时变温差工况下直流GIL/GIS盆式绝缘子动态电场畸变抑制

Electric Field Relaxation of Basin Spacer under Variable Temperature Gradient in DC-GIL/GIS

为了优化时变温差工况下直流GIL/GIS盆式绝缘子的沿面电场分布,基于表层电导梯度材料(σ-SFGM)设计了以室温(RT)电场均化为目标的RT-SFGM绝缘子与兼顾不同温度梯度(GT)条件的GT-SFGM绝缘子。迭代优化后,RT-SFGM绝缘子的涂层厚度从导体到外壳梯度减小,而GT-SFGM绝缘子的凸面涂层厚度则呈现U型梯度分布。室温条件下,均匀绝缘子的凹面高压三结合点处电场畸变严重,相同位置处的RT-SFGM绝缘子与GT-SFGM绝缘子电场强度分别下降了53.3%和49.5%。随着高压导体温度的上升,绝缘子最大电场位置逐渐向接地外壳附近转移。在40℃温差条件下,GT-SFGM绝缘子的电场畸变抑制效果明显优于RT-SFGM绝缘子,最大电场强度下降59.2%。在负荷加载与负荷波动工况下,GT-SFGM绝缘子的电场变化率分别仅为7%与13.1%,可实现时变温差工况下绝缘子直流电场分布的稳定控制。

In real applications of the DC gas insulated transmission line(GIL)and gas insulated switchgear(GIS),there are large temperature gradients between the HV conductor and the grounding shell of the spacer,which leads to a completely different electric field distribution compared to that at room temperature.The DC electric field distribution is mainly related to the conductivity parameter of the insulating materials.By applying the coating with conductivity gradient,the surface functionally graded material(SFGM)spacer is considered to be an effective way to uniform the electric field distribution in DC-GIL/GIS.Meanwhile,due to the change of power generation and load,the temperature of the HV conductor also fluctuates with time,which brings difficulties to the optimal design of SFGM spacers under complex working conditions.To optimize the surface electric field distribution of the DC-GIL/GIS basin spacer under variable temperature gradient,based on the surface conductivity graded materials(σ-SFGM),the RT-SFGM spacer with the goal of regulating the surface electric field distribution at room temperature(RT)and the GT-SFGM spacer with consideration of different gradients of temperature(GT)are designed in this paper.Firstly,an electric-heat coupling model of a±500 kV DC GIL/GIS basin-type spacer is modelled to calculate the electric field distributions under temperature gradients.Considering the gas flow inside the DC-GIL/GIS,the temperature distribution of the spacer is simulated.Experimental results show that the conductivity of the epoxy composites has a strong temperature dependence.As the temperature increases from 30°C to 90°C,the conductivity of the spacer bulk increases by more than 100 times.Compared to the spacer bulk,the conductivity of the coating has a smaller variation with the temperature.Different reference electric fields are selected as optimization goals for the RT-SFGM spacer and the GT-SFGM spacer.Based on the iterative optimization method,the thickness of the RT-SFGM spacer and the GT-SFGM spacer are designed.After iterative optimization,the coating layer thickness of the optimized RT-SFGM spacer decreases from the conductor to the shell,while the coating thickness on the convex surface of the GT-SFGM spacer presents a U-shaped distribution.Simulation results show that,at room temperature,the electric field at the high-voltage triple junction of the uniform spacer is seriously distorted,and the electric field strength of the RT-SFGM spacer and the GT-SFGM spacer at the same position decreases by 53.3%and 49.5%,respectively.With the increasing temperature of the high voltage conductor,the maximum electric field of the uniform spacer gradually transfers to the grounding shell.Under the temperature gradient of 40℃,the GT-SFGM spacer has a better electric field relaxation effect than the RT-SFGM spacer,and the maximum electric field strength decreases by 59.2%.Under current loading and fluctuation conditions,the electric field distribution of the uniform spacer presents a wide range of fluctuation with the current,and the maximum electric field position transfers between the conductor and the shell.The electric field of the GT-SFGM spacer does not change drastically with the current changing,and the electric field change rate is only 7%and 13.1%under current loading and fluctuation conditions,which achieves the stable control of electric field under the variable temperature gradient condition.