Diagnosis of power transformer insulation

Diagnosis of power transformers becomes important due to the age of the transformer in service. Diagnosis methods can be separated in integral or differential methods. Gas-in-oil analysis is a well known diagnosis method and gives information on different failures. Humidity measurements of the liquid component of the insulation system are possible and with a special sensor also for the solid part. Furan analysis is a further method to evaluate humidity in the solid part of the insulation. Partial discharge measurements can be used for failure detection and a new method allows the localisation of the partial discharge source. Dielectric parameters delivers a lot of information concerning the change in the insulation system, but reference measurements are required.