G-6 Setting SELOGIC
®
Control Equations Date Code 20001006
SEL-351 Instruction Manual
The Relay Word bits in this factory setting example are:
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)
OUT3 Output contact OUT3 is set as a breaker failure trip output (see Output Contacts in
Section 7: Inputs, Outputs, Timers, and Other Control Logic)
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.
Figure G.1: Result of Rising Edge Operators on Individual Elements in Setting ER
Note in Figure G.1 that setting ER sees three separate rising edges, due to the application of rising
edge operators /. The rising edge operator / in front of a Relay Word bit sees this logical 0 to
logical 1 transition as a “rising edge” and the resultant asserts to logical 1 for one processing
interval. The assertions of 51G and 51P are close enough that they will be on the same event
report (generated by 51G asserting first). The assertion of OUT3 for a breaker failure condition is
some appreciable time later and will generate another event report, if the first event report capture
has ended when OUT3 asserts.
Courtesy of NationalSwitchgear.com
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