This research responses to the growing need for
reliable on-site partial discharge (PD) measurement techniques
able to detect and identify defects in direct current (DC) operated
equipment such as power cables. Lately, beside high-voltage
direct current connections, also medium-voltage direct current
distribution networks are considered for prospective power systems.
In alternating current (AC) systems, phase-resolved partial
discharge (PRPD) analyses are state of the art to detect and
identify defects. However, PRPD analysis cannot be performed
under DC due to the missing phase reference. Moreover, under
direct voltage stress, charge carrier accumulation occurs over
time and hence, PD behaviour is related to the voltage stress
duration. Latest investigations proposed a composite voltage of
alternating and direct voltage components as test voltage for
PD measurement. This contribution broadens the knowledge by
investigating the impact of direct voltage pre-stress time and
direct voltage polarity on the PD measurements at a protrusion
defect in XLPE.