An experimental study on spectroscopic analysis of alternating liquid dielectrics for transformer

Conventionally, mineral oil impregnated with solid insulating materials has been used as an insulating medium in the transformers. On the other hand, mineral oil is less biodegradable than ester oils and it has poor fire-resistant characteristics. Therefore, the conventionally used mineral oils are not satisfying the new ecological requirements. Besides that the availability of fossil fuels is also going to run out. Consequently, several investigators have tried with different kinds of edible as well as non-edible oils for using them as liquid dielectrics in the transformers. This paper attempts to prove the feasibility of Pongamia pinnata oil (PPO) as an alternate liquid dielectric for transformer. At first, solid insulating material’s deterioration study was carried out using DGA, SEM, XRD and UV–Vis spectroscopy. Alongside, thermal stability of PPO and mineral oil was analyzed through FTIR spectroscopy. DGA results show that gas-generating phenomenon was found on both the oil samples. However, the generation of combustible gas in PPO impregnated with solid insulating material is found to be lower when compared with other oils. From the FTIR analysis, it is found that the structural difference between PPO and mineral oil is negligible. However, from XRD and UV–Vis spectroscopy, it is evident that depending on the type of material, the thus emitted spectra have different bandwidth and there is variation in the absorbance intensity. When the contamination rate is higher, the absorbance intensity of the insulating oil increased. SEM analysis shows that cellulose fiber’s width has drastically decreased in case of the solid insulation material immersed in mineral oil; also, there is evidence for bond breaking.