Calculating the Inrush Current of Superconducting Transformers

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.

Eliashberg Theory of the Superconducting State of Marginal Fermi Liquids

The marginal Fermi liquid (MFL) which describes the anomalous normal state of the cuprates is extended to a d-wave superconductive state. A phenomenological collective excitation, P0(ω,T), is taken such that it gives rise to, after renormalization, the MFL behavior in the normal state. With the P0, the renormalized excitation spectrum and pairing function in superconductive state are calculated self-consistently within the Eliashberg formalism. In the superconductive state, the self-energy deviates from the normal state MFL ω/T-scaling and develops a new energy scale of ω0≈2Δ, where Δ is the pairing amplitude.

A PAIR POTENTIAL FOR THE COOPER PAIR IN THE HIGH-Tc CUPRATES

Taking the two-local-spin-mediated interaction (TLSMI) as the pair potential for the Cooper pair and considering the long-range phase coherence (LRPC), the empirical formula of T c versus hole doping is explained and the physical picture for the pseudogap and the gap in superconductive state is set up. The superconductivity in PrBa 2 Cu 3 O 7-δ and CuCl at high pressure and Fe 1-x S is discussed.

X-Ray Photoelectron Study of Surface of Superconductive Y-Ba-Cu-O as Dependent on Cleaning, Temperature, Composition and Doping

The core level X-ray photoelectron spectra of the high-temperature superconductor system YBa 2 Cu 3 O x are studied in dependence on the oxygen composition x, temperature of the sample, doping by Ag and quality of cleaning the sample surface. Nowadays there are many X-ray photoelectron investigations, but comparative investigations of electron structure in superconductive and unsuperconductive states are absent in the majority of them. The X-ray electron magnetic spectrometer used in our work allows one to obtain spectra in the temperature range from room temperature to the temperature of liquid nitrogen with simultaneous mechanical cleaning of the sample surface from the contaminations and degraded layers. Thus the obtained results are unique and allow one to obtain for the first time the following conclusions. Three charge states of copper atoms are shown to exist in this system — Cu 1+, Cu 2+ and Cu 3+ — but only the Cu 2+ state plays the main role in the transition of the system to the superconductive state. New peaks arise in O1s, Ba3d and Ba4d spectra after the transition of the system to the superconductive state, which implies the changes in the surroundings of O and Ba atoms in this state. In Ag-doped samples similar changes in X-ray photoelectron spectra are observed and they are even more pronounced than in the undoped ones.