M. Abdel-Salam

Finite Element Solution of Monopolar Corona Equation

In this paper, the monopolar corona equation is solved using a modified finite element method (FEM) to give the corona current caused by overhea dc transmission lines without using the commonly-used Deutschs assumption The method is free from empiricism and entails implicitly a decrease of thsurface field intensity of the conductor with the applied voltage in the same manner as observed experimentally. This in itself represents an additional improvement for the analysis of ionized field where the approximation pertinent to the assumption of constant surface field intensity is mitigated. The calculated corona current as well as the current density at the ground plane agreed with those measured experimentally for a laboratory model.

Positive Wire-to-Plane Coronas as Influenced by Atmospheric Humidity

A method is suggested for calculating the inception voltage and corona current in humid air. It is found that the photoelectrons distribution within the ionization layer, which depends upon the gap geometry, plays an important role in deciding whether the inception voltage increases or decreases with relative humidity. The inception voltage is one of the boundary conditions required in the theoretical analysis of the corona V-I characteristics also presented. The experimental results reported in the literature which differ widely can be explained in the light of the present findings.

On Power Quality of Variable-Speed Constant-Frequency Aircraft Electric Power Systems

In this paper, a comprehensive model of the variable-speed constant-frequency aircraft electric power system is developed to study the performance characteristics of the system and, in particular, the system power quality over a frequency range of operation of 400 Hz to 800 Hz. A fully controlled active power filter is designed to regulate the load terminal voltage, eliminate harmonics, correct supply power factor, and minimize the effect of unbalanced loads. The control algorithm for the active power filter (APF) is based on the perfect harmonic cancellation method which provides a three-phase reference supply current in phase with its positive-sequence fundamental voltage. The proposed APF is integrated into the model of a 90-kVA advanced aircraft electric power system under VSCF operation. The performance characteristics of the system are studied with the frequency of the generators output voltage varied from 400 Hz to 800 Hz under different loading conditions. Several case studies are presented including dc loads as well as passive and dynamic ac loads. The power quality characteristics of the studied aircraft electric power system with the proposed active filter are shown to be in compliance with the most recent military aircraft electrical standards MIL-STD-704F as well as with the IEEE Std. 519.

Monopolar Corona on Bundle Conductors

In this paper, the monopolar corona equation is solved for bundle conductor using a modified iterative procedure to give the corona current contributed by each subconductor of the bundle. Some of the main underlying assumptions are waived in the present calculations. The variation of ion mobility with its life time as well as the change of corona onset voltage from point to point on each subgonductor ore taken into account for the first time. The calculated corona currents from each subconduotor are compared with those measured experimentally for a laboratory model.

The onset voltage of coronas on bare and coated conductors

This paper concerns theoretical and experimental investigations of the effect of a conductor coating on the onset voltage of a corona on overhead transmission-line conductors. The onset voltage for a self-maintained discharge on the basis of discharge physics is evaluated. This calls first for accurate calculation of the electrical field in the vicinity of a coated conductor and its correlation to the field values near a bare conductor of the same radius. The well-known charge simulation technique is used for field calculation. The calculated electrical field values are utilized in evaluating the onset voltage of positive and negative coronas on bare and coated conductors. The onset voltage increases with a conductor coating. The calculated onset-voltage values agreed satisfactorily with those measured for laboratory models and full-scale test lines.

Analysis of monopolar ionized field as influenced by ion diffusion

This paper aims at the analysis of the monopolar ionized field in conductor-to-plane configurations without resorting to Deutschs assumption. A new iterative finite-element technique is proposed to solve Poissons equation. Satisfying the current continuity condition and updating the space-charge density are based on the application of Kirchoffs current-balance law at each node of the finite-element grid and take the ion diffusion into account. The proposed method of solution has been applied for laboratory and full-scale models of a monopolar transmission line. The calculated V-I characteristics, the current-density, and electric field profiles at the ground plane agreed well with those measured experimentally in comparison with previous calculations. Fast convergence and simplicity in programming characterize the proposed method. >

On assessment of ozone generation in dc coronas

A review is made of the theories proposed for quantitative assessment of ozone generation in dc-energized electrostatic precipitators. The underlying simplifying assumptions adopted by these theories are discussed. Among the most important assumptions is ignoring the ozone destruction which takes place at high ozone generation rates. Therefore, a modification is proposed to account for ozone destruction in assessing the generation of ozone. Subsequently, a linear relationship between the ozone generation rate after being modified and the discharge power is obtained by using the present experimental results or the data published previously.

Calculation of corona onset voltage for duct-type precipitators

A method is described for calculating the onset voltage of corona in duct-type electrostatics precipitators whatever the arrangement of discharge wires relative to the collecting plates, without the need of experiments. This method is based on a criterion for self-recurring single electron avalanches in a known field distribution in the ionization-zone surrounding the discharge wire. The results computed by this method are in reasonable agreement with those measured experimentally.<<ETX>>

Characteristics of corona and silent discharges as influenced by geometry of the discharge reactor

This paper is aimed at investigating how the characteristics of corona and silent discharges including ozone generation are influenced by geometry of the discharge reactor. The corona discharges have been generated in coaxial wire–cylinder and wire–duct reactors stressed by dc and ac voltages. The silent discharges have been generated in the same reactors in addition to tubular reactors under ac voltage after pasting a dielectric barrier on the ground electrode of the reactors. The reactors were fed by dry air flowing at atmospheric pressure and temperature. The pulse characteristics of silent discharges are compared with those of ac corona discharges. The current–voltage and the ozone generation characteristics of silent and ac discharges are recorded. These characteristics depend significantly on the geometry of the reactor irrespective of the discharge type.

Finite-element analysis of monopolar ionized fields including ion diffusion

This paper aims at analysis of the monopolar ionized field in conductor-to-plane configurations. An iterative finite-element technique is used to solve Poissons equation. Two algorithms are proposed for satisfying the current continuity condition and updating the space-charge density. The first algorithm is a modified method of characteristics, which neglects ion diffusion. The second algorithm is based on application of Kirchhoffs current-balance law at each node of the finite-element grid and takes ion diffusion into account. The proposed method of solution has been applied for laboratory and full-scale models of monopolar transmission lines. The calculated V-I characteristics, current-density and electric field profiles at the ground plane agreed well with those measured experimentally in comparison with previous calculations. Fast convergence and simplicity in programming characterize the proposed method.