D90
PLUS
LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL
627
D90
Plus
Line Distance Protection System
Chapter 15: Theory of operation
Theory of operation
This section describes the basic theoretical principles behind the operation of D90
Plus
.
The D90
Plus
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 545: 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 (5) 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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