Electric Field Analysis And Structure Upgrading Of 12kV Ring Main Unit’s Sheds Bushing

Ring network power supply has a wide application in the power grid due to its stability, safe reliability and economical efficiency. In traditional Ring Main Unit(RMU), the earth switch is enclosed in SF6 gas box. There are many earth switch accidents caused by false operations, because the fracture of earth switch is invisible. A type of RMU with external earth switch, called RX3, has been designed by Xu Ji(Xiamen) Intelligent Switchgear Manufacturing Co., Ltd. This RMU has visible earth switch fracture, and it also reduces the volume of gas box and consumption of SF6.The main contents of this thesis are about the simulation analysis and the structural design optimization of the external earth switch and sheds bushing of 12 k V RX3 RMU. By simulation research and testing experiment, the improved schemes are proposed. These schemes reduce the peak electric field of the external earth switch within air and sheds bushing respectively. The electric field distribution is more uniform and the insulating property is improved. And the optimal scheme has carried out experimental test. The contents of the research as follows:(1) Structure design and electric field analysis of the external earth switch and sheds bushing. For the need of the external earth switch, a kind of cable bushing combined static contact of earth switch is designed. In order to enhance the insulating property of the external earth switch, this bushing introduces a sheds structure. The electric field distributions of sheds bushing under different voltages are described by ANSYS. The maximum electric field value of the sheds bushing, the electric field values at the contact surface between static contact and air, and also between static contact and the epoxy resin insulation material are analyzed.(2) Power frequency high voltage test of the sheds bushing. For the initial sheds bushing, an experimental platform is built. Then power frequency voltage withstand test of total eight models with mesh, half mesh and not mesh is carried out. The test results show that the incipient discharge voltage is 10 k V for sheds bushing without mesh and with half mesh. For sheds bushing with mesh, the incipient discharge voltage is 25 k V, which is consistent with the simulation result.(3) Structure optimization of the external earth switch and the sheds bushing. According to the analysis of the electric field distribution for original model, three kinds of schemes to improve the electric field distribution are proposed and researched. The optimal scheme has been selected through simulation result. Then the experiments have been tested for the optimal scheme. The experiment results show that the optimized sheds bushing model meets the national standard of partial discharge and withstanding voltage, which could be applied to RX3 RMU.