基于隐性故障模型和风险理论的关键线路辨识

在大规模电网中,由简单故障触发的电力系统连锁故障常常会引起大停电的灾难性后果。为了研究复杂电网连锁故障的传播机理,同时找出对连锁故障产生重要影响的关键线路,文中基于模拟连锁故障的隐性故障模型和风险理论,提出了复杂电力系统的线路故障风险评估方法,并辨识出了对系统大停电产生重要影响的一系列关键线路。模型考虑了线路过负荷保护、隐性故障、控制策略及系统运行等参数,对IEEE118节点系统仿真结果表明,在重负荷状态运行下只对辨识出的少量关键线路加以改善,就可以使系统停电概率大幅减小,特别是大停电概率;在临界状态运行下改善少量关键线路,则可以使系统脱离临界状态,避免大停电发生。     

Anatomy of power system blackouts: preventive relaying strategies

Major blackouts of electric power systems in which many customers are left without power are rare events. However, the effects of blackouts, for instance, can be catastrophic. It has been observed that protective system failures are a contributing factor in a large proportion of these blackouts. The most troublesome protection system failures are hidden failures, which remain dormant during normal system conditions, and are exposed during system disturbances. A study of hidden failures of the protective systems is undertaken to uncover their modes of failures, and to determine means of supervising their actions in times of highly stressed power system operations. The main contribution of this paper is to develop and document a method of quantitative analysis of the significance of hidden failures of protection systems. A complete protection system was designed for the New England 39-bus system and the hidden failure modes were used to develop regions of vulnerability and a vulnerability index. Through this analysis, critical protection systems, whose hidden failures would have a major impact on cascading failures or blackouts of the power system, can be identified These protection systems are candidates for increased monitoring and control, which would help alleviate the problems posed by hidden failures     

Data-mining model based adaptive protection scheme to enhance distance relay performance during power swing

The paper presents a data-mining model based adaptive protection scheme enhancing distance relay performance during power swing for both compensated and uncompensated power transmission networks. In the power transmission network, the distance relays are sensitive to certain system event such as power swings, which drive the apparent impedance trajectories into the protection zones of the distance relay (zone-3) causing mal-operation of the distance relay, leading to subsequent blackouts. Further, three-phase balanced symmetrical fault detection during power swing is one of the serious concerns for the distance relay operation. This paper proposed a new adaptive protection scheme method based on data-mining models such as DT (decision tree) and RF (random forests) for providing supervisory control to the operation of the conventional distance relays. The proposed scheme is able to distinguish power swings and faults during power swing including fault zone identification for series compensated power transmission network during stress condition like power swing. The proposed scheme has been validated on a 39-bus New England system which is developed on Dig-Silent power factory commercial software (PF4C) platform and the performance indicate that the proposed scheme can reliably enhance the distance relay operation during power swing.     

A new optimal unified power flow controller placement and load shedding coordination approach using the Hybrid Imperialist Competitive Algorithm-Pattern Search method for voltage collapse prevention in power system

As power systems become more complex and heavily loaded, voltage collapse has become one of the most destructive events in modern power systems leading to blackouts in electric utilities worldwide. Voltage collapse is mainly caused by operating power systems at lower stability margins due to a surge in electric power demand. This paper presents an optimal unified power flow controller (UPFC) placement and load shedding coordination approach for voltage collapse prevention in N − K (K = 1, 2 and 3) contingency condition using Hybrid Imperialist Competitive Algorithm-Pattern Search (HICA-PS). ICA is the main optimizer of the proposed algorithm while pattern search is applied to further fine tune the results of the ICA. To show the effectiveness of the proposed approach in preventing voltage collapse in complex power systems, we implemented it on the New-England 39 bus power system. Its performance was also compared to that of some classical optimization techniques. Decrease in load shedding amounts, continuity of energy supply and voltage collapse prevention is the main positive features of the proposed approach.     

Optimal coordination of directional over-current relays using Teaching Learning-Based Optimization (TLBO) algorithm

Relay Coordination in a big distribution system with multiple meshes and bidirectional power feed becomes very Complex for protection engineers. Manual and graph theory based approaches were applied successfully in small power system. In a big distribution system linear and non-linear programming based optimizing techniques are applied for relay coordination. Presently, artificial intelligence techniques are applied for optimal co-ordination of directional overcurrent relays. This paper discusses the application of Teaching Learning Based Optimization (TLBO) algorithm for optimal coordination of DOCR relays in a looped power system. Combination of primary and backup relay is chosen by using Far vector of LINKNET structure, to avoid mis-coordination of relays. Coordination of DOCR is tested for IEEE 3, 4 and 6 bus systems using the TLBO. Also, the objective function is modified to optimize the operating time between backup and primary relays. The results are compared with the optimized values of Time dial setting and Plug setting values obtained from modified differential evolution algorithm. The proposed algorithm TLBO gives optimal coordination margin between 0.3 and 0.8 s and no miscoordination between primary and backup pairs. Results are also verified using Digsilient power factory simulation software.     

