Schweitzer Engineering Laboratories SEL-421-4, Instruction Manual

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5.7
Date Code 20171006 Instruction Manual SEL-400 Series Relays
Control
Disconnect Logic
89OIP
m
When Relay Word bit 89OIP m asserts, a disconnect switch operation is in prog-
ress. Relay Word bit 89OIP asserts when the states of the 89BM m and 89AM m
Relay Word bits are the same, i.e., both asserted or both deasserted.
89CLB m
This Relay Word bit is used for bus-zone protection and asserts when the discon-
nect is no longer open (89BM
m deasserted).
89CL
m
When Relay Word bit 89CL m asserts, the disconnect switch is closed.
89OPN
m
When Relay Word bit 89OPN m asserts, the disconnect switch is open.
Disconnect Switch Status and Alarm Logic Processing
Figure 5.3 shows the Disconnect Switch Status and Alarm Logic. Inputs to this
logic are the normally open (89AM m ) and normally closed (89BM m ) disconnect
switch auxiliary contacts.
To understand the logic in Figure 5.3 , 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, 89AM
m is deasserted and 89BM m is asserted. Once a close command is
initiated in the relay, the disconnect switch starts to move and 89BM m deasserts.
When 89BM m deasserts, the 89ALP m pickup timer starts to time. With 89BM m
deasserted, the state of the disconnect switch cannot be determined, because both
disconnect switch auxiliary contacts are deasserted. Set the 89ALP
m timer longer
than the expected undetermined disconnect state time, but less than the 89CST m
or 89OST m seal-in timers. If the 89ALP m timer expires, the 89AL m Relay Word
bit asserts. Relay Word bit 89AL m asserts when the disconnect operation does
not complete successfully. When the 89ALP m timer begins timing, the operation
in progress, Relay Word bit 89OIP m , and Relay Word bit 89CLB m assert. The
89CLB m Relay Word bit is for bus-zone protection, this bit asserts when the
89BM m input deasserts.
During the disconnect switch operation-in-progress condition, Relay Word bits
89CL
m and 89OPN m are both deasserted because the state of the disconnect
switch is undetermined. Once the disconnect switch auxiliary contact Relay
Word bit 89AM
m asserts, the condition has been met to declare the disconnect
switch closed. When 89AM m asserts, the 89CL m Relay Word bit asserts,
89ALP m stops timing, Relay Word bit 89OIP m deasserts, and Relay Word bit
89CLB m remains asserted. This sequence completes a successful open-to-close
disconnect switch operation.
The second disconnect operation scenario is for an unsuccessful open-to-close
operation, which, until 89ALP
m starts timing, is identical to the successful oper-
ation in the previously discussed first scenario.
During operation of the 89ALP m timer, the disconnect switch begins moving.
The close disconnect switch output signal 89CLS m clears upon expiration of the
89CST m seal-in timer. The logic then provides the disconnect switch additional
time to complete the close operation, in case some inertia from the motor rotor
keeps the disconnect motor in motion. By setting the 89ALP
m timer longer than