Due to the expansion of high-voltage direct current (HVDC) power systems, manufacturers of high-voltage (HV) hardware for alternating current (ac) applications are focusing their efforts towards the HVDC market. Because of the historical preponderance of ac power systems, such manufacturers have a strong background in ac corona but they need to acquire more knowledge about direct current (dc) corona. Due to the complex nature of corona, experimental data is required to describe its behavior. This work performs an experimental comparative analysis between the inception of ac corona and positive and negative dc corona. First, the sphere-plane air gap is analyzed from experimental data, and the corona inception voltages for different geometries are measured in a high-voltage laboratory. Next, the surface electric field strength is determined from finite element method simulations, since it provides valuable information about corona inception conditions. The experimental data obtained are fitted to an equation based on Peek’s law, which allows determining the equivalence between the visual corona surface electric field strength for ac and dc supply. Finally, additional experimental results performed on substation connectors are presented to further validate the previous results by means of commercial high-voltage hardware. The results presented in this paper could be especially valuable for high-voltage hardware manufacturers, since they allow determining the dc voltage and electric field values at which their ac products can withstand free of corona when operating in dc grids.
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.
Abstract-The electrical contact resistance greatly influences the thermal behavior of substation connectors and other electrical equipment. During the design stage of such electrical devices it is essential to accurately predict the contact resistance to achieve an optimal thermal behavior, thus ensuring contact stability and extended service life. This paper develops a genetic algorithm (GA) approach to determine the optimal values of the parameters of a fractal model of rough surfaces to accurately predict the measured value of the surface roughness. This GA-optimized fractal model provides an accurate prediction of the contact resistance when the electrical and mechanical properties of the contacting materials, surface roughness, contact pressure and apparent area of contact are known. Experimental results corroborate the usefulness and accuracy of the proposed approach. Although the proposed model has been validated for substation connectors, it can also be applied in the design stage of many other electrical equipment.
Abstract:Power devices intended for high-voltage systems must be tested according to international standards, which includes the short-time withstand current test and peak withstand current test. However, these tests require very special facilities which consume huge amounts of electrical power. Therefore, mathematical tools to simulate such tests are highly appealing since they allow reproducing the electromagnetic and thermal behavior of the test object in a fast and economical manner. In this paper, a three-dimensional finite element method (3D-FEM) approach to simulate the transient thermal behavior of substation connectors is presented and validated against experimental data. To this end, a multiphysics 3D-FEM method is proposed, which considers both the connector and the reference power conductors. The transient and steady-state temperature profiles of both the conductors and connector provided by the 3D-FEM method prove its suitability and accuracy as compared to experimental data provided by short-circuit tests conducted in two high-current laboratories. The proposed simulation tool, which was proven to be accurate and realistic, may be particularly useful during the design and optimization phases of substation connectors since it allows anticipating the results of mandatory laboratory tests.
In the last years there has been a considerable increase in electricity consumption and generation from renewable sources, especially wind and solar photovoltaic. This phenomenon has increased the risk of line saturation with the consequent need of increasing the capacity of some power lines. Considering the high cost and the time involved in installing new power lines, the difficulty in acquiring tower sites and the related environmental impacts, some countries are considering to replace conventional conductors with HTLS (High-Temperature Low-Sag) conductors. This is a feasible and economical solution. In this paper a numerical-FEM (Finite Element Method) approach to simulate the temperature rise test in both conventional and high-capacity substation connectors compatible with HTLS technology is presented. The proposed coupled electric-thermal 3D-FEM transient analysis allows calculating the temperature distribution in both the connector and the conductors for a given current profile. The temperature distribution in conductors and connectors for both transient and steady state conditions provided by the proposed simulation method shows good agreement with experimental data.
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