Diagnostic methods for transformers on-site

The diagnosis of transformers is based on the monitoring of different parameters and its evaluation and engineering judgement. The relevant parameters should be measured under service condition, that means under a high level of noise or disturbances. The main goal of the diagnosis is the judgement of the actual situation of the insulating material in order to prevent unexpected failure and may be outages of a transformer and to evaluate the expected life time of the insulation. Therefore the monitoring should be done continuously or in regular time intervals depending on the failure mechanism and the judgement should taken into account the different situations e.g. no-load or full-load condition. All the numerous diagnostic methods are influenced by the factors safety, availability and economy.