Study On The Electromagnetic Shielding Effectiveness Of The Step-up Transformer With Large Capacity

Leakage magnetic field exists in transformer and is directly proportional to the transformer in capacity. When the capacity increases, the leakage magnetic field caused in metal parts shall also increase which results in eddy current loss increasing and may even leads to overheating of a certain part to speed up the insulation aging and accelerate transformer oil decomposition so as to affect the reliability and safety of transformer. Therefore, for transformer with large capacity, its inner magnetic flux leakage distribution and the eddy current loss of metal parts should be calculated and analyzed specifically and exactly by commercial software to determine the internal structure of transformer, material of metal structures and shielding ways and so on to prevent local overheating.This paper is generally divided into three parts. The first part summarizes the development situation of power transformer in our electric power industry and introduces the electromagnetic field theory, the finite element analysis method and Mag Net software in detail. Through introduction of these knowledge, the main idea of this paper is illustrated.The second part analyzes and introduces the causes, types and effects of leakage magnetic field in power transformer winding. Meanwhile many kinds of additional loss of transformer caused by leakage magnetic field is analyzed which further illustrates the point of view of this paper and the necessity of the work undertaken in this paper.The third part mainly analyzes and studies electromagnetic shielding effectiveness of large capacity step-up transformer. Based on different structures of several nos. of step-up transformer with large capacity and electromagnetic shielding of different places, through reasonable simplify and software Mag Net as calculation tools, calculation models of electromagnetic shielding of different places in transformer are set up. First, the electromagnetic shielding effective of the tank wall is studied. In order to reduce the eddy current loss of the tank wall more efficiently, magnetic shielding model and electric shielding model under different tank wall thickness are built by Mag Net software and defines them as Model 1 to Model 3. Shielding effects caused by three shielding models are comparatively analyzed and on this basis proposal for production is concluded. Secondly, shielding models on ascending flanged base and its strengthen iron of step-up transformer with large capacity are built. By changing the material, structure and location of shielding, effectiveness of several models for reducing local overheating is respectively studied and on this basis, reasonable conclusion is made. Finally, different thickness shielding models on core web are built and related shielding effectiveness is compared and some meaningful conclusions are made.This paper analyzes and studies inner magnetic field distribution, material properties and shielding ways of transformer through software MAGNET to get the optimized shielding structure and blocking way so as to make large capacity transformer partial overheating problem solved. Meanwhile, the possibility of replacing copper shielding by aluminum shielding is also analyzed and effect after the replacement is comparatively analyzed.