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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.
illustrates how the LOP logic processes an LOP decision.
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
Summary of Contents for SEL-421-4
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