Christian Weindl

Feasibility of HVDC for Very Weak AC Systems with SCR below 1.5

This paper exposes the feasibility to connect high voltage DC transmission (HVDC) systems to very weak AC networks leading to short circuit ratios (SCR) lower than 1.5. The existing literature does not provide solutions for such a low SCR systems and often the HVDC expansions cannot grow enough as expected. The studies developed are for the short-term voltage stability phenomena, where a solution using the PSCAD/EMTDC program for a very weak AC network with SCR=1.0 is presented. The reactive power characteristics are shown since they are important to judge the behavior of solutions for AC/DC interactions

Perspective on spatially-resolved diagnostic methods for power cables

In modern power networks supply reliability is still one of the fundamental requirements. In this context, the information about condition and even remaining lifetime of power cable grids and related equipment is interesting. Especially methods with spatial resolution are of interest due to the wide spectrum of applicability in cable networks. In this paper current methods in use like time and frequency domain reflectometry (TDR and FDR), line resonance analysis (LIRA) or approaches like the standing wave principle will be briefly introduced, compared and evaluated. This evaluation will be performed in terms of practicability, reliability and reproducibility of measurements. Some key requirements regarding the measurement can be defined. First, different and unknown parts of a cable transmission line should be acquired and determined correctly by the method of choice and the spatial resolution should be as accurately as possible. Second, the measurement method must be non-destructive with the aim that the cable condition will not be degraded. Further development of such diagnostic methods will be presented and discussed. The implementation of a measurement method with a spatial resolution of the physical condition of cables causes different problems, which will be specified in this article. New approaches are necessary that lead to a reliable and accurate measurement system with spatial resolution of the power cable condition.

Arc Movement Inside an AC/DC Circuit Breaker Working With a Novel Method of Arc Guiding: Part II—Optical Imaging Method and Numerical Analysis

This paper aims at understanding the design concept and behavior of the ionized gases inside a new electrical contactor. The switching device is designed for ac and dc operations up to 3.5 kV and nominal currents up to 800 A. The contactor consists of five electrodes: two anodes, two cathodes, and a moving electrode or bridge which works as an anode and a cathode simultaneously. In order to increase the safety, the electrical contactor includes two contact points. The line current can be diverted into an arc between the electrode and the bridge and an arc between the runner electrodes. The movement of the ionized gases is controlled by two permanent magnets and two coils installed near the electrodes. The arc plasma itself feeds the coils with current. The arc plasma velocity increases if more current is allocated in the arc plasma. The dynamics of ionized gases in the contactor is analyzed using two optical methods, viz., optical imaging method and high-speed camera (HSC). The optical imaging software has been developed to generate dynamic images of the high-speed ionized gases at a rate of 50 000 frames/s. The results of this method have been compared with those obtained using an HSC. A transient numerical model has been developed to simulate the arc plasma inside the main runner for the case of dc current. The properties of the air plasma are considered variable with temperature and pressure. The calculation shows the position and temperature of the arc plasma as a function of time.

Arc Movement Inside an AC/DC Circuit Breaker Working With a Novel Method of Arc Guiding: Part I—Experiments, Examination, and Analysis

Within this project, the mode of operation of the circuit breaker and its new innovative method of arc guiding were analyzed and verified. The solution refers to a switching device that is able to deal with both ac switching loads and bidirectional dc switching loads. It is primarily intended for use in UIC-capable switching units for voltages up to 3 kV and currents up to 800 A. The concept uses a combination of permanent and electromagnetic blowout fields. This completely new and innovative approach is intended to permit activation of the blast coils by the arcs themselves to generate the electromagnetic blowout fields without need for additional electrical switching contacts. The combining of a newly developed optical data acquisition system together with the conventional recording of electrical parameters made the verification of the working hypothesis of the switching process possible. A numerical model is used for the simulation of the later stage of the extinguishing process, where the arc is driven toward the arcing chamber by the superposed magnetic fields of permanent magnets and blast coils, until it is extinguished due to elongation and cooling by the arc splitter stack. The results of the measurement data analysis and theoretical modeling and simulation of the extinguishing process led to the identification of critical operational areas and resulted in a successful optimization of the contactor.

