Research On Additional Losses Calculation And Structure Parts Temperature Rise Distribution Of High-voltage Converter Transformer

High-voltage converter transformers are important equipment in high-voltage DC transmission and transformation.With the continuous increase of grid scale and generator capacity,it's voltage levels are higher and higher.As it is subjected to AC-DC interaction during operation and its high frequency harmonic current,which lead to high-voltage converter transformers more complex than ordinary transformers in construction,the insulation problems and local overheating are even more pronounced.So it is meaningful to carry out research on 3D modeling,distribution of magnetic leakage field,the calculation of additional losses,reducing the loss and temperature rising of high-voltage converter transformers.This thesis takes a 500 kV high voltage converter Transformer with ZZDPZ-321100 / 500 model as the research object.The main study work of this thesis is as follows.(1)Two methods(surface impedance method and hierarchical method)are adopted in the numerical calculation of TEAM Problem 21 with software Magnet respectively.Comparison experiment data with simulation result indicates the surface impedance method is more suitable than the hierarchical method in the stray loss calculation of transformers.(2)According to the theories of finite element analysis about eddy current field,a program MA-3D based on Visual Basic 6.0 is proposed.It is specifically used for high-voltage converter transformers additional losses calculation.Firstly,parametric modeling and solving are available by calling Magnet.Secondly,calculation of additional losses under fundamental wave is obtained by script,combining with IEC6 1378-2 to get the harmonic losses calculation of winding and structural parts.Because skin depth on eddy losses of winding under harmonics is different,a harmonic losses factor is introduced to correct the result.After correction,error reduces from 13.70% to 9.75%,which indicates the correctness of the revision factor.Finally,error between load losses and measured value is 0.65%,which proves the correctness of the proposed software.(3)The principle of tank shielding is analyzed,and the additional losses of copper shielding and magnetic shielding are calculated at different thickness respectively,theresults show that 10 mm tank magnetic shielding is more suitable for high-voltage converter transformers.Then high-voltage converter transformer is analyzed with clamping shielding,indicates that appending clamping magnetic shielding can reduce structure losses and it is suitable for high-voltage converter transformers.(4)Combining the basic theories of heat transformer and empirical formulas,the surface heat transfer coefficients and surface temperature conditions are determined.Then the thermal field is calculated by the Magnetic-thermal coupling method with the software ThermNet.And the temperature distribution and hot spot temperature of structures with and without clamping magnetic shielding are got.It shows that the clamping magnetic shielding can reduce the temperature rise of the structure by reducing the loss of the structure.