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While dielectric spectroscopy is useful in understanding weak molecular interactions such as hydrogen bonds in biological systems, the large number of interactions and the mean field data obtained lead to ambiguities in interpretation of the results. The study of weak interactions in small molecule prototypes is one way to reduce this problem. The fact that weak molecular interactions are short-ranged,...
The system of electrohydrodynamic equations at a pre-breakdown liquid insulator is given. The influence of electric field on the partial dissociation molecules rate is taken into account. The stationary and nonstationary solutions for electric potential and hydrodynamic velocity distributions are obtained. The theoretical results are compared with experiments.
The phenomenon of fault gas generation out of insulating fluids at moderate temperatures, based solely on their constituent and not related to an equipment failure is described with the term “straygassing”. Straygassing is not a new phenomenon, but it seems to be stronger manifisted with modern mineral oils. Especially the use of some additives, mainly passivators may accelerate strongly the straygassing...
This paper presents the results of computer simulation of EHD flows in a symmetric wire-wire electrode system at different values of low-voltage conductivity. The simulation used the finite element method on the basis of the Poisson, the Navier-Stokes, and the Nernst-Planck equations. The level of the low-voltage conductivity was found not only to affect the electrical current, but also to change...
Determination of the thermal endurance of transformer oil Nynas Lyra X was studied. The oil was exposed to thermal treatment at temperatures of 110, 120 and 130 °C for times ranging from 100 to 2400 hours. New methods for determination of material's thermal endurance were searched. Attention was drawn to the group of structural analyses from which two methods were selected: Fourier transform infrared...
Mineral oils, which are currently used as electrical insulation liquids, have due their uneasy biodegradability significantly negative impact on ecology and human health. Thus it is necessary to search for new possible liquids based on vegetable oils or natural esters, which might substitute crude oil products in practical applications. These liquids are easy biodegradable while economically acceptable...
Frequency Domain Spectroscopy (FDS) is successfully being used to assess the insulation condition of oil filled power transformers. However, it has to date only been implemented on de-energized transformers, which requires the transformers to be shut down for an extended period which can result in significant costs. To solve this issue, a method of implementing FDS under energized condition is proposed...
Two different kinds of attempts were made to measure ion mobilities in EHD liquids by using the time-of-flight technique. The first attempt was a reverse polarity method which was similar to that used by L. Yang et al. [5]. The stainless steel coaxial cylindrical electrodes with the effective length of 55 mm and the electrode spacing of 1.5 mm were utilized. The purified two sample liquids; hydrofluoroether...
The influence of the electric field on surface waves in diesel oil is studied experimentally. The experimental device is mainly composed of a tank filled with diesel oil and two parallel metallic electrodes: one of them is immersed in the liquid and brought to a high potential, the other one is placed above the liquid. The surface waves are generated by a vibrator for which the frequency and amplitude...
This work reports on an experimental study of the improvement of the viscosity and cold flow behavior of natural ester liquids without compromising on the excellent fire safety (> 300°C). Material variations in the form of a change in the molecular structure of the natural ester oil and as blends of a natural ester liquid with two different compounds are investigated. The impact of the molecular...
This paper deals with the characteristics of partial discharge in oil/pressboard composite insulation system, which is adopted in oil-immersed power transformer. In the insulating structure of the transformer, large oil gaps are often subdivided by pressboard barriers into small ones. Once partial discharge occurs at the point where the electric field is enhanced and progresses, the electric field...
It is crucial for reasonable transformer insulation design to understand the characteristics of discharge progress under the application of a standard lightning impulse voltage. This paper deals with the fundamental discharge characteristics of oil/pressboard (PB) composite insulation system. We obtained discharge images using a digital camera equipped with an image intensifier. In this research,...
Refinery processing determines the chemistry of the base oils used in transformer oils. Increasing the severity of the processing leads to a more stable base oil. Performance additives can modify the chemistry of the system and potentially lead to unintended consequences. This study examines how processing differences and additives affect the generation of stray gasses at low temperatures.
Silicone oils are possible replacements for mineral oils in transformers. Many investigations on their electrical and thermo-physical properties have been carried out. Few reports on the measurements of the mobilities of positive and negative ions in these liquids exist in the literature. The present contribution summarizes data published and discusses the modes of charge transport in these liquids.
The insulation properties of aged transformer oil-based TiO2 nanofluids were investigated in this paper. Firstly, both pure oil and TiO2 nanofluids were accelerated thermal aged at 130 °C for 36 days. During the accelerated thermal aging process AC (50Hz) breakdown voltage, lightening impulse breakdown voltage, and partial discharge inception voltage (PDIV) of both samples were measured periodically...
The electrohydroyanmic (EHD) plume induced by charge injection from a hyperbolic blade into a dielectric liquid was considered to actively enhance heat transfer. We numerically studied an upward-facing hot plate with constant temperature cooled by an impinging ionic jet that results from a strong and autonomous injection. It is shown that the heat transfer rate expressed with the local and averaged...
We performed a numerical study of two-dimensional electroconvection in a dielectric liquid contained between two concentric circular cylinders with the radius ratio of 0.5. The convection is induced by unipolar injection from the inner or outer cylinder. Both the weak and strong injection regimes were considered. We determined the linear stability criterion from direct numerical results and compared...
Poly(2-methoxy, 5-(4-decyloxy-biphenyl-4′-(1, 10-dioxydecane))-p-phenylenevinylene), MDBD-PPV, wih a long side chain containing alkoxybiphenyl mesogenic unit has been synthesized and its electrical and optical properties have been investigated. This polymer showed a microscopic texture typical to the liquid-crystalline phase and a sharp X-ray diffraction peak due to the smectic layer structure. The...
We systematically investigated and discussed the ac breakdown (BD) characteristics and mechanisms of liquid nitrogen (LN2) for different pressures (0.1–0.3 MPa) and temperatures (65–77 K) under quasi-uniform electric field (field utilization factor ζ = 0.986-0.674). The BD strength (EB) in sub-cooled LN2 (SLN2) was analyzed and discussed in terms of size effect, taking account of the stressed liquid...
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