计算双层土壤参数的一种新方法

针对接地系统电气参数计算需要建立准确的大地模型和土壤参数问题,分析了水平分层土壤结构的地表电位,定义了土壤的视在电阻率,建立了土壤模型目标函数,并对建立的函数模型进行了最优化计算.计算分析结果表明,采用改进的Levenberg - Marguardt最优化方法计算所得的双层土壤模型可以反映实际地下土壤分层状况,可快速求出双层土壤参数.     

A new method to calculate thermally balanced windings of power transformers

Contents Windings of large power transformers are usually cooled by a directed and pump forced oil flow. This so-called OD cooling is the most effective method to extract the heat generated by losses inside the transformer. Thereby, the distribution of the entire oil flow rate to the individual windings determines the thermal condition inside the transformer and is for this reason of essential interest for the construction of the core-and-coil assembly. This article describes a new calculation method for the oil flow rate distribution. Using this method, thermally balanced windings can be achieved. Thermally balanced windings lead to an optimal layout and ensure optimal thermal operating conditions. Thermal stresses of the oil/paper insulation system are minimized which also leads to a positive effect on the transformer's lifetime.

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Eine neue Methode zur Berechnung thermisch ausgeglichener Wicklungen bei Leistungstrans-formatoren

Übersicht Bei Transformatoren mit sehr großen Leistungen werden die Wicklungen durch einen gezielten und durch Pumpen forcierten Ölstrom gekühlt. Diese als OD-Kühlung bezeichnete Kühlungsart ist die effektivste Methode, um die durch die Verluste im Transformator entstehende Wärme abzuführen. Wichtig für das Funktionieren des Verfahrens ist die richtige Aufteilung der gesamten zur Verfügung stehenden Ölmenge auf die einzelnen Wicklungen. In diesem Beitrag wird ein Berechnungsverfahren vorgestellt, mit dem die Ölmengenaufteilung so berechnet wird, daß thermisch ausgeglichene Wicklungen entstehen. Thermisch ausgeglichene Wicklungen bedeuten für den Transformator eine optimale Auslegung und stellen optimale Betriebsbedingungen in thermischer Hinsicht sicher. Die thermische Beanspruchung der Öl/Papier-Isolation wird minimiert, was auch einen positiven Effekt auf die Lebensdauer haben dürfte.

     

一种计算三相不对称系统视在功率的新方法--BG法

视在功率是一个重要的电气物理量，在三相不对称系统中有两种不同的视在功率定义，即算术视在功率和相量视在功率，多年来这两个视在功率的争议不断，不同的功率定义导致了不同的计算结果及测量手段上的混乱，本对现行的视在功率的定义进行了讨论，介绍了计算三相不对称负载和非正弦交流电路视在功率的一种新算法——BG法。     

一种估计小电流系统线路对地电容的新方法

中性点绝缘系统的接地电容电流 ,是电力系统的重要参数之一。通常采用附加电容法和金属接地法进行测量和计算 ,但前者测量方法复杂 ,并且附加电容对测量结果的影响较大 ,而后者试验中又具有一定的危险性。为此 ,提出了一种利用单相接地故障数据估计小电流系统对地电容电流的新方法。该方法适用于对误差要求不很严格并且工作量较大的场合 ,经过仿真表明 ,结果基本准确。     

一种估计小电流系统线路对地电容的新方法

中性点绝缘系统的接地电容电流,是电力系统的重要参数之一.通常采用附加电容法和金属接地法进行测量和计算,但前者测量方法复杂,并且附加电容对测量结果的影响较大,而后者试验中又具有一定的危险性.为此,提出了一种利用单相接地故障数据估计小电流系统对地电容电流的新方法.该方法适用于对误差要求不很严格并且工作量较大的场合,经过仿真表明,结果基本准确.     

