大型发电机定子排间绝缘老化的热性能分析

针对大型电机排间绝缘可能发生的绝缘老化或故障情况,分别采用了等效和实际处理的方法对其进行了分析。建立了定子径向通风沟内的二维流体场的物理模型和数学模型,采用有限体积法对其进行了求解,确定了各散热表面的散热系数;建立了定子三维温度场的物理模型和数学模型,采用有限元法计算了不同处理情况下的定子温度场,明确了定子排间绝缘对定子温度场的影响。     

大型同步发电机定子主绝缘结构优化热性能分析

大型同步发电机的绝缘减薄问题是对发电机进行研究的一个重要方面,本文着重研究了由于主绝缘的减薄所导致的股线涡流损耗的变化;采用有限体积法对定子径向沟内的流体场进行了数值计算,得出径向通风沟内不同位置处的流体速度,并由此计算出表面散热系数.此外建立了定子三维温度场的数学模型和物理模型,采用有限元法对定子三维温度场进行了数值计算,将求解结果和试验值进行了比较.最终讨论了由于绝缘减薄对发电机定子三维温度场造成的影响.     

Optimization on the internal insulation system of gas‐insulated bushing for 1100‐kV GIS based on multiobjective optimization method

In this paper, we first study the voltage and electric field distribution characteristics under the basic lightning impulse level (BIL) of 2400 kV by finite element method (FEM) calculation which are affected by the internal shielding structure of the gas‐insulated bushing for the 1100‐kV gas‐insulated substation (GIS). On this basis, four parameters of the shielding structure are determined to be the decision variables in the optimization process. Four electric field objective functions and four potential objective functions are also proposed. Using a multiobjective optimization method, we then construct an evaluation function with the eight objective functions mentioned above, which are used to evaluate the electric field and potential distribution synthetically. Furthermore, a combination of FEM and the evolution strategy is used to construct the stochastic optimization objective function with the multiobjective evaluation function. The electric field and potential distribution of the gas‐insulated bushing are greatly improved after optimization, and the electric field strength at key spots is effectively reduced. The insulation system of gas‐insulated bushing for 1100‐kV GIS designed by this method has passed type tests and worked well nearly 3 years. So, this optimization provides a constructive method and useful basis for the design of gas‐insulated bushings for 1100‐kV GIS and other electrical equipment. © 2013 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Assessment of dynamic stability of large-scale power system by Rayleigh's quotient

A method of assessing dynamic stability of large-scale power system by Rayleigh's quotient is proposed. One-machine infinite-bus systems show damping torque characteristics similar to diagonal components of operational transfer matrices for original multimachine systems, which means that design of PSS with one-machine systems controls those components. An expression for damping constants of oscillation modes is derived based on an energy function and its time derivative for a simplified system representation. This expression demonstrates that oscillations do not necessarily become unstable even if there are some generators with negative damping; and the effect of damping torque is determined by eigenvectors. The expression is generalized with Rayleigh's quotient, and a method of estimating eigenvalues of large-scale power systems is proposed. With this method, approximate eigenvalues are refined to accurate eigenvalues. Only a specified number of eigenvalue analyses are required irrespective of the number of generators, hence much calculation is saved. Finally, this method is applied to a 107-machine system to verify its effectiveness.     

A memory efficient testing scheme for combined field integral equation for solving scattering problems using adaptive integral method

A new memory efficient testing procedure for method of moment (MoM) has been proposed for solving combined field integral equation (CFIE) using adaptive integral method (AIM) for closed perfect electric conductor (PEC) scatterers. CFIE is a linear combination of electric field integral equation (EFIE) and magnetic field integral equation (MFIE) and hence the iterative solution for CFIE requires the simultaneous evaluation of both EFIE and MFIE. Using AIM, the MoM testing procedure is obtained by interpolating the grid potentials, computed using fast Fourier transform (FFT), onto the testing functions. For EFIE, the same set of multipole coefficients of the basis functions can be used as the testing functions, without the need to store additional interpolation coefficients. In this paper, we propose a similar simple but efficient and accurate method for the testing procedure for the MFIE using the same multipole coefficients for the basis functions. This enables CFIE to be solved using the same memory resources as EFIE. The accuracy of the radar cross section (RCS) computed for various geometries using CFIE with the proposed testing procedure is shown to be as accurate as the existing method. Copyright © 2005 John Wiley & Sons, Ltd.     

