Maintenance of insulating oils in service is very essential to prolong their life and also of the equipment in which they are filled.
The various codes of practice for maintenance of such oils in service lay down a number of tests to judge oil quality, none of which reveal the overall quality of the oil with respect to the various types of contamination it may have undergone. Moreover these tests do not give any indication as to when the oil is likely to sludge.
The search therefore of a single lest which fulfils these needs has led to the possible use of the interfacial tension value of oils against water as a criteria for judging the oil quality.
This paper presents results of exhaustive experimental work done by the authors to study the IFT value of oils in service in relation to its other properties.
The results obtained clearly indicate that IFT value of oils is very useful in predicting sludge formation, thus providing a guide to take corrective measures before any adverse effects are noticed.
The IFT value along with either the ‘Power Factor’ or ‘Resistivity’ value of an oil can be used to compute the ‘Quality index’ which serves effectively as a guide of the overall contamination of the oil. Monograms to compute this index are incorporated in this paper.
