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Keywords

high‑voltage power cable; distance protection; distributed capacitance; capacitance current compensation

Abstract

Large‑scale offshore wind farms are one key tendency of wind power generation development. Submarine cables, as an important link between offshore wind farms and grids, are with much higher distributed capacitance than overhead lines, and thus will generate a non‑negligible capacitance current. In case of the long‑distance high voltage transmission, this may lead to the refusal‑operation of relays in the distance protection area. The reliability of distance protection operation criterion depends on the accuracy of measurement impedance. Therefore, in this paper, combined with the actual physical structure of cables, the calculation of relevant electrical parameters is studied, and the accuracy of the corresponding formulas are demonstrated. According to the consequent calculation results, a distributed parameter model is established for cable lines, and the influence of distributed capacitance on the measured impedance at the protection installation is analyzed. It is proved that the measured impedance of long distance cable lines is a function of hyperbolic tangent to the fault distance. On the basis of the traditional capacitive current semi‑compensation scheme, an improved scheme is proposed. A cable model for fault simulation is carried out through PSCAD. The simulation results show that the improved scheme can effectively compensate the line capacitive current, reduce the portential refusal‑operations in the distance protection area and the misoperation outside the area, with a better anti‑transition resistance ability at the same time, which will assist in distance protection performance.

DOI

10.19781/j.issn.1673-9140.2023.03.018

First Page

166

Last Page

173

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