Speaker
Andrew Ash
(CCFE)
Description
It is conceivable that electrical arcs can occur during the failure of a large superconducting magnet following an unmitigated quench accident. To assess such accidents, it is important to employ appropriate arc models to calculate the voltage current characteristics and heat dissipation as a function of conditions such as pressure and arc length. Although electrical arcs have been studied for many decades, the complex and destructive nature of arc phenomena has not allowed detailed models to be well established. During an unmitigated quench, resistive heating raises the conductor and the insulator temperature. Subsequently, the electrical and mechanical properties change. This can lead to dielectric breakdown of insulators and arc formation. Inline and bypass arcs can form that are sustained by the massive stored magnetic energy – of the order of gigajoules for ITER. If windings are bypassed by shorts, the arc current and the arc column diameter of inline arcs increases. Cable-in-conduit conductors limit the maximum arc column diameter and if limited, the arc properties change rapidly as the arc changes from a free arc to a confined arc. We assume ITER relevant conditions and for arc current 100 A – 100 kA we calculate the arc column electrical properties and temperature, by solving a set of equations describing the arc physics. The equations describe the arc column heating, gas ionisation, heat loss and electrical properties. By constraining the maximum arc column diameter in the solution, the transition between free and confined arc can be included. The calculations are compared to other relevant arc models and measurements to understand the sensitivity of their application to magnet safety assessment.
Co-authors
A. J. T. Holmes
(Marcham Scientific Ltd., Sarum House,10 Salisbury Rd., Hungerford, Berkshire, RG17 0LH, United Kingdom)
Andrew Ash
(CCFE, Culham Science Centre, Abingdon, OX14 3DB, United Kingdom)
E. Surrey
(CCFE, Culham Science Centre, Abingdon, OX14 3DB, United Kingdom)
F. Domptail
(CCFE, Culham Science Centre, Abingdon, OX14 3DB, United Kingdom)
K. Cave-Ayland
(CCFE, Culham Science Centre, Abingdon, OX14 3DB, United Kingdom)
K. Hamada
(Magnet Division, ITER Organization, Saint-Paul-lès-Durance, France)
N. Mitchell
(Magnet Division, ITER Organization, Saint-Paul-lès-Durance, France)
N. Taylor
(CCFE, Culham Science Centre, Abingdon, OX14 3DB, United Kingdom)
S. McIntosh
(CCFE, Culham Science Centre, Abingdon, OX14 3DB, United Kingdom)
S. Zheng
(CCFE, Culham Science Centre, Abingdon, OX14 3DB, United Kingdom)