Condition monitoring of transformer oil using thermal analysis and other techniques

Any transformer oil undergoes continuous degradation because of all electric, thermal, mechanical, and climatic stresses it suffers while operating in the transformer. Therefore, the oil has to be checked on regular basis in order to decide whether it is necessary to regenerate or replace it, avoiding thus a sudden failure of the transformer. This article presents results of in-the-laboratory-performed experiments on transformer mineral oil samples. Those samples came from a power transformer that works in the Romanian power network. There were three monitoring stages conducted over four-and-a-half years. We used two measuring techniques: (i) measurement of the state parameters of transformer oil (breakdown voltage, loss factor, water contents, acidity index, interfacial tension, number of particles larger than 5 microns, and gas contents) in order to describe the oil condition during the monitoring period and to anticipate any severe fault. This enables the user to take preventive action before a severe fault might eventually occur; (ii) thermal analysis (TA) and Fourier transform infrared spectroscopy (FTIR), in order to determine the stability of oil samples. By using TA and FTIR, and by evaluating each and every significant parameter, it has been proven that the tested oil is still adequate for further employment in the power transformer.