Analysis Of The Risk Assessment Of Hidden Failures In Protection System

With the growing complexity and uncertainty of power system, the operatingreliability of power grid has gotten increasingly tough challenges. The hidden failures(HFs) in protection system have been proved to be one of the main reasons whichaffect the operating reliability of power system. The analysis of HFs model is useful tostudy the mechanism of HFs and identify the weak links of protection system. Therisk assessment of HFs can help to conduct the analysis of cascading failures, find thekey lines and high-risk contingencies in the grid. The analysis of HFs plays animportant role in improving the operating reliability and security of power system.Firstly, the mechanisms causing HFs in protection system have been analysedwhich are divided into four aspects: internal components failure, inappropriate relaysettings, instantaneous failure, and associated components failure. The analysis showsthat the HFs are correspondings to multiple modes. The analysis methods of HFs havebeen reviewed from probability and risk aspects and the mechanisms of each methodare also studied.Secondly, the HFs in protection system for extra high voltage network areconducted, which considered HFs in line main protection, backup protection, breakerand breaker failure protection. The analysis of power system N-k contingency basedon multiple modes has been conducted through three angles: vulnerability zone,ability for zone III to avoid load impendence and breaker failure. The results show thatthe method can be used to study the mechanism of cascading failures and identifyimportant N-k contingencies.Thirdly, the risk of HFs has been studied which is conducted by the analysis ofthe risk of N-k contingency. A method based on event tree and group functions tocalculate probability and a severity index including independent power lose, load lossand transmission sections loss have been proposed. The results show that this methodcan be used to improve accuracy of calculating the probability of N-k contingencies,identify key lines and weak links, and prevent cascading failures.