发电机通风系统流场及转子温度场分析

针对电机温度场与通风系统流场间的耦合问题,依据流体力学和热传导理论,建立了某电站700kW灯泡贯流式水轮发电机的通风系统流场及转子温度场的三维有限元模型.采用有限元分析方法,分析了通风系统的流场,获得了通风系统压降和流体流速的分布,进而得到各表面的散热系数,并结合电机各部分损耗热源的计算,分析了发电机的转子温度场分布.结果表明:在满足风机流量下的电机通风压降为464 Pa,与实际运行时的实测数据483 Pa基本吻合;转子温度在其设计的绝缘容许温度范围内,且有足够裕度.     

Analysis of Probabilistic Optimal Power Flow Taking Account of the Variation of Load Power

This paper presents a probabilistic optimal power flow (POPF) algorithm taking account of the variation of load power. In the algorithm, system load is taken as a random vector, which allows us to consider the uncertainties and correlations of load. By introducing the nonlinear complementarity problem (NCP) function, the Karush–Kuhn–Tucker (KKT) conditions of POPF system are transformed equivalently into a set of nonsmooth nonlinear algebraic equations. Based on a first-order second-moment method (FOSMM), the POPF model which represents the probabilistic distributions of solution is determined. Using the subdifferential, the model which includes nonsmooth functions can be solved by an inexact Levenberg–Marquardt algorithm. The proposed algorithm is verified by three test systems. Results are compared with the two-point estimate method (2PEM) and Monte Carlo simulation (MCS). The proposed method requires less computational burden and shows good performance when no line current is at its limit.      

基于小干扰稳定分析的电力系统稳定器配置研究

鉴于小干扰稳定在现代电力系统中的重要地位,在对系统进行建模、仿真、计算的基础上,得到系统振荡模式的特征值、阻尼比、频率和机电回路比,并通过对多机系统的计算分析,研究电力系统稳定器（PSS）的配置策略对低频振荡的抑制作用,从而得出对电力系统小干扰稳定性能的改进办法。     

A practical closed form solution for systems with variable eigenvalues via bilinear system theory

This paper treats systems in state variable formulation with non-constant, parameter controlled system matrices. The synthesis of a system with controlled eigenvalues (ECS) is given. The synthesized system is a commutative bilinear system. Its solution has a closed form and is based on the solution of just one time invariant system although as many arbitrary time functions are involved as the system has independent states. The ECS is homologous to any system with a system matrix being an arbitrary, possibly time-dependent function of a single constant system matrix. All results are deduced for multiple eigenvalues of the system matrix including single eigenvalues as a special case. They are fully analogous to the solution of time invariant systems by means of the Laplace transformation.     

异步发电机自激建压临界值的计算

以自激异步发电机ab轴等值电路为基础,结合系统稳定性理论说明了异步发电机自激建压的条件。对系统的特征值进行分类,定义特征值实部函数,并对不同自激电容和转速下的函数值进行计算。以特征值实部函数绝对值作为目标函数,采用一维搜索优化方法对样机的建压临界电容和临界转速进行计算。新方法与传统方法计算结果一致,验证了新方法的正确性。     

换流变压器出线装置的绝缘结构分析

换流变压器直流出线装置的可靠性是换流变压器研制的关键问题之一,长期以来直流出线装置依靠进口,优化出合理的直流出线装置绝缘结构对进一步促进换流变压器设备制造全面国产化具有重要的意义.笔者总结了换流变压器的运行特点,研究了直流出线装置的绝缘结构,并进行了直流出线装置绝缘结构的电场计算.换流变压器的运行特点为短路阻抗大、直流...     

The simplified method for transient thermal field analysis in a polymeric DC cable

The simplified method of analysis of the thermal field in the futuristic model of a DC cable is presented. The thermal conductivity of a non-conducting layer is very small comparing with the same parameter of conducting regions. The above causes very fast heat propagation in the core and coating, which in the consequences are approximated by inert elements of the first order. Spatial changes in the field in insulation cannot be neglected, because of the significantly slow heat transfer. For that reason, insulation is treated as an element of distributed parameters. The boundary-initial parabolic problem of a non-conducting region is solved by means of Duhamel’s theorem. The fundamental solutions of superposition integrals are determined by the separation of variables method. The maximal deviation of results obtained by the finite element method does not exceed 7.2%. The heating curves and results of verification are presented in a graphic form.     

