Reliability analysis of protection systems thanks to fault tree and block diagram method and its application to Turkish power transmission system with proposal solutions

Protection systems play a vital role in maintaining the high degree of service reliability required in present day power systems. For this reason the reliability level of power systems is closely related to the reliability of protective relays, whose working condition will greatly impact the operation of power systems. The study of some reports indicate that protection systems frequently play a role in the sequence of events that lead to distribution and transmission power system disturbances.In this study, general information about protection systems, fundamental of reliability and reliability calculation methods are given; the studies which are related to reliability of protection systems that has been done in literature lately are flicked through; the influence of non sinusoidal condition on protection relays is investigated; general information about network probabilistic reliability calculation making method is given; some information about protection systems and high voltage substations of Turkish Electricity Transmission Company (TEİAŞ) are given in Turkey; the statistical failure data of 154-380 kV over head line and transformer feeders for 2009 year which was taken from TEİAŞ are presented as detailed.A protection system consists of circuit breaker, measuring transformers, auxiliary systems and protection relays. When reliability of protection relay is taken into account, it is defined as maloperation and trip-rejection. Although there are many factors which affect these two failure modes, in literature there is no study which defines these problems detailed as in this study. As a result in this study, in order to define all these failure modes, a detailed fault tree is created for over head line and transformer feeder then some proposal solutions for improvement of reliability, which cover every aspect of protection systems, from current transformer to circuit breaker and auxiliary DC supplies are presented as detailed, thanks to not only some technical information that was taken from TEİAŞ but also my professional design experience in protection and control systems of high voltage substations via more than hundred projects in Turkey, Iraq, the UK (England, Northern Ireland), the Netherlands and Germany.Current situation and proposal solutions of reliability is calculated with reliability block diagrams which are created thanks to the projects are still being used by TEİAŞ in Turkey and result of numerical application indicates that my proposal is better than the current situation.The reliability calculation of five different case studies with 154-380 kV nominal voltage level are done with DigSilent computer software for three different regions in Turkey thanks to real datas and results of calculation are given in this study.