Visual corona tests are useful to identify the critical corona points of substation connectors and other high-voltage components, thus allowing to apply corrective actions. RIV (radio interference voltage) and PD (partial discharge) measurements also allow detecting corona activity. However, these techniques require expensive screened laboratories, sophisticated instrumentation and usually do not provide the exact location of the discharges. Corona tests are often performed in external and expensive laboratories, where customers habitually have to face long waiting times. The tests in such laboratories must be totally planned beforehand, as they are habitually done by external engineers, so little information about the behavior and possible modifications of the product is acquired by the customer. This paper proposes a feasible solution to perform routine corona tests for product optimization in industrial facilities, while greatly reducing the voltage applied, the laboratory size and requirements, assembly and testing times, and thus the test related costs. In addition, this paper detects the visual corona onset by means of a commercial digital camera, which allows locating the critical corona points, thus greatly decreasing the costs of the corona detection instrumentation, while maintaining the accuracy and sensitivity of the detection method. The methodology proposed in this paper can be applied to many other high-voltage devices such as conductors, spacers for bundle conductors, vibration dumpers, corona protections, and different types of hardware and fittings for power lines and substations.

This work proposes a method to estimate the electrical constriction resistance of two mating metallic rough surfaces based on the finite element method (FEM). The FEM-based method generates a random array of three-dimensional orthogonal parallelepipeds to simulate the stochastic distribution of the asperities across the contact interface. The effect of the contact pressure is studied in detail, since once the contact materials and the topology of the contact area are settled, the contact pressure plays a critical role in determining the electrical constriction resistance. The proposed model is based on two critical variables, the contact pressure and the surface roughness of the mating surfaces, which must be measured in the laboratory to calibrate the model. Results provided by the FEM-based model are compared with experiments for three geometries, thus validating the accuracy of the proposed approach. Although the apparent contact areas of the analyzed specimens have a rectangular shape, the proposed method is also applicable to determine the electrical constriction resistance of other geometries. It is also proved that depending on the pressure applied to the contact interface, the electrical constriction resistance can be almost independent of the apparent area of contact. Although the aim of this work was to generate an electrical constriction resistance model for power connectors, it is also applicable to many other power devices.Peer ReviewedPostprint (author's final draft

Corona is a critical effect that must be considered during the design and optimization stages of high-voltage hardware such as substation connectors, since due to the harmful effects, corona threats power systems reliability. Visual corona tests allow detecting and identifying the critical corona points on the surface of substation connectors, so corrective actions can be applied for product optimization. This paper focuses on reduced-scale visual corona tests intended to verify and optimize the behaviour of such high-voltage hardware. Reduced-scale visual corona tests allow reducing the voltage to be applied, laboratory size, instrumentation requirements, assembly and test times, and finally the overall costs of the tests compared to standard corona tests carried out in large-size high-voltage laboratories. A hybrid approach combining experimental tests and finite element method (FEM) simulations is presented, which allows obtaining the equivalent visual corona onset voltage between reduced-scale and full-scale tests. Although the paper focuses on the analysis of aluminium substation connectors, the proposed approach can be applied to many other hardware intended for high-voltage applications.

-This paper proposes a simple, fast and accurate simulation approach based on one-dimensional reduction and the application of the finite difference method (FDM) to determine the temperatures rise in substation connectors. The method discretizes the studied three-dimensional geometry in a finite number of one-dimensional elements or regions in which the energy rate balance is calculated. Although a onedimensional reduction is applied, to ensure the accuracy of the proposed transient method, it takes into account the three-dimensional geometry of the analyzed system to determine for all analyzed elements and at each time step different parameters such as the incremental resistance of each element or the convective coefficient. The proposed approach allows fulfilling both accuracy and low computational burden criteria, providing similar accuracy than the three-dimensional finite element method but with much lower computational requirements. Experimental results conducted in a high-current laboratory validate the accuracy and effectiveness of the proposed method and its usefulness to design substation connectors and other power devices and components with an optimal thermal behavior. . The use of 3D-FEM simulation tools often requires the use of costly licenses and the implication of specialized engineers to carry out tedious and time-consuming tasks associated to the preparation of 3D geometries, generation of the 3D mesh, or settling of boundary conditions among others. Therefore the development of accurate fast models [12] which can be based on model reduction techniques [13] and are highly appealing to overcome the abovementioned drawbacks. Different approaches have been applied to reduce the computational burden in complex 3D problems. For example in [14] a co-simulation strategy combining 1D finite difference and 3D finite volume codes are applied. In [15] a1D analytical model for simulating the response of piezoelectric transformers was compared against 3D-FEM simulations. In [16] a 1D finite difference approach to model mass conservation in ducts of an internal combustion engine was studied. Cerfontaine et al. [17] proposed a 1D-finite element formulation to model the grouting and field temperatures of borehole heat exchangers. This paper proposes a one-dimensional fast method based on nodal equations and finite differences formulation to accurately predict the temperature evolution in substation connectors during the standard temperature rise test. This is a multiphysics electromagnetic-thermal problem since the main heat source is the Joule loss due to the electric current whose time-profile is known, although there is a minor contribution due to the induced eddy currents. The proposed method discretizes the analyzed domain in finite one-dimensional regions in which the energy rate balance due to the flow of heat is calculated. To accurately predict the temperature profile along the connector and the surrounding conductors, the proposed transient model takes into account the three-dimensional ge...

Abstract-Low-and medium-voltage connectors are designed for a service life of more than 30 years, during which they have to withstand extreme conditions, so it is primordial ensuring their thermal performance. Mandatory standardized short-circuit tests are required to homologate electrical connectors which are conducted in singular and scarce laboratories, so it is essential to dispose of fast and accurate simulation tools to predict the thermal performance of the equipment during the design stage. This paper focuses on the application of a fast and accurate simulation method to reproduce the transient thermal behavior and to estimate the transient temperature rise and the subsequent cooling of power connectors during short-circuits. To minimize the computational burden, this paper proposes a fast FDM (finite difference method) approach, based on one-dimensional reduction of the analyzed geometry. To improve accuracy, key three-dimensional information is retained, such as the convective coefficients, the incremental resistance or the cross-section of each node. Results attained by means of the proposed method are validated against experimental results conducted in a high-current laboratory, thus corroborating the usefulness and accuracy of the proposed method. The methodology exposed in this paper can be applied to many other hardware for power lines and substations.