对称通信电缆工作电容及缆芯外径的计算

利用计算机对塑料绝缘多芯对称通信电缆工作电容与缆芯外径关系进行数值分析后 ,发现引入缆芯外径系数不仅能计算缆芯外径 ,而且还能较精确地计算工作电容。     

基于表面电荷法的输电线路表面电场强度计算

三相输电线路导线表面电荷的分布是不均匀的,各点电场强度的大小也不同.文中采用表面电荷法计算导线表面的电荷密度,然后求出导线表面各点的最大电场强度值.计算方法能够反映出电荷密度及电场强度沿导线圆周分布的情况,根据计算结果优化高压输电线路的布置.     

Moment method analysis for capacitance and charge distribution of dielectric coated metallic disk and closed truncated cone isolated in free space

This paper presents a method for the evaluation of capacitance and charge distribution of a dielectric coated metallic disk and a dielectric coated metallic hollow truncated cone with top and bottom cover plates using the method of moments (MoM) based on pulse basis function and point matching. Boundary conditions for the potential on the conductor surfaces and continuity of the normal component of the displacement density at the dielectric‐free space interface is used to generate two integral equations. Two sets of simultaneous equations are formed from the two integral equations by using MoM. The total free charge on the conductor surface is found from the solution for the set of simultaneous equations. The validity of the analysis has been justified by comparing the data on capacitance available in the literature for metallic disk and hollow truncated cone with top and bottom cover plates, with the data on the capacitance, computed by the presented method for similar structures considering very low dielectric constant as well as very thin dielectric coating. Copyright © 2012 John Wiley & Sons, Ltd.     

Calculation of distribution system voltage and power flow state using measured values

This paper describes a techique of calculating voltage and power flow state of a distribution system using the information measured with two or more switches with sensors installed in a distribution system. In the proposed technique, a set of the power distribution section where two or more switches with a sensor are connected is defined as the large section, and the active power and reactive power consumption in the large section are calculated based on measurement information, voltage (RMS), current (RMS), and power factor. Using the simple distribution system model consisting of the large sections, the power consumption of the large section is calculated by the power flow calculation to separate power consumption and power distribution loss. It is distributed to the small sections that constitute the large section, and detailed power flow calculation is performed. Verification of the proposed technique and basic estimation of the calculation error were performed using the simple power distribution system model. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 164(4): 33–42, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20416     

高压配电网剩余供电能力计算及应用

传统最大供电能力模型未计及电网现有负荷变化规律,计算结果偏理想化,剩余供电能力概念的提出解决了这一问题,但未考虑高压配电网对负荷增长的影响,因此本文提出高压配电网剩余供电能力计算模型.首先对高压配电网的正常运行方式和故障后运行方式进行总结和等效处理,定义独立供电区域的概念,然后在N-1安全准则的基础上,建立剩余供电能力...     

Tuning a three-loop steam temperature regulation system using the method of evolutionary simulation

We present the results from tuning a PI controller and two differentiators for a three-loop steam temperature regulation system with two leading speed signals. The calculation was carried out with a numerical method using a simulation model and with the application of the authors’ version of the evolutionary optimization algorithm.     

Modeling and simulation of an electronically commutatedpermanent-magnet machine drive system using SPICE

This paper describes the design of high-efficiency, electronically commutated, permanent-magnet machine (ECPM) drives based on the finite-element/difference method, and the solution of the ensuing differential equations with the Simulation Program with Integrated Circuit Emphasis (SPICE). The permanent-magnet motor model includes the computation of load-dependent components of the motor-equivalent circuit (e.g., induced voltages and inductances). A new SPICE metal-oxide semiconductor field-effect transistor (MOSFET) model reflecting the reverse-recovery current phenomenon-which is very important for the design of variable-speed drives operating in the pulse-width-modulated (PWM) mode-is introduced. Results of this new model are compared with measurements. Since ECPMs lend themselves well to vehicle propulsion due to their inherent high efficiencies at light weight, it is desirable to have a very high output-power-to-weight ratio for such applications. In addition, high ECPM drive efficiencies are important for recovery of the braking energy     

TDX-200透射电镜照明系统的计算与仿真

透射电子显微镜(transmission electron microscopy,TEM)的照明系统包括电子枪和聚光镜,它要求能提供最大亮度的电子束,照射在样品上的电子束孔径角必须能在一定范围内调节,照明斑点的大小可按需要选择。在调试过程中需要预先对照明系统激励参数进行计算。基于TDX-200透射电子显微镜,对双聚光镜照明系统的功能实现进行了理论分析,结合实际尺寸进行了理论计算与实际仿真,并在实际调试过程中进行了初步验证。     

