Schweitzer Engineering Laboratories SEL-351 - Loss-Of-Potential Logic; Section 4: Loss-Of-Potential, Load Encroachment, and Directional Element Logic

Date Code 20001006 Loss-of-Potential, Load Encroachment, and Directional Element Logic 4-1
SEL-351 Instruction Manual
SECTION 4: LOSS-OF-POTENTIAL, LOAD ENCROACH-
MENT, AND DIRECTIONAL ELEMENT LOGIC
LOSS-OF-POTENTIAL LOGIC
The loss-of-potential (LOP) logic operates as shown in Figure 4.1.
Figure 4.1: Loss-of-Potential Logic
Inputs into the LOP logic are:
3PO three-pole open condition (indicates circuit breaker open condition
see Figure 5.3)
V
1
positive-sequence voltage (V secondary)
I
1
positive-sequence current (A secondary)
V
0
zero-sequence voltage (V secondary)
I
0
zero-sequence current (A secondary)
V
2
negative-sequence voltage (V secondary)
The circuit breaker has to be closed (Relay Word bit 3PO = logical 0) for the LOP logic to
operate.
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