Characterization Of Dynamic Hysteresis And Deep Saturation Of Iron Core And Wideband Nonlinear Transient Transformer Model

Transformers are one of the most important pieces of equipment in the generation,transmission,transformation,distribution,and utilization of modern power systems.They also play an increasingly important role in the industries of rail traffic,electric vehicles,electric ship,and electric aircraft.However,the varied application scenarios,which result in the complex electromagnetic transient processes on the transformer,present the higher technical challenge to the safe and stable operation of the transformer.Therefore,the development of the physical model of the transformer,which can accurately represent the electromagnetic transient characteristics,can be used to simulate the transformer in the complex operating conditions.It is of great significance for the electromagnetic transient analysis,condition prediction,active forewarning,fault tracing,electromagnetic transient protection,and reliable operation of the transformer.The physical essence of the transformer is the interaction between the electric field,magnetic field,and material.The interaction would result in the complex electromagnetic properties including core nonlinearity and frequency-dependence.However,the existing transformer model cannot completely and accurately represent these electromagnetic properties.As a result,it is difficult to accurately simulate the electromagnetic transient process of the transformer under the wideband and wide-amplitude excitation.Therefore,the purpose of this thesis is the development of the transformer model which can accurately simulate the electromagnetic transient properties of the transformer under the wideband and wide-amplitude excitation.The dynamic hysteresis model considering the magnetization loss characteristic is first developed for describing the dynamic magnetization properties of the transformer core.The composited magnetizing branches are built for the representation of the core spatiotemporal nonlinearity.The duality-derived transformer model considering dynamic hysteresis and deep saturation is developed.Then the equivalent circuit of the wideband admittance model is proposed for the representation of the frequency-dependence.The wideband nonlinear transformer coupling model is developed by coupling the wideband admittance model with the duality-derived model.Finally,the representations of the dynamic hysteresis,nonlinearity and frequency-dependence of the coupling model are validated.Then the model is compared with the typical transient transformer model.The main work and important achievements of this thesis are as follows:(1)The development of the dynamic Preisach hysteresis model considering magnetization loss properties and its parameter determinations.The dynamic magnetization experimental platform is built to research the dynamic magnetization process and characteristics of the transformer core.Based on basic principle and the common parameter determination methods of the Preisach hysteresis model,an improved centred cycle method for Preisach distribution function determination is proposed,which could solve the contradiction between the efficiency and accuracy of the existing determination method.The inverse Preisach model,represented by the flux and current,is proposed.Combining the eddy current loss and residual loss in the magnetization of the core,the dynamic Preisach hysteresis model is then developed.(2)The development of the duality-derived transformer model considering dynamic hysteresis and deep saturation.Based on the duality principle,the topology of the duality-derived model of the single-phase two-winding transformer is derived.The representation of the magnetizing branch coupling the dynamic hysteresis with the deep saturation is proposed to solve the description problem of the spatiotemporal nonlinearity of the core.The test method of the deep saturation inductances and the computation method of the deep saturation characteristic curve is also proposed.Then the duality-derived transformer model considering dynamic hysteresis and deep saturation is developed and realized in ATP-EMTP.(3)The development of the wideband nonlinear transformer coupling model considering core nonlinearity and frequency-dependence.The wideband admittance transformer model is derived based on the parameter matrix of the two-port network.And the frequency domain expression of the wideband admittance is obtained by the vector fitting method.The discrete state equation of the wideband admittance is then derived to develop the equivalent circuit of wideband admittance model in ATP-EMTP.And the wideband admittance model characterized by the NORTON current source and the physical Cauer circuit is further developed for the stability correction.The wideband nonlinear transformer coupling model,which can describe the core nonlinearity and frequency-dependence,is developed by the mathematically coupling of the wideband admittances model and the duality-derived ? model using complementary filters with complete compensation.(4)The accuracy and effectiveness of the wideband nonlinear transformer coupling model are validated.The parameter identification tests of the model are carried out on a single-phase test transformer.And the wideband nonlinear transformer coupling model is built in ATP-EMTP.The representations of the dynamic magnetization,nonlinearity,and frequency-dependence of the wideband nonlinear transformer coupling model are validated by the experiments.Finally,the wideband nonlinear transformer coupling model is compared with the typical transient transformer models,which further validates that the proposed model has the ability to simulate the complex electromagnetic transient including inrush current,lightning impulse,and ferroresonance.The results of this thesis show that the proposed wideband nonlinear transformer coupling model can accurately describe the dynamic magnetization process of the transformer core,and can also accurately represent the nonlinearity and frequency-dependence of the transformer.The wideband nonlinear transformer coupling model can realize the precise simulation of the transformer under the wideband and wide-amplitude excitation,which can satisfy the requirement of transient analysis under multi-scene complex conditions.It can also provide the basic support for the condition prediction and the reliable operation of the transformer and the system.