Surge analysis of the tank of a gas-insulated line using lumped constant circuits

Surge voltages evaluated by a digital analysis method, for example, electromagnetic transients program (EMTP) and by an analog analysis method (transient network analyzer: TNA) are compared with experimental results on a scaled model of a gas insulated line. From the results, it is confirmed that the analog analysis method has a satisfactory accuracy and its computing speed is quite high. The error caused by the lumped element modeling of the gas insulated line is comparatively small, and the line is not necessary to be treated as a distributed parameter line. The lumped element model is advantageous to understand the mechanism of the transient characteristic of the induced transient voltage. A simple equivalent circuit of the gas insulated line is proposed and its accuracy is confirmed by a comparison with the calculated result obtained by an accurate line method. The transient overvoltages of the tank and across the insulated flange can be analytically calculated using the equivalent model.     

采用单、三相变压器混合线路降低线损

降低线损是供电部门的一项重要工作,而大部分线路损耗是在10kV以下的配电线路上。在配电线路上采用单、二相变压器混合供电方式．以高压进户、缩短低压线路降低线损为目的,使配电线路线损有了较大幅度降低,提高了供电可靠率和电压合格率。     

Three winding transformer s-domain model for modal analysis of electrical networks

This paper describes an s-domain sequence model for three winding transformers to be used in modal analysis of ac networks. The model takes into account off-nominal tap positions and the phase shifts among the windings. The main contribution of this proposed model is to complete the set of s-domain models of electrical system components already developed (loads, transmission lines, generators, harmonic filters, shunt elements) suitable for modal analysis of complex electrical networks. Modal analysis provides an important set of system information that is hard to be obtained using the conventional time simulation and frequency response methods. This information may be effectively used to improve the harmonic performance of electrical networks, to build linear equivalents for harmonic and electromagnetic transient studies and to perform linear dynamic performance analysis.     

A study of modeling of EMTP analysis for indoor distribution line

Damage to home electric appliances due to lightning surges has recently become more common. The installation of SPDs (surge protective devices) in interior wiring is a countermeasure against damage and is also becoming more widespread after amendment of the regulation on indoor wires in 2005. Past study showed an effective method in which the earth line of the SPD is connected with that of home appliances and is grounded at one place in the home. However, because the methods of installing the distribution line in homes vary, it is difficult to estimate the effect of SPDs in every home, and high‐precision analysis by EMTP for interior wiring and SPD in the home is required. In this study, experiments were conducted with interior wiring and varistors, which constitute SPDs, and this paper reports the results of those experiments and of EMTP analytical models. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 175(4): 24–33, 2011; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21062     

Statistical analysis of lightning surges on distribution lines based on the observation

Probability distribution of surge discharging current of arresters provided a basis for conventional theory of grounding systems. In order to rationalize the grounding systems, it is necessary to grasp the statistical data of lightning surges on distribution lines caused by direct lightning strokes and indirect lightning strokes. Lightning phenomena on TEPCO's distribution lines had been continuously observed for the rationalization of lightning protection design of distribution lines. The observation had been carried out with still cameras and monitoring sensors of lightning surges. This makes it possible to discover new interesting facts that can be useful for rationalization of lightning protection design of distribution lines. Cumulative frequency distribution of conventional data is close to that of ZnO discharging current in the case of direct strokes and indirect strokes through TEPCO's observation. Moreover, to verify the cumulative current distribution in concrete poles, the authors have compared the cumulative distribution of current through ground lines with that of current through ground lines and concrete poles. The results show that the distribution of current through ground lines and concrete poles is larger than that of current through only ground lines for high currents exceeding 1 kA. This fact suggests that lightning surge current flows not only in ground lines but also in concrete poles. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 165(2): 36–44, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20468     

Modal decoupling of overhead transmission lines using real and constant matrices: Influence of the line length

The Clarke’s matrix is a well-known real and constant transformation matrix used for modal transformation in three-phase transmission lines modeling. Although modal analysis has been widely discussed in the technical literature on power system modeling, a new content is approached in this research proving that the approximation using an exact and constant modal transformation matrix depends on both the frequency-dependent parameters and transmission line’s length. As an important conclusion, the approach using the Clarke’s matrix leads to more accurate results considering long transmission lines. There are two methods for modal decoupling in power systems modeling. The first uses only a single constant and real transformation matrix during the entire modeling/simulation routine. The second uses the frequency-dependent transformation matrix for parameters decoupling into the propagation modes and the Clarke’s matrix for mode-to-phase transformation of voltage and current values during simulations. The accuracy of these two modeling/simulation processes are evaluated, in the time and frequency domains, based on results obtained from a reference routine that employs the exact frequency-dependent matrix in modal transformations and numerical transforms for simulation in the time domain. The proposed analysis proves that the accuracy of both methods varies with the line length during electromagnetic transient simulations that leads to peak errors up to approximately 10%. The influence of the line length in modal analysis techniques was not approached in previous references on power system modeling, which represents the original contribution of this paper.     

