A. El-Zein

A numerical model of electrical tree growth in solid insulation

A new model for investigating the electrical tree growth in solid insulation using a hyperbolic needle-to-plane gap is presented. The needle is embedded in the insulation medium. Classification of tree shape depends on the electric field value is presented. Then, accurate computation of the electric field is a pre-requisite for calculating electrical tree growth. The electric field distribution is obtained from Laplaces equation by treating the tree structure as an extension of the stressed electrode i.e., conducting medium. The electric field is redistributed during each growth of the electrical tree. This is achieved by using the charge simulation method. The charge at the needle surface is simulated by a group of ring charges. To determine the appropriate arrangement of simulating ring charges inside the needle, a genetic algorithm is used. A number of series finite line charge is used for simulating the charge over each branch and sub-branch during the treeing progress. The presented model for simulating electrical tree growth is a three dimensional field problem. The used needle tip radius was 3 ¿m while the gap spacing varied from 0.3 to 15 mm. The results have been assessed through comparison with available analytical and experimental data.

A Simulation Model for Electrical Tree in Solid Insulation Using CSM Coupled with GAs

A new model for investigating the growth of electrical tree in solid insulation using hyperbolic needle-to-plane gaps is used. Accurate computation of electric field is a pre-requisite for calculating the growth of electrical tree. The electric field distribution is obtained from Laplaces equation by treating the tree structure as an extension of the stressed electrode i.e. conducting medium. The electric field is redistributed during each growth of the electrical tree. This is achieved by using charge simulation method coupled with genetic algorithms. Series of vertical and inclined line charges are used for simulating the tree, for these inclined line charges, a coordinate transformation is performed. Then, the electric field is calculated in the original coordinate system. The used needle tip radius is 3 mum while the gap spacing varies from 0.3 to 15 mm. The results have been assessed through comparison with experimental data.

Types of electrical trees in solid insulation under electrical and mechanical energy basis

The shape of electrical trees is critical in determining the life of electrical insulation subject to this type of degradation. This paper identifies a physical basis for determining tree shape. A quantitative physical model for propagation of electrical tree structures in polymeric insulation is presented. In the present model the propagation of trees arises from the formation of electrodamage that precedes and surrounds the tree tip during the tree propagation process. A kinetic model for the electrical tree structures in solid polymeric insulation is developed, that allows for combined electrical and mechanical stresses. Also present an energy balance analysis during the tree growth process, and present results which show that the proposed model can give predicted tree shape type which in a good agreement with the experimental data of the tree growth subjected to a combined electrical and mechanical stress.

Electrical Characteristics of Nonthermal Gliding Arc Discharge Reactor in Argon and Nitrogen Gases

Gliding arc discharge (GAD) has the properties of both thermal and nonthermal plasma conditions. GAD plasma in the atmospheric pressure with argon/nitrogen and its characteristics are described. Some experimental results about alternating current gliding arc plasma generator have been obtained. It seems that the current density strongly depends on the gas type, and increased with increasing discharge current and gas flow rate. In addition, the discharge current of GAD in nitrogen gas (N2) is greater than one in argon gas (Ar) because of N2 needs more breakdown voltage than Ar. The intensity of GAD increased with increasing the gas flow rate. The oscillograms of discharge current in each case of Ar and N2 were obtained. The electron temperatures of Ar and N2 plasma were calculated to be 22 800 and 8400 K, respectively. The characteristics of both Ar and N2 gases in atmospheric pressure, such as current density, electron density with flow rates (5, 10, 20, and 40) standard cubic foot per hour, were investigated and all experimental results were classified. An experimental study was carried out through using of GAD device for medical treatment by exposing three human blood samples of leukemia to the nonthermal GAD plasma for different periods.

A numerical model of investigating the electric field in dielectric liquid

The initial filamentary streamers in liquid dielectrics drastically changes by the tip curvature of the electrode and the applied voltage. In this paper to get the non uniform field a sphere-to-plane electrodes configuration is used. Also, an immersed air bubble adjacent to the sphere electrode is presented, to obtain the sharp tip, after the air bubble compressed against the sphere electrode i.e., sharp conducting protrusion tip, which considered as a source of high non-uniform field and streamer initiation. A simulation model for field distribution in the dielectric medium is presented by using Finite Element Method. An experimental technique was used to investigate the accuracy of the field simulation. Also an analytical equation for field calculation was used to investigate the percentage field error.