A canonical model for the study of faults in power systems

The authors introduce a general class of fault conditions encompassing all possible faults in a power system, e.g., simultaneous symmetrical and unsymmetrical short circuits, line interruptions, and predicted breaker operations at different locations. The influence of mutually coupled lines, static VAR systems and/or faults at several busbar systems are also considered. The fault conditions are described in both the (three) phase and sequence domains, with the same simplicity. The proposed model of a faulted power system, is in a canonical form, over the general class of fault conditions. It is found that its effectiveness is equal in both domains. The authors also present the model solution procedure for various fault conditions in the general frame of the study of faults. They present the derivation of the canonical model and numerical examples. The application of the canonical model to faults that include buses of distinct voltage levels is stressed     

Analysis of shunt faults in the laterals of overhead power distribution feeders using superimposed components

In this study, a digital fault location and monitoring technique for overhead power distribution lines with laterals is presented. The technique is based on utilising the fault voltage and current samples obtained at a single location. In the implementation of the algorithm, the superimposed voltage and current components rather than total values are used to minimise the effects of preloading on the accuracy. The effectiveness of the method is verified through electro-magnetic transients program simulations.     

k-means algorithm and mixture distributions for locating faults in power systems

Enhancement of power distribution system reliability requires of a considerable investment in studies and equipment, however, not all the utilities have the capability to spend time and money to assume it. Therefore, any strategy that allows the improvement of reliability should be reflected directly in the reduction of the duration and frequency interruption indexes (SAIFI and SAIDI).     

Induction motor transient response to multiple faults in unbalanced power systems

Although the effects of an unbalanced supply on overheating induction motors have been known for some time, little or no attention has been paid to the dynamic response of such a system. A recent investigation though has evaluated the effects of an unbalanced distribution system, unbalanced single-phase loads, unbalanced shunt faults, and series faults (open conductor) on the transient behavior of a three-phase induction motor. This paper extends that work to the case of motor transient response due to multiple asymmetrical faults in an unbalanced power system. The paper investigates the dynamic behavior of an induction motor connected to an unbalanced three-phase power system subjected to a shunt fault at one location and blown fuses or open conductor at another location. The method involves phase frame representation of the line. A significant finding is that certain multiple faults cause the induction motor to lose stability.     

光伏并网系统送出线路不对称故障的差动保护灵敏度研究

针对光伏并网发电系统的故障特性,分析了在并网送出线路发生不对称跌落时,比率制动特性差动保护在光伏逆变器有无无功补偿条件下的灵敏度。结果表明,在无功补偿状态下,光伏并网发电系统送出线部分的传统比率制动特性差动保护灵敏度下降。通过比较传统比率制动特性曲线的整定方式,不过原点的特性曲线在灵敏度的方面具有更大优势。在此基础上,考虑到不对称故障中零序电流受故障电阻和负荷电流影响小及低电压穿越(LVRT)期间以电网电压正序分量定向的逆变器控制策略,零序电流作为保护判据的传统比率制动式差动保护,由于不受无功补偿电流的影响且保护动作整定值较小,具有更高的灵敏度,作为光伏送出线路的保护效果更佳。通过Simulink搭建光伏并网发电系统仿真模型验证了这一结论。     

Fast isolation of faults in transmission systems using current transients

This paper presents a protection scheme that is capable of very fast isolation of faults in high voltage transmission systems. Proposed scheme comprises set of relays connected through a telecommunication network, located at different nodes of the system. Relays use wavelet coefficients of current signals to identify the fault directions relative to their location. Fault directions identified at different locations in the system can be combined to determine the faulted line (or busbar) and isolate it. A robust single ended traveling wave based fault distance estimation approach is proposed as a backup in case of communication failure. Investigations were carried out using time domain simulations in PSCAD/EMTDC for a high voltage transmission system.     

不对称短路故障下非故障6kV电动机速断保护动作行为分析

根据对称分量法,分析了单相接地短路和两相接地短路两种不对称短路故障下的电压向量.对 6 kV 电动机在不同序电压下的运行情况进行了分析,表明运行在同一 6 kV 母线上的非故障电动机速断保护在不对称短路情况下,特别是在两相接地短路时,负序电压产生的较大电流可能会导致电动机速断保护误动作.提出在进行电动机速断保护定值整定校核时,不仅需要考虑启动电流,还需要考虑不对称短路故障时的负序电压影响的问题.     

