Design And Optimization Of Superconducting Transformer

The daily operation of China’s power grid and railway system consumes a lot of electricity.The transformer is the core part of the power and railway system.As the input end of the distribution network power supply,the loss accounts for a relatively high proportion.The use of superconducting transformers to replace traditional transformers is beneficial to reduce operating losses and improve operating stability.At present,the development technology of superconducting transformers is still immature in China,and there is still a certain gap in performance indicators compared with foreign countries,and there are few design manuals with reference value.Due to the anisotropy of superconducting tapes,it is difficult to achieve optimal levels of efficiency.In order to overcome the influence of the anisotropy of the superconducting tape on the performance,the performance of the superconducting transformer is further improved.This research topic establishes a superconducting transformer design and optimization system for this problem,and applies it to the40 k VA superconducting transformer designed in this thesis,which effectively reduces the AC loss and verifies the effectiveness of the optimization measures,which has certain reference significance.In this thesis,the simulation calculation method of the two-dimensional axisymmetric model of superconducting transformer based on H equation is adopted.the relationship between superconducting tape and superconducting transformer efficiency is studied,and the structure of superconducting winding and iron core is summarized.According to the influence law of its electromagnetic performance,optimization measures are proposed according to the law.And the 40 k VA single-phase high temperature superconducting transformer is optimized as the research object,and the accuracy of the simulation model is verified.In the aspect of core structure optimization,the influence law of the presence or absence of iron core and the diameter of iron core on the electromagnetic performance of superconducting transformer is explored.The study found that the AC loss generated by the superconducting winding is reduced when the iron core is operated compared with the ironless operation.Due to the magnetic permeability of the silicon steel sheet,the horizontal field at the end of the winding is converted into a vertical field,which reduces the critical current density at the end of the superconducting winding,thereby increasing the loss;as the diameter of the iron core increases,the required number of coil turns The smaller it is,the more economical the superconducting transformer is.However,if the iron core diameter is too large,the weight of the transformer will increase,and the proportion of iron loss will increase and the efficiency will decrease.At the same time,the reduction in the number of winding turns will cause a reduction in the short-circuit impedance.In terms of winding arrangement optimization,the influence of superconducting high and low voltage winding spacing,inter-turn air gap size,and reactance height on the electromagnetic performance of superconducting transformer windings was explored.With the expansion of the high and low voltage winding spacing and the reduction of the reactance height,the short-circuit impedance of the transformer becomes larger,and the AC loss increases.With the increase of the inter-turn air gap,the AC loss decreases,and the short-circuit impedance has little effect.Therefore,under the condition of a certain reactance height,sufficient inter-turn air gap should be left as much as possible.Finally,this thesis optimizes the designed 40 k VA superconducting transformer according to the existing rules,improves the iron core and winding structure,and adds magnetic conductive rings at both ends of the superconducting winding to reduce the vertical field at the end of the winding,thereby improving the The critical current density at the end of the superconducting winding is reduced and the resulting loss is reduced,and the anisotropy problem existing in the superconducting tape is solved.According to the simulation results,the final superconducting transformer critical current is 25%,the short-circuit impedance is 25%,and the efficiency is99.17%,which meets the requirements and verifies the correctness of the design and optimization method.