一例500kV变压器感应耐压试验击穿原因分析及处理

本文针对一例出厂验收过程中的耐压击穿事故,通过油色谱分析、吊芯检查找到了放电击穿点,通过对比设计图确定了中性点和低压引线间缺少绝缘垫块的施工缺陷,分别采用模拟电荷法和有限元法搭建模型,计算了引线间的场强分布。计算结果表明在幅值电压下,无垫块时极间场强达到200 kV/cm,发生油中放电击穿概率大,按标准安装后最大场强不超过40 kV/cm,绝缘裕度较大。文中最后对此提出了预防措施,有利于设备质量管控和绝缘考核分析工作的开展。     

Determination of Electric Field and Space Charge in the Insulation of Power Cables With the Thermal Step Method and a New Mathematical Processing

This paper proposes a technique for determining the distributions of the electric field and space charge in the insulation of power cables by using the data acquired with the thermal step method (TSM). The TSM consists of applying a low-temperature step to a short-circuited or dc-energized cable and of acquiring a transient capacitive current. The processing technique described in this paper is based on a series decomposition of the electric field, the coefficients of the series being identified via the measured current. The accuracy and the stability of the calculation method are evaluated by simulations performed using various distributions of the electric field and different noise levels. An application of the technique to space charge measurements in a dc conditioned power cable is then presented.     

灰色聚类与模糊聚类集成诊断变压器内部故障的方法研究

根据反映变压器绝缘状态的模糊和灰色特征，采用模糊聚类方法，对若干典型故障样本聚类成C个灰类，得到C个最优聚类中心。依据聚类中心矩阵并借助灰色系统理论，提出了一种确定故障诊断各灰类白化权函数的原则和算法，根据该算法，首先求出各待检模式状态的灰色聚类系数，进而建立了一种灰色聚类与模糊聚类相结合的变压器故障诊断的新模型，进行了大量的该模型应用实例分析，结果表明该文方法的诊断准确度高于现有的常用方法。     

A simple and fast algorithm for determining asymptotic stability of linear autonomous systems

The method introduced here determines explicitly whether a given system has only eigenvalues with negative real parts, without determining these eigenvalues, but rather by determining the eigenvalues of a related symmetric matrix which are always real and hence easy to calculate. The new method is similarly applied to linear autonomous discrete systems where all the eigenvalues of the system matrix are required to be positioned within the unit circle in the z-plane.     

超高压电力变压器绝缘计算

本文对SFP400000/500超高压电力变压器的绝缘进行了仿真计算.对主绝缘电场的计算应用有限元法,计算时将主绝缘电场场域划分为三个子区域,得出了各区域中的电位分布和电场强度分布,并计算了相关的绝缘裕度,找出了绝缘的薄弱环节.对纵绝缘电场,建立了绕组在雷电过电压下的电路模型,分别计算了高、低压绕组在全波和截波作用下的电位分布和梯度分布,确定了梯度最大的油道,并计算了相应油道在的全波和截波下的绝缘裕度,为变压器绝缘设计和改进提供了理论上的参考依据.     

Bootstrap方法在局部放电特征提取中的应用

介绍了用Bootstrap方法对局部放电特征的小样本原始数据集重复再采样 ,提取其特征参量的统计信息 ,建立绝缘缺陷特征隶属函数 ,并应用遗传编程分类方法对缺陷模型进行模式识别的方法。试验结果表明该方法有效、可行。     

A computer method for formal linearization of nonlinear systems by the discrete fourier expansion and its applications

This paper proposes a numerical computer method for formal linearization of nonlinear systems by using the discrete Fourier expansion. A nonlinear system is described by a system of nonlinear ordinary differential equations. A linearizing function is given by a sequence of trigonometric functions. The nonlinear terms of the differential equations are expanded into finite sums of trigonometric functions by the method of the discrete Fourier expansion. As a result, a formal linear system is derived from the given nonlinear system. A computer algorithm of the linearization is acquired and numerical computation is easily carried out with the aid of computers. Further, as the application of the linearization, both a nonlinear observer and a nonlinear filter are synthesized in this paper. Examples show that the accuracy of the method is improved as the order of the trigonometric functions increases.     

基于节点电荷电位有限元法的油纸绝缘结构极性反转电场分析

基于电荷一电位有限元法分析换流变压器的油纸绝缘结构极性反转电场,该方法可以直接得到节点电位和节点电荷。对各个时刻节点电荷进行处理,提出得到电荷密度的方法。通过提取一类边界上的节点面电荷密度,可以准确地计算出第一类边界上的法向电场强度,从而可以更好地指导绝缘强度设计。通过一个有解析解的双层有损同轴绝缘结构模型,验证了方法的有效性。最后,分析了一个换流变压器阀侧绕组典型绝缘结构的极性反转电场变化过程。