Analysis and prevention of animal-caused faults in powerdistribution systems

The reliability, security and quality of power systems are significantly affected by distribution faults. One of the trends concerning distribution faults is the implementation of more preventive measures instead of reactive measures. In other words, we would like to prevent faults from happening rather than to restore the system after faults occur. Among the different categories of power distribution faults, animal-caused faults are probably the ones that can be prevented most easily and effectively if appropriate control actions are taken. This paper discusses and analyzes animal-caused faults in power distribution systems. The results of an animal fault prevention technique that can effectively reduce these faults is also presented     

Synchronous generator stability due to multiple faults on unbalanced power systems

This paper investigates the dynamic behavior of a synchronous generator connected to an unbalanced three-phase power system which is subjected to a shunt fault at one location and blown fuses or open conductors at another location. The method involves phase frame representation of the line. The imbalance created by large single-phase loads, untransposed lines, conductor bundles, etc., is reflected in polyphase impedance matrices. Consequently, line removals, additions, impedance changes, conductor and faulted phase openings can be simulated based on the boundary conditions. Thus, the proposed method makes it possible to study the synchronous generator stability due to any combination of single or multiple asymmetrical series and shunt faults occurring anywhere in the system and the results of several case studies are presented. A significant finding is that certain faults cause the generator to lose synchronism only after several cycles of the rotor angle swing curve. In such cases it is therefore no longer correct to judge the system's stability only on the ‘first swing cycle’ of the rotor angle.     

北京电网2004年设备故障情况分析

电网中运行的电气设备会发生各种故障，这些故障有的是人为原因造成，有的则是设备自身问题或自然因素引起。为防止、减少设备故障的发生，对已发生的故障情况进行统计和分析，是研究故障发生规律，采取预防措施所做的不可缺少的工作。2004年，随着北京经济的快速增长，北京电网用电最大负荷逃到9.4GW，电网运行方式调整频繁，设备经受了大负荷的冲击，全年发生了多次电网和设备故障。通过对2004年北京电力公司管辖的输电、变电、配电设备故障情况的综合分析，总结出在技术因素与部件、原因与责任方面存在的主要问题，并提出针对性的防范措施。     

A method of analysing asymmetrical short-circuits on power systems including several synchronous machines

This paper contains a new method for analysing symmetrical and asymmetrical faults at any point in a power system, which may include several synchronous machines connected together with transmission systems. The method is developed by using the symmetrical components, the axial components and a modified compensation theorem.Comparative experimental and theoretical results are given for a line-to-line, a single line-to-ground and a double line-to-ground short-circuit on a transmission system connecting two synchronous machines.     

Diagnosis of incipient faults in power transformers using CMAC neural network approach

Dissolved gas analysis (DGA) is one of the most useful techniques to detect the incipient faults of power transformer. However, the identification of the faulted location by the traditional method is not always an easy task due to the variability of gas data and operational natures. In this paper, a novel cerebellar model articulation controller (CMAC) neural network (NN) method is presented for the fault diagnosis of power transformers. By introducing the IEC standard 599 to generate the training data, and using the characteristic of self-learning and generalization, like the cerebellum of human being, a CMAC NN fault diagnosis scheme enables a powerful, straightforward, and efficient fault diagnosis. With application of this scheme to published transformers data, the diagnoses demonstrate the new scheme with high accuracy and high noise rejection ability. Moreover, the results also proved the ability of multiple incipient faults detection.     

微机保护装置逆变电源故障原因分析

针对逆变电源模块故障频繁发生的情况,整理和统计了某省电网近年来与逆变电源模块故障相关的继电保护装置故障数据,介绍了在继电保护及安全自动装置有关标准中对逆变电源性能的技术要求.对故障数据从故障类型和使用寿命两方面进行归类分析,举出两例相关故障案例;分析了逆变电源模块的工作原理,并指出电容元件损坏或失效、抗电磁干扰性能差、...     

基于临界惯量和预想故障的含风电电力系统暂态功角稳定在线预警

大规模风电接入使得电力系统惯量水平降低,暂态功角失稳风险加剧,开展含风电电力系统故障前的暂态功角稳定在线预警对保障其安全稳定至关重要。提出了基于临界惯量和预想故障的含风电电力系统暂态功角稳定在线预警方法。首先,通过理论分析得到风电场在故障清除后短时间的功率恢复过程不能忽略的推论,并建立等效外特性模型,进而基于扩展等面积定则构建了计及风电场多阶段外特性的暂稳数学模型。其次,定义了含风电系统暂态功角稳定的临界等效惯量,并通过匀加速分段等效提出了实用化的求解方法,进一步提出了暂态临界惯量指数,实现稳定裕度量化分析并给出风险等级。最后,以含风电接入的四机两区域系统和IEEE39节点系统为例,仿真验证了所提方法的有效性和适用性。     

Analysis of interruptible electric power in deregulated power systems

Assuring appropriate levels of generation capacity adequacy at the minimum possible cost using market-based approaches is a contemporary issue attracting much attention in deregulated power systems. Introduction of interruptible electricity contracts could provide a possible solution to such a problem. However, theoretical frameworks for examining the impacts of these contractual arrangements on system operations have not been maturely developed. This paper presents a probabilistic production simulation based framework for modeling and analyzing interruptible electricity contracts. The interdependence between the pricing models of interruptible electric power and the operations of the whole system is addressed and solved by an iterative coordinating algorithm. The probabilistic production simulation framework allows the uncertainties inherent in both the forced outages of generators and system load demand at the contract delivery time to be taken into account. The proposed approach is capable of achieving comprehensive analysis and systematic pricing for interruptible electric power. A numerical case study is presented to illustrate the effectiveness and validity of the methodology.     

