For the reliable and safe operation of electrical installations, the dissipation of natural and human-made electrical currents into the earth is of great importance. In order to safely dissipate such currents into the earth in a well-controlled manner, blank electrical conductors are specifically inserted into the earth and galvanically connected to the electrical installation. The construct of earth-sensitive conductors (earth electrodes) forms the earthing arrangement. Due to the present conductivity of the earth, galvanically separated earth electrodes interfere electrically through mutual transiting currents. This paper shows geometric arrangements of earth electrodes inserted vertically into the earth, including the effects of the electrical interference on the currents dissipated into the earth, (partial) fault voltages, as well as the resistance to earth by means of calculations. The soil layering and the varying electrical conductivity of the layers are also taken into account. In order to verify the calculations, measurements of the resistances to earth of the vertical earth rods were carried out in a substation in construction.

ZusammenfassungDer Blitzschutz von Hochspannungs-Schaltanlagen liefert einen wesentlichen Beitrag für den zuverlässigen Betrieb unserer Hochspannungssysteme. Da Schaltanlagen die Knotenpunkte der elektrischen Verteil- und Übertragungsnetze darstellen, können direkte Blitzeinschläge zu Beeinträchtigungen der Versorgungssicherheit und des zuverlässigen Betriebs dieser Anlagen führen. In diesem Zusammenhang sind besonders Hochspannungs-Freiluftschaltanlagen den direkten Einwirkungen von Blitzentladungen ausgesetzt, da sich deren spannungsführende Anlagenteile im Freien und in exponierter Lage befinden. Der Blitzschutz von baulichen Anlagen und Personen ist in der Norm ÖVE/ÖNORM EN 62305‑3 definiert. Die Norm bietet unter anderem verschiedene Methoden für die Auslegung des Blitzschutzes und kann auch auf Freiluftschaltanlagen umgelegt werden. Andererseits werden in der Norm ÖVE/ÖNORM EN 61936‑1 die Anforderungen an Hochspannungsanlagen behandelt, wie beispielsweise Mindestabstände und Mindesthöhen von aktiven Teilen sowie die Definition einer Gefahrenzone. Am Beispiel der praktischen Auslegung des äußeren Blitzschutzes einer 380-kV-Hochspannungs-Freiluftschaltanlage werden beide Normen miteinander kombiniert.

The present paper shows measurement data of cloud-to-ground flashes in the Austrian Alpine region with a focus on single-stroke flashes. The data were recorded over six thunderstorm seasons from 2009 to 2018 within the framework of a research project. The aim of the project was to generate a ground truth dataset of ground strikes of flashes. The used Video and Field Recording System (VFRS) consists of a high-speed camera and an electric field measurement system to be able to optically analyze the spatial and temporal sequences of lightning discharges and record the transient electric field. The VFRS measurements were performed at 33 different measurement locations in the Austrian Alpine region, and a total of 735 cloud-to-ground flashes with negative polarity were recorded on 61 days. For the evaluation, data from the Austrian Lightning Detection and Information System (ALDIS) are correlated with the VFRS data. The percentage of single-stroke flashes influences the multiplicity (strokes per flash), which is relevant, e.g., for the design of lightning protection measures of high voltage systems. The calculated percentages of single-stroke flashes for the present dataset (27%) are compared with previously published values from different countries (12% to 24%). In order to investigate the influence of the thunderstorm organization on the percentage of single-stroke flashes, weather radar data and wind measurements are additionally used and analyzed for the classification of the different thunderstorm types.

Elektrische und elektronische Systeme sowie informationstechnische Infrastrukturen sind den Ein- und Auswirkungen atmosphärischer Entladungen ausgesetzt. In diesem Beitrag sollen die Zusammenhänge zwischen atmosphärischen Entladungen in Verbindung mit elektrischen Systemen, elektronischen Geräten und integrierten Schaltungen aufgezeigt werden. Dabei wird auf die Prüfverfahren und Normen zur Sicherstellung der elektromagnetischen Verträglichkeit gegenüber transienten Störgrößen eingegangen.

Gasometers are used in Austria to store a big quantity of explosive gas and represent exposed objects due to lightning of their height of several 10 meters. A floating disk on the top of the gas inside the tank divides the gasometer volume into two chambers, one at the bottom filled with gas and one above the disk with seldom explosive gas mixture (gas and air). According to the lightning protection standard EN 62305 on structures are taller than 60 m a lightning stroke to the side of the structures may occur, especially to corners and edges of the surface. Due to the average lighting flash density in Austria it is important to ensure the protection against direct strokes and to ensure no uncontrolled discharge inside the gasometer tank. To evaluate the effect of lightning inside the gasometer shell, a numerical simulation model was performed to investigate the current distribution and electric field strength inside the gasometer. With the distribution of the electric field strength, the voltage potential in several points and furthermore the voltage difference could be calculated.

