N.H. Ahmed et al. demonstrated a VHF spectrum analyser-based PD detection method for power cables. When compared to other detection techniques, the authors claim that the VHF approach, which does not need costly heavy equipment, is the most cost-effective option for detecting PD in cables during onsite testing .
DC high potential testing of field-aged cable reduces its life. DC high potential testing of field-aged cable generally increases water tree growth. DC high potential testing before energizing new medium-voltage cable does not cause any reduction in cable life.
The local field strength is a function of applied test voltage, defect geometry, and space charge. After partial discharge is initiated, the partial discharge channels develop into breakthrough channels within the applied test period.
Upon comparing Figure 10a,b, it can be seen that the absolute value of electric field strength is equal, which means that the electric field under 10kV unipolar square wave voltage can be seen as the sum of the electric field under 5 kV bipolar square wave voltage and electric field under 5 kV (V DC × duty) DC voltage.
The current pulses induced by PD via the magnetic field can be measured using inductive sensors. As the magnetic field of the pulse creates a voltage, a signal may be sent inductively by adding a coil to the cable.
It is difficult to measure electric field strength without interference by the measuring instrument. Dielectric bodies develop surface charges that usually lead to moderate distortions of the field, while large, electrically conducting bodies generate significant field distortions in their proximity.