Schweitzer Engineering Laboratories SEL-421-4 - Table 5.27 LOP Logic Setting; Table 5.28 LOP Logic Relay Word Bits

5.29
Date Code 20171021 Instruction Manual SEL-421 Relay
Protection Functions
Loss-of-Potential Logic
Setting ELOP := Y
If you set ELOP to Y and an LOP condition occurs, the voltage-polarized direc-
tional elements and all distance elements are disabled. The forward-looking
directional overcurrent elements effectively become nondirectional and provide
overcurrent protection during an LOP condition.
Setting ELOP := Y1
If you set ELOP to Y1 and an LOP condition occurs, the voltage-polarized direc-
tional elements and all distance elements are disabled. This setting for ELOP also
disables the overcurrent elements that these voltage-polarized directional ele-
ments control.
Figure 5.18 illustrates how the LOP logic processes an LOP decision.
Figure 5.19 provides a logic diagram for the LOP logic.
Table 5.27 LOP Logic Setting
Setting Prompt Range Default
ELOP Loss-of-Potential Y, Y1, N Y1
Table 5.28 LOP Logic Relay Word Bits
Name Description
ILOP Internal loss-of-potential from ELOP setting
LOP Loss-of-potential detected