Study On The Key Technology And Engineering Prototype Of The Transformer Using The Second Generation High Temperature Superconductors

With the development of the manufacturing technique of the high temperature superconductors,the electromagnetic and mechanical properties have been improved significantly.Therefore,high temperature superconducting(HTS)power applications have attracted attentions of many domestic and foreign scholars.HTS transformers have the advantages of smaller size,higher efficiency,non-pollution,fault current limiting and so on.The research of the HTS transformer using the first generation(1G)superconductors has been gradually moving from the laboratory stage to the practical stage,and moving from the miniaturized experimental prototype to the large-scale commercial transformer.However,the research of the HTS transformer using the second generation(2G)superconductors still stay in the stage of laboratory prototype and conceptual design.This paper is to study the design processes and electromagnetic characteristics of the 2G HTS transformer from three aspects,i.e.,winding material selection,iron core structure selection and engineering prototype development.The main contents are as follows:1)The thermal stability of HTS coated-conductors in the lightning current process is studied.The maximum endurance lightning current value of different high temperature superconductors are obtained by experiments.And then,the influence of the encapsulation layer and the substrate layer on the thermal stability are experimentally and numerically investigated,respectively.The numerical method is based on a proposed homogenization model.The experimental and simulated results show that an HTS coated-conductor with copper encapsulation layer and stainless steel substrate layer is a more wise choice for an HTS transformer that might suffer a lightning current process.2)HTS air core transformer(ACT),HTS paritial core transformer(PCT)and HTS full core transformer(FCT)are deeply studied in turn in theory and experiments.No-load,load,short-circuit and current limiting tests are performed in liquid nitrogen(LN2).For HTS-ACT,an analytical method based on vector magnetic potential for calculating the inductance of circular HTS coils is proposed.For HTS-PCT,a modeling method of the equivalent circuit based on interaction solutions is introduced.For HTS-FCT,an experimentally verified “circuit-field” coupled finite element method(FEM)is proposed to study its electromagnetic characteristics.The experimental and simulated results show that HTS-FCT is feasible to be applied in a power system.3)Based on the former researches,the winding material and the structure of iron core are confirmed.The preliminary design of the single-phase330 k VA/10 k V/0.231 k V HTS-FCT is completed after the design of the current lead and cryostat.Then,the final design is finished after the optimization of the current distribution and magnetic field using the“circuit-field” FEM.Finally,we fabricated and tested the 330 k VA HTS transformer based on Chinese standard.The research in this paper presents the design considerations and engineering prototype experiments of the 2G HTS transformer.It is very useful for the industrial application of 2G HTS transformer.