G.6
SEL-351A Relay Instruction Manual Date Code 20080213
Setting SELOGIC Control Equations
SEL
OGIC Control Equations
If both 51P and 51G are deasserted [i.e., 51P = 0 and 51G = 0 (logical 0)], the
unlatch condition is true:
ULTR = NOT(51P + 51G) = NOT(0 + 0) = NOT(0) = 1
and the trip condition can unlatch, subject to other conditions in the trip logic
(see Figure 5.1).
SELOGIC Control Equation Rising-Edge Operator /
The rising-edge operator / is applied to individual Relay Word bits only–not to
groups of elements within parentheses. For example, the SEL
OGIC control
equation event report generation setting uses rising-edge operators:
ER = /51P + /51G + /OUT103
The Relay Word bits in this factory setting example are:
When setting ER sees a logical 0 to logical 1 transition, it generates an event
report (if the relay is not already generating a report that encompasses the new
transition). The rising-edge operators in the above factory setting example
allow setting ER to see each transition individually.
Suppose a ground fault occurs and a breaker failure condition finally results.
Figure G.1 demonstrates the action of the rising-edge operator / on the
individual elements in setting ER.
Relay Word
Bit
Description
51P Maximum phase current above pickup setting 51PP
for phase time-overcurrent element 51PT (see Figure 3.14)
51G Maximum residual-ground current above pickup setting 51GP for
residual-ground time-overcurrent element 51GT (see Figure 3.19)
OUT103 Output contact OUT103 is set as a breaker failure trip output (see Output
Contacts on page 7.31)
Courtesy of NationalSwitchgear.com
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