Degree Name

Doctor of Philosophy


Department of Electrical Engineering


The electrostatic precipitator has been widely used for many years in the electricity supply industry to remove particles from a gas stream.

The collection of particles in an electrostatic precipitator is adversely affected if the resistivity of the particles is high. Attempts to overcome this problem have been made by: flue gas conditioning , operating at high and low temperatures, modifying the shape of the applied voltage. This project is limited to the investigation of the last method.

Effects of negative pulsed voltage on the characteristics of corona discharge in clean atmosphere are investigated when the laboratory scale electrode system is clean with collector electrode in clean and contaminated conditions respectively.

Fundamental characteristics of clean electrode system are investigated to check whether there is any difference in the discharge mechanism under negative pulsed and negative D.C. voltages. From the measurement of the light intensity emitted from the discharge electrode, the ionisation activities in the high field strength region are interpreted both in the forms of average corona current and the temporal development and movement of ions and electrons. Linear relat ionship is found to exist between the average photon current and the average corona current under both negative D.C, and pulsed voltages. When the average photon current is the same, the discharge patterns are similar for both kinds of voltage. The collisions of highly energised ions with neutral gas molecules give rise to the phenomenon which is known as Electrical Wind is studied. Experimental evidence of these characteristics coupled with a theoretical study of corona discharge indicate that within the frequency range of 13 Hz -150 Hz the discharge mechanism is the same for both voltages, and the instantaneous properties of the corona current pulse are affected by the accumulation of negative and positive space charges in the neighbourhood of the discharge electrode. Sparking mode is studied with a multiple-point electrode and the results are compared with that obtained with a single point electrode to check the role of negative streamers in forming the complete breakdown . Sparkover voltage is measured when the electrode system is energised by negative D.C. voltage and is compared with that which is obtained with pulsed voltage.

The characteristics of the electrode system are changed when the anode plane is covered with a layer of highresistivity, porous material which is used to simulate the contamination condition. The sparkover voltage of the system is drastically reduced by the local gas discharge which takes place in the contaminant. In order to explain the change of sparkover voltage with pulsed energisation, some important properties of the discharge are studied, such as: the distribution of surface charge which accumulates on the layer, the conduction of current and the electrical breakdown in the contaminant, the effect of surface potential gradient on the formation of a stable back discharge. These features are summarised in a proposed mechanism of the formation of back corona discharge. This is extended to explain an increase in sparkover voltage when the system is energised with pulsed voltage in comparison to that with negative D.C. voltage.