The Simulation And Research Of Operating Characteristics Of New-type Converter Transformer Under DC Bias

UHV power grid will be the major development of China Power Grid in the next 20 years,and DC transmission which fits for transmiting electrical power in long distance and large capacity will bewidely used in UHV engineering.The existence of DC magnetic bias has also become the focus of research.The converter transformer is the core equipment of HVDC transmission system.Self-coupled compensated and shielding harmonic converter transformer has a very good application prospect for having the merits that traditional transformer doesn't.This paper research the operating characteristics of new transmission system using new-type converter transformer under DC bias.The main job of this paper includes the following:Firstly,this paper analyzes the causes of DC bias of converter transformer, introduces the effect mechanism on the converter transformer of DC bias and the harm of transformer and power system operation.Secondly,this paper gives the connection schemes of new-type converter transformer and the circuit model of new-type converter transformer under DC bias.The harmonic current suppression mechanism of new-type converter transformer under DC bias is analyzed and the filter for DC bias is designed.Using PSCAD/EMTDC to build the new AC-DC transmission system model of new-type converter transformer, the magnetization curve characteristics, exciting current distortion characteristics and harmonic content is analyzed. Using a new inductive filtering technology to restrain the harmonic of DC bias and comparing with traditional converter transformer, the result shows the inductive filtering technology has the good suppression effect for harmonic pollution caused by DC bias.Thirdly, the simulation model is built when DC and AC transmission lines are set along the same right of way.As transmission corridor land tension, there will be AC line and DC line running parallel.The case of electromagnetic induction will lead to inductive current and voltage in DC line,which leads to the occurrence of DC bias.By using PSCAD/EMTDC the AC/DC transmission system model is established with AC and DC line parallel based on new-type converter transformer.The inductive components and DC bias current are calculated at the different factors and the effective rule of limit DC bias is summarized. In the actual project the flexible application of appropriate suppression methods with new-type converter transformer and inductive filter device can achieve effectively to suppresses DC magnetic bias.