The main PRPD characteristic of the resulting partial-discharge pattern for internal discharges is the symmetry between the positive and negative PDs, resulting in rounded shape PD clouds in PRPD map, as illustrated in Fig. 3.14.
Part of the book series: Power Systems ( (POWSYS)) Partial discharges are small electrical discharges that can occur in the interior or on surfaces of electrical insulation systems (International Electrotechnical Commission, High-voltage test techniques-partial discharge measurements. IEC, Publication-60270, 2000).
Internal partial discharges are generated in air or gas-filled pockets embedded in the main insulation of power generators. These arise from the manufacturing process, and typically do not cause significant degradation under normal circumstances.
Metalized polypropylene films are used to build power capacitors for ac voltage. The objective of this paper is to study the de-metallization processes that may occur under high electric field. A laboratory model of capacitor is first described.
The capacitors act as a medium for the transmission of PD electrical energy from the winding to the sensors, providing accurate measures of the electrical signals generated by the PDs. In order to accurately measure the PD conduction signals, the coupling capacitors and other sensors must be carefully designed and tested.
Internal voids range from a few kHz to 700 MHz, delamination from a few kHz to 800 MHz, corona activity at the surface/conductor and stress grading coating from a few kHz to 500 MHz, slot discharges from a few kHz to 1000 MHz, gap type discharges from a few kHz to 300 MHz, and surface discharges tracking from a few kHz to 900 MHz.
Nondestructive ultrasonic detection was used to measure pore size in ceramics while the partial discharge characteristics were evaluated by a discharge detector. It is found that the partial discharge quantity and discharge inception voltage …