Frequency Domain Measurements for Diagnosis of Power Transformers: Experiences from Australia, Malaysia, Sri Lanka and UK

This is the author accepted manuscript. The final version is available from CIGRE via the link in this recordPower transformers and their performance and reliability in electric power networks are important research issues of power systems. Much information has already been collected and reported; however, it is rare to report comparisons of transformer service performance under different geographical locations and working conditions. CIGRE Working Group A2.37 collected information on 964 transformer failures from 58 utilities and 21 countries covering the period from 1996 to 2009. The main failure modes included failures in windings, tap changers, bushings, insulation, and core. As estimated, based on available literature, nearly 50% of the failures could be related to transformer windings and insulation. This collective paper summarizes experiences from the use of diagnostic tools based on frequency domain measurements at different geographical regions of the world. It starts with a short introduction to response measurements in frequency domain for condition assessment of transformers; then theoretical backgrounds of the two widely used response measurements, namely Frequency Dielectric Spectroscopy (FDS) and Frequency Response Analysis (FRA), are presented. Afterward details of tested transformers and measurement procedures are described for which selected set of FDS and FRA measurement results are analysed for respectively elucidating their potential in assessment of moisture content, ageing degree and fault identi cation

Effects of the insulation quality on the frequencyrResponse of power transformers

This paper presents results of frequency domain spectroscopy (FDS) measurements on oil-impregnated pressboard insulation, their analyses and use of the data for modelling high frequency response (FRA) of transformers. The dielectric responses were measured in a broad frequency range, i.e. from 0.1 mHz to 1 MHz, on model samples containing different amount of moisture. The responses were parameterised with terms representing dc conductivity, low frequency dispersion and Cole-Cole polarisation mechanisms and they were thereafter used to model the FRA response of a three-phase transformer