Determination of the Fire Resistance Characteristics of Transformer Insulating Oils Through Pool Fire Experiments

Abstract

Fire safety is crucial for oil-immersed power transformers due to the potential destruction of infrastructure, environmental damage, and risks to human health and safety caused by transformer fires and explosions. One of the essential elements of oil-immersed power transformers is the insulating oil, which is used for insulation and cooling purposes. However, the
insulating oil can pose significant fire hazards, particularly mineral oil, which is highly flammable. Hence, it is crucial to perform fire resistance tests to determine the fire resistance characteristics of transformer insulating oils. This study investigates the fire resistance characteristics of O-class (mineral oil and fatty acid methyl ester) and K-class (natural and synthetic esters) transformer insulating oils through pool fire experiments simulating realistic fire scenarios. During the fire resistance test, ignition time and oil temperature were recorded. Subsequent Fourier transform infrared was used to analyse the chemical bonds of the transformer insulating oils. The Fourier transform infrared results revealed that mineral oil has strong aliphatic C-H stretching bands, characteristic of a straight hydrocarbon chain and with lower thermal and oxidation stability. On the other hand, the ester’s oil has strong carbonyl C=O stretching peaks, characteristic of polar
functional groups associated with increased oxidative stability. Results showed that mineral oil and fatty acid methyl ester ignited upon thermal exposure, while natural and synthetic esters did not ignite, even at temperatures exceeding 300 °C. These findings demonstrate that natural and synthetic esters exhibit superior fire resistance compared to mineral oil and fatty acid methyl esters.