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Insulation
Published in Fang Zhu, Baitun Yang, Power Transformer Design Practices, 2021
Ideal transformer oil has low viscosity, a low pour point, a high flash point, excellent chemical stability to resist to oxidation, and high dielectric strength. However, there is no such oil on earth, so compromise has to be made.
RCAM Case Reliability and Maintenance Component Modeling
Published in Lina Bertling Tjernberg, Infrastructure Asset Management with Power System Applications, 2018
The transformer oil is a highly refined product from mineral crude oil and consists of hydrocarbon composition of which the most common are paraffin, naphthene, and aromatic oils. The oil serves as both cooling medium and part of the insulation system. The quality of the oil greatly affects the insulation and cooling properties of the transformer. The major causes of oil deterioration are due to moisture and oxygen coupled with heat.
Insulation, Coatings, and Adhesives in Transmission and Distribution Electrical Equipment
Published in Bella H. Chudnovsky, Electrical Power Transmission and Distribution, 2017
At high temperatures, a transformer oil ages rapidly; however, there are multiple factors that accelerate oil aging, such as moisture, copper, paint, varnish, and oxygen. There are limits for the oil temperature of transformers and bushings that are defined by the standards.
Understanding the effect of oil on phytoremediation of PCB co-contamination in transformer oil using Chromolaena odorata
Published in International Journal of Phytoremediation, 2021
Transformer oil also known as insulating oil is a highly refined mineral oil that is stable at high temperatures and usually possesses excellent electrical insulating properties. Transformer oil is mostly used in oil-filled transformers, in high voltage capacitors, fluorescent lamp ballast, as well as in some high voltage switches and circuit breakers. The function of transformer oil on these types of equipment ranges from insulation, suppression of corona and arcing, and also as a cooling liquid (Gray 2010). Properties of transformer oil in transformers require periodic testing to make sure that the basic electrical properties of the oil are intact as it is in operation. This informs the filtration and regeneration activities on transformers (Gray 2010). Therefore, once transformer oil is contaminated above its recommended value with PCB, it becomes hazardous and should be discharged. During the process of discharge, the environment becomes the recipient. PCB release to the atmosphere has been through the following means: from uncontrolled landfills and hazardous waste sites; incineration of PCB containing wastes; leakage from older electrical equipment in use and improper disposal of spills (USEPA 1997; Bremle and Larsson 1998; Sun et al. 2014).
Refuse-derived fuel for diesel engine utilizing waste transformer oil
Published in Biofuels, 2021
T. R. Preethivasani, T. Senthilkumar, M. Chandrasekar
The oil used for insulation in an electrical power transformer is commonly known as transformer oil. Fractional distillation and subsequent treatment of crude petroleum are carried out in the process of production of transformer oil. Transformer oil is employed for two reasons, for insulation and heat dissipation. Since the core and the winding of the transformer are fully immersed inside the oil, it preserves the core and also prevents the direct contact of oxygen with the paper insulation windings. Transformer oil is generally used as a coolant in welding transformers, power transformers and electromotive units. Transformer oils are of two types, namely paraffinic and naphthenic based. In India, naphthenic-based oil is employed in transformers. It contains little or no trace of wax content. Despite its high pour point, it is used in India because of the warm temperatures there. The important parameters of transformer oil are electrical, chemical and physical parameters [4]. It possesses excellent dielectric strength (minimum 30 kV) resulting in minimum power loss. If the value is less than 30 kV, this implies that unwanted moisture is present in the oil. A leakage current will flow if an insulating material is placed between grounded and live parts of electrical equipment. As insulating material is dielectric in nature, the current through the insulation ideally leads the voltage by 90°. But in reality, this is not so. The loss factor or tan delta of transformer oil is the tangent of the angle by which it is short of 90°. High resistive insulation means a good insulator. So, it is preferable to have a loss angle as small as possible. If the value of tan delta is high, this is an indication of the presence of contaminants in the transformer oil. If the resistivity of the insulating oil is less, the value of tan delta is high and vice versa. The resistivity of the insulating oil must be high at room temperature as well as at a higher temperature. For this reason, the resistivity of the transformer oil is checked at two temperatures, 90 °C and 27 °C. The minimum standard specific resistance of transformer oil at 90 °C is 35 × 1010 ohm·m and at 27 °C it is 1500 × 1010 ohm·m. It has high flash point (more than 140 °C) and thermal stability to reduce the evaporation losses. Water or the moisture content in transformer oil not only affects its dielectric properties but also affects the paper insulation of the core and the winding of the transformer, as paper is hygroscopic in nature. Under normal conditions, paper would absorb the maximum amount of water. The water becomes more soluble in oil during oxidation and acids are formed. This causes an increase in the rate of degradation of the oil. The water content is measured in ppm and the maximum allowable level of water is 50 ppm. The viscosity of transformer oil should be low so that it offers less resistance to the conventional flow of oil, thereby effecting the cooling of a transformer. It is also important to keep the increase of viscosity as low as possible. The transformer oil is virtually devoid of corrosive sulfur, enabling it to enhance stability [5].