Influence of thermal ageing and electrical discharges on uninhibited olive oil properties

Abstract

International audienceIn recent years, significant attention has been paid to biodegradable vegetable oils as an alternative to mineral insulating oils. This study presents the influence of electrical discharges and thermal stress on the variation of the properties of uninhibited olive oil. This latter constitutes a serious environmentally friendly and renewable substitute for currently used mineral oils. The investigated properties are: dielectric loss factor and permittivity, resistivity, acid number, cinematic viscosity, water content, breakdown voltage, flash point and colour index. To analyse the effect of thermal stress, the uninhibited olive oil was aged in sealed bottles at 110°C for durations up to 716 h. As concerns the electrical stress, series of 200 up to 1600 low energy discharges are applied under 50 Hz alternating divergent electric field. Frequency domain spectroscopy has also been performed in order to assess the oil behaviour in a large frequency range (20 Hz-1 MHz). The real part of the complex dielectric permittivity of oil tends to increase with ageing. The obtained results show an acceptable stability with regard to thermal ageing and even an improvement of the oil key properties when submitted to discharges of controlled low energy level

Studies of different types of insulating oils and their mixtures as an alternative to mineral oil for cooling power transformers

“…The presence of water content and oxygen in the insulating oils at high temperature causes its oxidation, which leads to its ageing and consequently to the degradation of the characteristics of this liquid [7, 11]. The influence of the degree of the insulating oil ageing on the phenomenon of initiation and development of electro convection and especially on the variation of the breakdown voltage of the insulating liquid attracts the attention of several researchers [2, 7, 9, 11, 15].…”

“…For decades and precisely with the beginning of energy evolution, insulating liquids have been used for the insulation and cooling of electrical devices such as transformers, cables, switches and capacitors. Naphthenic mineral oil has long been the most preferred insulating liquid for power transformer insulation because it has a good pouring point at low temperatures, good thermal cooling capacity, low cost, high efficiency and availability on the transformers market [1, 2, 3, 7]. Despite the previously cited advantages, the disadvantages of naphthenic mineral oil, such as its high fire risk and low biodegradability potential in addition to its scarcity in the future because the oil resources will run out, have made it necessary to look for another ecological insulating liquid which has a high solubility in water and an excellent biodegradability [4, 13].…”

“…Despite the previously cited advantages, the disadvantages of naphthenic mineral oil, such as its high fire risk and low biodegradability potential in addition to its scarcity in the future because the oil resources will run out, have made it necessary to look for another ecological insulating liquid which has a high solubility in water and an excellent biodegradability [4, 13]. In order to find an alternative insulating liquid to the mineral oil used for the insulation and cooling of transformers, many studies have been carried out by several university research centers and by the manufacturers and users of power transformers [5, 6, 7, 16]. These studies deal mainly with the physicochemical properties of natural esters as ecological and low-flammable esters [8, 21].…”

Dissolved gas analysis differences between natural esters and mineral oils used in power transformers: a review

“…Data on the physical, chemical and electrical behaviour of natural esters compared to mineral oils have been analysed in numerous works [35–39]. However, the gas generation behaviour is still under study.…”

Performance studies on dielectric and physical properties of eco‐friendly based natural ester oils using semi‐conductive nanocomposites for power transformer application

“…The complement of an angle between voltage and current vectors is called the dielectric loss of angle δ or dielectric loss angle [26,27]. Dielectric permittivity is the measure of the capacity of the capacitor filled with a dielectric (C) to the capacitance of the capacitor filled with air (C 0 ), ɛ r = C/C 0 and real part of complex permittivity provides the dielectric constant and imaginary part be the loss tangent [7,15,28,29].…”