Statistisk analys av partiella urladdningar
This thesis concerns partial discharges in stator windings and the possibility of analyzing data using statistical methods. Partial discharges, or PD, are a physical phenomenon in which discharges occur locally due to large electric fields. PD can occur in or adjacent to the insulation of stator windings and causes breakdown of the insulating materials. PD measurement can provide an idea of how widespread the PD activity is. A technique to measure and analyze PD that has become very popular over the last few decades is phase resolved PD patterns. These patterns supplies a "fingerprint" of the PD activity and by visually interpreting this patterns one can, in addition to read the intensity of the PD, also get a picture of what type of PD that is active. The problem with phase resolved PD patterns is that they are very complex and difficult to interpret. By applying statistical methods to PD patterns it has been investigated in this thesis whether the interpretation of the PD patterns can be simplified. The results show that the proposed methods have some advantages as they can quantify trends in the patterns. The methods have also shown to have severe limitations due to the fundamental properties of the PD patterns.