Transformer GIC DC Bias Magnetic Treatment Device And Its Optimization Design

DC bias will cause serious damage to the transformer.There are two main reasons why the transformer will generate DC bias:One is the geomagnetically induced current(GIC)generated by the geomagnetic storm;the other is the induced current generated in the system under the direct current grounding pole unipolar operation mode.So far,we has already dealt with DC bias magnetism caused by grounding poles.However,the geomagnetic storm mainly invades the power grid above 500kV in China,therefore,there is a higher requirement for the treatment device,and geomagnetic storm has a great suddenness,so need a device with more complete functions.lt is very important to optimize the design of the bias magnetic treatment device.The main research work and results of this paper are as follows:(1)Based on the analysis and research on the effects and safety of three kinds of bias magnetic treatment devices,such as capacitance,resistance and reverse compensation at home and abroad,combined with the characteristics of GIC bias in Chinese power grid and the GIC calculation results based on Gansu 330kV and 750kV power grids,proposed to use 3D resistor to control GIC and develop small resistance GIC suppression device,and the influence of the device connected to the grid on the zero-sequence current protection and the impedance measurement of the impedance relay is studied.(2)The ANSYS finite element analysis software was used to simulate the thermal stability of the resistor.The structural form of the resistor was selected according to the analysis result,and the dynamic stability check was performed;after selecting the resistor with appropriate performance,the whole device is developed,designed and fabricated with a 35kV voltage level,which can withstand large current surges.It has automatic and manual control functions and remote monitoring functions to control GIC bias.(3)Propose the test plan of the device.At present,according to the State Grid Corporation of China’s "power transformer neutral point capacitance isolation/resistance current limiting device test procedures" industry standards,the China Electric Power Research Institute and Suzhou Electric Apparatus Science Research Institute completed the test of some of the projects,the test results are in line with expectations Claim.State Grid Corporation of China’s "Power Transformer Neutral Point Capacitance Isolation/Resistance Current Limiting Device Test Procedures" industry standard was just promulgated in March 2017.Before the end of 2018,the capacitive isolation/resistance current limiting devices used in China’s power grid did not test according to the standard.In this paper,the 35kV voltage level developed by GIC is also important for the small-magnetism biasing device that can withstand large current surges.