The use of SF6 Gas-Insulated Systems (GIS) is increasingly taking the place of conventional air-insulated systems. It may appear that the reliability of gas-insulated systems has been proven through its satisfactory operating experience, however, partial discharge (PD) detection technique is still required to check the integrity of SF6 in GIS. Patrial Discharges can be a major cause of deterioration of the dielectric efficiency of GIS. This study has been performed with the aim of examining the various possible techniques available for impurity determination in GIS. In addition the effects of PDs on electrodes have been examined. Detection of partial discharges has been obtained by using the Computer-Based Data Analyser (CDA3) and Fourier Transform Infra Red (FTIR). Other possible methods have been investigated such as the Nuclear Magnetic Resonance (NMR) method and the Raman technique. The changes on the surfaces of the electrodes have been studied using the Scanning Electron Microscope (SEM) and the Electron Probe X-Ray Microanalyses. Partial discharges have been generated in pure and contaminated SF6. Moisture and oxygen have been used as a contaminants in our experiments- these are common contaminants in GIS. To have a complete picture about the effect of PD in SF6 Gas-Insulated Systems all the three elements (electric discharges, gas and electrodes) involved during the existence of partial discharges should be considered: first of all, by the usage of a Computer-Based Data Analyser (CDA3) the electric partial discharge activity is studied. To simulate PD activity in GIS a point-plane pd source in SF6 was used. Very little can be found in the literature about the details of partial discharge, obtained by a point-plane geometry stressed by negative DCHV, magnitude and its repetition rate in SF6 for long periods of time. Its behaviour over a period of 60 hours is monitored and studied. There have been no such long term (60 hours) studies of PD effects reported. The second element is the gas analysis. Fourier Transform Infra Red (FTIR) method had received only a little attention compared with other methods. After detailed studies and investigation FTIR has been found to be very suitable for gas analysis. The author has proposed this technique for monitoring SF6 integrity in GIS maintenance. Moreover, the author has an expectation that on line monitoring with the FTIR method is possible and should not be difficult. No previous attempt has been made to use the Nuclear Magnetic Resonance (NMR) method or Raman technique. Therefore, we decided to take the initiative to apply these methods for the gas analysis. The NMR results revealed some hope in applying this method for the gas analysis however the Raman technique results did not show any promising signs for use of this method for the gas analysis. Beside that, the third issue is the effect of discharge on the morphology of the surfaces of the electrodes and what are the changes that can be responsible for the behaviour of PDs. This is also part of this study. Because the issue of the affect of partial discharges on the surfaces of the electrodes has not yet been tackled in detail elsewhere many original results have been obtained from this research. This investigation has taken two directions: one was to study the morphology of the reacted surfaces of the electrodes after being exposed to discharges and the second was to quanti fy the changes in the percentages of the elements on the surfaces of the electrodes. The first direction has been achieved using the scanning electron microscope (SEM) and the other second direction has been achieved using the electron probe microanalyses. Furthermore, the affect of the changes of the surfaces of the electrodes on the PD behaviour has been studied too. The results did show that the surfaces roughness of polished electrodes has increased from 3 pm to about 30 pm because of PD activity and that has enhanced the electric field and increased the magnitude of PD by 4 times higher.