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This paper aims to analyse the behavior of dc corona discharge in wire-to-plane electrostatic precipitators (ESP) depending on the pressure. Current-voltage curves are analyzed particularly. Experimental results show that discharge current is strongly affected by the pressure for a given atmospheric condition. Changing the values pressure does not only changes the property of the gas but also affects the corona onset conditions and ion mobility. The finite-element method is used to solve Poisson?s equation and a modified method of characteristics is used to satisfy the current continuity condition. The two methods are repeated iteratively to obtain a selfconsistent solution of the describing equations. We used the model which separates the corona in two distinct regions. Comparing the computed results with previously obtained experimental and calculated values tests the effectiveness of this approach. The agreement with experimental results is found to be satisfactory. [ABSTRACT FROM AUTHOR]

As natural contamination of insulators may lead to flashover, its determining factors should be studied to prevent the occurrence of pollution flashover. In this paper, the fluid mechanics models of insulators with typical shed types were established to simulate their flow field distribution and particle collision coefficient (P). At the same time, a natural contamination test lasting for 8 months was carried out in order to contrast the experimental data and simulation results. The research results have shown that: wind velocity and shed type affect the flow field near the insulators; P is affected by particle diameter and wind velocity; under certain particle diameter and wind velocity, P reaches the maximum value; rainfall has different effects on contamination of insulators with different shed types; wind causes non-uniformly distribution of pollution on the surfaces; the simulation test and the experimental test are comparable. The research method and results can provide not only reference to establishing natural contaminating model but also significant meaning for the external insulation design and selection. [ABSTRACT FROM PUBLISHER]

In this paper, a proposed electro-thermal model of cable terminations is presented. The cable terminations under study are exposed to a square-pulse voltage applied at different switching frequencies. The purpose of the model is to predict the temperature distribution inside the cable termination as a means of determining the location and value of the maximum temperature. The model is based on fundamental heat transfer mechanisms: conduction, convection, and radiation. Two different distribution classes of cable terminations have been examined. A comparison of the simulated temperature rises with actual measurements reveals good agreement. [ABSTRACT FROM AUTHOR]

Charge accumulation on a solid insulator surface is one of the critical factors for the development of dc gas-insulated equipment since it will lead to the overstress of polymeric insulation due to local field distortion and enhancement. Therefore, it is important to study the charge accumulation phenomenon on spacer surface under dc field. For decades, researchers have made tremendous progress on this subject by measurement and simulation. However, measurement results are quite different by different researchers due to various electrode configurations and experimental conditions. Further, most researchers use potential to represent charge density, which is not rigorous in that many charge density distribution details are hidden behind the potential. As for pure numerical simulation, reports are rather academic and sometimes cannot accord with the real fact. In this paper, attempts are made to characterize the charge accumulation patterns on spacer surface in HVDC gas-insulated system. Surface charge distributions on a model GIL spacer in 0.1 MPa air under DC voltage are obtained by an advanced measurement method, from which the dominant uniform charging pattern and random charge speckles are separated. Mechanism responsible for the dominant uniform charging pattern is discussed with the aid of a simulation model. Results indicate that, in a well-cleaned system, the electric current through the spacer bulk is the principal factor, but gas conduction is not negligible due to some inevitable ion sources. Highly localized pockets of charge are also observed, which are referred to as speckles. They may originate from micro discharges due to tiny metal particles on the spacer surface or microscopic protrusions on the electrodes. [ABSTRACT FROM PUBLISHER]

Analysis of breakdown mechanism in gas-insulated trigatron switches is important for the engineering design and function prediction. Based on the gas discharge theory, a physical model was proposed to estimate the breakdown time for gas-insulated trigatron switches. And the model can explain the breakdown in the trigatron switches with two modes of the breakdown mechanism, i.e., fast breakdown mode (FBM) and slow-breakdown mode (SBM). Based on Raether breakdown criterion, this paper discussed the factors affecting on the E-field enhancement. The E-field is composed of the static E-field and the dynamic E-field, which leads to transformation of breakdown mechanism. Some coefficients could be determined by experiment and simulation, which are helpful to get the quantitative solution of breakdown time. [ABSTRACT FROM AUTHOR]

