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The influence on the quality of the electrical insulating fluids on the safety in operation of the transformers has been evaluated. After processing the comparative experimental data obtained by gas chromatography technique on 5 different sorts of electrical insulating fluids (a sort of vegetable oil with high oleic content and with addition of 0.5% antioxidant "functional model" - compared with two commercial sorts of mineral oil, 1 mainly vegetable commercial oil, 1 commercial synthetic ester), thermal aged in contact with electrical insulating paper and copper for electrical use, at 110 ± 3 °C for 1000 hours in closed vessels (limited access to atmospheric oxygen) it has been found that at the transformers filled with mineral oils, the risk of explosion and fire is approx. 10 times higher than those filled with synthetic or vegetal ester. It has also been found that the ageing of the insulation paper is approx. 15 times slower in the synthetic and natural ester than in the mineral oils normally used in transformers.

The By gravimetric measurements and coupled thermal analysis techniques (DTG+TG+DTA) the aging of different sorts of insulating oil was studied by thermal cycling between -400C and 850C. The experimental results showed that, during the thermal cycling of the investigated mineral oils, their composition changes due to the volatilization of the volatile fractions (mass losses between 3.9% and 5.8%), unlike the investigated vegetable oil that showed a mass increase of approx. 0.66%. It has also been found that the mineral oils can be ensure a safe operation, without significant changes up to a maximum of 1000C, as long as investigating vegetable oil can be used without degradation risk up to 2000C.

Determining the working life of the anticorrosive protection layers is of great importance for electro-energetic installations. In order to assess the durability of the paint layers have been achieved films of 100 ÷ 120µm from six different commercial types of paint. After polymerization/drying, the dielectric characterization of the obtained films has been achieved by dielectric spectroscopy - both before and after their exposure to controlled doses of UV radiation. The experimental results have been revealed that the polymer matrix of the painting materials, over a critical dose of UV radiation (specific commercial sort), suffers a complex process of aging after which the anticorrosive insulation capacity decreases.

The widespread use of insulating oils (transformer oils) having mineral origin, because of their toxic organic substances and xenobiotic, poses a serious risk to the environment. Synthetic ester oils, although limited risk to the environment, its use is limited due to their relatively high price. This paper presents the preliminary results of the studies of the possible use of the natural ester oils of vegetable origin in the electrical equipment.

Mineral insulating oils used in electrical equipment because of their toxic organic substances and xenobiotic, represents a major risk to the environment - to accidental spills pollute soil, groundwater and surface water. By microbiological tests were evaluated the biodegradability of some insulating oils used in electrical equipment. The assays were performed in comparison with edible sunflower oil and with a control sample (culture medium - without oil). The experimental results indicate that the mineral oils are more readily biodegradable than synthetic ester oil and vegetable oils. It was also found that oils with high sulfur content are more readily biodegradable.