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Impedance Monitoring Scheme for Ground Electrode Line of Ultra High Voltage DC Transmission System
Pages: 157-164
Year: Issue:  11
Journal: Transactions of China Electrotechnical Society

Keyword:  Ultra-high voltage DC transmission systemground electrode lineimpedance monitoringimpedance-distance characteristicfrequency of injection signalfull frequency range;
Abstract: A novel impedance monitoring scheme is proposed in this paper in order to detect faults occurring in the ground electrode lines of ultra high voltage DC( UHVDC) transmission systems reliably and rapidly. Firstly,the theoretical analysis of the full-band impedance vs. distance characteristic of the ground electrode line is carried out.Because a high frequency signal injection-based method is used in the proposed scheme,the principle of determining the frequency of the injection signal is discussed and the criterion of fault alarm are given. The study shows that the imaginary part of the measured impedance has a periodic variation with the distance of the bolted fault when the length of the ground electrode line is larger than half the injection signal’s wave length,which increases the difficulty of setting the criterion. Therefore the selected frequency of the injected signal should ensure that in case of a bolted fault the line impedance changes monotonically with the fault distance,and the modulus value of the maximum fault impedance should be less than that of a normal operation case with a certain margin. Some PSCAD based simulations are performed to verify the proposed scheme. The results show that the faults occur in the ground electrode line can be detected rapidly and reliably,and the proposed scheme has good practice perspective.
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