Abstract
In November 2017, the first ±1100 kV high-voltage direct-current power transformer in the world, which was made by Siemens in Nurnberg, passed its type test. Meanwhile, in early 2017, a ±1000 kV ultra-high voltage (UHV) substation was officially put into operation in Tianjin, China. These examples illustrate that the era of UHV power transmission is coming. With the rapid increase in power transmission voltage, the performance requirements for the insulation of power transformers are getting higher and higher. The traditional mineral oils used inside power transformers as insulating and cooling agents are thus facing a serious challenge to meet these requirements. In this review, the basic properties of traditional mineral insulating oil are first introduced. Then, the variation of electrical properties such as breakdown strength, permittivity, and conductivity during transformer operation and aging is summarized. Next, the modification of mineral insulating oil is investigated with a focus on the influence of nanoparticles on the electrical properties of nano-modified insulating oil. Recent studies on the performance of mineral oil at molecular and atomic levels by molecular dynamics simulations are then described. Finally, future research hotspots and notable research topics are discussed.
Highlights
Insulating oil is widely used as an insulating medium in oil-immersed transformers, allowing the safe and reliable transmission of electrical energy
The increase electrical conductivity of mineral insulatinginsulating oil over time mainly caused acid, the increasing contentofofthe aging products dissolved in the mineral oil,issuch as water, by thecompounds, increasing content of aging aging products dissolved small in the particles, mineral insulating oil, such as water, and furan during
The breakdown voltage was up to 8 kV higher than that of the unmodified mineral insulating oil. These results show that the dielectric breakdown voltage and partial discharge inception voltage of. These results show that the dielectric breakdown voltage and partial discharge inception voltage of mineral insulating oil can be effectively improved by modification with nano-TiO2
Summary
Insulating oil is widely used as an insulating medium in oil-immersed transformers, allowing the safe and reliable transmission of electrical energy. With the development of science and technology, more and more types of transformer oil have been developed, but mineral insulating oil is still used widely because of its low cost, good insulating properties, low condensation point, and low viscosity. The two main components are alkanes and cycloalkanes [4], and the only difference between crude oils is the proportion of each component. The specific charts showing the classification and an introduction about different types of insulating oils can be found in reference [2]. Energies 2018, 11, 487specific charts showing the classification and an introduction about different types of insulating oils can be found in reference [2]
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