G-8 Setting SEL
OGIC
®
Control Equations Date Code 990430
SEL-351P Manual Técnico
only effective input into logic gate OR-1 in Figure 5.1 is SELOGIC Control Equation trip setting
TR.
TR = 51P1T+51G1T+50P1*SH0 (fuse saving example)
TRCOMM = 0 (not used – set directly to logical 0)
TRSOTF = 0 (not used – set directly to logical 0)
ULTR = !(51P1 + 51G1) (discussed in preceding subsection)
Analysis of SEL
OGIC
Control Equation Trip Setting TR
Again, the example trip equation is:
TR = 51P1T+51G1T+50P1*SH0
The Relay Word bit definitions are:
51P1T phase time-overcurrent element timed out
51G1T residual ground time-overcurrent element timed out
50P1 phase instantaneous overcurrent element asserted
SH0 reclosing relay shot counter at shot = 0
In the trip equation, the AND operator * is executed before the OR operators +,
Table APPENDIX G: .1:
50P1*SH0
Element 50P1 can only cause a trip if the reclosing relay shot counter is at shot = 0. When the
reclosing relay shot counter is at shot = 0 (see Table 6.3), Relay Word bit SH0 is in the following
state:
SH0 = 1 (logical 1)
If maximum phase current is above
the phase instantaneous overcurrent element pickup setting
50P1P (see Figure 3.1), Relay Word bit 50P1 is in the following state:
50P1 = 1 (logical 1)
With SH0 = 1 and 50P1 = 1, the ANDed combination results in:
50P1*SH0 = 1*1 = 1 (logical 1)
and an instantaneous trip results. This logic is commonly used in fuse saving schemes for
distribution feeders.
If the reclosing relay shot counter advances to shot = 1 for the reclose that follows the trip, Relay
Word bit SH0 is in the following state:
SH0 = 0 (logical 0)
If maximum phase current is above
the phase instantaneous overcurrent element pickup setting
50P1P for the reoccurring fault, Relay Word bit 50P1 is in the following state:
50P1 = 1 (logical 1)
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