Analyses of the electrical parameters of liquids used in high voltage technology

In the world, with the increase of the need for electrical energy, the need for power equipment such as transformer, load tap-changer, breaker, capacitor, cable and bushing is also increasing. Worldwide, several million liters of insulating liquids are used as coolant liquid, insulation between phases and impregnant of paper compositions. Having long life, not being failure and regular operation of these equipment have great importance in term of steady, reliable and economic operation of the power system. In electrical facility, various insulating oils, which have different chemicals, physical and dielectric properties used for this purpose are needed. Properties of insulating liquid used have also a significant effect on the price of the insulating liquid. Although there are many liquids for cooling and insulating, it is known that mineral oils are the most commonly used insulating oil in electrical equipment. In industrial power equipment, the reasons of preference of these oils for more than 100 years can be listened as being economical, avaliability and proven reliability. In this thesis, the parameters which affect the electrical dielectric properties of mineral oils are experimentally investigated and the results obtained are presented. For the optimal design of equipment used in high voltage, it is necessary to known how the oil parameters change in different voltage levels, electrode geometry, frequency and temperature. Therefore, in the first experimental study, the effects of electrode geometry, voltage rise rate and humidity factors on breakdown voltage has been investigated. Then, the effects of temperature, frequency and voltage changes on dielectric dissipation factor, power loss and relative permittivity of mineral oil have been analysed. Thesis study consists of six chapters. In the first chapter of the study, studies in literature and aims and objectives of the thesis are given. In second chapter, insulating liquids used in power equipment of electrical systems and dielectric properties of these liquids are given as comparative. In third chapter, concepts such as breakdown theory, dielectric dissipation factor, power loss, relative permittivity and the effect of humidity are explained. In fourth chapter, the electrical, physical and chemical tests and the standard test methods used in these tests are presented. In fifth chapter, measurement methods of the parameters obtained in the experimental studies are introduced. The last chapter, the experimental results obtained from the tests are presented and discussed. Keywords: Insulating liquids, breakdown voltage, dielectric dissipation factor, dielectric power loss, relative permittivity