Study On Loss And Temperature Rise Of 27.5kV Dry Type Transformer

With the maturity of dry transformer manufacturing technology and its advantages of small size,oil free,fire prevention,safety and reliability,it is gradually applied to the lowvoltage distribution system of traction power supply system.However,the traction load always has nonlinear and impact characteristics,resulting in a large number of high-order harmonics in the catenary.These harmonics of traction power supply system will cause additional loss of electrical equipment,temperature rise,efficiency reduction and other problems.One of the common faults of transformers is the overheating fault caused by losses.When the temperature continues to rise,it will accelerate the insulation deterioration of transformers,and even cause transformer fire and explosion accidents.In this thesis,a traction substation used 27.5k V dry transformer as the research object,on the high voltage side voltage and current harmonic characteristics analysis,harmonic influence on the loss calculation and harmonic influence of dry transformer loss and temperature rise changes.(1)Combined with the harmonic generation mechanism of traction power supply system,the frequency and content of voltage and current characteristic harmonics of catenary are analyzed,and the harm of high harmonics of catenary to low voltage distribution system is expounded.Based on electromagnetic field theory,the influence of skin effect and proximity effect on transformer winding under harmonic background was analyzed,and the current density distribution function in dry transformer winding was deduced,and the distribution of current density in round copper conductor at different frequencies and radii was analyzed.Considering the skin effect and proximity effect of winding,the formulas of harmonic core loss and harmonic winding loss of dry transformer are derived.(2)The coupling relationship between magnetic field and circuit is analyzed,and the mathematical model of field-circuit coupling method is established to improve the accuracy of calculation of core loss and winding loss.ANSYS Maxwell was used to establish a THREEDIMENSIONAL finite element model of 27.5k V dry transformer.The field coupling method was used to solve the flux density distribution,and the loss was analyzed and calculated according to the solution results.The accuracy of the simulation model was verified by the secondary side rated voltage,rated current,iron core loss and winding loss.The loss of harmonic winding varies with the content of harmonic current and the number of harmonic waves.The total winding losses of single harmonic current and compound harmonic current are obtained by simulation calculation,which verifies the superposition of harmonic losses and provides theoretical basis for the calculation and analysis of transformer harmonic losses.(3)ANSYS WORKBENCH software was used to establish the electromagnetic and thermal multi-physical field simulation model of the dry transformer used for 27.5k V,and the boundary conditions were set according to the actual operating conditions of the dry transformer for temperature field simulation calculation,and the temperature field distribution of the iron core and high and low voltage winding of the dry transformer used in the fundamental wave condition was obtained.And the axial temperature distribution of the core and winding,the core and winding of the hottest temperature and its location,and the high voltage winding inside the upper part of the temperature for the whole dry transformer hot temperature;In the case of harmonic current,the temperature rise of dry transformer varies with the content and number of harmonic current.