Study of Second Generation High Temperature Superconducting Coils for Energy Storage System

Abstract

Emerging energy technologies give us the opportunity to manage the challenges posed by climate change, environmental degradation and oil shortages. Superconducting energy storage system (SMES) is a promising candidate technology due to its potential for promoting renewable energy and stabilising grid systems. It enables improvements to power grid capacity, reliability and efficiency. SMES also has the advantages of high cyclic efficiency, quick response times, deep discharge and recharge abilities and being easy to build hybrid energy storage system. This dissertation studies the key technologies for the design and application of SMES using 2G HTS materials.The first part of this dissertation investigates through experiments the behaviour of 2G HTS tape under an external magnetic field and impregnation. It is found that that the critical current and n value are closely related under a magnetic field, which can be verified by theoretical analysis. Different impregnation materials are tested to enhance the superconducting tapes. The experiments find that Gallinstan does not cause degradation of the impregnated tape. However, the degree of degradation caused by different resins varies: Stycast Black degrades the tape a small amount, while Stycast 1266 and Araldite degrade the tape considerably. Reasons for the degradation are discussed and suggestions for coils fabrication are presented.Superconducting coils are studied experimentally and numerically under self field and an external field. This numerical model is based on minimization of the magnetic energy using the line current assumption. Good agreement was achieved between the numerical model and the experiments. Then the coils with two different tapes are investigated under a DC magnetic field. The load line method is improved to take into account the anisotropy in 2G HTS coils. In order to calculate the magnetic field and AC losses of a stack of superconducting coils, coupling of the critical state model with the line front track approximation is proposed and validated. Some critical issues related to SMES design are discussed. A conceptual design of a 60 kJ SMES is presented. The design process includes magnetic optimization, current lead design and cooling system selection. This SMES is then hybridized with a battery and applied in wave generator system to analyse the extension of battery life. Finally, different configurations of SMES are compared and an economic analysis is performed.Original work in this dissertation includes:1. Multiphysics modelling of HTS coils using magnetic energy minimization based on homemade finite element analysis code. This method couples the magnetic energy minimization with magnetic, thermal and mechanical fields for the first time, and efficiently simulates the superconducting coils using fewer elements and avoiding high non-linearity.2. Efficient numerical modelling of a stack of HTS pancake coils using the line front track approximation. Accurate current distribution, magnetic field and AC losses are calculated and compared to established H-formula methods. This method is further applied to a real 2G HTS SMES design for the first time.3. Detailed conceptual design of a 60 kJ HTS SEMS, which is hybridized with a battery to smooth the output of the renewable energy system. Extension of the battery lifetime is modelled and discussed for the first time, based on the rainflow counting method.

Date of Award	20 Apr 2016
Original language	English
Awarding Institution	University of Bath
Supervisor	Paul Leonard (Supervisor) & Weijia Yuan (Supervisor)