Abstract
Long-distance high voltage alternating current (AC) submarine cables are widely used to connect offshore wind farms and land power grids. However, the transmission capacity of the submarine cable is limited by the capacitive charging current. This paper analyzes the impacts of reactive power compensation in different positions on the current distribution on long-distance submarine cable transmission lines, and tests the rationality of the existing reactive power compensation schemes based on electrothermal coordination (ETC). Research shows that compensation at the sending end has obvious impacts on current distribution along the cable, and the maximum current occurs at the sending or receiving end. Moreover, the reactive power compensation at sending end will reduce the current at receiving end of the line. On the contrary, it will increase the current at sending end. Compared with the directly buried laying method of the submarine cable in the landing section, the cable trench laying method can increase the cable ampacity of the landing section and reduce the reactive power compensation capacity at the sending end. The ampacity is the current representation of the thermal limits of the cable. ETC exploits the cable ampacity to coordinate current distribution on transmission lines under existing reactive power compensation schemes, thus optimizing the reactive power compensation schemes and avoiding the bottleneck point of cable ampacity.
Highlights
Wind energy, as an efficient clean energy, has been increasingly valued
This study considers a long-distance high voltage alternating current (AC) three-core submarine cable from a real offshore wind farm project
An accurate cable model is used to analyze the influence of reactive power compensation in different positions on the current distribution on the line, and optimizing the existing reactive power compensation schemes based on electrothermal coordination (ETC)
Summary
As an efficient clean energy, has been increasingly valued. The utilization of wind energy to generate electricity can enrich energy supply systems and reduce environment pollution. When the transmission distance is long, the transmission capacity of high-voltage AC cables is greatly affected by the charging current, and the loss caused by reactive power exchange will be more obvious [3,4]. Aiming at the losses problem caused by the transmission system of high-voltage AC submarine cables in offshore wind farms, there are two common methods. In 2017, Gustavsen and Mo [6] proposed to improve the transmission capacity of the submarine cables by continuously changing the operating voltage of the long-distance submarine cables according to the output power of the wind farm. An accurate PI equivalent model is used to calculate the current distribution in the long-distance submarine cable transmission line Based on this model, impacts of various reactive power compensation schemes on the current distribution in the transmission line is analyzed and simulated.
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