Patrick J. Baird

Non-destructive measurement of the degradation of transformer insulating paper

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.

Spectroscopic measurement and analysis of water and oil in transformer insulating paper

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.

On-site analysis of transformer paper insulation using portable spectroscopy for chemometric prediction of aged condition

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.

Non-destructive condition assessment of insulating materials in power transformers

Rapid in-situ analysis of the condition of power transformer winding insulation to provide information on its aged condition and water content is important for both transformer manufacturers and also asset managers in power utilities. The ability to achieve this with portable instrumentation would be very beneficial. The insulation paper degrades over time, and the degree of polymerisation of the paper affects its structural integrity and its capacity for water absorption. The use of spectroscopy together with multivariate statistical analysis provides a powerful non-destructive tool for the condition assessment of these materials both in the laboratory and in the field. We have developed a simple, portable system (TRANSPEC) using fibre-optics and broad-band spectroscopy that can measure the degree of polymerisation in the range from 100 to 1200, water content from 0.4% to almost full saturation to an accuracy of 0.1%, and oil content of new and aged transformer paper also to high precision. Multivariate statistical analysis regression models have been constructed from spectral library data and these models are used to predict the parameters above and also other physical properties e.g. tensile strength. We have also confirmed that both the water absorption kinetics and water capacity of the paper are strongly affected by the degree of degradation. With a single TRANSPEC system, in-situ analysis of the degree of polymerisation of insulating paper, the water content and, if required, a chemical analysis of the insulating oil and its water content.

Nano- and meso-measurement methods in the study of dielectrics

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.

Non-destructive and in-situ analysis of insulating materials in high-voltage power transformers

Rapid in-situ analysis of the condition of power transformer winding insulation kraft paper, to provide information on its aged condition, is an imperative in the power industry. The ability to achieve this with portable instrumentation would be very beneficial. The insulation paper degrades over time, and the degree of polymerisation (DP) of the paper affects its structural integrity. At low DP levels the risk of electrical breakdown increases. Currently used methods of estimating DP are only 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 fibre-optics and broad-band spectroscopy that can measure the degree of polymerisation of various aged transformer papers to a precision of approximately 50 DP units with a spatial resolution of 25 mm/sup 2/, and 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 water content can be determined to an accuracy of approximately 0.1%. Very low to high concentrations of water have been determined using this method. We have also confirmed that both the absorption rate and water capacity of the paper are strongly affected by the degree of degradation. With a single TRANSPEC system, in-situ analysis of the degree of polymerisation of insulating paper, the water content and, if required, a chemical analysis of the insulating oil and its water content is possible providing a rapid cost-effective method for transformer insulation condition assessment and monitoring, which correlates well with current established methods.

Rapid Assessment of Electronics Enclosure Plastics

Current recycling qualification methods for plastic materials such as polycarbonate (PC), acrylonitrile butadiene styrene (ABS), PC/ABS blends, high-impact polystyrene (HIPS) and polyphenylene oxide (PPO) are inefficient and any recycling that is performed generally produces relatively poorly qualif...