Year

2005

Degree Name

Doctor of Philosophy

Department

School of Electrical, Computer and Telecommunications Engineering - Faculty of Informatics

Abstract

Micro-Superconducting Magnetic Energy Storage (μ-SMES) technology has emerged as a method for mitigating voltage sags for smaller scale applications using energy storage capacities of less than 100kJ. These units are designed to mitigate low frequency (<1kHz) voltage sags in power distribution systems extending the lifetime of electronic loads by reducing voltage fluctuations and reducing load outages due to under-voltage trips. Improvements in cryogenic and switching technologies indicates that μ-SMES are becoming a competitive alternative to other medium voltage sag mitigation devices such as Uninterruptible Power Supplies (UPS) in terms of both efficiency, reliability and economics. This thesis details the work performed in the design, implementation and testing of a prototype High transition Temperature Superconductor (HTS) SMES device. The design and construction of the prototype includes development of the energy storage medium, cooling system and the Power Conditioning Circuit (PCC). The energy storage medium for the SMES prototype is designed using theoretical and Finite Element Modelling (FEM) tools and the initial design fabricated using HTS BSCCO- 2223 tape manufactured by Australian Superconductors. The refrigeration system to cool the HTS coil comprises of a gaseous helium cold head cryocooler used to maintain the coil at a temperature of 30K, via the onduction cooling method, with a maximum heat load of 25W when mounted in the prototype vacuum sealed cryostat. This design improves the Ic characteristic of the coil compared to that at 77K by a factor of 4.7, and hence improves the energy storage by a factor of 22. The prototype SMES PCC is capable of supplying a three phase load, accurately maintaining the current flowing in the energy storage medium during the steady state and reacting almost instantaneously to deliver energy to the load during voltage sags; successfully maintaining the load voltage at a specified level. The PCC has been constructed as a part of the process of developing a larger 20kJ system aimed at industrial applications, with reference to a particular power quality study performed that represents the typical application. Further, to improve the efficiency of μ-SMES systems, an in-depth investigation into incorporating alternative switching technologies, such as cryoelectronics and Persistent Mode Current Switches (PMCS), into various size μ-SMES systems is presented.

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