Inrodroduction Partial discharges

 introduction partial discharges

Partial discharges (PD) are localized electrical discharges within an insulation system, restricted to only a part of the dielectric material and only partially bridging the electrodes. The insulation may consist of solid, liquid or gaseous materials, or of any combination. Partial discharges can be considered as:

1. Internal discharges that may occur in voids or cavities within solid or liquid dielectrics.
2. Surface discharges appear at the boundary of different insulation materials
3. Corona discharges are related to discharges in gaseous dielectrics, if strongly inhomogeneous fields are present

Every discharge event deteriorates the material by the energy impact of high energy electrons or accelerated ions, causing chemical transformations of many types. It is obvious that the actual deterioration is dependent upon the material used. Corona discharges in air will have no influence on the life expectancy of an overhead line; a PD within thermoplastic dielectric as, PE, may cause breakdown within a few days. The detection of discharges is based on energy exchanges which take place during the discharge. These exchanges are manifested as:

• electrical impulse currents
• dielectric losses;
• e.m. radiation (light)
• sound(noise);
• increased gas pressure;
• chemical reactions. 

The most frequently used and most successful detecting methods are electrical ones. These methods aim to separate the impulse currents linked with partial discharges from the other phenomena.