特快速暂态过电压下特高压变压器绕组的建模算法研究

Rising time of Very Fast Transient Over-voltage(VFTO) is up to ns and vibratory frequency of which is up to MHZ. If such steep voltage intrudes Ultra High-voltage(UHV) power transformer, insulation of windings may be seriously damaged. Some inland and overseas cases have been reported recently; related research is still in underway,especially about damage of VFTO on UHV transformer wingdings insulation. In this item, investigative object is UHV transformer windings and investigation is divided into three steps: firstly self-adjusted and various welding resistance is equaled as that of isolated switch and Fuzzy Neural Network is used to compute discrete capacitance off-line in order to improve computational precision; secondly synthetically transient time-domain-model+frequency domain model+S-paparmater model are established, that is, time-domain transient algorithm having time-varying impedance solved by difference method, frequency-domain model used to confirm vibrancy and orientation of already destroyed windings, distributed model based on s-parameters gotten by theoretical formula and equipment of network tester. The reduced models are based on vector fitting method and optimal Pade method. And in the case of mechanical and damage characteristics of isolated switch, and effect of multi-damage of VFTO on insolation of windings, self-adapted various step is used in simulation. Lastly above results are collected to develop expert simulation platform for calculating over-voltage distributions of UHV power transformer under VFTO. Inquisitive results of this item will reduce insulation cost, optimizing design of windings and widen use, which may supply reference for theory and engineering application.

特快速暂态过电压(VFTO)上升时间为ns级、振荡频率高达MHZ，若侵入特高压电力变压器必将严重影响其绕组绝缘，国内外已发生多起击穿事故，但其研究尚处于起步阶段。本项目以特高压电力变压器绕组为研究对象，研究分为三步：1、引入自调节变焦弧阻等效隔离开关的电弧电阻，FNN离线计算分布电容以提高计算精度。2、提出时域+频域+散射参数的综合暂态算法：含频变阻抗用Lax和Weno差分法求解的时域算法；分析谐振及击穿绕组定位的暂态算法；基于理论推导+网络测试仪获取散射参数的算法，采用矢量匹配法和最优Pade算法降阶；考虑隔离开关的机械特性、击穿特性及多次重击穿过程对VFTO的影响，仿真计算采用自适应变步长求解。3、基于以上研究所得数据开发专门的仿真平台，用于计算VFTO作用下特高压电力变压器绕组的暂态过电压分布。本项目的研究成果将为绕组绝缘的低成本设计、优化与拓展应用提供重要的理论参考及工程实际作用。

气体绝缘变电站GIS中的隔离开关在分、合闸操作过程中，触头间产生多次击穿，击穿过程中产生波头很陡的行波，在GIS内传播、折反射和叠加，形成特快速暂态过电压VFTO。VFTO频率高达MHz，波头时间达ns，一旦侵入大型电力变压器，极易损坏匝间绝缘和主绝缘。. 本项目以特高压电力变压器绕组为对象，研究基于 VFTO 作用下其内部暂态过电压的分布情况。第一，提出时域+频域+散射参数的综合暂态算法，使用三对比+一结合(对比Matlab编程+电磁暂态软件EMTP电路仿真+物理实验，结合实际运行数据)的方法，设计专业的仿真平台，形成特高压电力变压器绕组安全预测方案。1.时域：分别采用时域有限差分法、Lax-Wendroff差分法、时域有限元+加权余量法三种方法建模，并给出时域算法稳定区域。矢量匹配法处理高频作用下出现的频变效应，最优Pade降阶算法简化模型，提高计算速度。2.频域：根据短路导纳参数计算暂态过电压的分布，分析谐振机理并提出解决方案，实现对绕组中可能发生击穿位置的定位。3.散射参数：采用分布参数代替传统的集中参数建模。第二，从三方面提高计算精度。1.构建精确的隔离开关的电弧模型，采用自调节变焦弧阻等效隔离开关的电弧电阻。分析影响VFTO暂态计算精度的主导因素，考虑隔离开关的间隙击穿、高频电弧熄灭、介质恢复和多次击穿的相互作用。2.建模的基础是分布电容的精确计算，将特高压变压器绕组分成6类，用9×45×25×25×4的模糊神经网络实现饼间、对铁芯、匝间和对壳体电容的精确计算。3.仿真计算采用自适应变步长方法。第三，将电力变压器的暂态建模方法应用到超高压换流变压器。1.提出了基于有限元分析材料绝缘特性对超高压换流变压器电场分布的影响；2.采用VBscript+Magnet混合编程计算高压换流变压器附加损耗，解决商用软件无法提供相关数据的问题。本项目的研究成果为特高压电力变压器绕组绝缘的低成本设计、优化结构与拓展应用提供了重要的理论参考依据及工程实际作用。