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Liquid Dielectrics
Published in N. H. Malik, A. A. Al-Arainy, M. I. Qureshi, Electrical Insulation in Power Systems, 2018
N. H. Malik, A. A. Al-Arainy, M. I. Qureshi
Insulating oils can be broadly divided into two categories: organic and inorganic. The most commonly used organic liquid dielectrics for electrical power equipment are mineral oils. Beside the naturally occurring oils, a variety of synthetic organic insulating liquids are also available in the market. Most common of these are silicone oils and chlorodiphenyles. Recently some new synthetic organic oils such as high molecular weight hydrocarbons and tetrachloroethylene have also been introduced. They possess excellent dielectric and thermal properties but are expensive. Among inorganic insulating liquids, highly purified water and its aqueous solution are being used for pulsed power applications, such as capacitors and modulators. At present, water-filled discharge lines for pulsed power are under intensive investigation and development [1]. Similarly, liquefied insulating gases are commonly employed for cryogenic applications. A brief description of most commonly used insulating liquids is given below.
Dielectrics and Dielectric Loss
Published in John Bird, Newnes Engineering Science Pocket Book, 2012
Liquid dielectrics used for insulation purposes include refined mineral oils, silicone fluids and synthetic oils such as chlorinated diphenyl. The principal uses of liquid dielectrics are as a filling and cooling medium for transformers, capacitors and rheostats, as an insulating and arc-quenching medium in switchgear such as circuit breakers, and as an impregnant of absorbent insulations for example, wood, slate, paper and pressboard, used mainly in transformers, switchgear, capacitors and cables.
Critical review on the impact of EDM process on biomedical materials
Published in Materials and Manufacturing Processes, 2021
In the EDM process, the dielectric medium contributes an important role in plasma channel dispersion, material erosion, and flushing of debris. In wet EDM, hydrocarbon oil, deionized water, and single-phase liquid dielectric mediums are used .[160] For example, hydrocarbon oil (such as kerosene and mineral oils) can be used as a dielectric medium because they possess high aging corrosion resistance properties gives low surface finish along with a high tool wear rate, and also hazardous to the environment. Therefore, many researchers focus their work to reduce the limitations of wet EDM. Whereas in dry EDM, instead of liquid medium, gas can be used. Mostly, air or oxygen is used. By using a dry medium, the tool wear rate is reduced. But the limitation of dry EDM is low MRR with the low surface finish which is caused due to reattachment of debris with the base material .[161,162] Some researchers studied two-phase (liquid-gas) and three-phase (liquid-gas-solid) powder mixed dry-EDM to improve machining performance .[163] As the discharge energy of plasma is established by the electro-thermal conductivity of the dielectric medium which is determined as Eqn (3):
Performance Analysis of Alternative Solid Dielectrics of Power Transformers with a Blend of Mineral and Silicon Oils
Published in IETE Technical Review, 2018
Chilaka Ranga, Ashwani Kumar Chandel, Rajeevan Chandel
Liquid dielectrics inside the transformers are used for cooling and insulation [25]. During the past ten decades, mineral oil has been used in liquid-immersed transformers. Though the cost of mineral oil is reasonably satisfied, it has limited fire resistance [26]. Also, it is dependent on petroleum sources which pollute the soil in case of leakages. Such shortcomings of mineral oil have motivated the researchers to look for alternative liquid dielectrics [8]. In contrast, silicone oils, natural and synthetic esters can overcome few of the shortcomings of mineral oils [12]. Thus, the application of these alternative oils in transformers is becoming more popular amongst the utilities. The performance of silicone oils and synthetic esters in conjunction with Kraft and TUK has been studied by a few researchers [27]. However, the majority of the studies have been focused in the thermal evaluation of some commercial natural esters such as coconut, palm, and rapeseed [9]. Some authors have compared the main properties of these new fluids with mineral oil in order to evaluate their suitability [21]. More recently, many investigations have been carried out on a blend of vegetable and mineral transformer oils [27]. These studies found that the operating characteristics of a mix of liquid dielectrics are better than those of mineral transformer oil. Also, the operation of transformers having such mixed insulations is more economical [26]. Therefore, there is still a need to do much detailed thermal ageing study of the new dielectric materials and a blend of liquid dielectrics. This has been the main motivation of the present work. Detailed comparative study on the performance of mineral and a blend of mineral and silicon oils in conjunction with alternative solid dielectrics of transformers has been accomplished under accelerated ageing tests in the present work.