Harmonic Analysis Of Transformer Under DC Magnetic Bias Condition

In order to meet the requirements of long-distance and large-capacity power transmission,China has established a number of ±500kV and ±800kV DC transmission lines.When the DC transmission system adopts a single-maximum operation mode,the DC current flowing into the earth will be large,and a DC current component as large as several tens of amperes appears in the AC grid,which will be caused when the DC current flows into the transformer winding which is grounded at the neutral point.Transformer DC bias phenomenon.This phenomenon will affect the normal operation of the transformer,which will distort the transformer excitation current and generate large harmonic currents.The DC bias magnetic resonance will amplify or generate resonance in the transformer low-voltage reactive power compensation device under certain conditions,which seriously threatens the operational safety of the power capacitor.In this paper,the actual production problem of the 500 kV Fuyuan station of Huizhou City affected by DC bias is studied.The system simulation model of transformer neutral point after DC is established in the PSCAD environment;the mechanism of DC bias is studied.Based on the harmonic response of the shunt capacitor,the influence of the DC bias magnetism on the harmonic content and the variation law of the transformer winding excitation current are analyzed.The capacitor harmonic current amplification factor.In order to avoid the harm of DC bias on the power equipment,the technical principles of several common current methods for suppressing DC bias are analyzed and compared in this paper,and their advantages and disadvantages are pointed out.According to the actual situation of Huizhou power grid and the combination of the development of new technologies,the capacitor blocking device applied in the neutral point of the 500 kV Fuyuan station transformer is described in detail,and the 35 kV side power quality of the main transformer before and after the installation of the capacitor blocking device is also combined.Monitoring data,comparative analysis,demonstrated the feasibility and effectiveness of capacitive blocking device to suppress harmonic harm of DC bias.