理论线损分析系统在上海电网的实现和应用

指出理论线损分析系统由理论线损计算系统和理论线损分析系统组成,其功能包括分析功能、数据输入编辑功能、计算功能、查询功能等,按照配电网的电压等级区分理论线损分析系统的计算方法的特点,对分析系统的分析功能、输入、计算等方面进行说明,介绍了理论线损分析系统在上海的实现和应用.     

特高压杆塔的非均匀传输线模型

随着输电电压等级的提高,线路杆塔也越来越高,其从底部到顶部空间结构变化也越大。如果特高压杆塔仍采用多波阻抗模型,则不能反应其呼高的空间结构变化所产生的影响。文中首先介绍了杆塔的多波阻抗模型,然后指出多波阻抗模型的不足,再从杆塔物理结构出发搭建了杆塔简化的非均匀传输线模型。文中还将杆塔呼高用多段波阻抗模拟,研究杆塔呼高空间结构变化对其电磁暂态特性的影响。最后,对比了非均匀传输线模型和分段多波阻抗模型下杆塔的雷电电磁暂态响应,表明相比于多波阻抗模型,非均匀传输线模型更适用于特高压杆塔雷电暂态分析。     

Efficiency evaluation of lightning fault inspection in 66‐kV transmission line

A transmission line must be immediately inspected when it is struck by lightning, and damaged parts must be found and changed promptly if the damage is serious. However, such cases are now uncommon owing to the effective design of the lightning protection system now in use. Therefore, it is important to compare data on past lightning events and on transmission lines and to formulate criteria for deciding more precisely in which cases an actual inspection should be carried out. The criteria identified are as follows: (1) the insulator voltage exceeds the critical voltage; (2) the arc current and arc duration exceed the characteristic of insulator breakdown; (3) the number of accident phases is more than 3 ground faults per circuit; (4) the tower foot resistance is 10 ohms or more; (5) the lightning current has a positive characteristic. By using these criteria, the number of lightning fault inspections was reduced by 34%. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 166(2): 15–22, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20724     

An impedance measurement of a small‐capacitance circuit using transient responses for lightning surge analysis

A method to measure a small capacitance with its loss resistance using a set of transient current waveforms is proposed in this paper. The parameters are obtained from the time constants in the time domain. The method has high resistance to extraneous noise, because a time‐to‐frequency transformation, which is sensitive to noise, is not required. The transient current waveforms are obtained by a voltage or current source, a current transformer, and a waveform recorder. The measured capacitance by the proposed method is not affected by the capacitance of the voltage probe, because it is obtained without any voltage information. The sheath surge impedance of the current injection cable, which is indispensable for the transient measurement, is corrected. The application of the method has the advantage in that it allows the modeling of a fast transient of a power apparatus, comparing it with the steady‐state measurement using an impedance measuring instrument. The proposed method is applied to create an equivalent circuit between electrodes implanted into a piece of wood, and its reliability is confirmed by comparison between the measured and calculated results. Stray capacitances of a miniature circuit breaker are also measured, and the results show that the proposed method is applicable to equipment in power systems. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Statistical analysis of lightning performance of distribution lines based on observation in fields

Because of the lower insulation level than for transmission lines, in this study on lightning protection design of distribution lines, not only direct lightning strokes but also induced voltages caused by nearby strokes must be taken into account. Thus, it is necessary to grasp the frequency of occurrence of lightning phenomena around distribution lines. For this aim, lightning phenomena on TEPCO's distribution lines in use were continuously observed for 6 years (1996 to 2001). Through this observation, new interesting statistical data that can be a useful basis for rationalization of lightning protection design of distribution lines were obtained. Two hundred and four lightning strokes were observed through the six‐year period. Probability of occurrence of a direct stroke was 22% (45 direct strokes were obtained). The fact that in 47% of direct strokes the electric outage did not occur is very interesting. Moreover, the value of surge discharge current of the arrester in the case of nearby stroke is the basis for conventional theory of grounding system. Therefore, statistical analysis of ZnO discharging current in the case of nearby strokes was carried out. As a result, in the case of nearby strokes, 5% value of cumulative frequency of discharging current is 0.5 kA. This value is half the conventional data. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 155(2): 8–16, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20180     

随机脉动风场作用下输电塔线体系的动力响应分析

输电杆塔及塔线耦联体系是电力系统输电过程的重要载体,沿海地区的强风对输电杆塔及塔线体系有着重要影响,为研究在随机脉动风场作用下输电杆塔及塔线体系的动力响应特性,本文以广东某地区的1W2C9型鼓型自立式输电杆塔为研究对象,建立了输电杆塔的单塔及一塔两线的塔线耦联有限元模型,结合Davenport风速谱与四阶自回归法模拟了具有空间相关性的单塔9节点及塔线49节点的脉动风场,研究在此脉动风场下的单塔及塔线体系的动力响应,并探究不同风向角对其动力响应的影响。研究结果表明:无论是单塔还是塔线体系,其动力响应最大值都要大于其拟静力响应;输电线的存在会增加输电塔线体系的稳定性,降低其位移及动力响应;90°是输电杆塔及塔线体系动力响应的最不利风向角。     

