Voltage sags in industrial systems

The cause of voltage sags in industrial plants, their impacts on equipment operation, and possible solutions are described. The definition proposed focuses on system faults as the major cause of voltage sags. The sensitivity of different types of industrial equipment, including adjustable speed drive controls, programmable logic controllers, and motor contactors is analyzed. Available methods of power conditioning for this sensitive equipment are also described     

Before and during voltage sags

The relationship between the voltages and the tripping level for line-operated synchronous machines is discussed. Voltage sags may cause tripping and large torque peaks in electrical machines. Tripping is caused by undervoltage protection or overcurrent protection. The ability to keep synchronism for the synchronous machines is mostly related to the loading of the machine and not very related to the voltage before and after the voltage sag.     

基于改进S变换的电压暂降识别

电压暂降分类识别是合理选择电能质量治理方案的前提。提出一种基于改进S变换的电压暂降识别方法。首先根据电压暂降特征频率范围自适应确定改进S变换的调节因子,计算所得模时频矩阵作为电压暂降标准模板;再比较待测试暂降的改进S变换模矩阵特定频段与各标准模板之间的相似度,实现扰动分类。在比较相似度值的过程中,为凸显不同暂降类型的相似性及差异性,采用分频逐行计算相似度值,从而实现异类模板差异最大化。该方法充分挖掘各类暂降的特征差异,通过简单的相似度计算对扰动进行分类,无需添加辅助分类器。仿真和大量实测数据研究表明,该方法分类过程简单,抗干扰能力强。     

电压暂降指标的探讨

对IEC、IEEE等国际组织以及国内外相关文献中给出的暂降指标进行了详细的总结分析与比较,按照暂降指标反映的不同特征将其分为9大类分别概述,对其中的SARFI指标、暂降能量指标、暂降严重性指标以及一些暂降经济损失评价指标等指标的适用性和优缺点进行了讨论,对严重性指标进行了改进。提出了推荐使用的四个方面的暂降指标即：统计指标、严重性指标、次数指标和经济损失指标并给出了推荐理由,有助于我国电压暂降标准制定工作的开展。     

Reducing voltage sags through fault current limitation

Short circuit current limitation in distribution utilities can be an effective way to improve power quality, since the expected voltage sag amplitude during faults can be dramatically reduced. A simple series LC circuit tuned at the net frequency, with the capacitor shunted by a metal oxide varistor (MOV), proves to be a well suited limiter to reach the goal. In the paper, the properties of such a circuit are analyzed and its operation is investigated through computer simulation. The relevant pro and con aspects are outlined and discussed     

电压暂降指标的探讨

对IEC、IEEE等国际组织以及国内外相关文献中给出的暂降指标进行了详细的总结分析与比较,按照暂降指标反映的不同特征将其分为9大类分别概述,对其中的SARFI指标、暂降能量指标、暂降严重性指标以及一些暂降经济损失评价指标等指标的适用性和优缺点进行了讨论,对严重性指标进行了改进.提出了推荐使用的四个方面的暂降指标即:统计指标、严重性指标、次数指标和经济损失指标并给出了推荐理由,有助于我国电压暂降标准制定工作的开展.     

基于HyperSIM的电压暂降问题仿真研究

为解决电力用户电压暂降问题,避免因电压暂降影响敏感设备正常运行而造成的巨大经济损失,分析高压故障引起的用户电压暂降问题有重要意义.采用电力系统数字仿真软件HyperSIM建立大型电力用户的实际输电系统和配电系统模型,对输电系统中的各种故障进行仿真,分析其对用户电压暂降问题的影响,并将仿真波形与变电站实际记录的波形对比,验证了该模型的正确性.通过仿真不同地点、不同类型的故障对用户10 kV进线的电压暂降造成的影响,得出高压系统的不同故障对用户电压暂降的影响程度.根据仿真结果可以进一步针对用户研究解决电压暂降的方法.     

The influence of motor reacceleration on voltage sags

The assumption that a voltage sag is rectangular is not correct in a power system with large induction motor loads. The motors decelerate during the short circuit. After fault-clearing, they will accelerate again, drawing a high reactive current from the supply, causing a prolonged postfault voltage sag. This is aggravated by the removal of branches by the protection. The resulting shape of some voltage sags in an example power system is shown and discussed. For the example power system, a stochastic voltage sag table is determined. This table gives the expected number of sags of different depth and duration. The influence of faster protection and of reduced transformer impedance on the table is presented. A simple motor model is implemented in a method for including interruptions due to voltage sags in the reliability analysis of power systems. This model is presented briefly and used to show the influence of motor parameters on the number of sags that lead to an interruption of plant operation     

全钒液流电池在电压暂降中的应用

随着配电网的发展,配电网接入的非线性负荷及冲击性负荷越来越多,电压暂降问题对负荷的影响越发凸显。全钒液流电池具有大规模、响应快、寿命长等优点,非常适合用于抑制电压暂降带来的影响。提出了全钒液流电池最优容量配置计算方法,针对不同的电压暂降深度,对其效果进行仿真,仿真结果表明,该配置能够避免电压暂降对生产设备造成的停机影响;对其投资回收期进行分析,指出随着全钒液流电池的产业化应用,其成本将大幅降低。     

Characterization of voltage sags in industrial distribution systems

This paper describes the various characteristics of voltage sags experienced by customers within industrial distribution systems. Special emphasis is paid to the influence of the induction motor load on the characterization of voltage sags. During a fault, an induction motor operates as a generator for a short period of time and causes an increase in sag magnitude. Its reacceleration after the fault clearance results in an extended post-fault voltage sag. The influence of the induction motor on the imbalanced sags caused by single line-to-ground faults (SLGFs) and line-to-line faults (LLFs) has been analyzed in detail. For an imbalanced fault, the induction motor current contains only positive- and negative-sequence components. Induction motors create a low impedance path for the negative-sequence voltage due to an imbalanced fault. This causes a small sustained nonzero voltage with large phase-angle jump in the faulted phase and a voltage drop in the nonfaulted phases with a small phase-angle jump. The symmetrical components of the induction motor during the imbalanced sags have been studied. The results show that induction motor behavior is determined by positive- and negative-sequence voltages during the imbalanced sag     