Experimental results of a diagnostic measurement method for power cables using interference characteristics of travelling waves

In this paper, experimental results of a diagnostic measurement method for power cables will be presented. This new method uses travelling waves and their interference characteristics to generate local energy losses inside the test object. This losses can be measured and give a qualitative indication of the local physical condition of the cable insulation. The method has been tested in several simulations, which are based on discretized cable models, which were sectionally degraded. Also different lengths and different types of cables have been tested. From this set of experiments, the most significant results will be presented in this paper. In the described experiments, the proposed approach of a diagnostic method shows local degradations of power cables and coaxial signal cables both in simulation and laboratory measurements, which cannot be detected by established reflectometry methods.

Alterung und Ästimation des Zustands von Papier-Masse-Kabeln in Mittelspannungsnetzen

SummaryA fundamental background of an optimal investment strategy and maintenance planning is build-up by a reliable knowledge about the network components condition, their reliability and consumption of the rest lifetime. In the medium voltage (MV) power networks and especially in urban regions cables present a significant part of the network components and its costs. Worldwide but especially in the early industrialized regions of the northern hemisphere (e.g. Europe, Northern America, partially Asia) paper isolated cables partially still make up more than 50 percent of the electrical distribution systems. In general, diagnostic systems for energy cables are based on partial discharges (PD) measurements but also on measurements based on polarisation effects and the dissipation factor. However, there are still no established criteria for the evaluation of the cable condition and time to the next failure. For that reason, a unique system for the artificial and accelerated ageing of MV PILC cables was developed and realized. The fully automated ageing system additionally facilitates a continuous, highly sensitive and selective PD-detection and accurate tan(δ)-monitoring. In this way, a knowledge data-base, based on the physical ageing process, will be formed up which enables the definition of suitable ageing models and significant diagnostic criteria.ZusammenfassungWesentliche Grundlagen zur Optimierung der Instandhaltungsplanung und Investitionsstrategie in Mittelspannungsnetzen stellen fundierte Kenntnisse über den aktuellen Zustand, die Zuverlässigkeit und den Lebensdauerverbrauch der in den Netzen eingesetzten Betriebsmittel dar. In Mittelspannungsnetzen und speziell in urbanen Regionen stellen Kabel einen signifikanten Teil der Betriebsmittel und Investitionskosten dar. Weltweit, insbesondere aber in den früh industrialisierten Regionen der nördlichen Hemisphäre (u. a. Europa, Nordamerika, teilweise Asien), werden noch immer papierisolierte Kabel, z. T. mit einem Anteil von mehr als 50 Prozent, für die Energieverteilung eingesetzt. Allgemein werden zur Zustandsdiagnose bei Energieversorgungskabeln Teilentladungs-, aber auch vermehrt auf Polarisationseffekten beruhende Verfahren und Verlustfaktor-Messungen angewandt. Allerdings gibt es derzeit noch keine verlässlichen und anerkannten Kriterien, die zuverlässige Aussagen über den aktuellen Kabelzustand und die zu erwartende Restlebensdauer des Betriebsmittels Kabel erlauben. Daher wurde in den vergangenen Jahren ein einzigartiges System zur künstlichen und beschleunigten Alterung von Papier-Masse-Kabeln entwickelt und realisiert. Das vollständig automatisierte Alterungssystem ermöglicht zusätzlich eine versuchsbegleitende, hochempfindliche und selektive Erfassung der Teilentladungscharakteristik und des Verhaltens des Verlustwinkels tan(δ). Während des Projektzeitraums von zwei Jahren soll so eine auf den physikalischen Alterungsprozessen beruhende Datenbank aufgebaut werden, die eine nachfolgende Definition geeigneter Alterungsmodelle sowie aussagekräftiger Diagnosekriterien ermöglicht.