Research And Design Of Shielding Structure For Leakage Field Of Large Oil Immersed Transformer Box

The construction direction of China's power grid is"large power grid,ultra-high voltage and automation".Therefore,it is necessary to vigorously develop the R&D technology and manufacturing level of ultra-high voltage transmission,converter station,large transformer and related supporting equipment.Safe operation of large oil immersed transformer ensures the stability of the power system and the flexible distribution and use of electric energy.However,due to the existence of leakage magnetic field,the winding,iron core,box and other metal structures inside the transformer will produce eddy current loss under its action,and then the loss will be reflected in the form of thermal effect.Generally,where the eddy current loss density is large,there is more heat.The increased heat makes the internal devices and the surrounding temperature rise.At the same time,due to the uneven distribution of the leakage flux,it will lead to over hot spots in parts of the device.It can be seen that the distribution of leakage magnetic field and the size of leakage magnetic flux have a great influence on the safe operation of large oil immersed transformer.The ultimate goal of this paper is to reduce the magnetic field strength of leakage flux continuously.The leakage flux is closed by the box,and the magnetic field intensity on its inner surface is high,so it is urgent to study the shielding of the transformer box.In this paper,Ansoft Maxwell finite element analysis software is used to study the leakage field of large oil immersed transformer with high voltage and large capacity model OSFPS-120000/220 under normal symmetrical operation.At the same time,a large number of shielding experiments are carried out to optimize and improve the shielding structure and parameters.First of all,five types of shielding are simulated,which are the length of the box top shielding,the thickness of the box top shielding,the height of the box wall shielding,the distance between the box wall shielding and the box wall,and the box bottom shielding.The magnetic field intensity of the leakage flux in each case is obtained by simulation,and the shielding structure and parameters of the above five shielding types are determined.Among them,the top shield can reduce the leakage flux magnetic field strength by about 10%,and the wall shield can reduce the leakage flux magnetic field strength by about 80%.Then,we use the causal chain analysis,the final ideal solution,the resource analysis,the matter field model and the physical contradiction in TRIZ theory to analyze.The shielding structure of the transformer is optimized by using the small man method,and the angle shielding structure at the end of the tank wall of the large oil immersed transformer is designed.It is found that the combination of±60~ohas the best effect,which is 12.30%lower than the leakage field strength without adding.Finally,it is determined as the final scheme.In this paper,how to reduce the magnetic field strength of leakage flux in the case of large oil immersed transformer is studied,which can provide constructive suggestions for the shielding direction of this case.