DC component effect on Electrical Ageing tests

The Partial Discharge phenomenon represents one of the major causes of the deterioration and ageing of the insulating systems of electric machines and, consequently, leads to a considerable shortening of their lifetime. Although the theory and practice focus more on partial discharges caused by a sinusoidal power supply, this study aims to analyze the possible consequences due to the presence of a DC component. This objective in fact has been taken into consideration due to the numerous and continuously increasing use of power electronics in the electrical systems: this can introduce a DC offset into the power supplies. A circuit capable of combining a high voltage AC supply with a high voltage DC one has been therefore designed and realized. Several specimens based on twisted pair wires have been subjected to the resulting voltage. During the degradation process the Partial Discharges activity has been monitored. The obtained results suggest that, in the here considered case, the presence of a DC component does not significantly affect the specimen lifetime and the activity of Partial Discharges.