03_application_scopy - F E A T U R E A R T I C L E...

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
Applications of Dielectric Spectroscopy in Time and Frequency Domain for HV Power Equipment Key Words: Dielectric measurements, dielectric response (frequency and time domain), aging, power transformers, current transformers, moisture content, cables. P art I of this article, published in the last issue of this magazine,[1] gavean introductioninto the theoret- ical background of dielectric spectroscopy in the time as well as in frequency domains. It also gave an over- view of the most essential measurement methods pres- ently applied to diagnosing HV power equipment. This second part deals with specific applications of such meth- ods, especially applied to current and power transform- ers, and high voltage cable systems. Most of the discussed investigations are based on quoted references. An often-made assumption is that the results of dielec- tric response measurements are independent of the geo- metricstructureand composition of aninsulationsystem, if the latter does not exclusively consist of a single insula- tion material which completely fills the gaps between the electrodes. A typical example is the insulation system of HV power transformers, which is composed of oil gaps and pressboard barriers that are arranged differently, ac- cording to the manufacturer. All transformer manufac- turers are well aware that even the results of the simplest C - tan - measurement at power frequency will be de- pendent, not only upon the construction of the insulation system, but also on the quality of the materials used and the quality of the impregnation processes to reduce the water content in the pressboard. This article, therefore, starts with investigationsto assess the moisture content in power transformers. Dielectric Spectroscopy Applied to Power Transformer Insulation Manufacturers of HV power transformers, as well as electric utility companies, are increasingly aware that the agingand dry states of oil-paperinsulationare key factors in both the short- and long-term reliabilityof such expen- sive and essential components in a power transmission system. Moisture has very adverse effects on the dielec- tric integrity and insulation aging rates [2]. As moisture occurs in oil as well as in paper or pressboard, which will be unequallydistributed within both these components, a quantitative knowledge about the moisture concentra- tions (m.c.) within each component is of the highest im- portance. It is also well known that the m.c. equilibrium in oil and pressboard is highly temperature dependent, with most of the moisture residing in the solid, and that — for moderate temperatures — this equilibrium will only be reached after a long time [3, 4]. Therefore, the measurement of moisture in the oil is not a reliable indi- cator of the dryness of the pressboard, particularly for lightly loaded transformers. Since the solid insulation within the transformer is not accessible, the main aim of any diagnostic procedure is thus a measurement of the November/December 2003 — Vol. 19, No. 6 0883-7554/03/$17.00©2003IEEE 9 Walter S. Zaengl
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

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.

Page1 / 14

03_application_scopy - F E A T U R E A R T I C L E...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online