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Featured researches published by M. Muhr.


ieee international symposium on electrical insulation | 2012

Developments of high voltage porcelain post-insulators

T. Morocutti; T. Berg; M. Muhr; G. Gödel

The main purpose of this work was to investigate the development trends of high voltage porcelain post insulators over the last decades. It also shows an analysis of the performance of a contemporary design of a shorter nonstandard layout and its agreement with the IEC standards. Despite of high demanding requirements on Ceramic Solid Core Post Insulators, the economical aspect becomes more and more important. Therefore the objective of insulator design is to develop a technically and economically optimized HV component, with a high grade of reliability over decades. If some parameters can be optimized like, arcing distance and length of the insulator, maximizing the mechanical strength and stiffness, minimizing the core diameter, maximizing the form factor and finding an optimal shed profile, material can be saved and therefore weight can be reduced also and costs. Due to a more sophisticated manufacturing process of high voltage insulator, they can be produced in a bigger length in one piece and thinner sheds than 40 years ago. The result of these measures are a longer arcing and creepage distance, less weight and most of all less electrically conducting parts. 40 years ago, the column design for an 800kV AC post insulator was a stack of 6 insulators, compared to two insulators nowadays. This work reflects the different developments of design between the past and in these days, because the question was raised: do post insulators need to have the same total height than 40 years ago despite of an improvement of manufacturing them.


ieee international conference on condition monitoring and diagnosis | 2012

Partial discharge behavior of mineral oil and oil-board insulation systems at HVDC

Jürgen Fabian; M. Muhr; Stefan Jaufer; Wolfgang Exner

Power transformers have been built successfully with oil-board insulation systems for many years. Oil has the function of being a coolant as well as an insulator, whereas the board serves for electrical and mechanical purposes. When dealing with solid insulating materials, special focus has to be set on partial discharges (PD), as they have a destructive nature. On the one hand they may supply charge carriers for breakdown mechanisms and on the other hand they can lead to a carbonization of the organic insulation. In the case of AC, phase-resolved patterns, so called finger prints, can be used to interpret the type of partial discharge. These methods are in use for many years and have proven successful in interpreting possible PD sources. However, in the case of DC, no phase information is available. Therefore other methods for interpreting the behavior of PD at HVDC have to be found. In this paper, a non-uniform test setup for mineral insulating oil and a small oil-board model was used. The different observations were evaluated to discuss the issues of PD measurements at HVDC. In addition to conventional electrical partial discharge measurements also optical detection of partial discharges was used. Furthermore, a scanning electron microscopy (SEM) was used for the high voltage electrodes to gain information about surface changes of the needle electrodes.


ieee international conference on condition monitoring and diagnosis | 2012

Partial discharge behavior of environmentally friendly and hardly inflammable ester liquids compared to mineral oil for power transformers

Jürgen Fabian; B. Wieser; M. Muhr; Robert Schwarz; Georg Pukel; M. Stössl

Conventional insulation systems of power transformers consist of mineral oil, cellulose paper, and pressboard. Due to the low biodegradability level of mineral oil and its susceptibility to fire, there has been an increase in the use of environmentally-friendly fluids such as synthetic esters and natural esters in recent years. To improve personal safety and to reduce the environmental impact of electrical power supply, alternative insulation fluids are demanded for large power transformers. These liquids are already used in the area of distribution transformers, but in case of large power transformers insignificant experience exists so far with alternative insulating fluids. For characterization of the insulating material and optimization of electrical design different electrical test methods (e.g. breakdown voltage, partial discharge) are used. The partial discharge behavior is a distinguishing characteristic of an insulating medium. In conclusion, it can be said that this paper shows the partial discharge behavior of alternative insulation liquids compared to commonly used mineral oil based on various investigations of an inhomogeneous test setup to generate reproducible partial discharges.


