Date Code 20020129
Differential, Restricted Earth Fault,
3-55
Overcurrent, Voltage, and Frequency Elements
SEL-387E Instruction Manual
overvoltage element operates when the maximum phase-to-phase voltage exceeds the set
threshold.
Phase undervoltage elements operate using the minimum of the measured phase voltage
magnitudes, operating if any single-phase measurement falls below the set threshold. The
phase-to-phase undervoltage element operates using the minimum of the measured
phase-to-phase voltages. The positive-sequence (V1) undervoltage element operates when the
measured positive-sequence voltage falls below the set threshold.
Figure 3.34 and Figure 3.35, respectively, diagram the logic for the overvoltage and undervoltage
elements.
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Figure 3.34: Overvoltage Element Logic Diagram