线路避雷器在广东电网输电线路上异常运行情况的分析

对广东电网应用线路避雷器作为输电线路防雷新措施实施9年以来线路避雷器所发生的异常运行情况进行了分析,包括了产品质量原因引起的故障、安装或选点不当等原因引起的运行异常以及自然灾害或极端气象条件引起的线路避雷器损坏等。总结了安装及运行经验,提出相应的对策,为线路避雷器这项新技术的推广应用提供了指导。     

湖南500kV输电线路覆冰倒塔原因分析

对湖南500kV复沙Ⅰ线倒塔段应用大型通用有限元程序ANSYS建立单元模型,计算出铁塔随导线覆冰厚度变化的极限承载力,分析了该事故段铁塔倒塌的原因.根据计算结果,对铁塔的2种局部加强方案进行核算,并提出改造建议.     

复沙500kV输电线路Ⅱ回拉线门型塔屈曲分析

复沙Ⅱ回500kV输电线路ZH91拉线门型塔为新设计塔型,使用前未进行真型试验,运行中该塔失稳。应用有限单元法对该塔的不同荷载工况进行了屈曲分析。结果表明,在覆冰荷载和导线不平衡张力荷载下,该塔横担下边框主材屈服;事故后的真型试验验证了计算结果的正确性。最后对铁塔进行了改进验算,将横担下边框主材规格由80mm×6mm改为100mm×8mm时,铁塔强度满足设计要求。     

Insertion of wind generators in electrical power systems aimed at active losses reduction using sensitivity analysis

The study evaluates the electrical power system behaviour when wind turbines are inserted into the power grid. The assessment is made using a sensitivity analysis technique applied to the power flow solution. Unlike the typical algorithms, the sensitivity analysis technique does not require an iterative process, resulting in a fast method with great precision. This proposed method make easy to check the wind turbine behaviour to the changing of wind speed. Initially, the power flow solution is obtained and identified as the base case. When there are perturbations in the generators, the new solution is obtained directly by sensitivity analysis technique. The technique was applied in 34-bus, 70-bus and 126-bus test distribution system. The places chosen to connect the wind turbines were determined by the Incremental Transmission Losses method. The results demonstrate the effectiveness of the methodology. When wind turbines are inserted in the studied systems, active and reactive losses are reduced and voltage profile is improved.     

单相电源法测量单回不对称线路阻抗参数的误差分析与改善措施

随着高压输电线路数量的日益增多,因此大多数线路都采用不换位的架设方式,该文对单回不换位线路三相阻抗参数测量时所采用的单相电源测量方法产生误差的原因进行了分析,由于测量电路考虑了大地电阻对阻抗参数的影响,因此提出了一种新的测量大地电阻的方法。在进行单回不换位线路三相阻抗参数的计算时,电流矩阵的求逆运算给三相阻抗参数的计算带来了很大的误差,并且推导出了误差项的表达式,为了减小误差,文中提出了采用双端测量方法测量出三相线路首、末端的电压和电流,最后以一条500 k V的单回不换位线路为例,利用首、末端得到的三相电压、电流量在进行单回不换位线路三相阻抗参数的计算时可以减小误差,验证了文中方法的可行性。     

葛洲坝220 kV开关站葛陈线线路保护动作行为分析

2003年8月24日,葛洲坝220kV开关站葛陈线发生C相瞬时接地故障,线路没有进行重合而直接三相跳闸。该文先简单介绍了葛陈线故障发生时系统的运行工况和各侧线路保护的动作情况,然后通过系列的推导和相关的试验,全面分析了葛陈线两侧线路保护装置在此次线路故障中的动作行为。     

A transient current based double line transmission system protection using fuzzy-wavelet approach in the presence of UPFC

This paper presents a wavelet fuzzy based protection scheme for a double line transmission system with unified power flow controller. The protection scheme makes use of current signals at both the ends of transmission line which are synchronized with the help of global position system clock. A wavelet based multiresolution analysis is used to find the detailed coefficients of these signals which are utilized to calculate fault index. These fault indexes are compared with a threshold value to detect and classify faults on transmission system. The approximate decomposition of the current signals is utilized to locate the fault using Fuzzy logic from their respective terminals. The proposed algorithm has been tested successfully for various faults at different locations.     

保护在同杆双回线动模试验中的动作分析

对一种超高压数字式线路保护装置在同杆并架双回线路500kV动模系统上的试验情况进行了分析。与单回线保护相比，同杆并架双回线保护必须解决在跨线、转换性等复杂故障下的选相跳闸问题。在500kV系统200km及400km线路长度的同杆并架双回线模型上，以及41km的三角环模型上所做的动模试验，表明所采用的突变量选相元件及负序零序电流选相元件不能完全正确地选相，阻抗元件一般情况下可以满足双回线故障的要求，但应注意跨线不接地故障及零序互感对阻抗元件的影响，长线路重负荷下转换性故障可能使纵联零序电流保护灵敏度不足。试验是在RTDS设备上进行的，试验表明解决这些问题所采取的措施可行。