Elektrotechnik Und Informationstechnik | 1998

Technische Diagnostik — Strategie für eine moderne Instandhaltung

M. Muhr

ZusammenfassungDie Werterhaltung von elektrischen Betriebsmitteln wird seit langem durch die Instandhaltung sichergestellt, wobei nach verschiedenen Strategien vorgegangen wird. Ausschlaggebend für die optimale Strategie sind die Bedeutung und die Kosten eines Betriebsmittels. Die Instandhaltung umfaßt die Technische Diagnostik, die Wartung und Instandsetzung. Die Technische Diagnostik ist dabei die Wissenschaft von der Erkennung des Zustands technischer Systeme.AbstractThe quality of electrical equipment is secured for a long time by maintenance. On that occasion the maintenance uses different strategies. The importance and costs of the equipment are decisive for the optimal strategy. The maintenance contains technical diagnostics, service and reconditioning. On that occasion the technical diagnostics is the science of the identification of the condition of technical systems.


ieee international conference on properties and applications of dielectric materials | 2012

Impact of small voids in solid insulating materials

M. Lerchbacher; Christof Sumereder; Gerhard Lemesch; Franz Ramsauer; M. Muhr

Due to recent developments in insulation technology extensive knowledge of the impact of small voids on the dielectric behaviour and lifetime of the insulating system is required. Our objective is to investigate the PD behaviour of epoxy resin specimens with embedded artificial micro voids in order to determine the degradation mechanisms of insulating materials due to air filled micro voids. Therefore we carried out experiments, where a set of cylindrical test specimens were positioned in an oil vessel between metal electrodes. Whilst applying high electric field strength (up to 15 kV/mm) we determined the electrical partial discharge inception at different temperatures by heating the oil vessel (22 to 85 °C). Besides the partial discharge inception and extinction voltage, the level and rate of PD inception and extinction were also monitored. We found that PD inception took place at a lower voltage level or field strength respectively for specimens with hollow glass microspheres than for specimens of pure resin. Furthermore we recognised different PD patterns for specimen with and without microspheres respectively. The impact of temperature on the PD behaviour of the tested specimens can be described as marginal for temperatures between room temperature and about 50 °C but differs for higher temperatures. The influence of temperature seems to correlate with the properties of the epoxy resin used.


Elektrotechnik Und Informationstechnik | 2012

Anwendung des Paschen-Gesetzes für die Optimierung des Wickelkopf-Abstandsdesigns von großen rotierenden elektrischen Maschinen

M. Lerchbacher; Christof Sumereder; M. Muhr; Gerhard Lemesch; Franz Ramsauer; Werner Ladstätter

ZusammenfassungModernen großen rotierenden elektrischen Maschinen wird ein höchstmögliches Maß an Effizienz abverlangt, was Optimierungen in allen Bereichen erfordert. Im Wickelkopf haben z. B. Maßnahmen, wie das Verringern der Abstände nebeneinander liegender Stäbe und Windungen, sowie die Reduktion der Isolierdicken bei gleichbleibender Spannungsbeanspruchung erhöhte Anforderungen an das Isolationssystem zur Folge. Daher ist man bestrebt, das Wickelkopf-Design hinsichtlich Korona-Entladungen und axialer Ausladung zu optimieren.Im Rahmen der hier beschriebenen Arbeit wurden physikalische Zusammenhänge bei Entladungsvorgängen in Gas-Festkörper-Isolationssystemen bei unterschiedlichen Umgebungsbedingungen untersucht. Im Speziellen wurden bei den Versuchen Platte-Platte-Modellanordnungen aus isolierten Elektroden mit und ohne Abstandshalter untersucht, wobei insbesondere die Korona-Ein- und Aussetzspannung und die aufgetretenen Teilentladungen (anhand von phasenaufgelösten Teilentladungsmustern) betrachtet wurden. Ein Abgleich der Erkenntnisse aus den Untersuchungen mit dem klassischen Paschen-Gesetz soll in Zukunft eine optimierte Auslegung der Wickelkopfabstände ermöglichen.AbstractToday there is a great demand for optimization of the overall performance of high voltage rotating machines. In the endwinding minimized distances between adjacent insulated bars or coils and reduced insulation thickness at constant voltage stress increase the requirements on the insulating system. Therefore the endwinding design has to be optimized with regarding to corona discharges and axial size reduction.This paper describes our research about physics of gas discharges under various environmental conditions. In particular we investigated plane-plane arrangements of insulated electrodes with and without spacers. Thereby, special attention is paid to corona inception and extinction voltage as well as the occurred level of partial discharges (on the basis of phase resolved PD patterns). Comparing the obtained results with the classical Paschen’s Law will allow an optimized endwinding design in future.