An analytical approach for assessment of voltage sags

In this paper, analytical expressions for the calculation of remaining voltages due to fault at bus and along the line are derived. Balanced and unbalanced faults are considered and the effects of different fault distributions are taken into account. The proposed analytical methods are compared with the method of critical distance in order to achieve the acceptability of the proposed method. The developed method is applied to the IEEE 30-bus test system and a real Indian distribution system.     

基于DSP的电压凹陷检测装置的研究

根据瞬时电压d-q分解法原理,利用Motorola DSP56F807研制出一台电压凹陷的检测装置,详细讨论了其硬件和软件的设计.在装置上完成对电压凹陷的检测,并通过选取不同截止频率的低通滤波器,达到不同的检测效果.实验结果证明该装置对电压凹陷的检测具有快速性和准确性.     

Voltage sags: their impact on the utility and industrial customers

This paper describes the impact of voltage sags on the electric utility and industrial customers. Several utility measures are presented to minimize the customer's exposure to voltage sags. These measures cannot completely eliminate the impact of voltage sags on sensitive equipment, however. A case study is presented in this paper that includes measurement results that were used to characterize the voltage sags experienced on the utility system and in the industrial facility. Simulation results used to develop “area-of-vulnerability curves” for the industrial facility, mitigation equipment that was employed to improve the sensitive equipment's ridethrough capability and the lessons learned from the systems approach analysis are presented     

电压暂降耐受能力的经济分析——电能质量变化对用户系统经济影响和实施改善措施费用的权衡

在商业机构,如银行、数据中心和客户服务中心,停电造成的损失可能是巨大的。一次停电损失高达几千至几百万美元。停电对制造厂造成的损失即使不是更高,也是相当高的。除了停电外,制造厂对更多的电能质量扰动都可能是敏感的。停电一般被统计在传统的供电可靠性之中。对于工业加工生产线,持续100 ms之内的电压暂降可能和停电几分钟造成的影响是一样的。对于工业设备,确定最佳供电系统和电气系统特性需要对多个可选方案进行评估。无论对于电力公司或是计量侧的末端用记,为改善电能质量,可以对所选设备附加电力调节措施,或者选用比规范规定截面…     

配电系统电压跌落问题的研究

电压跌落问题已成为影响配电系统电能质量的一个重要因素。如何提高配电系统的动态电能质量,抑制系统电压跌落对敏感电力用户的干扰已成为急需解决的问题。随着高压大功率开关器件的出现,基于电力电子技术的动态电能质量调节技术已成为解决上述问题的有效手段。实时检测技术和动态补偿技术是动态电能质量调节技术中最关键的两个环节,它们实现的效果好坏从根本上决定了动态电能质量调节技术能否取得令人满意的效果。本文对目前常用的检测手段和动态补偿方法的原理及优缺点进行了系统的阐述和深入的分析。最后,还介绍了现今已推出的几种动态电能质量     

配电系统电压跌落问题的研究

电压跌落问题已成为影响配电系统电能质量的一个重要因素.如何提高配电系统的动态电能质量,抑制系统电压跌落对敏感电力用户的干扰已成为急需解决的问题.随着高压大功率开关器件的出现,基于电力电子技术的动态电能质量调节技术已成为解决上述问题的有效手段.实时检测技术和动态补偿技术是动态电能质量调节技术中最关键的两个环节,它们实现的效果好坏从根本上决定了动态电能质量调节技术能否取得令人满意的效果.本文对目前常用的检测手段和动态补偿方法的原理及优缺点进行了系统的阐述和深入的分析.最后,还介绍了现今已推出的几种动态电能质量调节装置,并对其性能做了详细的比较.     

基于DSP的电压凹陷检测装置的研究

根据瞬时电压d-q分解法原理,利用Motorola DSP56F807研制出一台电压凹陷的检测装置,详细讨论了其硬件和软件的设计。在装置上完成对电压凹陷的检测,并通过选取不同截止频率的低通滤波器,达到不同的检测效果。实验结果证明该装置对电压凹陷的检测具有快速性和准确性。     

A method for estimating the frequency and cost of voltage sags

The annual number and cost of voltage sags were determined for five Finnish distribution companies. The method of fault positions was applied for the calculation of voltage sag frequency. The economic consequences were assessed by multiplying the sag frequency and cost by the number of customers. The cost of a single sag was taken from a survey that had been carried out in three Nordic countries in the mid 1990s. This paper proposes a method for retrieving sag-related information from statistics originally prepared for other purposes. In addition, this paper provides an estimate of the total annual sag-related cost for each of the companies considered in this study and for each customer category. The total cost per company appeared to be much higher than had generally been assumed     

Fast assessment methods for voltage sags in distribution systems

Based on a simple voltage divider model, a relation is derived between the load sensitivity to voltage sags (expressed as a critical voltage) and the exposed area (expressed as a critical distance). The critical distance increases about linearly with voltage level. The relation found is remarkably similar to relations found in power quality surveys. An equivalent expression is found for the critical distance as a function of the critical phase-angle jump. Realizing that faults downstream of a transformer do not significantly influence the expected number of sags, it is possible to estimate the number of sags at a specific load location. The method is extended to some nonradial systems: simple subtransmission loops, local generation, feeding from two substations, and operating with a normally open breaker