Non-destructive Dp Analysis of Kraft Paper from Shell-type Power Transformers

Rapid, cost-effective, non-destructive diagnosis of power transformer condition is an increasingly important area of asset management – this includes the need to be able to estimate the aged condition of the coil insulation nondestructively. This is necessary to assess the reliability and potential risks presented by transformers in a particular population as well as gauging the prospective life expectancy of individual transformers. A portable fiber-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 40 DP units in the presence of the insulating oil. The system uses a hand-held optical probe that gathers spectral information which is analysed using dedicated multivariate analysis software. Following calibration and measurement trials in the laboratory, the instrument has been used in the field, to provide DP values based on in-situ measurements of the exposed windings of de-tanked transformers, and can also be used to determine water content. The method is still in development, but already it is highlighting ageing differences between core and shelltype transformers. These values have been validated against DP measurements using conventional viscometric methods.