9-20 D30 LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL
SERIES COMPENSATED LINES CHAPTER 9: THEORY OF OPERATION
9
takes place. The relay does not reduce its reach as it is not necessary. Section (c) shows a high-current internal fault.
Because of the large current, the reach is not reduced and the element responds to this internal fault. Traditional approach
leaves this fault out of the relay reach.
The neutral and negative-sequence directional protection functions of the relay cope with the voltage and/or current
inversions by adding appropriate offset to their polarizing signals as explained in the Ground Directional Overcurrent
section. The offset impedance can always be selected successfully to guarantee correct fault direction discrimination
regardless of the degree of compensation and location of the series capacitors and the potential source.
See the Application of Settings chapter for recommendations on settings for series compensation applications.
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