Portable Wide Wavelength Spectrometer with Diffuse Reflectance Probe and Transformer Condition Assessment
For the purpose of undertaking broad band spectroscopic measurements directly on the windings of de-tanked transformers to determine insulation condition, a miniature spectrometer probe system is currently under development. The advantage of a portable system is to enable us to make direct spatial measurements on the insulated windings while they are still wrapped around the transformer core, thus enabling us to determine the dependence of paper ageing, such as degree of polymerisation (DP), and also water content on position along the windings.
System
The system consists of two miniature spectrometers covering the wavelength range of approximately 400 to 2200 nm (from optical to the near infrared range), and a diffuse reflectance probes incorporating integrating spheres together with a light source and fibre optic links between the components. A third design of the probe system is currently under development. The system is run from a laptop computer for convenience in field measurements.
Application
After some preliminary lab tests, the system will be adapted for use in the field. The fibre optic probe is flexible for up to 4 metres enabling positioning of the probe along whole transformer windings. Initially the probe will be hand-held but future measurements may include a motion control system that will enable us to scan the probe in a linear direction across the windings, thus giving us a more reliable distribution of spectra.
A later development is likely to include a transmission probe to analyse the oil simultaneously with the paper analysis before the transformer is de-tanked. Laboratory measurements have shown that both the oil and paper spectral information can be separated efficiently. It may also be possible in the future to perform in-situ measurements; this will depend largely on the ease of access to the transformer windings from outside the tank.
Analysis and modelling
To interpret the spectroscopic measurements, multivariate data analysis techniques (chemometrics) are being applied to the spectra to extract important information and generate models to predict the aged condition with respect to a number of material parameters such as paper type, degree of polymerisation and water content.
A further application of our analysis will be to validate software that is currently used for calculating temperature distributions across transformer windings. The software will be modified to calculate the spatial distribution of DP for different transformer thermal histories using detailed data on the degradation kinetics determined in earlier PRC work. By combining kinetic theory and spatial temperature information ageing distributions can be predicted and then validated using the spectroscopic probe. The result will be a validated generalised thermal ageing model for transformer insulation.