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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

Static secondary ion mass spectrometry was used to study the corrosion inhibitor Irgamet ® 39 on the surface of copper treated in insulating oils and the effect of temperature changes, by means of temperature programmed desorption experiments under vacuum, on metal coverage. Four commercial oils, both corrosive and non-corrosive, showed no significant influence on the stability of the tolyltriazole layer and the energy of its main desorption event from copper was calculated around 100 kJ mol −1 . Finally, an example of ion imaging as diagnostic tool to track the distribution of corrosion inhibitor and by-products in decommissioned or failed power transformers is described. [ABSTRACT FROM AUTHOR]