A two-dimensional (2D) self-consistent fluid simulation of dual frequency capacitively coupled radio discharges of helium plasma is presented. The model solves the continuity equations for charged species and the electron energy balance equation, coupled with Poisson's equation by finite element method, using COMSOL Multiphysics software. In this study, the low frequency (LF) is set to 13.56 MHz with low frequency voltage of 250 V and the high frequency (HF) is set to 54.24 MHz with high frequency voltage of 100 V. The simulations yield the two-dimensional profiles of plasma components as well as the charge densities, electric field, electron temperature and ionization rate between symmetric parallel plate electrodes. The effects of low and high frequency sources parameters such as frequency values and applied voltage amplitude on the discharge characteristics are investigated. It is shown that the increase of the HF frequency causes a moderate increase of electron temperature and plasma density, whereas, the increase of the LF potential produced an increase in the plasma potential, the voltage of the sheath and the ion energy. [ABSTRACT FROM AUTHOR]

Though there is no exact analytic solution for the capacitance between two cylinders near a dielectric interface, the method of images is used to derive analytic expressions that are accurate for widely separated cylinders, cylinders in close proximity, and widely separated cylinders near a dielectric interface. These solutions are compared with numerical simulations to verify the utility of the derived expressions. The necessity for numerical simulation in the general case is demonstrated. These analytic solutions can be incorporated into self-capacitance terms for solenoids and transmission lines. [ABSTRACT FROM AUTHOR]

A nonlinear lumped element transmission line (NLETL) that consists of a nonlinear LC ladder network whose capacitors are nonlinear and inductors are linear can be used to produce oscillating pulses. This article describes the implementation of an oscillating pulse generator based on such high voltage nonlinear capacitive lines (NLCL) using commercial-off-the-shelf (COTS) components. Instead of using complex pulse forming networks or pulse forming lines, a storage capacitor and a fast semiconductor switch are used to provide an input pulse onto the cascading LC-elements of the NLCL with good approximation of a rectangular pulse-shape. The design of the NLCL is based on the NLETL circuit model that was developed earlier in-house. Experimental results are compared with simulations predicted by this NLETL model. The voltage modulation and the frequency content of the output pulses are analyzed. The conventional single NLCL produces a signal with a DC offset and a decoupling capacitor is needed at the end of the line to extract the AC component before injecting onto a load such as an antenna. A novel method of directly extracting the AC component without the use of a decoupling capacitor is proposed and investigated. Results of this direct AC extraction, which show the possibility of better performance, are discussed. The frequency tunability of this nonlinear line was also demonstrated. [ABSTRACT FROM AUTHOR]

Nowadays, computer simulation of processes during current interruption is widely used in design optimization of HV circuit breakers. A simplified physical enthalpy flow arc models provide possibility to get relatively simple, and easy to use, simulation software for HV SF6 circuit breakers. Such software has been developed and successfully used in development of various SF6 circuit breakers, based on classical puffer and puffer assisted self-compensated principle. General outline of the computer program, as well as some simulation results and their experimental verification obtained on a real 245 kV SF6 circuit breaker, are presented. The interrupter is based on puffer assisted selfcompensated principle where arc energy is used to partly compensate compression forces during high current interruptions. It additionally uses a double speed contact stroke created by a simple mechanism placed below the moving contact. [ABSTRACT FROM AUTHOR]

The arc behavior in the current zero region is critical in the case of very steep rising TRV, such as after clearing a short-line fault. Therefore, intensive and abundant shortline fault tests (L90) of a 245 kV SF6 circuit breaker were performed at the KEMA High Power Laboratory. For the purpose of a comparative analysis three different sets of data were obtained during the tests: 1) High-resolution measurements of near current-zero arc current and voltage were carried out. The current zero measurement system (CZM) works as a standalone system in addition to the standard laboratory data acquisition system. The arc conductance shortly before current zero and the arc voltage extinction peak give a clear indication of the interrupting capability of the breaker under test. 2) From the measured traces of every individual test, arc parameters (3 time constants and 3 cooling-power constants) were extracted for the composite black box arc model, which has been developed by KEMA High Power Laboratory and is based on more than 1000 high-resolution measurements during tests of commercial high-voltage circuit breakers. Its aim is to simulate interruption phenomenon in SF6 gas, evaluate performance of HV SF6 circuit breakers in testing and enable the prediction of the performance under conditions other than those tested. 3) After each test, using specially developed computer software, based on a simplified physical enthalpy flow arc model, the values of the arcing contact distance, gas mass flow through the nozzle throat and pressure inside the compression cylinder were calculated. The values of these characteristic quantities at the current zero are relevant indicators for successful interruption. In the comparative analysis, mathematical relations and statistical correlations between the evaluated parameters of the composite black box arc model and the characteristic output quantities are established and discussed. The link has been verified by MatLAB simulation of every individual test. This approach enables acceptable prediction of interruption success in a similar circuit and with a similar interrupter without SLF tests and CZM. [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]