Research on the Technical Scheme for Conversion of 500kV Submarine SCLF AC Cable Circuit to DC Operation in Hainan Grid-connection Project

摘要

The first AC 500 kV submarine cable circuit in China was put into operation on June 2009. In order toincrease the transmission capacity, it is under consideration to convert this kraft paper insulated SCLFcable circuit from AC to DC operation.From the existing single circuit AC cable line, two circuits can be arranged under DC operation, onebipolar and one monopolar. The bipolar circuit consists of two cables, a DC plus pole and a DC minuspole. The monopolar circuit consists of only one cable. According to the cable structure and circuitgrounding mode, return current will flow through the coaxial metal layers of the cable as well as theseawater and earth.The long term operation voltage is to be designed as 500 kV based on the insulation withstand levelsof DC voltage, polarity reversal voltage and DC superimposed impulse voltage. The permissible loadcurrent is determined as 1150 A and 1000 A using the calculation method recommended by IEC60287for different current return modes. Under the designed DC operation scheme, the transmissioncapacity will be 2.5 times more than the existing AC.The follow-up testing and checking work is underway.