Successful detection of an incipient electrical failure within the windings of power transformers is based upon the possibility of determining the amount and nature of the gases evolved by the oil when subjected to the impact of a strong electric or thermal stress. The cause of the deficiency can be established by analyzing the gases dissolved in the oil. While under normal operating conditions the amount of gas evolved is minimal and therefore of little importance, a significant increase in the concentration of gaseous decomposition products gives cause for concern.
Since a large amount of vulnerable hydrocarbon molecules can also be the source of dissolved gases, the gassing tendency of oil should be taken into consideration. The lack of a reliable procedure capable of establishing a quantitive relationship between laboratory results and the performance of oil in service can influence the interpretation of dissolved gas analysis (DGA). Just as the chemical stability of oil is accepted as an indication of the ability of insulating oils to resist oxidation, the concept of electrochemical stability is introduced as a measure of the capacity of the oil to counteract gas evolution under the impact of electrical stress. Knowledge of the amount of gas generated by a sample of oil, when subjected to the influence of a standard high-voltage field, can improve the interpretation of DGA of that oil. This concept also provides a better understanding of the mechanism by which the high-voltage field negatively affects the chemistry of insulating fluids.