• Energy Research

AbstractOne of the most critical problems in operation of modern power systems is static electrical load dispatch (SELD) between the energy generator units with minimum production cost. In recent years, more complete and accurate models of the problem have been presented, which made it non-linear or non-convex. For example, the input–output characteristics of power plant units are non-linear or non-convex due to existence of valve-point effect. It is a non-convex optimisation problem with some constraints, which cannot be solved using ordinary mathematical methods; it requires intelligent evolutionary optimisation methods to resolve. In this paper, a novel approach called improved exponential harmony search algorithm is presented for improving the HS algorithm to solve the SELD problem considering the valve-point effect. The numerical results show that the proposed method has better convergence and also lower production costs than the two other compared methods i.e. conventional HS and particle swarm opti...

In recent years, using high-temperature superconductor (HTS) transformers in transportation and electrical power systems has attracted much interest. The major advantages of HTS transformers compared with conventional ones are much smaller size and volume and lighter weight in confined spaces of urban areas or transportation devices. One of the most critical parameters to design, fabricate, and commercialize HTS transformers is hysteresis loss in HTS tapes. Using numerical methods, the accurate value of hysteresis loss and efficiency can be calculated or estimated in HTS transformers. In this paper, two innovative techniques to reduce the leakage flux and thereby hysteresis loss in HTS transformers have been proposed. In the first technique, the concentric windings of HTS transformer are apportioned into a certain number of sub-windings. In the second one, with optimizing the distributive ratios of sub-windings, the windings become unsymmetrical. In order to demonstrate the effectiveness of proposed techniques, an accurate and advanced numerical method based on finite element analysis has been used to design four symmetrical and unsymmetrical primary (P)-secondary (S)-P-S-P and P-S-P-S-P-S-P winding schemes. The simulation results prove the effectiveness of both techniques in reducing the radial and axial leakage flux magnitudes and thereby hysteresis loss in HTS windings.

The offshore wind power system is expected to grow rapidly during the upcoming years. Simultaneously, the capacity of wind generators can surpass the rating of 15 MVA, necessitating step-up transformers to match this increased capacity. However, the main challenge is maintaining the compactness and lightness of the transformers while meeting high power demands. With this contribution, we explore the feasibility of a superconducting transformer with very high current density. This study delves into the mitigation of AC losses in a 15 MVA HTS transformer for wind energy applications by means of numerical simulations based on the finite-element method. Employing a 2D axisymmetric T-A formulation coupled with an electrical circuit, we estimate AC losses across hundreds of turns of REBCO tapes within a full transformer at reasonable computational time. The T-A formulation considers the superconducting layer of REBCO tapes as infinitely thin, thus allowing to overcome the problem of simulating a superconductor with an extremely high width-to-thickness ratio. To address the substantial transport current value on the high-voltage side, we utilized several parallel Roebel cables, optimizing parameters such as the number of strands in each cable, inter-strand gaps, and vertical separations between cables. Our findings suggest that altering the winding voltage and hence conductor length is not an effective strategy for reducing AC losses. Furthermore, for mitigating the high AC losses at winding ends, we integrate magnetic flux diverters into the transformer structure. Eventually, we propose two distinct designs operating at temperatures of 20 K and 70 K. This research introduces valuable insights and approaches for designing, optimizing and developing HTS transformers.