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The phase directional element is the positive-sequence voltage (eight cycles of memory
polarization) times the positive-sequence current minus four times the negative-sequence
voltage times the negative-sequence current, adjusted by the MTA setting.
TIME-OVERCURRENT ELEMENTS AND CURVES
The 51N and 51P time-overcurrent elements provide directional-forward or nondirectional
protection. The trip (51NT and 51PT) states for both elements are available in the Relay
Word for programming into any masks. The TOCP (time-overcurrent pickup) bit in the
Relay Word is formed by either the 51N pickup or 51P pickup or both (51NP + 51PP).
You can select the time dial and the curve shape with the setting procedure. Four curve
shapes are available. The curves and equations are provided at the end of this section.
The 51N and 51P characteristic is formed by a recursive sum of the magnitude or magnitude-
squared of the residual current for the 51N or maximum phase current for the 51P, adjusted
by the pickup setting for the appropriate element.
The time dial setting determines the limit the recursive sum must reach for a trip.
Date Code 920326
Specifications
SEL-267D/167D Instruction Manual
2-25
Summary of Contents for SEL-167D
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