Simulation Research On Ultrasonic Signal Propagation Law Of Partial Discharge In Transformer

The safe operation of the power equipment is directly related to the safe supply of the high voltage power system.As the core of energy conversion in the process of power transmission,transformation,transmission and distribution,power transformer is the key power equipment to the reliable operation of the power grid.Therefore,partial discharge detection of power transformer is of great significance to ensure the stable operation of power grid.Due to no electrical parameter is detected,along with strong electromagnetic interference ability and high sensitivity,EFPI optical fiber PD detection system has been widely used online in recent years.Therefore,it is very important to study the positioning method of transformer PD.The mechanism of partial discharge,associated ultrasonic wave in the air gap of transformer oil and its propagation theory are introduced in this paper.On the basis of this,the ultrasonic signal propagation process of the transformer partial discharge is studied as follows:According to the mechanism of partial discharge generation,a mathematical model of partial discharge point source function,single exponential decaying oscillation pulse function,is constructed.Two-dimensional models of ultrasonic waves traveling through transformer oil and oi1 with steel plate are simulated by the method of finite element method respectively.EFPI optical fiber PD detection system is built to measure the attenuation and delay of ultrasonic signal when through the plate generated.Compared with the simulation data,the rationality of the two-dimensional simulation model is verified.A three-dimensional finite element model of 35kV oil immersed power transformer in true size is set to simulate and research the time domain ultrasonic signal propagation in transformer.A simplified cylindrical coil model,that the winding coil structure simplified into a cylinder and no oil channel inside the coil,is set based on structure characteristics to analyze the influence of oil channel inside the coil to ultrasonic signal propagation;of the 18 typical discharge location in power transformer model is selected using the geometrical symmetry.A database is established to locate the PD source location accurately,which contains two features of delay and attenuation of pressure waveforms in observation points.In order to verify the rationality of the three-dimensional model,using the existing equipment in the laboratory,the propagation process of ultrasonic signals in the circle is studied by experiments and time domain simulation.The experimental data and simulation results not only verify the propagation law of ultrasonic signals in transformer and the rationality of the three-dimensional model,but also provide the theoretical support to the realization of transformer partial discharge location based on EFPI optical fiber PD detection system.