BE1-951
Protection and Control
4-39
Figure 4-20. 79 Function Block
Holdup
Timer
255
0
Holdup Timer
RI
Initiate
Reclose
Timer
D2635-07
03-04-98
Recognition
Dropout Time
RI
52
Status
52
Status
Figure 4-21. Recognition Dropout and Timing
reclose that uses a slow 51 curve. Detailed information
about relay setting groups can be found earlier in this
section under the heading of
Setting Groups. Recloser
function block inputs and outputs are shown in Figure
4-20 and are described in the following paragraphs.
Reclose Initiate (RI). The RI input is used with the 52
status input to start the reclose timers at each step of
the reclosing sequence. To start the automatic reclose
timers, the RI input must be TRUE when the breaker
status input indicates that the breaker has tripped. To
ensure that the RI input is recognized, a recognition
dropout timer holds the RI input TRUE for
approximately 255 milliseconds after it goes to a
FALSE state. This situation might occur if the RI is
driven by the trip output of a protective function. As
soon as the breaker opens, the protective function will drop out. The recognition dropout timer ensures that
the RI signal will be recognized as TRUE even if the breaker status input is slow in indicating breaker
opening. Figure 4-21 illustrates the recognition dropout logic and timing relationship.
Breaker Status (STAT). This input is used to indicate to the recloser element that the breaker is closed. A
TRUE signal at this input indicates a closed breaker.
Reclose Wait (WAIT). A TRUE signal at this input disables the reclosing function. In this condition, recloser
timing is interrupted. When this input returns to a FALSE state, reclosing is enabled and recloser timing
resumes.
Drive to Lockout/Block Recloser (DTL/BLK). When TRUE, this input forces the reclosing function into the
Lockout position, Lockout persists for the period defined by the Reset time after the DTL/BLK input becomes
FALSE and the breaker is closed.
Close (79C). The 79C output becomes TRUE at the end of each reclose time delay and remains TRUE until
the breaker closes. Any of the following conditions will cause the 79C output to become false.
The STAT input indicates that the breaker is closed.
The reclose fail timer times out.
The recloser goes to Lockout.
The WAIT logic is asserted.
Recloser Running (79RNG). The 79RNG output is TRUE when the recloser is running (i.e., not in Reset or
Lockout). This output is available to block the operation of a load tap changer on a substation transformer
or voltage regulator during the fault clearing and restoration process.
Lockout (79LO). This output is TRUE when the recloser is in the Lockout state. It remains TRUE until the
recloser goes to the Reset state. The recloser will go to Lockout if any of the following conditions exist.
More than the maximum number of programmed recloses are initiated before the recloser
returns to the Reset state.
The BLK/DTL input is TRUE.
The Reclose Fail (79F) output is TRUE.
The maximum reclose cycle time is executed.