复杂电力系统连锁故障的风险评估

电力系统中的连锁故障是一种发生概率低但后果严重的事故,严重的连锁故障可能导致大面积停电甚至整个系统崩溃。文章提出了一种复杂电力系统连锁故障的风险评估方法,模拟连锁故障的一般发展过程,将事故发生概率及后果联系起来,提出了量化的风险指标,能发现系统运行中更深层次的问题,暴露安全隐患。以此为基础开发了基于风险理论的电力系统连锁故障风险评估软件,并以美国东北部 NPCC 48机测试系统为例验证了该方法的先进性和有效性。     

基于实时运行条件的电力系统连锁故障风险性评估

电力系统中的连锁故障是一种发生概率低但后果严重的事故,严重的连锁故障可能导致大面积停电甚至整个系统崩溃.基于风险理论提出了一种复杂电力系统连锁故障的风险评估方法,该算法根据线路潮流实时运行条件来确定引发大停电初始故障的概率,然后根据系统运行状况基于层次分析法和灰色关联度的分析方法模拟连锁故障的一般发展过程,将事故发生的...     

A hierarchically distributed non-intrusive agent aided distance relaying protection scheme to supervise Zone 3

The post-mortem analysis of few blackouts in US and Europe has revealed that the Zone 3 of step-distance protection is one of the primary causes of blackouts in power systems. In order to provide the Zone 3 relays with situational awareness and prevent its undesirable tripping, we propose a non-intrusive agent based relay supervised distance protection scheme. In the proposed scheme, every relay protecting a transmission line is associated with an agent that has the ability to sense and communicate with the other agents in the network. Based on the responsibilities assigned to them, the agents are hierarchically distinguished as master and slave agents. Whenever a relay senses a fault, its associated slave agent communicates with the master agent to distinguish a fault as a real fault or unreal fault and respectively to trip or not to trip. Distance relay protection scheme is a time critical application. Therefore OPNET simulations are performed to evaluate different communication and networking topologies, physical media of communication, networking protocols to ascertain the topology that meets the timing requirements of the protection scheme. The problem of adapting the proposed scheme to a larger power grid is modeled as an integer programming Multiple Facility Location (MFL) problem.     

A novel power swing blocking scheme using adaptive neuro-fuzzy inference system

A power swing may be caused by any sudden change in the configuration or the loading of an electrical network. During a power swing, the impedance locus moves along an impedance circle with possible encroachment into the distance relay zone, which may cause an unnecessary tripping. In order to prevent the distance relay from tripping under such condition, a novel power swing blocking (PSB) scheme is proposed in this paper. The proposed scheme uses an adaptive neuro-fuzzy inference systems (ANFIS) for preventing distance relay from tripping during power swings. The input signals to ANFIS, include the change of positive sequence impedance, positive and negative sequence currents, and power swing center voltage. Extensive tests show that the proposed PSB has two distinct features that are advantageous over existing schemes. The first is that the proposed scheme is able to detect various kinds of power swings thus block distance relays during power swings, even if the power swings are fast or the power swings occur during single pole open conditions. The second distinct feature is that the proposed scheme is able to clear the blocking if faults occur within the relay trip zone during power swings, even if the faults are high resistance faults, or the faults occur at the power swing center, or the faults occur when the power angle is close to 180°.     

Cascading failures of power grids caused by line breakdown

In recent years, several large blackouts have drawn much attention to security problems in electric power transmission systems all over the world, which were triggered by initial minor disturbances and caused by cascading failures. Many models for cascading failures in power grids based on node attacks have been proposed, where only one kind of load is involved. In real power systems, however, strict measures are normally taken to protect the nodes, i.e. the power stations, so that failures at the nodes can hardly occur. It is much easier for transmission lines to break down, which may lead to cascading failures in entire power systems. Hence, a new model involving active and reactive loads and considering transmission line failures instead of node failures is proposed to understand cascading failures of power grids. When a transmission line breaks down, its load is redistributed to its neighbouring lines according to their respective capacities. It is well known that a power grid's topology and connectivity play a key role in determining its dynamic behaviour. Therefore, cascading failures of power grids with typical topologies, i.e. random, small‐world and scale‐free networks, are investigated using the model proposed and considering transmission line breakdowns. Finally, the model's effectiveness is validated employing real data of the European power grid. Copyright © 2014 John Wiley & Sons, Ltd.     

