1. Introduction
The analysis of insulating oils provides lots of information about the oil, and also enables the detection of other possible problems, including contact arcing, aging insulating paper and other latent faults. Thus it is an indispensable part of a cost-efficient electrical maintenance program [1].By accurately monitoring the condition of the oil, sudden faults can be discovered in a timely fashion and outages can potentially be avoided. Furthermore, an efficient approach to maintenance can be adopted and optimum intervals determined for necessary replacement. Similar to industrial oils, transformer oils are oxidized under the influence of excessive temperature and oxygen, particularly in the presence of small metal particles that act as catalysts and which, result in an increase in the (total) acid number, owing to the formation of carboxylic acids