GE D90 Plus - 15 Theory of Operation; Distance Elements

D90
PLUS
LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL 627
D90
Plus
Line Distance Protection System
Chapter 15: Theory of operation
Theory of operation
This chapter outlines advanced information on operation.
Distance elements
The distance element is composed of two separate algorithms. The first is a conventional
frequency domain (phasor) algorithm based on the UR-series D60 implementation. The
second is a time domain algorithm that achieves sub-cycle operating times. The two
algorithms run in parallel and each can independently issue a trip command.
Figure 548: D90
Plus
distance algorithm
Distance element arming logic
The distance element arming logic grants permission to the time domain algorithm only if
all of the following conditions are met for five cycles prior to a disturbance:
• Zero-sequence current is less than 0.2 pu
• Negative-sequence current is less than 0.2 pu
• Zero-sequence voltage is less than 0.2 pu
• Negative-sequence voltage is less than 0.2 pu
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