures, external to the relay, via the CLOSE command or the
SEL
OGIC control equation setting CL (see Figure 3.14).
Setting 79RSLD is also the reset timer used when the relay powers up or has
its settings changed (see Reclosing Relay States and General Operation on
page 3.22).
Typically, setting 79RSLD is set less than setting 79RSD. Setting 79RSLD
emulates reclosing relays with motor-driven timers that have a relatively short
reset time from the lockout position to the reset position.
The setting of 79RSD and 79RSLD is independent (setting 79RSLD can even
be set greater than setting 79RSD, if desired). SEL
OGIC control equation
setting 79BRS (block reset timing) can be set to control reset timing [see
Block Reset Timing (79BRS) on page 3.32].
Reclosing Relay Shot
Counter
Refer to Figure 3.16.
The shot counter increments for each reclose operation. For example, when
the relay is timing on the first open interval, 79OI1, it is at shot = 0. When the
open interval times out, the shot counter increments to shot = 1 and so forth
for the set open intervals that follow. The shot counter cannot increment
beyond the last shot for automatic reclosing (see preceding discussion on last
shot). The shot counter resets back to shot = 0 when the reclosing relay returns
to the Reset State.