A new approach for optimal coordination of distance and directional over-current relays using multiple embedded crossover PSO

Proper coordination between distance relays and Directional Over-Current Relays (DOCRs) in power systems is one of the important conditions for the system security. The coordination problem in interconnected systems, because of complexity of the system, is complicated and a powerful optimization program must be used in order to do the best and optimal relay coordination.In this paper at first, a new problem formulation for optimal coordination of distance relays in presence of DOCRs, as the backup relays, is proposed. Then to deal with this complex problem, as another contribution, a new Multiple Embedded Crossover PSO (MECPSO) is proposed. In the presented MECPSO by updating velocity vector, diversity of the swarm is enhanced and exploration and global search capabilities of the PSO is improved as well. In the proposed approach, with considering the effect of in-feed or out-feed currents, the optimal second zone timing of distance relays and optimal settings of DOCRs are computed. The proposed method is tested on two case studies and encouraging optimal results are obtained.     

电力系统连锁故障快速预测方法研究

近年来,电力系统大停电事故时有发生,而连锁故障是导致其发生的重要诱因,快速、准确地预测连锁故障可能的发展路径对预防大停电事故的发生具有重要的指导意义。针对过载主导型的连锁故障发展模式,充分利用连锁故障的前后因果关联性特点,定义关联性指标,提出基于故障路径树的连锁故障快速预测方法。该方法采用模糊聚类算法对关联性指标进行分类,选取关联性指标最高的一类支路为下级故障环节,在有效减少计算量的同时,改进了现有预测方法的不足。最后,对IEEE39节点系统进行仿真分析,仿真结果验证了所提预测方法的快速性和正确性。     

An adaptive approach for three zone operation of digital distance relay with Static Var Compensator using PMU

Modern energy transmission systems suffer from great voltage dropping due to enormous loads. Therefore appropriate schemes should be devised to regulate the voltage. FACTS devices such as Static Var Compensator are often used for this purpose. However, SVC at mid-point of transmission line may leads to deteriorate of distance relay operation, resulting in inaccurate estimation of faults locations i.e. over-reach or under reach for different cases. This paper proposed a new algorithm that utilizes synchronized phasors measurement (SPM) to enhance the operation of distance protection zone in many aspects. The proposed method is tested for 230 kV system simulated in EMTDC/PSCAD with Bergeron model of transmission line. The results prevailed for adaptive approach scheme are more accurate, victor and robust in equivalence with usable transmission line distance protection with SVC.     

低频功率振荡中距离Ⅲ段动作特性

电网事故过程中的低频功率振荡可以引起输电线路距离保护的不合理动作,扩大停电事故范围.提出距离Ⅲ段保护动作的临界振荡角度和临界振荡频率的直接算法.根据线路两端等值电源电压,建立多项式形式的保护动作条件,直接求解临界振荡角度,在此基础上,分析继电器参数设置、等值电源阻抗和线路充电电容对保护动作条件的影响.假设振荡频率恒定,根据临界振荡角度计算振荡轨迹在保护范围内的停留时间,从而得到不同保护整定时间下引起距离Ⅲ段保护动作的临界振荡频率.仿真分析验证了所提出的算法的可行性和有效性.     

基于交流潮流的连锁故障建模与鲁棒性评估

连锁故障是历次大停电事故的主要诱因之一,而脆弱线路对连锁故障演化路径的发展又起着极其关键的作用。为在连锁故障中识别电网潜在脆弱线路,基于复杂网络理论和电力系统实际特性,以线路视在功率值为线路流量,提出一种交流潮流连锁故障模型。在此基础上,从网络局部、全局和潮流功能特性三个方面分别提出电气入度中心性、电气出度中心性、电气介数中心性和加权电网潮流转移熵四个指标来辨识脆弱线路。最后通过6个IEEE标准测试系统对电网鲁棒性进行评估,结果表明基于电气入度中心性指标的蓄意攻击策略对电网连锁故障后造成的损害最大且随网络规模增加电网鲁棒性逐步提升。     

Low cost microcontroller based fault detector,classifier, zone identifier and locator for transmission lines using wavelet transform and artificial neural network: A hardware co-simulation approach

