Variation of Operational Reliability of Power Transmission System
The paper describes a security study of the Finnish power transmission system. The aim of the study was to discover variation of the operational security of the power transmission system. The study was a simulation study and the power system simulation model was a Nordic grid model. The Finnish main power transmission system is designed and operated with the n-1 criterion. This results to a situation where the security level of the power transmission system varies due to several factors. The dimensioning fault varies on the basis of the operational situation of the grid. The amount of load and generating capacity in the power system varies, which means that the damping and reserve volumes also vary. Therefore the response of the power system even to a similar fault is different depending on the power flow case. In addition, frequencies of grid faults vary depending on the season and on the weather conditions. The study was done based on a method presented in a doctoral dissertation “A method for the probabilistic security analysis of transmission grids 1 and in 2, 3. The method uses Probabilistic Safety Assessment (PSA), which uses event and fault tree analyses and takes into account busbar schemes of the substations, reliability of the protection and circuit breaker operations, and the frequency of faults. The study was carried out by creating five different representative power flow cases based on real data from the Nordic power system. Line and busbar faults in the Finnish 400 kV grid and production failures in the Nordic power system were included in the study. Dynamic simulations were done to determine whether the system acceptably withstood the faults and failures or not. The seasonal variations of the grid fault frequencies were taken into account in the study. The variation of the security of the Finnish power transmission system and the factors that define the security in different conditions can be seen from the study results. According to the results the system is more unsecure when power is exported to Sweden than when power is imported from Sweden. This is because not correctly cleared short circuit faults will cause more probably severe consequences in a large export situation than in a large import situation. The results also show that a circuit breaker failure after a line fault is the most probable cause of a system breakdown in summer conditions and a failure of a busbar protection relay after a busbar fault in winter conditions.
Transmission Power System Security Operational Reliability System breakdown Variation
J.LAMPONEN L.HAARLA
Helsinki University of Technology
国际会议
桂林
英文
1-8
2009-10-28（万方平台首次上网日期，不代表论文的发表时间）