Electro-Quasistatic Simulations of Gas-Insulated Systems Considering Nonlinear Field Control Techniques

Project description

In recent years, the demand of renewable energy has increased, to reduce the amount of carbon dioxide (CO2) in the atmosphere. Renewable energy, such as offshore wind power plants, are often located far from where it is needed. Thus High Voltage Direct Current (HVDC) is needed to transmit high electric power over long distances. Gas-insulated systems, e.g. gas insulated transmission lines (GIL), are a possible solution, resulting from low fault rates, considerably reduced apparatus sizes and a long lifetime. Within a gas system, the inner conductor is surrounded by the insulating gas, commonly sulphur hexafluoride (SF6), and kept in position by a massive insulating spacer.

Gas insulated systems under alternating current (AC) has been developed and optimized in the last decades. However, the experience under HVDC is limited. The main difference between AC and DC is the charge accumulation under a constant applied voltage, which yields in local field enhancement, a reduction of the lifetime of the solid insulating spacer and the reliability of the system. Especially the interface between the insulating gas and the solid spacer is sensitive to high electric fields and partial discharges can easily occur. Thus, the electric field under DC conditions needs to be determined accurately for the reliability and the design of the gas-insulated system. Numerical simulations are a powerful tool to determine the electric field distribution in gas-insulated systems. Resulting from slow charge accumulation, slowly time varying electro-quasistatic fields are seen under DC conditions.

Within this project, conductivity models for the gaseous and solid insulation materials are developed, to obtain accurate simulation results. Since the conductivity of the insulation materials has a nonlinear dependency on electric field, temperature and other parameters, nonlinear simulation of high-resolution three-dimensional geometries are applied to analyze novel field control techniques, to reduce electric field stress and charge accumulation. Furthermore, SF6 is a greenhouse gas, with a global warming potential 23,900 times higher than CO2 and an atmospheric lifetime up to 3,200 years. Therefore, more environment-friendly insulting gases as an alternative to SF6 are examined in this project.

Project-related publications