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 89OPNm
deasserts (see Figure 5.3). If the 89OPNm Relay Word bit deasserts, the close
immobility timer resets and 89CIMm remains deasserted. On the other hand, if
the 89OPNm Relay Word bit stays asserted, the close immobility timer does not
reset. After the close immobility timer expires, 89CIMm asserts for one second.
When 89CIMm asserts, the close operation is considered to have failed to initiate.
89CIMm 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 89CCMm 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 (89BMm asserted) is closed
➤ normally open Form A auxiliary contact (89AMm deasserted) is open
If the disconnect switch main contact is closed:
➤ normally closed Form B auxiliary contact (89BMm deasserted) is open
➤ normally open Form A auxiliary contact (89AMm 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 (89BMm deasserted) is open
➤ normally open Form A auxiliary contact (89AMm 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 89ALPm time. Figure 5.6 illustrates how the state of
the auxiliary contacts change for an open-to-close operation in progress and how
the 89CSTm, 89CITm, and 89ALPm 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 (89BMm asserted) and the normally open Form A auxiliary
contact is open (89AMm deasserted). The 89CSTm seal-in timer starts timing
when a disconnect switch close command is issued. The output of the 89CSTm
seal-in timer keeps the close signal asserted for the duration of the expected dis-
To Next Page
Loading...
