The side effects of gassing in transmission power transformers

The Dissolved Gas Analysis (DGA) of insulating oils has, over the last few decades, become a widely used technique for detecting and diagnosing incipient electrical failures inside the windings of power transformers. Since the decomposition of oil indicates a threat to the operational safety of these expensive machines, electrical engineers focus their attention on the amount and nature of the gases evolved. Based upon the relationship that was established between the results of DGA and the potential cause of such deficiencies, appropriate preventive measures are taken to protect the transformer. However, the side effects of a hydrocarbon chain breakdown on the insulating properties of oil are generally not taken into consideration. When a hydrogen atom is knocked out from a hydrocarbon it means that the two electrons of a covalent bond were homolytically separated. While the hydrogen content of oil and other low molecular weight gases is carefully monitored, the decay products generated by the chemically reactive large fragments of decomposed molecules are ignored. Significant technological progress has been made in the laboratory analysis of oil, which offers the opportunity to reveal the link between gassing and the deterioration of liquid insulation quality under service conditions. This paper describes the unavoidable implications of secondary chemical reactions, caused by the gas evolvement of oil subjected to thermal and electrical stress.