Partial Discharge Patterns during Accelerated Aging of Medium Voltage Cable System

Measurement of partial discharges (PDs) and its phase resolved patterns ($\varphi -\mathrm {q}-\mathrm {n}$ characteristics) is one of the most important diagnostic tools for testing of electrical insulation systems. Degradation mechanisms and identification of defects in electrical insulation systems have not been fully cleared yet. Development of knowledge about processes of PDs changes during aging of complex insulation systems is the next desired step. This paper concerns the measurement of the time dependence of phase-resolved PD (PRPD) patterns and PD parameters during combined thermal and electrical accelerated aging of medium voltage cable systems. The ensuing discussion tries to describe PRPD patterns changes. A comparison with PRPD patterns measured by others on insulation samples with internal voids or electrical trees has been carried out as well. PRPD patterns could be classified into four stages in this paper, including “rabbit-like pattern” in the second stage and “turtlelike pattern” in the fourth stage. Changes in PRPD patterns could be linked to initialization and development of electrical treeing. Creation of electrical trees was detected on the XLPE insulation and outer semiconducting layer interface in cable terminations, confirming the weakness part of medium and high voltage cable systems.