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Electric field distortion caused by space charge accumulation is one of the challenges in the development of insulating liquid immersed converter transformers and battery energy storage. This paper studies the impact of temperature and moisture content on field distortion in synthetic ester through an improved computational model incorporating the time-development permittivity of insulating liquid, and the test results indicated highly accurate simulation results of electric field distribution can be produced compared with the previous model. Charge mobility and charge density in synthetic ester were extracted from frequency dielectric spectroscopy test results, which were then used to calculate field distortion by the developed computational model. Simulation results indicated that the field distortion in synthetic ester decreases with temperature due to the enhanced permittivity caused by space charge accumulation, while it increases with moisture content due to the increased charge density from the dissociation of water. [ABSTRACT FROM AUTHOR]

Polarisation current profile varies non‐linearly with a magnitude of charging voltage. This implies performance parameters obtained from polarisation–depolarisation current and those measured using specialised equipment cannot always be compared. Results reported in this study suggested that the non‐linearity in insulation response can be explained in terms of the interaction between space charge and insulation conductivity. The influence of using different charging voltages and its effect on performance parameter calculation is investigated in this study with the help of laboratory samples. It is shown in this study that with the help of a trained artificial neural network, it is possible to identify the charging voltage at which insulation response exhibits minimum non‐linearity. To test the accuracy of the proposed method performance parameters measured using commercial equipment are compared with those calculated from the polarisation current profile. [ABSTRACT FROM AUTHOR]

In this study, results of polarisation and depolarisation currents measured on an insulating liquid are presented. The goal is to contribute to a better understanding of mechanisms occurring at the metal–liquid contact. Electrodes of different metallic nature are associated with the same mineral oil, the metal/liquid/metal structure is submitted to DC voltages and the transient current is recorded with a high sensitive electrometer. The current versus time feature shows that the conduction process is in good compliance with the metal work function rather than with its electric conductivity. The current versus field characteristics indicate a predominance of the ohmic behaviour for the low fields. The space charge limited conduction regime appears as soon as the electrical constraint exceeds ∼1 MV/m, which corresponds to 10% of the breakdown voltage. Schottky injection is suspected to occur from the metal into the liquid since the applied fields are uniform and non‐extremely intensified. [ABSTRACT FROM AUTHOR]

This paper deals with flow electrification phenomenon of liquids in channels of rectangular cross section. Different theoretical models are described and compared. For all the models, it is assumed that the flow and the diffuse layer are fully developed. The space charge density conveyed by the flow is computed. First, two cases are examined in the case of weak space charge density, the exact rectangular channel solution is compared with the approximate solution of two parallel planes. This comparison shows a rather small difference between the two models. Then, in the case of two parallel planes assumption, the charge conveyed is computed without any hypothesis on the magnitude of the space charge density and compared to the solution obtained for a weak space charge density commonly assumed. This comparison shows a big difference between the two models concerning the determination of the space charge density on the wall, and, therefore, the zeta potential [1]. [ABSTRACT FROM AUTHOR]

High-voltage storage capacitors, which have composite insulations of polypropylene film and paper impregnated with oil, are working under charge-discharge mode. The insulations are not only exposed to electrical stress but also to thermal stress. Failure factors of composite insulation in capacitors are analyzed from three aspects: partial discharge (PD), space charge, and thermal factors. In order to investigate the possible influences on the dielectric properties of materials in capacitors, aging tests were conducted on the capacitors. Some parameters were detected in aged capacitors compared with nonaged ones. Experimental results reveal that PD is the key factor leading to the breakdown of the capacitor, space charge is the direct factor that induces the breakdown, and thermal factor just accelerates the degradation process. [ABSTRACT FROM AUTHOR]

Conductivity and ionization mechanisms in liquid helium have been investigated by using high field conduction phenomena occurring near a sharp needle electrode. When the voltage Vs, applied between the needle and the plane is greater than some threshold voltage Vs, a corona-like discharge regime was observed. Charge carriers are generated in the high field region close to the point where an intense light emission is detected. Above Vs the mean current is space charge limited and the mobility of charge carriers has been deduced from analysis of current-voltage characteristics. Some parameters of the corona-like region have been deduced from a spectral analysis of the light emitted during the discharge. [ABSTRACT FROM AUTHOR]

