Calculation Of Wide Band Two-Port Admittance Parameters Of 10kV Power Transformer

The suppression and protection of over-voltage in power system, as well as the study of electromagnetic compatibility in power system need to build electromagnetic transient model of the components and equipments. The transformer model in the electromagnetic transient computer program EMTP, can only be used to the steady and transient calculation in 50Hz and low frequency(below 10kHz). Because of the lightning impulse voltage and VFTO caused by the switching operations in gas insulated substation made the calculation upper frequency limit in MHz and a few tens of MHz, the type of equipment of conventional transformer circuit model obviously does not meet the requirements of simulation, therefore, it is necessary to establish their high-frequency circuit model.Establish its black-box model is based on the network function.But,it is difficult to measure the wide band network functions of the large-scale equipments of transformer's type .Based on the National Natural Science Foundation project, Passive Method of Broadband Macro Model of Transformer Equipment, NO.50977301, in order to overcome this problem , the paper presents the finite element method to calculate the wide band admittance parameter based on the multi-conductor transmission line of the transformer.In this method, first establish the multi-conductor transmission line model of the transformer winding,and then apply the the finite element method to calculate multi-conductor transmission line per unit length matrix, at last based on boundary conditions and the telegraph equation derive the two-port admittance parameter matrix of transformer. In this paper, a continuous model of transformer winding and a 10kV two-winding transformer were calculated.Take the continuous transformer winding model as a autotransformer, the first turn is the input, the other turns of it is the output. Establish the MTL model of the continuous transformer winding, and then apply the the finite element method to calculate multi-conductor transmission line per unit length matrix, at last based on boundary conditions and the telegraph equation derive the two-port admittance parameter matrix of transformer's input and output.On this basis, establish the MTL model of the high voltage winding and low voltage winding of the 10kV two-winding transformer, using the finite element method to calculate the self capacitance and the mutul capacitance of the high voltage winding and the low voltage winding,and then calculate the L,R,G parameters. At last based on boundary conditions and the telegraph equation derive the two-port admittance parameter matrix of transformer's input and output. To verify the validity of the calculation, using Agilent 4395A network analyzer to measurement the scattering parameter of the continuous transformer winding model and the 10kV transformer and turn it into the admittance parameters. The comparison of calculation results and measurement results verify the feasibility and effectiveness of the demonstrated method.