Power Voltage Transformers are becoming increasingly present in different substation solutions on a world scale. Such units that are based on the open-core concept introduce several advantages in terms of transformer performance and reliability. This paper provides context for distinct open-core losses, expanding in detail on a measurement-based method for determining both total and specific losses in the open core. The approach is demonstrated on several core model configurations with varying parameters. Apart from loss measurement, the presented core configurations were used to determine and verify the distribution and magnitude of all flux density vector components. The proposed approach is validated by various accompanying measurements, but also through comparison with loss measurements performed on several Power Voltage Transformer units intended for commercial application.

Knowledge of lightning impulse (LI) voltage distribution over transformer windings during the design stage of the transformer is very important. Specific design differences in inductive voltage transformers make the transient analysis approach different to the approach to the power transformers. In this paper, a methodology for acquiring lightning impulse voltage distribution over high-voltage (HV) winding of inductive voltage transformers is presented and evaluated. Resistance, inductance, and capacitance matrices are calculated using the integral and boundary element methods (BEM) approach. Additionally, in order to improve the capacitance matrix solver, adaptive cross approximation (ACA) is applied. These parameters are then used to solve the equivalent circuit model in time domain. In order to evaluate the methodology, an experimental and numerical investigation of the layer discretisation, iron core influence, and accuracy of the proposed methodology is performed. The comparison of numerical results with measurements confirms the validity of the methodology.

Losses due to eddy currents in an open-type transformer core are significantly reduced by the lamination of the transformer core. In order to further reduce the eddy current losses, the open-type core often has a multi-part structure, i.e., it is composed of several more slender cores. The complete homogenization of such a core is not possible when an $\overrightarrow{A},V-\overrightarrow{A}$ formulation is used, where A and V represent the magnetic vector potential and electric scalar potential, respectively. On the other hand, an $\overrightarrow{A},\overrightarrow{T}-\overrightarrow{A}$ formulation, where T represents the electric vector potential, enables the complete homogenization of the general open-type core, but the simulation converges poorly due to the large number of degrees of freedom. By eliminating the redundant degrees of freedom, the convergence rate is significantly improved, and is at least twice as good as the convergence rate of the simulation based on the $\overrightarrow{A},V-\overrightarrow{A}$ formulation. In this paper, a method for the calculation of the eddy current losses in an open-type core based on the $\overrightarrow{A},\overrightarrow{T}-\overrightarrow{A}$ formulation with the elimination of redundant degrees of freedom is presented. The method is validated by comparison with a brute force simulation based on the $\overrightarrow{A},V-\overrightarrow{A}$ formulation, and the efficiency of the method is determined by comparison with the standard homogenization method based on the $\overrightarrow{A},V-\overrightarrow{A}$ formulation.

The main drawback of wind energy is its intermittent nature. While wind power plants have shown great potential for larger scale system integration and electricity production, the reliability of their output is still an issue. This article outlines one possible way of decreasing the variations of wind energy. By grouping several geographically dispersed wind power plants into a virtual unit, the intermittency of wind power can be reduced and the daily load curve smoothed. The main goal of this artcle is to present the analysis of interconnecting several geographically dispersed locations into a virtual power plant, while placing the emphasis on the actual benefits of such a synergy in terms of increased availability and production of stable power with a constant output. The analyses presented in this article are based on actual measurements on several locations in Croatia.

Relevant international instrument transformer standards specify internal arc testing to prove the transformer behavior under internal fault conditions. However, the test is defined in a way that does not recognize that it is possible to limit and reduce the total fault energy. For such instances, testing, as currently defined, is mostly inapplicable. The purpose of this paper is to address this issue by presenting a testing sequence that is applicable for verifying the behavior of transformers with sectioned active parts that contain energy-limiting features. Furthermore, the acceptance criteria for the successful completion of the test are also introduced. Every step of the proposed test sequence is discussed in detail and presented on a 145 kV inductive transformer, selected specifically for this purpose. This paper is a part of a continuous broad research with the aim of developing and specifying adequate routine, type and special testing sequences for qualifying paper-oil insulation systems that limit internal arc energy, with the aim of improving the performance of such systems and introducing test methods and criteria that exceed the practices of current standards.