Importance Sampling and the Impact of the Protection System on Power System Reliability

对北美可靠性委员会五年报告的研究表明，保护系统经常在导致电力系统干扰的一系列事件中发挥作用。在未来放松管制的系统中，可靠性很可能会被视为一种商品。例如，由于关键输电线路误跳，独立系统运营商（ISO）未能促进生产商和负荷之间的电力销售谈判，可能导致支付罚款或以其他方式影响输电服务的价格。尽管其重要性，但保护系统故障对整个系统可靠性的影响尚未得到很好的研究。现有的多保护区和冗余系统的保护系统倾向于可靠性，即故障总是通过一些继电器来清除。目前的继电系统是以牺牲安全为代价来保证可靠性的。虽然一般认为数字继电器的自监测和自检特性会降低继电器未检测到或“隐藏故障”的概率，但安装的微处理器继电器的数量仍然很少。此外，还没有对安装大量数字继电器对系统可靠性的影响进行定性评价。建议的研究是开发技术来评估保护系统对系统可靠性的影响，并评估安装内置自我监测和自检的新数字继电器或对保护系统进行其他修改的价值。似乎电力系统运行的新范式将为更现代化的保护系统提供动力。也就是说，传输系统可靠性的经济性将要求继电系统的现代化。该方法的两个关键要素是“重要抽样”的使用和电力系统运行条件的大型数据库的生成，例如用于各种人工方案的训练和新控制方案性能评估的数据库。“重要采样”技术是一种研究电力系统重大扰动等“罕见”事件的仿真技术。电力系统运行状态数据库的生成用于各种人工智能方案的训练已成为近年来的研究课题。它们已被用于暂态稳定性的预防性控制，用于从实时相量测量中预测不稳定性，或使用实时相量测量控制直流线路。所提出的研究的本质是结合这两种技术，即创建一个偏向于不可能事件的数据库，因为概率是基于重要抽样的。数据库生成已经被认为是一种统计方法，其中数据库可以通过随机抽样描述系统运行的参数来生成。这里提出的工作将使用数据库作为潜在概率空间的代理。数据库将偏向于不可能发生的事件，就像在重要性抽样中改变概率一样，以便通过模拟来研究减少“隐藏故障”的影响。所提出的研究涉及的具体任务是：*研究隐藏故障对系统条件依赖的概率模型。*修改重要性抽样，使其更适合电力系统应用*检查适合重要性抽样方法的性能指标*使用康奈尔生产超级计算机生成数据库***

9634823 Thorp The study of North American Reliability Council reports over a five year period indicates that protection systems frequently play a role in the sequence of events that lead to power system disturbances. It is likely that reliability will be treated as a commodity in the deregulated systems of the future. For example the failure of the Independent Systems Operator (ISO) to facilitate a negotiated sale of power between a producer and a load because of a false trip of a key transmission line could result in the payment of a penalty or otherwise effect the price of transmission services. In spite of its importance, the impact of protection system malfunctions on overall system reliability has not been well studied. The existing protection system with its multiple zones of protection and redundant systems is biased toward dependability, that is a fault is always cleared by some relay. Present day relaying systems are designed to be dependable at the cost of security. While it is generally believed that the self-monitoring and self-checking feature of digital relays will reduce the probability of undetected or "hidden failures" in relays, the number of installed microprocessor relays is still small. Further, there has been no qualitative evaluation of the effect on system reliability of the installation of large number of digital relays. The proposed research is to develop techniques to evaluate the impact on system reliability of the protection system and to appraise the value of the installation of new digital relays with built in self-monitoring and self-checking or other modifications of the protection system. It seems possible that the new paradigm for power system operation will provide the impetus for a more modern protection system. That is, the economics of transmission system reliability will require that the relaying system be modernized. The two key elements of the proposed approach are the use of "importance sampling" and th e generation of large data bases of power system operating conditions such as those used for training of various artificial schemes and evaluation of the performance of new control schemes. The "importance sampling" technique is a simulation technique to study "rare" events such as major power system disturbances. The generation of data bases of power system operating conditions for training of various artificial intelligence schemes has become a subject of recent study. They have been used for preventive control for transient stability, for prediction of instability from real-time phasor measurements, or the control of DC lines using real-time phasor measurements. The essence of the proposed research is to combine the two techniques i.e., to create a database biased toward the unlikely events as the probabilities are based in importance sampling. Data base generation has been recognized as a statistical approach where the data base could be generated by randomly sampling the parameters that describe system operation. The work proposed here would use the data base as a surrogate for the underlying probability space. The data base would be biased toward the unlikely events just as the probabilities are altered in importance sampling so that the impact of reducing "hidden failures" can be studied through simulation. The specific tasks involved in the proposed research are: * Investigation of probability models for the dependence of hidden failures on system conditions.. * Modifications of importance sampling to make it more appropriate for power system applications * Examination of performance indices appropriate to the importance sampling approach * Generation of data bases using the Cornell Production Super Computer ***