Supply and loading quality improvement in sinusoidal power systems with unbalanced loads supplied with asymmetrical voltage

Contents Asymmetry of the supply voltage of a load and variation of its RMS value deteriorate supply quality, similarly as asymmetry of the load current, its reactive component, and variation of the current RMS value deteriorate loading quality. A method for adaptively improving the supply and loading quality with respect to the load unbalance and the voltage asymmetry is suggested and analyzed in this paper. The discussed method can be implemented for the development of an adaptive compensator for both the load balancing and supply voltage symmetrization. It was shown, moreover, that only three samples per periodT of two voltages and two currents are needed for generating the control signals for the adaptive operation of such a compensator.

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Verbesserung der Versorgungsqualität bei dreiphasigen Energiesystemen mit unsymmetrischer Belastung und unsymmetrischer Spannung

Übersicht Eine unsymmetrische Versorgungsspannung stört die Versorgungsqualität ähnlich wie ein unsymmetrischer Laststrom. In diesem Beitrag wird ein Verfahren zur adaptiven Verbesserung der Versorgungsqualität bezüglich Unsymmetrien der speisenden Spannung und der Lastschaltung vorgeschlagen und analysiert. Das Verfahren kann für die Entwicklung eines adaptiven Kompensators verwendet werden, der sowohl die Last als auch die Klemmenspannung symmetriert. Außerdem wird gezeigt, daß nur 3 Abtast-werte pro Periode bei je 2 Spannungen und Strömen ausreichen, um die Steuersignale für den adaptiven Betrieb eines solchen Kompensators zu erzeugen.

     

Location of faults in power distribution laterals using superimposed components and programmable logic controllers

In this study, a digital fault location and monitoring technique using programmable logic controller (PLC) for primary overhead power distribution networks is presented. This technique employs pre- and post-fault current and voltage information along with data from the laterals. By using lateral current data transferred through shielded coaxial cables to the substation, the possibility of multiple fault point locations are eliminated. The effectiveness of this method is verified through Electromagnetic Transients Program (EMTP) simulations.     

An efficient faults calculation method taking into account mutually coupled lines of power systems

It is necessary to take into account the effects of mutual couplings when unbalanced faults are to be calculated in transient stability study. When the method based on symmetrical coordinates is applied to faults calculation, it has been necessary in the conventional method to construct the zero sequence network, the configuration of which is more complex than other networks so far. Then, the application of faults calculation including mutual couplings to the analysis on the bulk power system model has been considerably difficult for a long time. This report presents a newly developed method to calculate the effects of mutual coupling in multifaults calculation under the same configuration and with no change for all sequence networks. The validity of the proposed method was verified through the application of transient stability analysis for power system models.     

Improved phase selector for unbalanced faults during power swings using morphological technique

In order to prevent distance protection from tripping during power swing conditions, a power swing blocking device is often utilized. On the other hand, it has been an increasing requirement to achieve rapid clearance of internal faults during power swings. Accurate phase selection is a prerequisite to selective clearance of faults. An improved unbalanced fault phase selector during a power swing based on series multiresolution morphological gradient (SMMG) transform is proposed in this paper. As a feature extractor from raw signals, SMMG is employed to extract superimposed (fault component) current under the power swing condition in this paper. First, the operating characteristic of the sequence component fault phase selector during power swings is discussed. In order to overcome the disadvantage of the above selector, an improved fault phase selector for unbalanced faults during power swings is then proposed by using SMMG to extract superimposed components of modular current. The efficiency and feasibility of the proposed schemes are proven using a Power Systems Computer-Aided Engineering/Electromagnetic Transients including DC-based simulation on a sample power system.     

不对称故障下低电压穿越的多目标解耦控制策略

在传统不对称故障低电压穿越控制中,囿于控制自由度有限,并网逆变器控制存在输出电流负序分量和直流侧电压二倍频波动抑制两个目标无法同时实现的问题。针对该问题,本文提出了一种不对称故障下两级式光伏并网系统低电压穿越的多目标解耦控制策略。该策略将逆变器的控制目标设置为输出电流负序分量抑制,给出了综合考虑逆变器输出电流限幅和无功输出需求的逆变器电流内环控制参考值计算方法;通过双向Buck-Boost变换器将超级电容接入直流母线电容两端维持其电压稳定,并将直流侧电压二倍频波动转移至超级电容输入侧进行抑制。仿真结果表明,在所提控制策略下逆变器三相间的不平衡度降低,输出电流畸变得到改善,直流侧电压二倍频波动相比传统控制方法明显减小。