The safe and reliable operation of electronic equipment in modern low-voltage electrical, suitable for bidirectional energy and information flows, requires starting from the transformer stations via the mains connection to the location of the equipment in the buildings special attention with regard to the integration of grounding, equipotential bonding, shielding and lightning protection. As these themes so far in the planning, implementation and verification are considered mostly separately, in practice a variety of electro technical problems such as with stray currents, unwanted interference fields and inductive interference caused by low-frequency and transient currents result. In the following article new and old methods for a functional, comprehensive approach to planning and construction of electrical installations are combined, which takes into account the needs of various grid-bound supply systems such as electricity, gas, water and telecommunications.

High Voltage Engineering is an important task at the Graz University of Technology since the early 1970s. Additional importance was given by the national decission, to offer this university and research activities for Austria in Graz only. Therfore this paper reports—based on the history—the actual situation of university education and research activities in the field of high voltage engineering and gives impressions on high voltage (HV) and extra high voltage (EHV) test facilities and test examples at the accredited laboratory of this university.

For a high reliably and high-capacity electrical power supply, the most technical expedient and economized way is an intermeshed grid of power lines. For example in Europe, in the "Union for the Coordination of Transmission of Electricity" network (UCTE) are at the moment 24 countries with a providing area of 430 mil people with 200000 km of 230 and 400 kV lines. Parts of this grid are in operation since 1950 or earlier. Due to the operating time of more than 30 years each power grid operator must ask how reliable are the line components and how much load capability is remaining. Especially the components of an overhead line which are under mechanical stress and conducting the load current are critical parts for the personal safety and system protection. This combined stress is significant for the condition and behaviour evaluation of the equipment. This contribution gives an overview about the theoretical interrelationship of the mechanical and thermal behaviour of new and aged overhead line conductors. The behaviour of typical overhead line conductors will be shown. The mechanical and thermal elongations of the conductor influence the sag and thereby the required safety margins to the ground or objects. The knowledge of the sag behaviour is the base of an overhead line monitoring system based on thermal rating.

On overhead distribution lines, lightning usually causes temporary faults. If the fault is cleared by a circuit breaker, the connection may be successfully reclosed. In the past, this was acceptable, but now with the rapid growth of sensitive loads, momentary interruptions are a major concern. With the demand for improved system reliability and performance, electricity companies must focus on mitigating the effects of lightning, considered to be one of the most frequent causes of transmission line problems today. The paper presents a project, which aims to increase reliability in an existing overhead distribution network by taking measures addressing lightning and grounding issues. Due to the fault statistic, a single overhead line was identified as a main reason for the lightning-caused outages in this area. Possibilities to reduce the lightning-caused outages are summarized and the measures taken in this distribution network are described. All considerations took the special geographical situation (2300 meter), the grounding resistance and the local lightning activities into account. Numerical calculations are performed to assess the application of surge arrestors regarding the transient voltage stress for the isolators. According to the simulation results, a strategy is laid out to implement surge arrestors in this overhead line. In this paper, the project steps and the results of the 3-years field-experience is discussed and presented.

Die elektrischen Systeme des gesamten Bereiches der Gebäude- und Haustechnik sind den Ein- und Auswirkungen atmosphärischer Entladungen ausgesetzt. Im Zeitalter modernster Architektur und hoch technisierter Infrastrukturen sind sowohl der Blitzschutz, ein Schutzzonen-Konzept und Maßnahmen der EMV an und in baulichen Anlagen nicht mehr wegzudenken. Bestand der klassische äußere Blitzschutz aus Fangeinrichtungen, Ableitungseinrichtungen und der Erdungsanlage, sind heute sehr oft zusätzliche darüber hinausgehenden Technologien, die zur Verminderung der elektromagnetischen Auswirkungen des Blitzstromes innerhalb des zu schützenden Volumens dienen, notwendig. In diesem Arbeitsfeld der Planung, Strukturierung, Umsetzung und Überwachung von Blitz- und EMV-Schutzzonen auf Basis der aktuellen Vorschriftensituation ist dieser Beitrag zu sehen.

Mobility support in IEEE 802.11 networks is a challenging issue. Recently, a new scheme, called proactive neighbor caching (PNC), was proposed and adopted as an IEEE standard. The PNC scheme introduces a neighbor graph, which dynamically captures the mobility topology of a wireless network for pre-positioning the context of a mobile host (MH). However, the PNC scheme may result in a significant signaling overhead because the MH's context is propagated to all neighbor access points (APs). We propose a selective neighbor caching (SNC) scheme, which propagates an MH's context to only the selected neighbor APs considering handoff frequencies between APs. When the context transfer is needed, neighbor APs with handoff probabilities equal to or higher than a predefined threshold value are selected. We also derive an optimal threshold value when the target cache hit probability is given. Simulation results reveal that the SNC scheme significantly reduces the signaling overhead while guaranteeing a comparable cache hit probability compared to the PNC scheme.

This article presents an algorithm for auto-reclosing of shunt compensated transmission lines. The algorithm uses signal analysis methods to estimate the future voltage shape over the circuit-breaker. Based on this voltage shape switching instants are estimated in the zero crossings. The minimization of the probability of a prearcing is reduced be adding time shift parameters. These parameters take the limited rise of strength recovery of the circuit breaker and the mutual influence of the coupling of the poles by a three-pole auto-reclosing into consideration. The advantage of the descript method is significant reduction of the switching overvoltage.