Condition monitoring of power transformers

Summary form only given. A set of diagnostic test methods are being used to monitor the insulation condition of power transformers. These include techniques such as gas chromatography for dissolved gas analysis of hydrocarbon and carbon oxide concentrations, others for measurements of moisture, acidity and electric strength and a high pressure liquid chromatograph for analysis of furfuraldehyde, a liquid residue of paper degradation. As means of assessing the usefulness of individual parameters and the degree of correlation between parameters, two sets of investigation were undertaken. Firstly, results of analysis of some 500 transformer oil samples were put in a database to determine the 'normal' for transformers of more than 20 years of age. Secondly, a 40 year old, 132 kV, 45 MVA grid transformer was subjected to an accelerated thermal ageing test for a period of 3 months with the winding temperature rising from 70 degrees C to 102 degrees C.