In order to reduce electric potential difference between the sheathings of single core three-phase cables, the sheathing is grounded and bonded at one or both ends of the cables.If the cable is long, double bonding has to be carried out which leads to circulating currents and increased power loss.Based on finite element (FE) calculations, this paper shows, that raising the sheath's resistance, by decreasing its cross section and increasing its resistivity, can significantly reduce this loss.The magnetic field close to the ground surface and the behaviour of the cable during fault conditions are also investigated.

This paper aims to represent when the primary lightning protection is not necessary for a photovoltaic power plant with a special dimension if the different security objects are not negligible during the probability and risk calculations. The calculations were made using the Probability Modulated Attractive Volume theory which is capable of special, complicated, or huge structures and objects like a high-performance photovoltaic park.

The aim of this article is to create a novel filtering algorithm for the emitted electromagnetic signals of corona discharges, using the special time-domain features of the continuous wavelet transform. The first part of this article therefore focuses on the time-domain examination of these signals to find characteristic features that are compatible with the wavelet transform. The second part of this article utilizes these features to create and validate the filtering algorithm. This is an important step toward creating an accurate three-dimensional partial discharge location approximation system that could contribute to preventing and finding partial-discharge-related faults. In the presented research, needle-plane corona discharge sources with different geometries are tested at both ac and dc voltages.

The electrostatic charge accumulation of extremely pure substances usually makes the manufacturing technology more difficult. The electrostatic behaviour of the materials can be examined by the measurement of charge decay time, but the conductivity of pure materials is very low, therefore they show very long charge decaying times. Hence, this quantity is not applicable for reliable electrostatic characterisation of pure powders. In this investigation, dielectric and charge accumulation measurements were executed on extremely pure powders. The results of leakage current and voltage response methods show significant difference between the powders according to their electrostatic behaviour. The result of dielectric measurements is confirmed by the charge accumulation measurement. The findings reveal the importance of the investigation of slow polarisation mechanisms in the charge accumulation processes of powders.

This paper focuses on the time and frequency domain examination of the emitted electromagnetic signals of corona discharges. The objective of the presented research is to find characteristic features that could be used to improve the noise filtering process of these signals. This is an important step towards creating an accurate three-dimensional partial discharge location approximation system that could contribute to preventing and finding partial discharge related faults. In the presented research, needle-plane corona discharge sources with different electrode distances and needle tip radiuses are tested for both AC and DC voltages.

This paper presents the analysis of the effect of different influencing factors on corona discharge in a point-plate arrangement. Initially this arrangement was used for laboratory-scale experiments for modelling lightning attachment and then it was found a useful way of the investigation of industrial technologies applying corona discharge. In the paper, we are focusing on the properties of the corona in electrostatic precipitators. Laboratory measurements and numerical calculations were made to evaluate the modification of voltage-current characteristics related to the initial condition in different modes of operation and predict the effect of the change of certain parameters. For the reliable comparison, a reference arrangement was constructed to handle the uncertainty caused by the presence of dust particles and dust layer in point-plate and wire-plate electrode arrangements.

High voltage live-line maintenance (LLM) is a commonly applied method worldwide to execute planned works in the grid economically [1]. In case of bare-hand technique workers wear a so-called conductive clothing acting as a Faraday-cage which protects them against the high electric fields during the work.

The tracking wheel method is an elaborate technique for evaluating the quality of non-ceramic insulators. Although it is not required by European standards, there is an interest in its application due to recent problems with the quality of these products. Despite the undeniable long-term positive effects, some utilities consider this method time consuming and expensive, especially when the products of numerous manufacturers are to be evaluated, or when the test is aimed to be performed frequently as sampling tests. This article presents partial discharge measurements performed during a complete cycle of the tracking wheel test. Various evaluation methods are investigated in order to find features that may be able to indicate the possibility of a failed test even at a lower number of cycles.

Live-line maintenance is an effective and economical way to guarantee the safe operation of the grid. The key of its safety is the protection of the working personnel against the possibly harmful effects of extra-low frequency electric and magnetic fields in the vicinity of the conductors. As the result of the spread of so-called compact geometries and the application of composite insulators with decreased creepage distances, both phase-to-phase and phase-to-ground distances become limited, so reduction of clearances and increment of electric filed-related hazards occur more and more nowadays. Transmitted power in the high voltage grid is increasing continuously. Current of the phase conductors may generate high magnetic fields and high induced current densities in the body of the workers. Protection against magnetic fields is a still unsolved problem; this paper introduces a possible method to do that to ensure the proper level of safety during this special kind of work executed on the live elements of the grid.

