Study On Lightning Stroke Modeling And Lightning Protection Of The Distribution Transformer

As an important part of distribution network,distribution transformer(DT)with low insulation level is easy to be violated by lightning and overvoltage.Its safe operation has a great influence on the stability and reliability of distribution network below 35 k V.More than 60% of the power outage trip accidents in China are caused by the low voltage distribution system.The overvoltages such as resonance overvoltage,operation overvoltage and lightning overvoltage caused by atmospheric lightning may cause the failure of distribution network.Because of the lightning is a natural phenomenon of atmospheric lightning discharge,from the over voltage control and produce high amplitude lightning,damage to the distribution network is the largest,it is very important for the lightning protection to establish the simulation model of the lightning strike of the distribution transformer and to study the transient process.According to the characteristics of distribution transformers under lightning stroke,a wideband distribution model suitable for lightning is constructed by using the scattering parameter measurement method and the circuit fitting method.The particle swarm optimization and simulated annealing algorithm is introduced to further optimize the model parameters.The validity of the distribution transformer model is verified by lightning surge generator in lightning condition.The distribution transformer model is used to analyze the internal overvoltage distribution of distribution transformers in ATP-EMTP.Besides the influence of the impact corona of the overhead transmission line on the transmission of the lightning overvoltage of the distribution transformer is also simulated and analyzed.According to the simulation results,find insulation weak positios of the distribution transformer and put forward four measures to increase the amplitude of lightning overvoltage in distribution transformers,which are installing lightning arresters,high voltage side plus reactor and cable,reducing grounding resistance and adding capacitor at low voltage side.The protection effect of four lightning protection measures is verified by simulation,and the recommended protectionscheme is put forward.The equivalent wideband model of distribution transformer under lightning strike provides reliable reference for the research of lightning overvoltage of distribution transformer in distribution network.The proposed lightning protection measures can effectively improve the lightning protection level of distribution transformers.