Transformer Oil Chromatography Analysis (Dga): What Faults Do the Seven Characteristic Gases Represent?

After studying electrical engineering for so many years, what truly gave me a visual perception of the internal state of transformers was the first time I received a DGA chromatographic report. The values of seven gases correspond to completely different types of internal faults. With this set of logic, one can understand what the transformer is saying.

Seven characteristic gases and their sources

The characteristic gases generated by internal faults in transformers come from the thermal cracking or discharge decomposition of insulating oil (hydrocarbons) and insulating paper (cellulose):

Hydrogen (H ₂): The most sensitive early fault indicator, partial discharge, moisture, and low-energy discharge will prioritize the production of H ₂

Methane (CH ₄): a low-temperature superheated product that typically rises simultaneously with other hydrocarbon gases

Ethane (C ₂ H ₆): a product of moderate temperature overheating

Ethylene (C ₂ H ₄): the main product of high temperature overheating, generated in large quantities above 300 ℃

Acetylene (C ₂ H ₂): a unique product of arc discharge, is a strong signal of the most serious faults, and even trace amounts require high vigilance

Carbon monoxide (CO): a sign of heat or aging of paper insulation (insulating paper), almost not produced in pure oil

Carbon dioxide (CO ₂): homologous to CO, but the CO ₂/CO ratio can assist in determining the type of fault

Three ratio method for fault diagnosis

The "three ratio method" recommended by the national standard GB/T 7252 uses the following three combinations of ratios to determine the type of fault:

CH ₄/H ₂: Distinguish between partial discharge and thermal faults

C ₂ H ₂/C ₂ H ₄: Distinguishing indicator between arc and thermal faults

C ₂ H ₄/C ₂ H ₆: degree of thermal failure (temperature differentiation)

Different ratio combinations correspond to fault types such as normal, partial discharge, low-energy discharge, high-energy discharge, low-temperature overheating, medium temperature overheating, and high-temperature overheating.

Precautions in practical applications

The gas chromatograph provides the concentration values (µ L/L) of each gas. To determine the fault, it is necessary to combine the growth trend of historical data - the absolute amount of a single detection value is only a reference, and the growth rate (monthly increase) can better reflect the degree of fault development.

At the same time, the absolute values and ratios of CO and CO ₂ (CO ₂/CO is normally between 3-10) can determine the degree of aging of solid insulation, which is an information source that cannot be replaced by pure overheating analysis tools.

HZGC-1212A, in conjunction with the supporting workstation software, can automatically complete the calculation and fault type judgment of the three ratio method, directly output conclusions, and greatly reduce the dependence on operator experience.