Experimental Study And Computationalanalysis Of Harmonic Stray Loss Of Transformer Structural Components

With the establishment and development of China’s HVDC transmission system,the actual working conditions of electrical equipment in the power transmission and transformation industry are becoming more and more complicated.The harmonics of electric power systems are more harmful to electrical equipment.The loss,temperature rise and noise of electrical equipment under the action of harmonic magnetic field increase significantly,which affects its safe and reliable operation.Under different harmonic excitation conditions(including high-order harmonic single excitation,fundamental wave superimposed high-order harmonic excitation),this paper focuses on the stray loss of different metal structural parts(including copper,non-magnetic steel 20Mn23Al and oriented electrical steel B30P105)of power transformers and smoothing reactors,different calculation methods are given,and the calculation results of stray loss are verified by experiments.The main research contents of this paper are as follows:(1)Based on the P21~a-0 benchmark model,the study of the stray loss of the non-ferromagnetic structure of the transformer under the action of harmonic magnetic field were carried out.By constructing the experimental platform,the time domain and frequency domain method are used to measure the loss of the low magnetic steel plate in the model under the harmonic excitation,and the two measurement results are compared and analyzed,furthermore,the practical measures for simulating the stray loss of non-ferromagnetic structural components by frequency domain method under the condition of fundamental wave superimposed harmonics excitation were proposed,and relevant experimental verification was carried out.The results show that the calculation accuracy of the frequency domain method meets the design requirements and the calculation time is shorter.(2)By referring to the calculation method of harmonic loss of converter transformer provided by IEC61378-2 standard,the analytical formula for calculating the stray loss of copper shield in transformer was derived.Based on the simplified model of P21~c-EM1,the experimental results of the analytical formula were verified experimentally.The results show that the calculation results of fundamental loss of copper plate are in good agreement with the experimental ones.The losses of copper plate under the multiple harmonic excitation of fundamental superposition are the same as the sum of the copper losses under the separate excitation of each harmonic.Under the same excitation current frequency,the stray loss of the copper plate meets a certain proportional relationship with the square of the current size.Under the same excitation current size,the ratio of copper loss to current frequency does not meet the frequency characteristics given by the IEC standard.The frequency characteristics are corrected by considering the influence of the magnetic field distribution on the loss of the structural member,and the correction results are compared with the experimental values to verify the rationality of the correction factor.(3)A simplified experimental model of an oil-immersed smoothing reactor was designed and manufactured.Under different harmonic excitation conditions,the stray loss in the outer magnetic shielding frame of the smoothing reactor was studied experimentally.Based on the magnetic performance data of the silicon steel lamination was measured by building a harmonic magnetic performance test platform,the finite element simulation calculation of the stray loss of the magnetic shield frame of the smoothing reactor was carried out by the query loss curve method,and the corresponding experimental verification was carried out.The results show that the calculation results of the harmonic loss of the magnetic shielding frame are in good agreement with the experimental results,and the correctness of the simulation calculation method is verified.The results and conclusions obtained in this paper can provide reference for the calculation of stray loss and structural optimization design of structural components of electromagnetic transformers such as power transformers under harmonic excitation.