Improving the reliability of transformer gas-in-oil diagnosis

Dissolved gas analysis (DGA) is widely used to detect incipient faults in oil-filled electrical equipment. There is always some degree of inaccuracy in laboratory dissolved-gas measurements, especially at low gas concentrations, which affects gas ratios and other diagnostic calculations. This paper examines the measurement inaccuracy problem in detail using recent CIGRE data. It shows how proper allowance for this inaccuracy can improve transformer condition assessment and diagnosis by DGA.