The present paper is mainly devoted to phenomena occurring in point-plane electrode geometry, where breakdown is the result of the initiation and propagation of prebreakdown phenomena called "streamers". In this configuration, an investigative study of the streamer initiation processes, requiring very high electric field strengths (~ MV/cm), and of propagation (requiring low electric field, ~ kV/cm) can easily be carried out for negative streamer development as well as for the positive case. From analysis of experimental results in pure liquids the physical processes connected with streamer initiation and propagation, particularly the electronic ones, are presented and discussed. Estimations of the main parameters of slower subsonic streamers and of the faster filamentary ones (such as field strength at the streamer tip, field inside the channel, charge density, etc.) have been obtained from qualitative considerations and compared to experimental data. [ABSTRACT FROM AUTHOR]

Colloids at water–oil interfaces can form ordered monolayers when surface charge–induced repulsion overcomes capillary attraction. Such particle monolayers play an important role in the stabilization of emulsions and also can serve as an exquisite model system to study fundamental physical phenomena. However, it is challenging to dynamically control the relative magnitudes of repulsion and attraction between the particles, especially with reversibility, to induce reversible aggregation and dispersion because forces that are relevant tend to be much greater than those induced by thermal fluctuation. Here, the authors show that reversible assembly, that is reversible aggregation and dispersion, can be induced by space charge injection from corona discharge. The authors find that space charge injection modulates the strength of charge‐induced repulsion. By injecting charges, it is possible to either induce aggregation of repulsion‐dominated colloids or dispersion of aggregated particles. Interfacial electrophoretic experiments show that the alteration of the repulsion is caused by the variation of the particle surface charge that results from charge injection. The authors also demonstrate that even particles that initially form aggregated clusters due to low surface charge can be induced to organize into a hexagonally ordered structure. This method can be a powerful tool for studying phenomena involving interface‐trapped particles. Charged colloids at polar–nonpolar liquid interfaces form ordered monolayer structures, which can serve as an exquisite model to study fundamental phenomena in condensed matter physics. Here, space charge injection from corona discharge is used to induce reversible aggregation and dispersion of particles at an oil–water interface by tuning the relative magnitude of attraction and repulsion between particles. [ABSTRACT FROM AUTHOR]

Two electrically insulating fuels of mineral and biological origins have been tested for electrostatic charging in single and multiple blade-plane configurations. The aim is to investigate methods to dramatically increase the total injected current, with a view to developing an atomization system where the charge injection and atomization units are separate. In this study, the fuel is quiescent and only the injected current is measured. Current flux - electrode surface electric field (J-E) characteristics at different bladeelectrode gaps are presented. A current density of 6.5 A/m2 is obtained at a surface electric field of 100 MV/m using the 1-blade configuration. From the measured data, the relation between the blade-electrode gap (d) and the injected current flux is found as Jα d-m at constant voltage, where m is found to be 2 for flat charge collectors and as high as 4 for rounded collectors. The physics of the swirl motion caused by the Coulomb forces are discussed. The size of this induced flow is correlated to the performance of the multiple blade design. Charge injection, dielectric liquids, electrostatic charging, induced flow, multi-blade injector [ABSTRACT FROM AUTHOR]

A charge injection atomizer functions by introducing electric charge discharged from a high voltage electrode into a dielectric liquid, which subsequently atomizes the ejected liquid jet. Atomizer evolution thus far has proceeded through trial and error analysis of the experimentally measured electrical characteristics of the atomizer and of the quality of atomization. Within the atomizer, a coupled space charge and electric field exist, which can alter the internal flow pattern, thus creating electrohydrodynamic (EHD) instabilities that affect atomizer operation. Such a system has not been simulated in the past under forced flow conditions. In this work we simulate the internal flow of such a charge injection device in two dimensions; using experimental based boundary conditions. Initial results indicate that in the linear injection regime defined by the experimental data, the flow is only slightly unstable but in the transitional and highly non-linear regimes, the coupled space charge and electric field produce more instability in the liquid that must be investigated further. [ABSTRACT FROM AUTHOR]