Reliability Studies Of Smart Substation Transformer Protection System

Smart substations are key nodes of power grid, responsible for electricity transmission and energy conversion. Protection relays play an important role in smart substations, its reliability is related to the power system safe continuous operation. With the development of IEC61850 standard, the state-of-the-art of electronic transformers and intelligent electronic devices (IEDs), the use of network transmitting of sampled values, station-wide information sharing in a substation becomes possible. This facilitates integrated secondary system. IEC61850 standard demands all devices to be time synchronized to external precise GPS clocks, enable devices connected to the process bus to synchronize the power grid precisely. The real-time performance of transmitting sampled values over the process bus may impact the reliability of protection system.The process bus architectures are investigated in this thesis:1) Sampled values and tripping signals are both transmitted over the process bus.2) Sampled values are transmitted over direct links while tripping signals over the process bus.3) Both sampled values and tripping signals are transmitted over point-to-point connections. It is of significant importance of studying the reliability of the process bus and its impact on smart substations. The introduction of redundant process bus, integrated merging unit with intelligent terminal unit, may facilitate better reliable transformer protection system. This thesis investigates three process bus architectures associated with transformer protection system, establish their reliability models, and calculates their reliability.It is observed that a great deal of changes have associated with the move from traditional to smart protection systems, not only in hardware but also in software design. It is facing challenges in reliability assessment when process and station buses are introduced, due to the parallel multiple paths for protective signals and its self-healing features. At present, there is no standard evaluation models and methodology to analyze the smart protection system reliability. This thesis investigates sampled values and GOOSE flows, and uses the minimal path algorithm to compute the connectivity rate of the information flow. A generalized reliability block diagram model is used for reliability assessment of the smart protection system, and its correctness is verified.