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Non-destructive diagnosis of power transformer condition is an increasingly important area of research. Power transformer coils are typically insulated with Kraft paper and immersed in mineral oil. There is a clear need to be able to estimate the aged condition of the coil insulation non-destructively. A portable fibre-optic spectroscopic probe system has been developed which can achieve this quickly by determining the degree of polymerization (DP), an indicator of degradation, to an accuracy of 30 DP units. The system can also determine water content to an accuracy of 0.1% w/w, and oil content and condition, very rapidly from the same measurements. The system uses a broadband spectroscopic diffuse reflectance probe operating in the visible and near infrared (NIR) range and interfaced to dedicated multivariate analysis software. Following calibration and measurement trials in the laboratory, the instrument has recently been adapted for use in the field, in which DP predictions have been made from in-situ measurements on the exposed windings of de-tanked transformers. These values have been validated when checked against DP measurements of the same paper taken in parallel using conventional viscometric methods. The system is now being further optimized and is being developed for other applications in the power industry and other industrial areas such as the paper industry and the plastics recycling industry. The system is modular and different probe types can be attached allowing the measurement of a wide variety of solid material surfaces and liquid media. Index Terms--Power transformers, transformer windings, paper insulation, aging, oil insulation, nondestructive testing, spectroscopy, multivariate statistical analysis

Knowledge of the condition of power transformer winding insulation paper is fundamental to making optimum asset replacement decisions in the power industry. The ability to assess the aged condition of Kraft paper quickly and non-destructively using portable instrumentation would significantly increase the opportunities for gaining this knowledge. Insulation paper degrades over time in-service and its degree of polymerization (DP) reduces, eventually affecting its mechanical strength. At low DP levels the insulation may start to disintegrate and the risk of electrical breakdown increases. Currently-used methods of estimating DP are either approximate or destructive. The use of spectroscopy together with multivariate statistical analysis (MVSA) provides a powerful non-destructive evaluation of the condition of paper. From initial feasibility studies, we have developed a simple, portable system (TRANSPEC) using fiber-optics and broad-band spectroscopy that can measure the degree of polymerization of various aged transformer papers to a precision of approximately 30 DP units with a spatial resolution of 14 mm. The system can also measure the chemical composition and condition of the insulating mineral oil. MVSA regression models were constructed from library spectral data, and these models are used to predict the DP of other papers with parameters that fall within the range spanned by the set of calibration samples. Separating oil and moisture information from wetted paper is possible and will be reported in a separate publication. With a single TRANSPEC system, non-destructive in-situ analysis of the DP of insulating paper is possible, providing a rapid cost-effective method for transformer insulation condition assessment and monitoring, which correlates well with current destructive methods. Index Terms--Cellulose degradation, multivariate statistical analysis, nondestructive testing, paper insulation, power industry, power transformers, spectroscopy, transformer windings

A portable fiber-optic spectroscopic system (TRANSPEC) has been developed for nondestructive measurement of aged transformer insulating paper. Following successful measurement of degree of polymerization (DP) of a range of transformer-aged paper samples, the system has now been shown to separate the oil and paper information for measurement of DP in oil-wetted paper samples. In addition, the system has been shown to be capable of the prediction of both oil and water content of paper to a high accuracy, and is also capable of identifying and quantifying different water species. Spectroscopic measurements have been used together with gravimetric water adsorption measurements to investigate the kinetics of uptake of water vapour into paper from air in the case of nominally dry and oil-impregnated samples. Relationships between water adsorption parameters and properties of the paper insulation have also been investigated using measurements under controlled conditions. Index Terms--Humidity control, multivariate statistical analysis, oil insulation, paper insulation, power transformers, spectroscopy, weight measurement, water content

Measurements of the physical form and morphology of dielectrics and of their chemical characteristics and physical properties have become increasingly important at micron and sub-micron length scales. Such length scales are accessible by different forms of microscopy but scanning probe methods allow both chemical and physical measurements to be made, in addition to morphological and typographical imaging, at nanoscopic and mesoscopic length scales. These measurements are described in this paper with examples drawn from many areas of dielectric research and applications, including polymer morphology, surface and subsurface charge measurements along with the dynamics of charge-decay, surface potential and work function, microelectronics, ferroelectrics, photocharging, dielectric response and nanoscopic relaxation and nanoscopic Raman spectroscopy. The future of scanning probe methods for dielectric measurements is assured but more effort is required to both develop and consolidate this form of nano-metrology Index Terms: Nano-, meso-, micro-measurements, dielectrics, scanning probe, polymer morphology