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.
Highlights
Energies 2021, 14, 6714. https://A high value current may flow through the transformer windings at short circuit or overload, but under certain circumstances even after the transformer has been connected to the mains
It is important to counteract the effects of this current [1,3,4]. This requires learning about the mechanism for the development of the inrush current in superconducting transformers, which are different from those in conventional transformers, as well as for the capturing of this phenomenon by mathematical relationships
The time for which the 8.5 kVA transformer winding is in the resistive state is 3.6 ms for the results obtained from the measurements and 4.4 ms for the results obtained from for the results obtained from the measurements and 4.4 ms for the results obtained from the calculations
Summary
A high value current may flow through the transformer windings at short circuit or overload, but under certain circumstances even after the transformer has been connected to the mains. It is important to counteract the effects of this current [1,3,4] This requires learning about the mechanism for the development of the inrush current in superconducting transformers, which are different from those in conventional transformers, as well as for the capturing of this phenomenon by mathematical relationships. Due to the importance of the inrush current envelope for transformer and system protection, analytical formulas to estimate the inrush current envelope are presented in [13,14,30]. These formulas require some detailed data like detailed core dimensions, in addition to the electrical parameters and magnetic core characteristics. Due to the limited amount of data concerning the inrush current phenomenon of superconducting transformers, the given dependencies were verified on the designed and built by the author of the paper transformers of this type
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