The international standard on lightning protection offers a framework to describe the risk of lightning damage for a given object to be protected and offers design tools to achieve proper protection with primary or secondary protection. Although it may be useful to improve the usability of this framework by simplifying some points, there is no doubt that the notion of risk and its application is currently covered extensively in the document. However recently more and more papers discuss the use of lightning hazard forecasting in lightning protection. The notion of risk in the international standard is not yet proper to discuss the application of such solutions nor would it be safe to directly use the standard to evaluate a solution like that. This paper aims to discuss the new problem that using forecasting means as opposed to primary or secondary lightning protection. Also it suggests the use of an adaptation of the notion of risk to be able to incorporate the using of forecasting.

The originally long and further prolonged lifespan of nuclear power plants poses tremendous long-term reliability requirements towards low voltage measurement and control cables. Strict requirements towards their performance are prescribed until the end of the operation of the power plant, including the adverse environment of a loss of coolant accident (LOCA). These requirements cannot be met and verified without diagnostic measurements performed at selected intervals. Various methods have been developed or are investigated to fulfill this task. This article compares the available techniques, mainly focusing on their ability to detect damages that are relevant to LOCA testing. Furthermore, the possible role of partial discharge measurement is proposed.

The IEC 62305, which was published 10 years ago, has fundamentally changed the structure of planning lightning protection [1]. The method determined in the standard — which requires a detailed risk assessment for each and every structure — has made the standard user's task more difficult due to the vast amount of parameters. Meantime many criticism, application examples and explanations of the risk assessment were published [2], [3], [4], [5]. We have elaborated a developed simplified risk assessment process based on the standard, which substantially facilitates the determination of the needed level of protection in most cases.

This paper is dealing with the comparison of the results given by different worn surface analysing methods. Maraging steel tool materials were used for the experiments. Specimens were produced by direct metal laser sintering from metal powder and by conventional way from rod having equivalent chemical content. The samples were age-hardened and surface treated by nitrocarburising and oxynitriding and they were tested by pinon-disc type tribometer. The tribological behaviour was compared by using different methods for worn surface analysis. Worn area of the surface was determined by the surface profiles of 2D measurements and the wear volume was calculated by using 3D images of focus variation microscopy measurements.

Live-line maintenance (LLM) has several technical and economic benefits. Planned works can be executed without any consumer disturbance, while the network is energized. Strict regulations regarding to the working method, well-educated workers and well-considered safety factors ensures the high level of safety of this technology. Although statistics show that the number of injuries is lower than in case of de-energized works, the unseen short- and long term effects of electric and magnetic fields also have to be taken into consideration.

Composite insulators are widely used on high voltage power lines because of their technical and economic benefits. In the recent years the number damaged composite insulators due to brittle fracture increased worldwide. In the High Voltage Laboratory of Budapest University of Technology and Economics a new technology has been developed to analyze high voltage composite insulators. As a part of a complex expert system this method can identify the critical, severe and hidden failures like brittle fracture with high accuracy. The accuracy, speed, efficiency and reliability of the new method are promising. The differences between the damaged, undamaged and new insulators are significant in the results, thus an all-new complex system is under development. The accurate prediction of critical insulators and power lines is essential because of the large number of damages caused by brittle fracture.

In the last few years bird protection became a more and more important aspect on medium voltage overhead lines. Injuries of birds related to electrocution endanger both the health of the different species and the reliability of the grid as well. International standards and national regulations based on the opinion of different associations for wildlife protection are often been accepted without any detailed inspection of equipment to be installed on the network. There are many types of insulators, cross-arms and poles even in a specific section of a medium voltage power line. The same type of rigid bird protector installed on them can easily increase the risk of failures caused by the wrong way of application or installation. A rigid bird protector - especially in case of rainy weather conditions or fog - acts as a floating object near the phase conductors. This electrode distorts the electric field distribution even in case of normal operational conditions and increase the risk of flashovers on the surface of the insulators caused by an overvoltage wave in the conductors. Use of conductor and insulator covers are also questionable from the aspect of live-line maintenance (LLM): inspection of working site became impossible and electrical and mechanical condition cannot been estimated at all. Operations with the hot stick method - which is a widely used LLM technique for example in Hungary - became especially difficult. Inspection of different bird protective equipment from electrical aspect is a very important question to keep the operation of medium voltage grids as reliable as possible. In the High Voltage Laboratory of Budapest University of Technology and Economics calculations, finite element simulations of electric field and potential on complex 3D CAD models and a set of measurements have been executed to inspect the exact effects of these equipment from the aspect of the reliability of the grid. Experimental studies in Hungary show that many failures are related to rigid bird protectors. There are often detectable marks on the surface of both the phase conductors and insulators. There are many bird protector-related switch-offs on the territory of different Hungarian DSOs, so the clarification of unexplained questions about this practical topic is urgent and become more and more important.