A method of mutual coupling effects of multi‐parallel routes in the presence of unbalanced faults

The symmetrical method is even now one of the common theoretical approaches to simulating the faulted state of an electric power system, despite this method having major disadvantages, especially for unbalanced fault calculation on multi‐parallel routes due to the necessity of forming a complex equivalent zero‐sequence network. In order to protect the power system, including the multi‐parallel routes in it, from disturbance, a method that can solve the faulted state accurately and efficiently when a disturbance occurs on a multi‐parallel route is needed. From this point of view, this paper presents a newly developed fault calculation method which can easily incorporate the zero‐sequence mutual coupling effect among multi‐parallel routes without any topological changes of the symmetrical network. In the proposed method, the mutual coupling effect is treated as a voltage source inserted into each parallel branch to compensate the mutual coupling effects of other circuits. Since the voltage source can be equivalently expressed as the injection currents of the connected nodes, the faulted state can be calculated easily without topological changes of the zero‐sequence network. Numerical results for several relevant cases are presented to demonstrate the effectiveness of the method. © 2001 Scripta Technica, Electr Eng Jpn, 136(2): 9–17, 2001     

三维表面电荷法在位场计算中的几点改进

针对常规三维表面电荷法在位场计算中采用平面单元剖分、常值电荷估计致使计算效率低内存消耗大的缺点,对表面电荷法进行改进。采用曲面三角形单元对曲面进行剖分并通过二次多项式进行插值,利用线性或二次插值估计电荷密度以反映电极表面电荷密度的线性及非线性分布的特点,在奇异积分处理上通过切平面法解决格林函数基本解的奇异积分,并给出其具体实现。最后通过两个典型算例进行了验证,结果表明该方法精度较高,具有一定可行性。     

A novel interpretation of the hyperbolization method used to solve the parabolic neutron diffusion equations by means of the wave digital concept

In this paper, the neutron diffusion equations in two energy groups will be dealt with. The underlying parabolic differential equations as well as a hyperbolized version of them will be numerically solved with the wave digital concept. While the hyperbolization process avoids delay-free directed loops in the wave flow diagram, a direct implementation of the parabolic differential equations does not. However, an iteration method can be used to overcome these problems. This results under certain conditions in the same wave digital model. This way, it can be shown that the commonly used hyperbolization can be interpreted as the application of an iteration method. Copyright © 2006 John Wiley & Sons, Ltd.     

一种含分布式电源的配电网三相潮流混合计算方法

针对现有配电网三相潮流计算方法的不足,提出了一种新的含分布式电源的配电网三相潮流混合计算方法。分析了配电网中相关元件的特点,建立了配电线路、配电变压器和负荷的三相数学模型。对4种不同类型分布式电源节点的处理方式进行了分析,采用前推回代法和牛拉法的混合计算方法建立了三相潮流计算模型。采用回路阻抗矩阵法来计算三相电压差,解决了单相潮流计算方法的适用性问题,采用以节点电压的收敛性作为潮流计算程序迭代与否的控制目标,可直接求取电压值,迭代计算简洁高效。最后,以包含分布式电源的IEEE 33节点网络模型和山滩变某10 kV配电线路为例,验证了该混合计算方法的收敛性与高效性。     

A comparative study on using linear programming and simulated annealing in the optimal realization of a SC filter

The switched‐capacitor (SC) circuit realization problem is traditionally solved by heuristic algorithms. However, an algorithm‐like simulated annealing (SA) is stochastic, and its behavior in solving a non‐convex optimization problem is unpredictable. In this paper, we make an investigation on using a deterministic and a stochastic optimization algorithm for solving the realization problem of the classical Fleischer–Laker SC filter. By considering minimum area as the design goal, we prove that the a linear programming‐based deterministic algorithm is capable of finding a global minimum. With the global optimality established, we then use an SA algorithm to solve the same problem in purpose of investigating the search capability of the SA algorithm. We find that the stochastic SA algorithm cannot always reach a suboptimal solution with quality comparable with the linear programming result. Other issues like convergence speed and the percentage of arriving at the global minimum are examined as well. This research exposes that understanding the underlying optimization problem structure for the realization of SC circuits is of fundamental meaning for developing more efficient heuristic algorithms. Copyright © 2017 John Wiley & Sons, Ltd.     

A study on condition assessment method of gas‐insulated switchgear. part II. influence of moisture in the SF6, detection of a partial discharge on a spacer,repetition discharge and overheating by incomplete contact

Rationalization of the maintenance of gas‐insulated equipment under operation and lifetime extension based on the results of appropriate diagnosis are necessary to reduce the cost of gas‐insulated equipment. Therefore, condition‐based maintenance (CBM) is required and accurate methods for observing the inside of equipment are important. In this report, we describe a diagnosis method that can be used for actual gas‐insulated equipment, such as to assess the deterioration of the spacers made of epoxy resin and to detect loose connections in the central conductor. The principal results are summarized as follows: (1) The quantity of decomposition gases depends on the moisture and magnitude of the partial discharge. However, decomposition gases were detected even if SF₆ had low moisture content (less than 100 ppm) similar to that used in actual equipment. This means that our method can be applied to actual equipment. (2) It became clear that CF₄ is a typical gas generated by partial discharge on the spacer surface. Therefore, it is possible to diagnose spacer deterioration by monitoring CF₄. (3) Decomposition gases (SF₄, SO₂, SO₄, SO₂F₂) were generated by impulse breakdown, which was assumed to be due to repetition discharge caused by insulation failure and loose connections. (4) SF₆ gas was assumed to be exposed to a loose connection and was heated from room temperature to 800 °C, and the generated decomposition gases were analyzed by FTIR in real time. As a result, the decomposition gases were generated at temperatures above approximately 500 °C in a heating time of 1.5 minutes. Therefore, a loose connection can be detected by analyzing the decomposition gas. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 176(2): 22–30, 2011; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21108