P.12.8
SEL-411L Relay Protection Manual Date Code 20151029
Bay Control
Disconnect Logic
89CLm
When Relay Word bit 89CLm asserts, the disconnect switch is closed.
89OPNm
When Relay Word bit 89OPNm asserts, the disconnect switch is open.
Disconnect Switch Status and Alarm Logic Processing
Figure 12.3 shows the disconnect switch status and alarm logic. Inputs to this
logic are the normally open (89AMm) and normally closed (89BMm)
disconnect switch auxiliary contacts. As discussed before, the relay supports
as many as 10 disconnect switches, depending on the one-line diagram
selected. For proper execution of this logic, the relay requires input from each
of the disconnect switch auxiliary contacts (89AMm, 89BMm). When
ordering the relay for bay control, remember that an optional I/O board may
be needed for some bay configurations.
To understand the logic in Figure 12.3, consider an open-to-close operation.
The first disconnect operation scenario looks at a successful open-to-close
disconnect switch operation; a successful close-to-open operation is similar. In
the open state, 89AMm is deasserted and 89BMm is asserted. Once a close
command is initiated in the relay, the disconnect switch starts to move and
89BMm deasserts. When 89BMm deasserts, the 89ALPm pickup timer starts
to time. With 89BMm deasserted, the state of the disconnect switch cannot be
determined because both disconnect switch auxiliary contacts are open. Set
the 89ALPm timer longer than the expected undetermined disconnect state
time, and slightly longer than the 89CSTm or 89OSTm seal-in timers in the
case when the relay provides the seal-in circuit. If the 89ALPm timer expires,
the 89ALm Relay Word bit asserts, indicating an incomplete operation. When
the 89ALPm timer begins timing, the operation in progress, Relay Word bit
89OIPm, and Relay Word bit 89CLBm assert. The 89CLBm Relay Word bit is
for bus-zone protection, this bit asserts when the 89BMm input deasserts.
During the disconnect switch operation-in-progress condition, Relay Word
bits 89CLm and 89OPNm are both deasserted since the state of the disconnect
switch is undetermined. Once the disconnect switch auxiliary contact Relay
Word bit 89AMm asserts, the condition has been met to declare the disconnect
switch closed. When 89AMm asserts, the 89CLm Relay Word bit asserts,
89ALPm stops timing, Relay Word bit 89OIPm deasserts, and Relay Word bit
89CLBm remains asserted. This sequence completes a successful open-to-
close disconnect switch operation.
The second scenario regarding the disconnect switch status and alarm logic
involves an unsuccessful open-to-close operation. The operation up to the
point when the 89ALPm starts timing is the same as discussed previously.
When the 89ALPm timer is timing, the disconnect switch has started to move.
Once the 89CSTm seal-in timer expires, the close disconnect switch output
s
ignal 89CLSm is cleared. Then the disconnect switch is given a little more
time to complete the close operation in case that some inertia on motor rotor
keeps the disconnect motor moving. Setting 89ALPm timer longer than the
89CSTm seal-in timer also guarantees that the close signal will not be
removed before the disconnect switch is completely closed. If the disconnect
switch operation does not complete in the 89ALPm time, the relay asserts
Relay Word bit 89ALmand reports the state of the disconnect switch as
undetermined.
The scenario in which both 89AMm and 89BMm are asserted simultaneously
would occur on a rare disconnect switch failure or a short-circuited auxiliary
contact wire connection. When this condition occurs for 89ALPm seconds, the
89ALm alarm status output will assert.
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