Modelling of Inrush Currents in Power Transformers by a Detailed Magnetic Equivalent Circuit

Static power converters powered by flywheel generators are used to feed the magnet coils of the ASDEX Upgrade tokamak – an experimental device for nuclear fusion research. The largest converters have a nominal power in the range of 100 MVA in pulsed operation (SN about 20 MVA in continuous duty). About twenty power transformers must be energised on a daily basis to get the pulsed power supply operational for plasma experiments. Nuisance interaction of inrush currents with the protection system of the synchronous machines, other on-line transformers or vacuum-switched static var compensators (SVC) must be avoided in present and future configurations. In order to investigate the effects of inrush transients in various configurations a detailed simulation model for one of the power transformers was derived. The paper describes the model which is based on an equivalent magnetic circuit representation of the transformer, results of simulation and measurement and gives an outlook on future activities.