摘要
换流变压器是特高压直流输电工程中的关键设备,换流变压器油纸复合绝缘的界面处在直流电压下易积聚电荷,诱发局部放电甚至击穿。当前对于界面电荷的积聚分布,多采用传统的阻容模型进行计算,存在较大的误差。该文提出一种简易的非线性电路等效模型,首先,分别测量变压器油和油浸纸板的电容、电阻参数与极化电流,获得油纸的拓展Debye模型;其次,在拓展Debye模型的基础上,将变压器油和油浸纸板的恒定电阻模型改为随电场变化的非线性模型,并加入反映极性效应的界面势垒限制电流源,以此建立等效模型;最后,将电路等效模型仿真结果与实际测量结果进行对比。结果表明,与实际测量结果相比,该等效模型具有良好的适用性。该文模型为油纸绝缘的电场分布、界面电荷积聚量的计算提供了一种准确度较高的简便方法。
In the operation of a converter transformer,the interface of its oil-paper composite insulation is prone to charge accumulation under DC voltage.A simple non-linear equivalent circuit model is proposed based on the extended Debye model in this paper,which can calculate the electric field distribution and interface charge amount of oil-paper insulation more easily and accurately.Firstly,the capacitance and resistance parameters of the transformer oil and the oil-immersed paperboard are separately measured,and the electric field strength in the oil is measured based on the Kerr effect method at applied voltages from 5 to 25 kV respectively.The electric field distribution in the oil-paper composite insulation is calculated for different applied voltages as well as different voltage polarities,and the measured results are compared with the calculated results from the RC model.Secondly,the conductivity of the transformer oil and oil-immersed paperboard are measured under different electric field strength to establish a non-linear conductivity model for the oil-paper composite insulation.Then the polarisation currents of the transformer oil and oil-immersed paperboard are separately measured and fitted to extract the branch parameters of extended Debye model.Finally,the interface potential barriers are derived from the measured polarisation currents,and the polarity determined interface potential barrier is then added to the model to limit the current through the interface,thus establishing a non-linear equivalent circuit model for the transformer oil and oil-impregnated paperboard where the resistances are the electric field strength dependent.The electric field distribution in the oil-paper composite insulation calculated by the established non-linear equivalent model is compared with those by the RC model,extended Debye model and actual measured results.The time to steady state calculated by the equivalent model is reduced to about 500 s,which is shorter than that calculated by the RC and Debye models,and is closer to the measured results.As regards the steady state electric field in oil at different applied voltages,it can be seen that the error between those by the equivalent model and measurment is less than 5%for both positive and negative polarities.The error between the electric field in oil calculated by the equivalent model and the measured results is greatest at DC voltage of 25 kV,but the maximum error is 4.8%.These indicate that the accuracy of this model is greatly improved compared to the RC and series extended Debye model.Comparing the results of the three models with the measured values for positive and negative polarities,the equivalent model is much closer to the measured values than the RC and extended Debye model,and just the equivalent model reflects a polarity effect.The absolute value of the measured negative interface charge amount at 25 kV is merely 1.07%higher than the proposed equivalent model calculation,and the measured positive interface charge amount is 0.95%higher than the proposed equivalent model calculation.The following conclusions can be drawn from the above:(1)Compared with the RC and extended Debye model,the dynamics of electric field distribution of the oil-paper insulation calculated by the proposed model reach the steady state faster and is closer to the measured situation.(2)The proposed model takes into account the polarity determined interface barrier to limit the current through the interface,so its calculation can reflect the polarity effect and the error between the calculated and measured electric field is less than 5%.(3)The model has incorporated the influence of nonlinear conductivity,relaxation polarisation and interfacial potential barrier limiting current,so it has a good applicability to the calculation of the interfacial charge of oil-paper insulation under different conditions more easily and accurately.
作者
黄猛
李怡然
吴延宇
陈良炯
齐波
Huang Meng;Li Yiran;Wu Yanyu;Chen Liangjiong;Qi Bo(State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources,North China Electric Power University,Beijing,102206,China)
出处
《电工技术学报》
EI
CSCD
北大核心
2024年第11期3422-3432,共11页
Transactions of China Electrotechnical Society
基金
国家自然科学基金(51807062)
北京市自然科学基金(3212035)资助项目。
关键词
油纸绝缘
界面电荷
界面极化
拓展Debye模型
电路等效模型
Oil-paper insulation
interface charge
interface polarization
extended Debye model
equivalent circuit model
