Impact Of Protection System On The Development Of Power System Cascading Failures

In recent years, with the continuous expansion of the scale of power grid construction, the number of users is also growing. At the same time, once fault occurs in the power system, the number of users and the influence of the geographical scope will also be bigger. The economic loss caused by the large scale power system accidents is immeasurable. Therefore, how to ensure the power grid work security and reliability is an important question in front of the electric researchers. Statistics show that large power accident is often expressed as the cascading failure and about 70% of the cascading failures relate to hidden failures.Based on this, outages at home and abroad in recent years are collected and analyzed first. Failure factors of major blackout events are classified from the perspective of internal factors and external factors, and the development process of the cascading failure is diagramed. According to failure mechanism, large-scale blackouts can be divided into overload-dominated model, coordinate-dominated model and construction-dominated model. The research methods and evaluation indexes of cascading failures are summarized and analyzed. Outages are classified according to the failure mechanism at the same time.Hidden failures of relay protection is one of the important factors causing cascading failures of power system. A protection hidden failures model considering line fault is built aiming at the factors affecting the protection hidden failures. This paper analyzes the protection failure rate from human error, protection device failure and environment impaction. A model of detailed line-protection state transition is built based on the Markov method, which contains two sets of main protection and two sets of backup protection of high-voltage system, to calculate the probability of undesired tripping and failure to operate of the protection system.As current model of power system is difficult to accurately simulate the action logic of relay protection, a detailed relay protection model is proposed in this paper. With user-defined model in PSASP, a protection model is built to simulate cascading failures.The simulation calculates the probability of hidden failures and the various factors that influence hidden failures first. The simulation also includes the act of relay protection and control system in different load levels and their effects to the development of cascading failures, and calculate the risk of undesired tripping and failure to operate of the protection system by the result of simulation at the same time. The results shows that simulation analysis of cascading failures based on this protection model can reflect the dynamic behavior of relay protection in power system. The rationality and effectiveness of the proposed protection model are verified.