Transformer failure modes and planned replacement

Transformers are usually very reliable and durable items of electrical equipment, so much so that their performance is often taken for granted, especially in a power station environment where there are often many more immediate claims on the attention of maintenance engineers. Unfortunately, when a fault occurs in a transformer, it can develop catastrophically and failures are usually very expensive if not uneconomic to repair, often resulting in the loss of what is the most expensive plant item in a substation. Costs of resulting loss of generation or transmission restraints until a replacement can be effected can also be severe. There has been considerable interest in the subject of life management of transformers. Planned replacement is the ideal from the point of view of maintaining system reliability in the face of an ageing population of transformers. To implement such a policy, information on failure modes and asset health is required, which necessitates a careful programme of inspections of redundant units, basic research and condition assessments