Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Electrical and Computer Engineering


An investigation of the electric field distribution near high voltage lines in the presence of vegetation medium has been made using a multilayer dielectric representation. Three multilayer models were derived, namely three, four and five different dielectric layers. Digital computer algorithms were used to generate the image charges in all models. In the three dielectric model, the vegetation was represented by a single dielectric layer. In the four and the five dielectric models, the vegetation was represented by two and three dielectric layers respectively, where the air and the perfect conductor ground represent the other two media. The solutions of the above three cases are obtained using the three phase line of charges with no vegetation. The representation of a cornfield by three dielectric layers in the five dielectric model resulted in a close agreement with the measured data. The thickness and the dielectric constants of the cornfield layer were found to be as follows: a top layer of 0.5 m and a dielectric constant equal to 1.3; the second layer from the top has a thickness of 1.0 m and a dielectric constant equal to 2.0; the third layer has a thickness of 1.0 m and a dielectric constant equal to 80.0. Analyses of these results show they are reasonable since the lower part of the vegetation is generally rich with moisture. Therefore, the water content will be the highest. The top two layers have less water content;In effect, the presence of a cornfield appears to change the field distribution near ground. Since the electric field has been shown to be drastically reduced in almost one meter of vegetation (corn) height, then the clearance between the three-phase conductor and the ground will vary. This will result in a change in the line of charges used with no vegetation. This might be true in a single phase conductor but not in a three phase case, because in three phase systems the line charges are dominated mainly by the phase separation rather than the height above ground.



Digital Repository @ Iowa State University,

Copyright Owner

Bashir Mohamed Jomaa



Proquest ID


File Format


File Size

200 pages