Study On The Generation Regularity Of Interharmonics And Its Effect On The Excitation Performance Of Transformers

With the development of power system,the complexity of power transmission and distribution network is increasing day by day.The large-scale application of various non-linear components and loads as well as power electronic devices has brought many advantages to the power system.It also brings the problem of harmonic pollution that cannot be ignored.A large number of literatures have studied and analyzed the harmfulness of harmonics and interharmonics to power grid stability and power transformer.Their existence will not only reduce power quality and cause power grid fault,but also seriously affect the excitation performance of transformer.Sponsored by the National Natural Science Fundation of China under grant No.51577066,in this paper,two main interharmonic sources in power system,AC arc furnace load system and doubly-fed wind power generation outgoing system,are selected respectively.Starting from the establishment of their mathematical models and the system simulation models,by changing the main parameters of the two simulation systems,the generation rules of interharmonic frequencies and contents in the two main interharmonic sources system are studied and summarized.Based on this,the excitation performance of transformer core under power frequency excitation with different interharmonic frequency and content is studied.Firstly,the simulation model of three-phase power system with AC arc furnace load is established.By changing the main parameters of AC arc furnace,the law of their influence on harmonic frequency and content of voltage and current at the load end of the model is analyzed.Secondly,the simulation model of doubly-fed wind power generation outgoing system with series compensation is established.By changing the line series compensation and wind speed in the system,the voltage and current of the line are studied and analyzed,and the influence of two main parameters of the system on the frequency and content of interharmonics is summarized.Finally,a test platform for transformer core excitation performance is built,and interharmonics of different frequencies and contents are superimposed on the basis of power frequency voltage.The relationship between interharmonic frequency?content and transformer core excitation current?excitation loss is studied,and the influence law of interharmonics on transformer core excitation performance is summarized.