OSCILLATORY SWITCHING SURGE BREAKDOWN OF INSULATORS

Walid  K. BAAYOUN

In a transmission system an increase in power necessitates either an increase in the current capability or an increase in the voltage or both. Increasing the voltage of a system results in switching surges which can be more dangerous than lightning strikes. This thesis examines some of the effects of oscillatory switching surges on a string of insulators. The main parts of this thesis concentrate on the following:

          i) The study of the breakdown mechanism of a string of insulators due to the effects of the following factors:

The waveshape parameters, that is, the type of oscillatory wave (uni- or bi-directional), the wavefront rise time, the oscillatory frequency and decay rate, the initial waveshape polarity and the oscillatory altitude, and

The configuration, that is, the number of insulators and stress relieving mechanism.

           ii) To give an explanation of the "voltage-time characteristic curve" and to show the difference between the breakdown mechanisms according to the wave type.

In addition, some considerations is given to:

            -  The stages of breakdown mechanisms for the generated waves, and

          -  Computer programs to predict the waveshapes of the generated waves, and to calculate the electric field around the string of insulators.