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5.10
SEL-400 Series Relays
Instruction Manual
Date Code 20171006
Control
Disconnect Logic
Disconnect Switch Close and Open Immobility Timer Logic Processing
The Close and the Open Immobility Timer Logic detect when one of the close or
open disconnect switch methods does not initiate successfully. In other words, it
reports when the disconnect switch failed to start moving. The open and close
immobility timer logic circuits are similar. When a close operation is initiated,
the rising-edge-triggered Close Immobility Timer starts timing. Once the discon-
nect switch starts to move away from its open position, Relay Word bit 89OPN
m
deasserts (see
). If the 89OPN
m
Relay Word bit deasserts, the close
immobility timer resets and 89CIM
m
remains deasserted. On the other hand, if
the 89OPN
m
Relay Word bit stays asserted, the close immobility timer does not
reset. After the close immobility timer expires, 89CIM
m
asserts for one second.
When 89CIM
m
asserts, the close operation is considered to have failed to initiate.
89CIM
m
is an input to the disconnect switch status and alarm logic for alarm
condition indications.
This logic also uses the LOCAL Relay Word bit to supervise front-panel opera-
tions. With the LOCAL Relay Word bit deasserted, no disconnect operations can
be initiated from the one-line diagram. With the LOCAL Relay Word bit asserted,
Relay Word bit 89CCM
m
asserts for one-quarter cycle when the
ENT
pushbutton
is pressed and a disconnect switch is highlighted in the one-line diagram.
Close, Open, and Undetermined State Indications
This subsection discusses the way the close and open immobility timers work in
conjunction with the disconnect alarm timer to provide disconnect control and
alarm indications. When the disconnect switch main contact is stationary (closed
or open) the state of the disconnect switch is easily determined.
If the disconnect switch main contact is open:
➤
normally closed Form B auxiliary contact (89BM
m
asserted) is closed
➤
normally open Form A auxiliary contact (89AM
m
deasserted) is open
If the disconnect switch main contact is closed:
➤
normally closed Form B auxiliary contact (89BM
m
deasserted) is open
➤
normally open Form A auxiliary contact (89AM
m
asserted) is closed
If an operation of the disconnect switch is in progress, the state of the disconnect
switch main contact is undetermined:
➤
normally closed Form B auxiliary contact (89BM
m
deasserted) is open
➤
normally open Form A auxiliary contact (89AM
m
deasserted) is open
Any undetermined state of the disconnect switch main contact should be moni-
tored. The relay can be configured to wait for the disconnect switch operation to
complete, and issue an alarm if the disconnect switch remains in the undeter-
mined state longer than the 89ALP
m
time.
illustrates how the state of
the auxiliary contacts change for an open-to-close operation in progress and how
the 89CST
m
, 89CIT
m
, and 89ALP
m
timers are configured to manage the unde-
termined time. The close-to-open scenario would be similar.
With the disconnect switch in the open state, the normally closed Form B auxil-
iary contact is closed (89BM
m
asserted) and the normally open Form A auxiliary
contact is open (89AM
m
deasserted). The 89CST
m
seal-in timer starts timing
when a disconnect switch close command is issued. The output of the 89CST
m
seal-in timer keeps the close signal asserted for the duration of the expected dis-
Summary of Contents for SEL-421-4
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