Investigation of AC breakdown strength and frequency varied dielectric response of the non-conventional vegetable oil

Abstract

Vegetable oil (VO) based liquid dielectric are gradually being implemented to improve the heat transfer in electrical appliances to enhance their life and improve efficiency. The conventional VO based insulating oil is being moderately researched to improve the understanding of the physical mechanisms involved in their enhanced performance compared to the existing mineral oil (MO) based transformer oil (TO). Despite of all the superior thermophysical and electrical performance of the conventional VO reported in few studies in the context of TO, its vast consumption as edible purpose may limit its application as liquid insulation. Therefore, in this study, a non-conventional VO such as pongamia oil methyl ester (POME) is chosen to be a liquid insulation for transformer. In this paper, the investigation is carried out to evaluate the AC breakdown voltage (ACBDV) of the POME and also the dielectric responses of POME at varying frequency is analyzed at transient condition. POME is extracted from the pongamia crude oil by two step transesterification process followed by refined bleached and deodorization. To understand the comparative enhancement in dielectric integrity, ACBDV analysis of MO and POME is carried out at a line frequency of 50 Hz as per ASTM 1816. The dielectric response such as AC resistivity and relative permittivity of the POME is studied from 50 Hz to 10 MHz. It is observed from the study that the mean BDV of the POME is superior than the MO. Moreover, to detect the probability of failure in ACBDV at different percentage such as 5, 10, 50 and 63.2%, Weibull statistical analysis of the ACBDV is carried for POME and MO. With the rise of frequency from 50 Hz to 10 MHz, the AC resistivity is observed to degrade for both the insulating oils. However, at higher frequency, the resistivity of the POME is not significantly altered and hence making the POME stable in dielectric response at higher frequencies. From the above study, the non-conventional VO and its suitable application in transformer as insulating liquid is a possible option for an efficient insulation.