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Title: Superconducting fault current limiter using magnesium diboride
Author: Oliver, Andrew
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 2008
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This thesis presents work carried out to design, build and test a superconducting fault current limiter (SFCL) of the resistive type utilising magnesium diboride (MgB2) in round wire form. It is believed to be the first time such a device has been manufactured. Electromagnetic design of the superconducting coil of the SFCL was carried out to minimise inductance and to evaluate the forces on, and magnetic flux density within, the conductors. A former was designed on which to wind the coil, taking into account the thermal performance, coil winding and manufacturing processes of the SFCL. Thermal performance of the SFCL during current limiting action was modelled using finite element (FE) software. A comprehensive test programme was carried out on the manufactured SFCL prototype. Separate constant voltage and constant current test circuits were built for this purpose. Data acquisition and control was provided by a PC based LABVIEW system. Tests showed that the MgB2 wire transitioned from a normal state resistance of O.31Wm to superconducting at a temperature of 37.SK. Good fault current limiting characteristics were displayed; currents above 180Apeak being limited when operating at a temperature of 30K. The current limiting process was seen to be consistent and repeatable, with the SFCL thermally recovering superconductivity between tests. The current level at which limiting was initiated could be controlled by the operational temperature, with lower temperatures giving a higher current level at which limiting begins. High voltage tests demonstrated that the prototype design was capable of withstanding approximately 15kV in air and in excess of 30kV in liquid nitrogen. Good thermal stability to long-cycle quench tests was also demonstrated; current was limited for up to 1.6 seconds without any degradation to the superconducting wire. Negligible temperature rise was measured in the SFCL during rated operation. When power dissipation calculated from experimental results was used in the thermal FE model, an average temperature rise in the region of from 30K to 65-8SK in the MgB2 wire was predicted during the first cycle of current limitation. A software model of the SFCL was made which accurately predicts the response of the SFCL to a fault current. This model has been optimised for inclusion in power network analysis models. Alternative MgB2 wire samples were tested for suitability in SFCL applications. These samples all showed good current limiting characteristics. Wire sheath material was seen to have an important impact on quench homogeneity and the developed current limiting resistance.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available