Introducing high-temperature superconductors (HTS) and their outstanding properties stimulates scientists and engineers in various fields to modernise the products with this new technology. Electric power industry also was affected by this finding in different branches including bearings. The idea of HTS bearings was rapidly developed due to its two main features, i.e. self-stability and contactless operation which leads to save remarkable amount of energy. However, a successful implementation of HTS bearing undoubtedly requires an accurate modelling in the beginning. The contribution of this study is an analytical method for simulating the electromagnetic behaviour of a radial HTS magnetic bearing. The governing non-linear system of partial differential equations in the HTS bulks deduced from the H-formulation along with the E-J power law and is efficiently solved using variational iteration method (VIM). The validity of VIM is ascertained by comparing the results with numerical two-dimensional axisymmetric finite-element method simulations.
Accurate modeling of transformer saturation characteristics is essential for analyzing inrush currents and harmonic overvoltages. This paper outlines a straightforward method for correct estimation of the transformer's inrush current where the residual flux effect is considered. The Ι-Λ nonlinear characteristic of transformer core is estimated by the sum of two exponential functions. The differential evolution optimization method is used to identify the parameters of the iron core model including the current flux nonlinear function and the core loss resistance. The objective function to be minimized is the root mean square difference between the measured and calculated inrush currents. The experimental iron characteristic is obtained from the secondary winding voltage and primary winding current waveforms produced during transformer energization. The performance and accuracy of the proposed method have been verified by a close agreement between simulation and measured inrush waveforms for a single-phase transformer.
Nowadays, after passing more than three decades from discovery of high‐temperature superconductors, they are widely used in different fields including power industry. High‐temperature superconducting (HTS) bearing is an electromagnetic machine that provides frictionless operation and intrinsic stability without requiring control equipment. Before entering to the fabrication stage, an accurate simulating model can satisfactorily reveal many of practical considerations. This work is based on the results of their previous study, delving into time steps of multi‐physical simulations juxtaposing electromagnetic and thermal characteristics of an HTS bearing. This is attainable by using multi‐physics analysis of radial HTS bearings based on a semi‐analytical method called variational iteration method (VIM). This is accomplished by coupling of the Maxwell equations and thermal equilibrium. The electrical behaviour of the superconductor is described by means of a B–T‐dependent modified E–J power‐law relation. To verify VIM results, the multi‐physics equations are also numerically solved using finite‐element method. In this research, two case studies are examined; failure of the cryogenic system and incorporating new materials in the stator part of the bearing in order to improve the cooling efficiency.
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