A low cost, fast and reliable microcontroller based protection scheme using wavelet transform and artificial neural network has been proposed and its effectiveness evaluated in real time. The proposed scheme, based on the hardware co-simulation approach performs all the functions of transmission line protection i.e. fault detection/classification, fault zone/section identification and location estimation. The fault detection/classification and zone identification algorithms use fundamental frequency current component to estimate a fault index. The fault location estimation module uses wavelet transform coefficients in hybridization with a parallel artificial neural network structure. For hardware implementation, a 8-bit ATmega microcontroller is used and interfaced with the simulated power system model using Integrated Development Environment (IDE). The scheme is tested on a power system model of 400 kV, 50 Hz three phase double circuit line with source at both the ends. Laboratory tests have been performed in real time for 20,000 fault cases including evolving faults with varying fault resistance, fault inception angle, fault distance, direction of power flow angle and its magnitude. The tests confirm the suitability and reliability of proposed scheme even with Current Transformer (CT) saturation. The implementation of the proposed approach on a low cost microcontroller with the lesser execution time, makes the prototype ideal for implementation on a digital platform (digital relay), thus leading to financial viability and sustainability of the protection scheme.     

Performance and reliability of electrical power grids under cascading failures

The stability and reliability of electrical power grids are indispensable to the continuous operation of modern cities and critical for preparedness, response, recovery and mitigation in emergence management. Because present power grids in China are often running near their critical operation points, they are especially vulnerable and sensitive to external disturbances such as hurricanes, earthquakes and terrorist attacks, which may trigger cascading failures or blackouts. This paper describes a quantitative investigation of the stability and reliability of power grids with a focus on cascading failures under external disturbances. The 118-bus (substation) power network in Hainan, China is employed as a case study to investigate the risk of cascading failure of the regional power grids. System performance and reliability of the power grids are evaluated under two hypothetical scenarios (seismic impact and intentional disturbance) that could trigger cascading failures. By identifying the most vulnerable (critical) edges and nodes, the robustness of the power network is evaluated under the triggered cascading failures. It is found that the system reliabilities could decline as much as 95% during the triggered cascading failure. This paper also explores the use of concepts from modern complex network theories such as state transition graph and characteristic length to understand the complex mechanism of cascading failures. The findings could be useful for power industries and emergency managers to evaluate the vulnerability of power systems, understand the risk of blackout induced by cascading failures, and improve the resilience of power systems to external disturbances.     

Agent-based self-healing protection system

This paper proposes an agent-based paradigm for self-healing protection systems. Numerical relays implemented with intelligent electronic devices are designed as a relay agent to perform a protective relaying function in cooperation with other relay agents. A graph-theory-based expert system, which can be integrated with supervisory control and a data acquisition system, has been developed to divide the power grid into primary and backup protection zones online and all relay agents are assigned to specific zones according to system topological configuration. In order to facilitate a more robust, less vulnerable protection system, predictive and corrective self-healing strategies are implemented as guideline regulations of the relay agent, and the relay agents within the same protection zone communicate and cooperate to detect, locate, and trip fault precisely with primary and backup protection. Performance of the proposed protection system has been simulated with cascading fault, failures in communication and protection units, and compared with a coordinated directional overcurrent protection system.     

电网连锁故障演化机理与博弈预防

连锁反应故障是导致大停电的重要原因。回顾了2003年以来世界范围内3次较为严重的连锁故障造成的大停电事故,通过对连锁故障发展过程的总结,得出了连锁反应故障的演化规律与一般特征。在此基础上,对连锁反应故障的机理进行了分析。文中将博弈思想应用于连锁故障的预防,将电网出现的扰动作为对弈中的进攻方,系统被动的调整作为被动的防御,提出连锁故障的对弈防御策略,一旦电网发生扰动则系统做相应调整,类似于对弈过程二人的交替走步。机理分析表明,这种调整削弱了元件间的关联作用,将系统运行点向远离临界状态的方向移动,因此可有效预防连锁故障。     

A Study of Self-Organized Criticality of Power System Under Cascading Failures Based on AC-OPF With Voltage Stability Margin

From the perspective of self-organized criticality, this paper develops a novel model with ac-OPF and ac grid upgrade to study the cascading failures and blackouts in power systems, which overcomes some shortcomings of existing blackout models. The proposed model contains two types of dynamics, one is fast dynamics which simulates the serial blackouts in power systems, the other is slow dynamics which reflects the tendency of the power systems time evolution. This model also has voltage stability analysis function and can reveal critical characteristics from reactive power and voltage viewpoint. Simulation results of the IEEE 118-bus system with this model show that the fast dynamics can capture the cascading process and the criticality property in micro scale. Besides, the macro scale of self-organized criticality of power systems can be revealed from the mean value of fractional overloads and the ratio of total load demand to the total network transfer capability. Furthermore, the voltage stability criticality status could be detected from the eigenvalue with the smallest magnitude through reactive power and voltage relevant modal analysis.