Oil analyses as a condition monitoring technique

The insulation of power transformers is generally very reliable. Transformer failures are usually due to problems with either HV bushings or tap-changers. Insulation ageing in transformers is most commonly associated with long-term effects of the operating temperature, moisture and air. Since a significant proportion of transformers on the network are over 30 years old, it is necessary to assess the “chemical” age of their insulations and, if possible, to predict their rates of ageing relative to their present and future loading conditions. Here, a method of condition monitoring of the oil-paper composite insulation of power transformers has been developed, based on measurements of moisture, electric strength, acidity, dissolved gases in oil by gas chromatrography, and furfuraldehyde by high performance liquid chromatography