Study Of Electromagnetic Simulation And Quench Charateristics Of Field Coil For High Temperature Superconducting Wind Generator

With the shortage of fossil energy and the increasingly severe environmental problems,offshore wind power generation has been paid more and more attention.In order to reduce the cost of offshore wind power generation,developing large capacity wind generators have gradually become the development trend of offshore wind energy utilization.High temperature superconducting(HTS)wind generator has the advantages of small size and light weight,so it is considered to be an ideal solution for large capacity offshore wind generator.In the study of HTS wind generator,how to make HTS coils run safely and stably is one of the key problems.When HTS wind generator occurs short-circuit fault,due to its small synchronous reactance,the short-circuit current and electromagnetic torque are much larger than the conventional generator,which may cause more serious harm.In addition,the HTS field coil has the potential risk of quenching when it is affected by the local defects of the tape,the resistance of the joint and the complex electromagnetic environment in the process of the short-circuit fault.It is not conducive to the long-term safe and stable operation of HTS field coil.Therefore,it is of great significance to study the electromagnetic simulation of HTS wind generator and the quench characteristics of field coil.The main study contents of this thesis can be divided into two parts:electromagnetic simulation of HTS wind generator and quench characteristics of field coil.The electromagnetic simulation study of HTS wind generator will be subdivided into the critical current simulation of field coil and the simulation of three-phase short-circuit fault.First of all,a fast algorithm for the critical current of large scale HTS coil is proposed.Based on this algorithm,the critical current of the field coil of 2.5 MW HTS wind generator is calculated,and the operating current of the field coil is preliminarily determined.Secondly,the operating current of the field coil is transferred to the finite element model of the HTS wind generator,and the output characteristics under the rated working condition are obtained by simulation.Then through the three-phase short-circuit fault model,the electromagnetic characteristics of the field coil in the three-phase short-circuit fault process are obtained.The study on the quench characteristic of the field coil will be subdivided into two parts: the study of the minimum quench energy(MQE)and normal zone propagation velocity(NZPV),and the study of the quench characteristics under the three-phase short-circuit.Firstly,the MQE and NZPV of HTS tapes and a small coil are studied by the quench experiment of thermal disturbance,and the electromagnetic thermal coupling model is built to simulate this quench process.The validity and accuracy of the electromagnetic thermal coupling model are verified by comparing the simulation results with the experimental results.Then,the MQE and NZPV of the field coil are obtained by using the electromagnetic thermal coupling model.Secondly,in order to simulate the quench caused by the change of the magnetic field during the short-circuit fault,the variable magnetic field is applied to the HTS tape and stacked tapes to cause quench.Then this quench experiment is simulated by electromagnetic thermal coupling model.By comparing the simulation results with the experimental results,the electromagnetic thermal coupling model is verified to be applicative under the condition of three-phase short circuit.Finally,the electromagnetic thermal coupling model is used to simulate the quench characteristics of the field coil under the three-phase short-circuit fault.If the quench of field coil is unrecoverable,the current margin of the field coil is adjusted,and the quench characteristic simulation of the field coil under the three-phase short-circuit fault is carried out again,until the quench of field coil is no longer unrecoverable,thus the safe current margin of the field coil is obtained,to guarantee the safety of the field coil under three-phase short-circuit fault.