冰蓄冷低温送风系统风管路计算与经济分析

与常规空调系统相比,由于冰蓄冷低温送风系统的送风量减小,可节省风管投资,减少风机轴功率。计算可知,当低温送风的风量减少一半时,低温送风与常规送风管路的保冷投资基本相当。而低温风管尺寸减少约50％,节省风管投资约30％,风机轴功率减少约48％。因此,低温送风空调输配系统,是一种经济的供冷输配方式。     

Evaluating the integration of wind power into distribution networks by using Monte Carlo simulation

This paper provides a probabilistic method to assess the impact of wind turbines (WTs) integration into distribution networks within a market environment. Combined Monte Carlo simulation (MCS) technique and market-based optimal power flow (OPF) are used to maximize the social welfare by integrating demand side management (DSM) scheme considering different combinations of wind generation and load demand over a year. MCS is used to model the uncertainties related to the stochastic variations of wind power generation and load demand. The market-based OPF is solved by using step-controlled primal dual interior point method considering network constraints. The method is conceived for distribution network operators (DNOs) in order to evaluate the effect of WTs integration into the network. The effectiveness of the proposed method is demonstrated with an 84-bus 11.4 kV radial distribution system.     

Point estimate method for probabilistic load flow of an unbalanced power distribution system with correlated wind and solar sources

Context: The electric parameters of the power networks are usually analysed through deterministic power flows; however, the variation in load demands and power fluctuation of renewable generators cannot be considered with the deterministic power flows because it uses specific power values. The probabilistic power flow methods are better for this purpose since they apply techniques to include and reflect the uncertainty of input variables on the results obtained.Objective: This paper extends the Point Estimate Method (PEM) applied to the probabilistic power flow of an unbalanced power distribution system with dispersed generation and variable power factors. This method is applied to include uncertainties of loads and power sources such as wind and solar. As PEM requires independent input random variables, but usually there is spatial correlation between loads or power sources; therefore, Cholesky decomposition is applied to deal with this situation.Method: In this paper are combined the scheme 2m+1 of the Point Estimate Method with the Cholesky decomposition and some approximation methodologies to estimate the cumulative distribution function of some electrical parameters.Results: The results obtained are the moments about the mean of the output variables, which are used in conjunction with some approximation methodologies to obtain an estimation of the Cumulative Distribution Function for nodes or branch parameters. The proposed methodology is tested on the three-phase unbalanced IEEE 123-node test system, and results are compared with those obtained from the benchmark Monte Carlo simulation.Conclusions: There are comments on some pertinent information about Point Estimate Method performance on this kind of power systems.     

Assessment and analysis of the reliability of an electrical distribution system integrated with a wind energy system

From the results of a report previously prepared by Systems Control Inc., it was recommended that a wind turbine generator (WTG) should be integrated with a conventional system to assess the reliability of the combined systems, estimated on yearly-based data. In contrast, in this paper, the issue is reinvestigated to get an accurate estimation of the capacity and energy credits, and the reliability level using monthly average daily climatic data.The second main contribution of this work is to find the effect of the WTG penetration level on its power and energy credits, reliability and costs and eventually on the distribution system reliability. In addition, the influence of different configurations of the distribution system on its reliability in the presence of the WTG will be investigated for all seasons of the year.New mathematical models explicitly describing these impacts are developed.     

DTS中继电保护仿真方法的比较和分析

阐述了继电保护仿真的重要性,以相间距离保护为例,比较和分析了逻辑判别法、定值比较法和半逻辑半定值法继电保护仿真的特点及实用性.     

工厂配电系统电能质量仿真与治理方案研究

针对某汽车厂车身车间电能质量治理的需要,提出了一种动态无功补偿器和有源滤波器并联运行的补偿方案.给出了无功补偿器和两台APF并联运行的主电路,优化CT的安装位置,实现了谐波电流的前馈、反馈控制.设计了无功补偿器的参数,分析了无功补偿器分组投切和有源滤波器的控制策略,并采用电磁暂态分析程序(EMTP)对提出的方案进行了仿真.仿真结果和现场测试结果吻合,该方案能显著提高10/0.4kV系统功率因数,并使注入电网的谐波电流达到IEEE 519.1992的要求.