Calculating the Inrush Current of Superconducting Transformers

Abstract

Under certain circumstances, after connecting a superconducting transformer to the power network, a high value current may flow through its windings. This current can exceed the critical value of the superconductor many times and cause the windings to lose their superconductive state. Loss of superconductive state of the windings may result in thermal interruption of their continuity as a result of conduction of a current of very high density. The mathematical relationships used to calculate the inrush current of conventional transformers do not work well for the calculation of superconducting transformers. This is due to the properties of superconducting materials used in the windings, first of all to the stepwise changes of the windings’ resistance when exiting the superconducting state and when returning to this state. The article presents the mathematical dependencies allowing to calculate the pulse waveforms of the inrush current of these transformers are derived. Basic electrical circuit sizes are used in the calculations, making the calculations quick and easy. Using the formulas, calculations of the inrush current of 8.5 kVA and 13.5 kVA superconducting transformers. The results were verified with the results of the inrush current measurements, achieving good compliance.