Related information shows that oil-paper insulation damage is one of the important reasons that causes the failure of most electrical equipment which led to blackout accident,and large-scale power transformer is one of the important and typical oil-paper insulation equipment in power system.So,real-time monitoring and diagnosing the oil-paper insulation state of power transformers is important to ensure the stable,reliable and safe operation of the power grid.Based on the equivalent circuit model of time-domain dielectric response,taking oil-paper insulation transformers as research object,the improved particle swarm optimization is used to estimate the equivalent circuit parameters,and the aging characteristic of oil-paper insulation under the time-domain dielectric response test method is extracted by simulation experiment and case analysis.A comprehensive evaluation method of oil-paper insulation state of transformers based on fuzzy-gray clustering and combination weighting approach is proposed.The main contents of this paper are as follows:(1)Based on the time-domain dielectric response theory,the equivalent circuit model of the oil paper insulation system is established,which is extended Debye equivalent model.The mathematic optimization model of equivalent circuit unknown parameters is established by the recovery voltage test circuit of dielectric time domain response,and the equivalent polarization branch number is determined by depolarization current curve differential spectrum method,which lays the foundation for the estimation of subsequent circuit parameters.(2)Because of the close relationship between the equivalent circuit parameters and the aging state of oil-paper insulation,an improved particle swarm optimization is used to estimate the established mathematical optimization model of equivalent circuit parameters,which is based on the interval particle swarm optimization,and the influence of the relation between the variables is fully considered.The accuracy and superiority of the algorithm are verified by parameter identification example.(3)Through the examples and the simulation analysis,several aging characteristic parameters which can reflect the insulating state of oil-paper under the extended Debye model,the recovery voltage method and the polarization/depolarization current method are obtained,and a hierarchical graph of several characteristic quantity index is determined,and the weight of each aging feature is determined by combination weighting method with subjective and objective significance.(4)Because the relationship between oil-paper insulation state and the characteristics of the aging index is not very clear,there is a certain fuzzy relationship between the two.So,the fuzzy comprehensive evaluation method and gray clustering method are used to evaluate the oil-paper insulation state.Based on the transformer test data collected over the years,the oil paper insulation state standard vector table is established by the fuzzy-mean clustering method.At the same time,the turning point of the first-level gray clustering whitening function is established.Finally,a comprehensive evaluation model of transformer oil-paper insulation state is established,which further improves the accuracy of oil-paper insulation evaluation. |