Elektrotechnik Und Informationstechnik | 2001

Technical diagnostics for power apparatus@@@Technische Diagnostik für energietechnische Geräte

H. Sander; J. Schwab; M. Muhr

The purpose of technical diagnostics and preventive maintenance for power apparatus should be recognized in protecting equipment against failures and malfunctions. Due to an earlier detection of incipient faults in power apparatus economic benefits can be gained. This is important to reduce operating costs.ZusammenfassungDer Sinn der technischen Diagnostik und der vorbeugenden Instandhaltung bei energietechnischen Geräten sollte die Früherkennung von Fehlern und Fehlfunktionen zum Schutz der Geräte und Anlagen sein, denn die frühere Erfassung von einsetzenden Fehlern in Apparaten wirkt sich wirtschaftlich vorteilhaft aus. Dies ist wichtig, um die Betriebskosten zu senken.


Elektrotechnik Und Informationstechnik | 2001

The deregulation of the electricity market from the perspective of a regional Austrian utility

H. Sander; J. Schwab; M. Muhr

The fundamental change of the electricity market results in an alteration of any national and regional market. New market structures, new thoughts and new skills are necessary to come across these challenges successfully. In addition to public permit requirements there is also the demand of serving the public.ZusammenfassungDer grundlegende Wandel des Strommarkts ruft eine Veränderung jedes nationalen und regionalen Elektrizitätsunternehmens hervor. Neue Marktstrukturen, neue Gedanken und neues Können sind erforderlich, um erfolgreich diese Veränderung zu überstehen. Zusätzlich zu öffentlichen Anforderungen kommt die Forderung nach einer Dienstleistung an der Öffentlichkeit.


Elektrotechnik Und Informationstechnik | 1997

Auswirkungen von Blitzschlägen auf 20-kV-Energiekabel

M. Muhr; Stephan Pack; H. Haidvogl; F. Kreyca

ZusammenfassungDie in jüngster Vergangenheit aufgetretenen Schäden an verlegten Hochspannungs-Energiekabeln machten Untersuchungen über die Auswirkungen von Blitzschlägen notwendig. In einigen Fällen können Überspannungen zwischen dem Kabelschirm und dem umgebenden Erdreich auftreten, die eine Beschädigung des Kabelmantels verursachen. Zur Erfassung der atmosphärischen Überspannungen am Kabelschirm wurden vorerst vor Ort Impulsmessungen zwischen Schirm und Erdreich einschließlich einer Klassifizierung der Scheitelwerte durchgeführt. Den Schwerpunkt bildet die Entwicklung eines numerischen Netzwerkmodells, mit dem in unterschiedlichen Kabelbereichen und an verschiedenen Orten der Trasse die Auswirkungen dieser transienten Spannungsbelastung abgeschätzt werden kann. In weiterer Folge kann damit auch die Wirksamkeit von verschiedenen Schutzeinrichtungen für verlegte Kabel beurteilt werden.AbstractRecently appeared defects on high voltage cables have required an urgent evaluation of the impact of lightning strikes necessary. In some cases overvoltages between the copper wire screen of the cable and earth may appear which cause damages of the cablesheath. Field measurements with a classification of the voltage impulses at the copper wire screen have been made to evaluate the number of events. Additionally a numerical model was developed to study the effects of atmospheric discharges on underground cables with emphasis to the influence on the cablesheath. This numeric method was also applied to estimate the effectiveness of different protection arrangements. This contribution presents evaluation methods for overvoltages of cables and a model used firstly for calculating the stress caused by differential voltages and secondly to determinate the influence of protection measures.


Electricity Distribution, 2001. Part 1: Contributions. CIRED. 16th International Conference and Exhibition on (IEE Conf. Publ No. 482) | 2001

Technical diagnostics for power apparatus

H. Sander; J. Schwab; M. Muhr

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Christof Sumereder

Graz University of Technology

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Jürgen Fabian

Graz University of Technology

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M. Lerchbacher

Graz University of Technology

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B. Wieser

Graz University of Technology

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G. Praxl

Graz University of Technology

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Stephan Pack

Graz University of Technology

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T. Berg

Graz University of Technology

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T. Morocutti

Graz University of Technology

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