一种谐波和无功电流检测的新方法

将自适应噪声对消技术用于谐波和无功电流检测,提出了一种基于神经网络的自适应检测的新方法。所提出的方法适用于有源电力滤波器的谐波和无功电流检测。理论分析和仿真结果证实了该方法的可行性。     

计算和分配输电成本的一种新方法

针对我国电力市场目前的特点,提出了厂网分开后参加交易的输电公司输电成本计算和分摊的新方法。在保留边际价格经济信号的同时,综合考虑了容量成本和固定成本的回收,激励输电公司为消除阻塞,提供容量备用及电网的健康发展做出贡献,同时进行了固定成本的回收,使模型更加合理、完善。算例结果表明,所提方法简单易算,具有重要的理论和实际意义。     

A new method for decaying dc offset removal for digital protective relays

Voltage and current signals used in protection devices may contain harmonics and decaying dc offset in transient states. Because of this, protection devices must contain filters to remove the part of the signal which is not of interest and estimate the value of the component or components which are to be used for protection functions.Traditionally, the discrete Fourier transform (DFT) filter has been used in digital protection devices. This filter has the advantage of being easily applied, but the disadvantage that when an exponentially decaying component is present the results obtained are incorrect. Because of this, different algorithms based on the DFT have been developed in order to remove the decaying dc offset and reduce digital processing errors.This paper describes a new method for removing the exponential component associated with electrical signals in transient states. Its ease of application results in a low computational load as compared with other methods. This characteristic, together with the accuracy of results, makes this new method suitable for application in real time on protection devices.     

一种滤除衰减直流分量的电流估计新算法

电力系统的故障电流中存在指数函数型衰减直流信号,直接采用离散傅里叶变换(DFT)算法测量基波电流的误差较大.提出一种从故障电流信号中消除衰减直流分量的新算法,基于纯正弦波信号在一个全波周期积分为零、而指数衰减信号在一个全波周期积分不为零的原理,用一个全波周期加前一个采样周期的采样数据,就能精确估计出指数函数型衰减直流信号的幅值和时间常数.每个采样数据减去衰减直流分量偏移量后,用全波DFT算法就可精确估计故障电流.在Matlab仿真平台上,进行综合仿真试验表明:所提算法测量精度高,易于用DSP实现,可应用到基于DSP的数字继电保护装置中.     

A high-precision real-time approach to calculate closest unstable equilibrium points

In this paper, an innovative real-time approach is presented in order to compute the closest unstable equilibrium points of system. The proposed approach estimates unstable equilibrium points of system at the first time step of fault duration and there is no need to post the fault data. To such aim, a new concept of equal area criteria is proposed in this paper which estimates the initial value of critical points of the system. This value is used in order to calculate corrected kinetic energy and as a result the closest unstable equilibrium point by taking into account the fault trajectory. Moreover, the details of power system are considered to calculate unstable equilibrium point by utilizing network preserving model. Finally, several case studies have been conducted on IEEE 9 bus and the New-England 39 bus test systems to illustrate the benefits of the proposed approach. It is worth noting that considering structure preserving in modeling and at the same time simplicity in implementation and low computational burden are the main salient features of the proposed approach. As a result, the proposed method is suitable for real-time applications.     

PCB导体电感的简化计算方法

本文提出一种对不规则形状印制电路板(PCB)导体进行简化计算的方法,以某变频空调室外机主板上的正、负直流母线PCB导体为例进行了简化,通过解析公式计算得到它们的电感,并与简化前用电磁场数值计算软件求得的电感进行比较,证明这种简化方法是有效的.通过在PCB导体的等效电路模型的输入端施加电压激励,比较输出端的仿真计算和实验测量结果来验证模型中参数,结果表明简化后PCB导体的电感参数是准确的.这种PCB导体的简化计算方法简便易行,具有较大的实用价值.     

A new symbolic analysis approach to the DC load flow method

A new symbolic analysis approach is proposed to the DC load flow method. The power system network parameters are given by symbols and the system active line power flows are derived analytically as closed-form symbolic expressions. An original program SALF is presented as a universal tool to find the line powers by an automated computer-aided algorithm. The theory of the DC load flow method is reviewed. The approach is illustrated by standard network examples. The approach exposed is targeted at researchers and experts dealing with analysis, planning and operation of transmission power system networks.     

