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The electro thermal convection in a plane layer of dielectric liquid subjected to simultaneous action of electric field and thermal gradient is studied. The influence of the dielectric forces on the convective flow is analyzed in the case of a weak charge injection. The set of equations associated with the thermo-electro convective phenomena is solved directly using a finite volume method. The results...
PD measurements in dielectric liquids have been normally performed in the past only using conventional narrow bandwidth detectors. The more recent use of ultra-wide bandwidth instruments has permitted to support once again the thesis that the PDs in oils are the consequence of the streamer (vapor phase) formation and its development. In the paper simultaneous PD measurements in insulating liquids...
A test procedure is proposed for the measurement of the partial discharge inception voltage (PDIV) in dielectric liquids. The antecedent IEC point-to-sphere test cell arrangement is replaced with that of a point-to-plane. A dual ultrawide-narrow bandwidth PD detection system is employed, which permits to distinguish the PD pulse-burst discharges that occur in liquid dielectrics from the normal PD...
The paper presents the application of the Cole-Cole model for determining the runs of the return voltage of the paper-oil insulation sample through a computer simulation. Different insulation conditions were simulated through an adequate selection of parameters alpha and tau of the Cole-Cole model. For calculation purposes, a series-parallel substitute scheme, obtained through approximation of a discrete...
We investigate the time evolution of finite amplitude electroconvection. A scaling analysis shows that both for weak and strong injection the most adequate time scale for describing the time evolution of the system is the viscous time, as the viscosity controls the evolution of the velocity field. In this work we present the numerical transients for the case of strong injection.
We investigated the processes of charge structures formation and the current propagation in a plane capacitor with low-conducting polar liquid under the steady or modulated electric field. The ternary ionic system is considered in dielectric medium. The first type of positive ions appear on the anode due to surface electrochemical ionization. Unipolar injection from the anode appears if the field...
We observed the infrared emission spectrum of Xe2 excimers produced by bombarding pure Xe gas and a Ar-Xe mixture with 70 keV electrons. The spectrum is a continuum centered around 7800 cm-1 of width 900 cm-1. A Franck-Condon analysis of its shape at low pressure (P=0.1 MPa) has allowed to infer that the emission is due to a bound-free transition between 0u+ and 0g+ molecular states correlated with...
Fluid flow generated by ac signals in a point-plane microsytem is studied. KCl aqueous solutions are used and fluid flow is observed for frequencies ranging from 100 Hz up to 1 MHz or 20 MHz depending on the electrolyte conductivity. Possible mechanisms for the explanation of the observed fluid flow are exposed.
In this contribution, Fourier transform of dielectric responses from Polarization and Depolarization Current measurements were investigated to evaluate temperature and aging effects on dielectric response of oil paper insulation system. Measurements of the dielectric response were performed at three temperatures and two aging conditions. To provide quantitative analysis from measurements, the current...
This paper discuss the relations between laboratory studies of breakdown precursors in liquids (usually called "streamers"), and practical applications such as high voltage insulation of power transformers and testing of liquids. The conditions existing within high voltage power transformers (ac voltage, moderately divergent electric field, presence of insulating solids, particles in the...
The behavior of the breakdown probability in distilled water was studied so far using short pulse 1.06 mum and 0.532 mum lasers. Results obtained were analyzed by a equation which was used in avalanche breakdown in gases and semiconductors under DC voltage application. This equation can not explain the electron mean free path dependence of the breakdown probability under optical field application...
The paper presents research results on ECT (electrostatic charge tendency) of cyclohexane and hexane mixtures, that is dielectric liquids of a simple chemical structure and high purity (pro analysi). The research tests are carried out in a spinning disk system, where the factors affecting the value of the electrification current registered are a varying composition of the mixture and the rotational...
Acoustic emission measurement results of acoustically induced cavitation bubbles in insulating oil are presented in this paper. Spectral analysis of acquired by a broadband transducer acoustic emission signals is proposed as a diagnostic tool for estimation of aging properties of mineral insulating oils. The article describes the main parts of the designed and built measurement apparatus used for...
Study of processes connected with formation of cluster ions with water molecules is of interest due to the fact that such ions can be produced by ionization of nonpolar dielectric liquids in conditions when the liquid has a contact with water or a humid air. In this work, results of investigations of the processes leading to the formation of the negative ion clusters A-(H2O)n are presented. Three...
This paper studies the feasibility of applying the electro-optical Pockels technique to measure surface discharge at a solid-liquid insulation interface. The principle of the method is based on the Pockels characteristic of the bismuth silicon oxide (BSO) sensing crystal. The presence of surface charge induces an electric field across the crystal which in turn linearly changes the polarisation state...
Dodecylbenzene (DDB) is now widely used in UK underground high voltage cables due to its biodegradability and improved gas absorbing properties. However, the potential of vegetable oils as high voltage insulation liquids has yet to be fully realized. These liquids could be used as direct replacements where traditional synthetic oils are currently used. In this paper we report on the ageing behavior...
The materials used as the dielectric media of choice in large transformers continue to be a combination of pressboard and mineral oil. These materials offer a cost effective solution and are backed by a historical knowledge base of performance data and lifetime characteristics. A proven method to prevent inter-phase flashover is to use successive layers of pressboard and oil gaps. However, a number...
In this study, investigation of the insulation performances of the silicone oil as an insulating medium is studied with aim of realization of environmental friendly electric power apparatus, which is considered to be flame retardant. This investigation is searching for the streaming electrification characteristics when silicone oil flows in consideration of cooling of electric power apparatus. In...
We have been discussing the partial discharge (PD) inception characteristics of liquid nitrogen (LN2) / polypropylene (PP) laminated paper composite insulation system for high temperature superconducting (HTS) cables. Based on the volume effect on PD inception electric field strength (PDIE) with a parameter called SSLV (statistical stressed liquid volume), in this paper, we evaluated PDIE of a full-scale...
In this paper, we present the electrical and physic-chemical behaviours of oil in high voltage transformers, under thermal ageing. Continuous thermal ageing tests were made on transformer oil BORAK22 during 5000 hours at two different temperatures 80degC and 120degC. Here, every 500 hours, the dielectric losses factor, the relative permittivity and the resistivity were measured. Other properties such...
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