Schweitzer Engineering Laboratories SEL-351-5, Instruction Manual

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5.3
Date Code 20070117
Instruction Manual SEL-351-5, -6, -7 Relay
Trip and Target Logic
Trip Logic
Set Trip
Refer to Figure 5.1 . All trip conditions:
➤
Communications-Assisted Trip
➤
Direct Transfer Trip
➤
Switch-Onto-Fault Trip
➤
Other Trips
are combined into OR-1 gate. The output of OR-1 gate asserts Relay Word bit
TRIP to logical 1, regardless of other trip logic conditions. It also is routed
into the Minimum Trip Duration Timer (setting TDURD).
As shown in the time line example in Figure 5.2 , the Minimum Trip Duration
Timer (with setting TDURD) outputs a logical 1 for a time duration of
“TDURD” cycles any time it sees a rising edge on its input (logical 0 to
logical 1 transition), if it is not already timing (timer is reset). The TDURD
timer assures that the TRIP Relay Word bit remains asserted at logical 1 for a
minimum of “TDURD” cycles. If the output of OR-1 gate is logical 1 beyond
the TDURD time, Relay Word bit TRIP remains asserted at logical 1 for as
long as the output of OR-1 gate remains at logical 1, regardless of other trip
logic conditions.
The Minimum Trip Duration Timer can be set no less than 4 cycles.
Figure 5.2 Minimum Trip Duration Timer Operation
(See Bottom of Figure 5.1 )
The OPEN Command Is No Longer Embedded in Trip Logic
In previous firmware versions of the SEL-351 Relay, the OPEN command
was embedded in the trip logic in Figure 5.1 . The OPEN command was
routed directly into the Minimum Trip Duration Timer, along with the output
of logic gate OR-1.
The OPEN command is no longer directly embedded in the trip logic. This
change was made so that users can supervise the OPEN command if desired
via setting TR.
Example output of
OR-1 (input into
Minimum Trip
Duration Timer and
OR-2)
Resultant logic
output of Minimum
Trip Duration Timer
(input into OR-2)
OR-combination of
above two logic
traces (inputs into
OR-2 to drive Relay
Word bit TRIP)
Rising-edge
input occurring
when the
Minimum
Trip Duration
Timer is reset
TDURD TDURD TDURD