A hybrid numerical method to calculate the sag of composite conductors

A modification to the numerical sag method (NSM) for predicting conductor sag is presented that accurately predicts the observed bilinear sag behavior of composite conductors. The modified method, called the hybrid sag method (HSM), uses the stress–strain curves of conductors to calculate the initial load distribution between the components of the composite conductors. In this study, the HSM is used to predict sag of conductors with conventional designs. The HSM predictions are compared with those obtained using a conventional graphical sag method as well as NSM. The HSM shows superior accuracy over NSM and virtually the same accuracy as the graphical method for predicting sag for composite conductors operated under specific conditions. The HSM predictions of sag are validated by comparisons with experimental measurements.     

A new PWM control method for AC to DC converters withhigh-frequency transformer isolation

A PWM control method for a switch-mode rectifier (SMR) based on the idea of coordinate transformation is presented. This method realizes sinusoidal input current waveforms, a controllable input displacement factor, and an arbitrary output voltage waveform. This method is advantageous for reducing higher and fractional harmonic components of the input waveforms and is suitable for real-time control. Simulations and experiments are carried out to confirm the feasibility of the proposed method     

A new methodology to calculate Carter factor using genetic algorithms

This paper presents a methodology to calculate the value of Carter's factor for airgaps with polygonal slots. A numerical evaluation of the Schwarz–Christoffel transformation is performed using Genetic Algorithms. The methodology presented here extends Carter's method to airgaps with more complicated geometry. Some case studies compare the results of the developed methodology to Carter's results. Copyright © 2010 John Wiley & Sons, Ltd.     

独立光伏系统最佳倾角计算新方法

对于有均衡或非均衡负载的独立光伏系统,在计算最佳倾角b时,可先计算出不同倾角下各月倾斜面上的辐射量占该倾角下全年总辐射量的比例以及各月负载耗电量占全年总耗电量的比例。将以上两种比例进行比较,取使得各月辐射比例与负载比例最匹配的倾角为最佳倾角。匹配程度可用最小二乘法计算。文章辐射数据使用上海市1961-1980年的太阳光辐射月平均数据,对均衡及非均衡负载计算了最佳倾角,并做了分析。     

一种新型单相DC/AC逆变器的并联控制方法

本文介绍了一种新型的单相逆变器并联控制方法.控制方法分为同步和均流控制两个部分,同步控制采用有功功率进行相位调节,均流控制采用注入的谐波信号进行幅值调节.这种新型的控制方法在逆变器之间没有任何的均流连接线,实现了无均流线的均流,它非常适合于远距离分布电源的并联控制.本文对这种方法进行了详细的介绍,并给出了仿真和实验结果,结果证明了这种方法的有效性.     

A new modeling approach to single-link flexible manipulator using singular perturbation method

This paper presents a new methodology for modeling a single-link flexible manipulator with an arbitrarily large (infinite) number of deflection modes based on the singular perturbation method. It is shown that a part of the fast dynamics of the singularly perturbed system representing flexibility is treated as a norm-bounded uncertainty. In other words, the proposed approach to modeling actually characterizes, in some sense, a reduced-order model of the system. Output feedback control of the tip position is controlled by utilizing the -dependent H technique on the rest of the certain dynamics of the manipulator. Robust regulation is obtained by minimizing the influence of the uncertainty on the tip position. The proposed strategy is applied to a single-link flexible arm and the simulation results verify the effectiveness of the analysis and design.     

A new approach to coal interface detection: the in-seam seismictechnique

A novel approach to detecting coal/roof and coal/floor interfaces during mining operations is presented that is based on a seismic acquisition method integrated with various signal processing techniques. Seismic transducers (accelerometers) are affixed to the roof, coal, and floor at a certain distance from the mining machine. Unique seismic signals are generated during mining, depending on which stratum is being cut. A discriminator extracts and stores mathematical parameters which are characteristic to the signals in the form of an adaptive learning network (ALN). The system is initially trained to recognize three cases by intentionally cutting reference samples of roof, coal, and floor. The computer uses the ALN to tell where unknown signals associated with the mining process originate. Via a feedback loop, the computer has potential for keeping the machine in the coal seam