Insulation failure has been identified as one of the main reasons for transformer breakdown. As one the most important assets in the high voltage system, the loss of a power transformer will cause significant effects to consumers and on the system. The condition of the insulation can directly be correlated to the presence of Partial discharge (PD). Therefore, the ability to accurately detect and analyse the information from PD could be the answer to avoid catastrophic breakdown. On top of that, the capability to pinpoint the location of the PD source would enable swift preventive action to be taken. Several methods have been researched and developed in those two areas. This paper will discuss such techniques. Included in the discussion is an introduction to some less conventional techniques such as optical and ionising emission detection.
