Antioxidant variations in the nature ester oil

The insulating liquids for power transformers are still evolving area. The current trend is to move away from currently used mineral oil because it poses a threat to the environment and use the renewable, biodegradable nature ester oils instead. These oils are now well known but what keeps them from widespread usage are unbalanced properties. In some areas these natural oils excel (fire point, sulfur content, etc.) but in others they still need improvement (dissipation factor, oxidative stability). This paper deals primarily with dielectric properties of the nature ester oil (rapeseed oil) with a focus on improvement of an oxidation stability. The emphasis is placed on a conservation of good dielectric properties for a long time thanks to the addition of an antioxidant. The experiment is based on preparation and measurement of the rapeseed oil with the different amount of several antioxidants. Evaluation of the impact of antioxidants on the dielectric properties of oils in the supplied state is performed via measurement of a breakdown voltage and a dissipation factor. The effect of antioxidant addition on the properties of oil, which is exposed to elevated temperature, is determined via a test of oxidation stability. The evaluation of this test is based on the comparison of values of the dissipation factor at the beginning and at the end of the test. The additional method for assessing of changes in the chemical structure (associated with oxidation processes) is Fourier transform infrared spectroscopy.