Partial discharge mechanisms in solid insulation systems

The fundamentals of partial discharges (PDs) are briefly reviewed, and the information needed to interpret PD measurements correctly is discussed. Two major types of defect are then considered: voids and delaminations in a solid insulator and field enhancing defects in a solid insulator. The case of a void is used as an example of physical modeling of an insulation defect including PD properties. A defect of the second type, namely treeing, is used as an example to show that PD measurements alone do not allow, in principle, a full assessment of the insulation state