“…This is due to the constant shape of the DC stress, which does not allow a phase value be assigned to the discharge event but only the time of appearance from t = 0. To overcome these main problems related to the PD measurements under DC stress, some authors have proposed new techniques mainly based on a DC voltage with superimposed periodic waveforms or ripples [12]- [16]. Furthermore, some IEC standards and recommendations of IEEE and CIGRÈ have proposed test methods for HVDC extruded cables and accessories adopting PD measurement techniques suitable for AC [17]- [20].…”