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Unformatted text preview: Dielectric Spectroscopy in Time and Frequency Domain for HV Power Equipment, Part I: Theoretical Considerations Key Words: Dielectrics, polarization effects, dielectric response function, dielectric measurements in time and/or frequency domain. T oday, the catchword in utility companies is condi- tion-based or predictive testing and maintenance, or even life management, as opposed to time-based or preventive maintenance only. The reasons for this evolution are well known: In North America, for instance, their roots can be found in the restructuring and de-regulation of the electric utility industry. Here in Eu- rope, it was the adoption of the “Single Market Direc- tive” which became the norm in February 1999, whereas it was still the exception many years before . The main issue of this de-regulation of the electricity market, now subdivided into independent power producers, transmis- sion companies, system operators and distribution com- panies, is to encourage competition while still maintaining basic public policy and service objectives. All partners within this new scheme are thus forced to cut costs in maintenance and operation without endan- gering a steady supply of electricity to demanding cus- tomers. Costs can be reduced, first of all, by a transition from time-based maintenance (TBM) to condition based maintenance (CBM), if the actual conditions of the ex- pensive high voltage components within the electric power transmission systems are reliably known. The ap- plication of “unscheduled maintenance,” a philosophy based on a reactive mode of operation, will not reduce costs. Unscheduled maintenance means that repairs and maintenance will be made only when the equipment, e.g. a transformer or cable, breaks down. But this generally causes a downtime of the electricity supply, so that break- downs become much more costly than planned mainte- nance. A CBM based on reliable diagnostic tools should thus be applied today. The driving force for the development and application of improved diagnostic methods is the steadily increasing age of expensive HV components. In many parts of the world, the majority of large power transformers were in- stalled in the 1960s and ‘70s. Also, cable technology changed at this time, and the first generations of PE or XLPE cables are still prone to breakdowns. All these facts are very well known. It is not the aim of this article to discuss the full com- plexity of all the existing diagnostic techniques that have been successfully applied to different HV components to support CBM. Most of the dangerous breakdowns, how- ever, are caused by the aging effects of HV insulation sys- tems used within these components, and there is still a lack of appropriate tools to diagnose such systems non-destructively and reliably in the field. New methods have been published in the last decade and even before, September/October 2003 — Vol. 19, No. 5 0883-7554/03/$17.00©2003IEEE 5 F E A T U R E A R T I C L E Walter S. ZaenglWalter S....
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This note was uploaded on 06/11/2011 for the course ELECTRICAL 124 taught by Professor Ghjk during the Spring '11 term at Institute of Technology.
- Spring '11