Studies on the ageing behavior of various synthetic and natural insulation oils

Dodecylbenzene (DDB) is now widely used in UK underground high voltage cables due to its biodegradability and improved gas absorbing properties. However, the potential of vegetable oils as high voltage insulation liquids has yet to be fully realized. These liquids could be used as direct replacements where traditional synthetic oils are currently used. In this paper we report on the ageing behavior of dodecylbenzene, mineral oil and a range of different vegetable oils. These were thermally aged under an oxidizing atmosphere and their ageing behavior was then characterized by ultra-violet/visible, infrared and dielectric spectroscopy techniques. Measurements of viscosity were also undertaken to supplement the spectroscopic data.

I. Introduction

Increasing awareness of the environment and the need to limit the impact of human activity gives a clear impetus to replace conventional insulating oils in high voltage plant with environmentally friendly alternatives. In addition, oil leakage from equipment is a serious concern, both in terms of the clear up operation and equipment replacement costs.