Calculation And Analysis Of Stray Losses In 220kV Ultra-High Capacity Transformers

Super large capacity transformer is one of the most important equipment in the electric power system.Due to its large capacity,the leakage magnetic field generated in normal operation is much greater than that of normal capacity transformer,and the stray loss caused by the magnetic leakage field is quite big.As a result,the large capacity transformer is more likely to be over-heated,insulated broken,and low operational efficiency,thus endangering the safety and stability of the large capacity transformer.Therefore,how to decrease the stray loss of large capacity transformer has always been a hotspot in domestic and foreign research.Based on this,the thesis firstly builds P21-B and P21-a two types international benchmark model using Mag Net electromagnetic simulation software and then analyzes their stray loss.Through the comparison between the calculated results and the measured ones,the precision of the software for calculating the magnetic steel and the non-magnetic steel is validated.Based on this,by comparing the calculation results of stray loss in magnetic steel using surface impedance method and layered method,it was determined that the surface impedance method should be used for magnetic steel.By comparing the calculation results of stray loss in non-magnetic steel with different numbers of slots,it was decided to process the non-magnetic steel by slotting.Secondly,after verifying the accuracy of the calculation method of Mag Net electromagnetic simulation software,a 2D and 3D computational model of an ultra-large capacity transformer,model SFP-800000/220,was built using the finite element method.The model was simulated and analyzed in terms of leakage field,short-circuit impedance,stray losses and other aspects,in order to obtain the distribution law of leakage field and stray losses of the ultra-large capacity transformer.Then,by comparing the calculated values of short-circuit impedance and stray losses with the measured values,the correctness of the calculation results was verified,providing a basis for further improving the shielding structure of the ultra-large capacity transformer.Finally,in order to improve the distribution of leakage magnetic field and reduce the stray losses of structural components in ultra-large capacity transformers,lobe type magnetic shielding was added to the original model,and electromagnetic performance parameters such as leakage magnetic field,short-circuit impedance,and stray losses of the ultra-large capacity transformer after adding lobe type magnetic shielding were solved using the finite element method.By comparing with the calculation results of the model without lobe type magnetic shielding,it was found that lobe type magnetic shielding can effectively reduce the stray losses of structural components.In order to investigate the factors affecting the shielding effect of lobe type magnetic shielding,the thickness and geometric position of lobe type magnetic shielding were processed by thinning and changing,and the calculated results of stray losses were compared and analyzed.The optimal thickness and position of lobe type magnetic shielding were found,providing a reference for the design of lobe type magnetic shielding in ultra-large capacity transformers.