Ossama E. Gouda

Effect of the Formation of the Dry Zone Around Underground Power Cables on Their Ratings

Many factors affect the loading of the underground power cables, such as ambient temperature, depth of laying of cable, number of parallel circuits of cable, and thermal resistivity of the surrounding soil. One important factor, usually ignored, is the formation of dry zones around the underground power cables. Dry zones are usually formed around underground power cables under loading conditions due to the migration of moisture within the soil. In this paper, the effect of the formation of the dry zone on the ampacity of underground power cables is investigated. The derating factor for the formation of dry zones around underground power cables is suggested and calculated for different types of natural backfill soil. IEC 60287-1-3 is taken as a reference. Experimental work was conducted to study the phenomena of the dry zone as related to different types of soils.

Influence of pollution of HV insulators

The factors affecting pollution-layer conductivity are reported and discussed. Pollution-layer conductivity is shown to depend on the contamination material, the wetting method, and the pollution-layer density. Tests to simulate pollution conditions in the desert and near cement factories are also discussed. The tests were carried out using the cap-and-pin type of insulator, which is commonly used in overhead networks in Egypt and neighboring countries. The process of wetting the polluted surfaces of transmission line insulators has a great effect on the conductivities and flashover voltages of the transmission line insulators.<<ETX>>

Experimental techniques to simulate naturally polluted high voltage transmission line insulators

This paper represents experimental techniques to simulate the naturally polluted high voltage insulators, under conditions that simulate the desert environment. Usually, the IEC fog method is used for testing the polluted insulators of high voltage transmission lines, but it does not simulate them under the desert pollution environments. For that reason, in this paper two other suggested techniques are added to the IEC one. The first one is to explain the performance of the polluted insulators under the dew and the second one is to explain their performance under the simultaneous fog and dew. The results of these three tests are compared with each other under different surface polluted layer conductivities. The aim of this paper is to record the leakage current and the warning voltage under different simulation weather conditions that to monitor the insulator strings before the occurrence of the flashover that of course is useful for the efficient maintenance. Also, in this paper, an attempt to simulate the flashover of the insulator in the field condition (actual outdoor condition) is presented. Where, the surface of the insulator is polluted naturally over a relatively long period, while it is permanently under high voltage.

Performance of crops growth under low frequency electric and magnetic fields

The biological effects of extremely low frequency magnetic fields (ELF MFs) on living organisms have been explored in many studies, but few of them investigate the combination effect of both magnetic and electric fields act upon their growth. In this study, the biological effects of electric and magnetic field on the early growth of plants are presented using different beans. The electric and magnetic fields are produced using a specially-made test cell. The results indicate that the electric field has an enhancing effect on the early growth of the tested crops, however some morbid state phenomena were observed on some crops. Also, the effect and morbidity rate increases with electric field intensity.

Effect of high frequency electromagnetic fields on homogenous and inhomogeneous human head models

This paper describes the research work done by using the method of moment in investigating the effects of high frequency electromagnetic field (EM) on a homogeneous and inhomogeneous human head at various frequencies. The behavior of the human head under EM radiation is modeled as a homogenous model and a multilayer model in order to assess biological effects on the human head. The specific absorption rate (SAR) in the human head model is calculated, where the SAR is the main parameter used for indicating the effects of EM field.

Factors affecting transient response of grounding grid systems

Grounding system behavior under transient condition is investigated. Transmission line approach has been chosen to simulate the buried grounding system under lightning condition. Different models of buried grounding grids have been studied under lightning conditions. Sensitivity analysis of soil parameters and grounding grid dimensions have been studied to understand the effect of each parameter on the performance of grounding systems subjected to lightning.

Electrostatic effects on the cable dielectric

In loaded cables, the copper and dielectric losses cause the conductor and insulation to heat up. Normally the dielectric expands 1 to 2 percent more than the conductor in radial direction. A cavity will form between the conductor and the insulation material. The change in the energy stored in this cavity creates an electrostatic force. This force leads to thermomechanical breakdown of cable dielectric. An experimental technique is suggested, designed, and used to measure the electrostatic force.<<ETX>>

The effect of the artificial backfill materials on the ampacity of the underground cables

The backfill materials around under-ground power cables affect the maximum current carrying capacity of these cables. Usually backfill soils around under-ground power cables lose their moisture content, forming dry bands around the cables and leading to an increase in the thermal resistance and decreasing in maximum current carrying capacity. But according to the results of the experimental works which are carried out in this paper, it is noticed that some types of soil lost their moisture content faster than the other. This means that the dry band around the cable in some soils form faster than the others. The aim of this paper is to determine the best type of artificial soil that can be used as backfill material to minimize the effect of dry bands that cause thermal failure to the cable insulation.

New mathematical model for water treeing in solid insulations

Foundation of water and electric field are essential and assistance requirements to initiation, growth and propagation of the water treeing. So that, this paper presents a new theoretical model of water treeing mechanism in solid insulation. Also, the aim of this paper is studying the effects of configuration parameters of our suggested model on the electric field strength inside microvoid and the interfacial energy between water and insulation material at high frequency for various dielectric insulation kinds (unique, binary-, and multimixture).

A new mathematical model for evaluating breakdown in solid insulations under impulse conditions

Breakdown, or channel formation, of a polymer under transient conditions occurs in a single step and generates a conducting pass, which indicates that the electric field in the breakdown region collapses extremely rapidly. In this contribution, a new mathematical model of a breakdown channel configuration in solid dielectrics under impulse conditions is investigated. Also, this paper studies the energy to form a breakdown channel and its effect on unique and mixture dielectrics.