Dissolved Gas Analysis of Methyl Ester-Mineral Oil Mixture Under Partial Discharge
Dissolved Gas Analysis of Methyl Ester-Mineral Oil Mixture Under Partial Discharge

Summary/Abstract: This paper deals with the dissolved gas analysis (DGA) of methyl ester and mineral oil mixtures under partial discharge (PD). Experiments were conducted on pure methyl ester and mixtures containing 5%, 7.5%, and 10% mineral oil to simulate transformer retrofilling conditions. PD was generated using a needle-plane electrode pair immersed in the oil sample and subjected to AC high voltage. The gases produced were analyzed using gas chromatography to evaluate gassing tendencies and fault diagnostics using the Key Gas, Duval Triangle, Duval Pentagon, and IEC 599 ratio methods. Results indicate that residual mineral oil reduces the partial discharge inception voltage (PDIV) and increases gas production. Hydrogen, constituting approximately 85% of total gas production, indicates the applicability of the Key Gas method. The Duval Triangle method consistently identified PD faults, whereas the Duval Pentagon method underestimated PD as stray gassing. In contrast, the IEC 599 method was ineffective for fault diagnosis in methyl ester-based oils under PD. These findings suggest that up to 10% residual mineral oil in a retrofilling scenario does not significantly affect DGA-based fault diagnostics in methyl ester but enhances gas production due to increased PD activity.

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