Transformer oil analysis – basic introduction

by N Robinson, WearCheck


Published in: Transformers and Substations Handbook: 2014

Chapter 4: Maintenance - page 68

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It is well known that regular transformer oil analysis is extremely useful in monitoring the condition of engines, drivetrains, hydraulics, turbines and many other types of oil lubricated equipment. The same can be said for transformer oils, which are used to insulate many transformers and other electrical distribution equipment. Transformer oil analysis not only provides information about the transformer oil, but also enables the detection of other potential problems, including contact arcing, ageing insulating paper and other latent faults, and is an indispensable part of a cost-efficient electrical maintenance programme.

Transformer maintenance has evolved over the past 20 years from a necessary item of expenditure to a strategic tool in the management of electrical transmission and distribution networks. Extreme transformer reliability is demanded of electric power distribution, and even though the failure risk of a transformer and other oil-filled electrical equipment is small, when failures do occur, they inevitably lead to high repair costs, long downtime and very real safety risks. Moreover, transformers are too expensive to replace regularly and must be properly maintained to maximise their life expectancy.

By accurately monitoring the condition of the transformer oil, many types of faults can be discovered before they become serious failures and outages can potentially be avoided. Furthermore, an efficient approach to maintenance can be adopted and the optimum intervals determined for replacement. Some of the checks are relatively simple: the operation of the gas relays, the operation of the on-load tap-changer, checks on oil leaks, etc. However, breakdown of one of the most crucial elements, the oil/ paper insulating system, can only reliably be detected by routine oil analysis. By measuring certain physical and chemical properties of transformer oil, in addition to the concentrations of certain dissolved gases, a number of problem conditions associated with either the oil or the transformer can be determined.


Take note

  • The ability of transformer oil analysis to provide an early warning sign of a problem condition, depends on the quality of the oil sample.
  • The same location should be used each time a transformer oil sample is collected.
  • Extreme transformer reliability is demanded of electric power distribution.