Effect of moisture on breakdown voltage and structure of palm based insulation oils

For use as insulating liquids in power transformers, palm based oils are gaining worldwide attention as biodegradable alternatives and competitors to the petroleum based oils. However, moisture ingress into insulation oils and its effect on the oil breakdown voltage (BDV) must be studied because moisture in oil can alter the physicochemical property of oil and drastically affects the breakdown voltage. This paper presents a comparative study on effect of increasing moisture content on physical structure and BDV of three palm based insulation oils (Red Palm Oil, Refined Bleached Deodorized Palm Oil (RBDPO) and Palm Fatty Acid Ester (PFAE)) at room temperature. Insulation oil is known to have the ability to sustain its good performance up to certain percentage moisture increase. In this paper, an empirical relationship between the palm based oil BDV and the percentage moisture added was developed to approximate oil BDV at various moisture increases. Fourier Transform Infrared (FTIR) Spectroscopy was employed to investigate changes in the oil samples' functional group to assess the physical changes. This equation has been tested and verified. This equation can be used to estimate the BDV of the palm based insulation oils as their percentage moisture increases.

1 Introduction

BIODEGRADABLE insulating oils made from vegetable oils are gaining wide usage in power transformers because when compared to the commonly used petroleum based mineral oils, they are environmentally safer, healthier and found to have better dielectric properties like breakdown voltage [1] [2]. In addition, these vegetable oils absorb much more moisture compared to mineral oils [3] [4]. However, vegetable oil's high concentration of unsaturated fatty acid makes them unstable and prone to oxidation [5]. Although the fatty acid composition in vegetable oils varies according to the base stock, they all are mainly composed of triacylglycerols (glycerol esterified by three fatty acids). These fatty acid hydrocarbon chains and their degree of unsaturation influence the dielectric and physiochemical properties of the vegetable oils.