Effect of Transients on HV Cables
The Effect of Transients on High-Voltage Cables and Accessories
The trend to underground considerable parts of the HV grid reinforces the need to study the effect of transients in the network on the most vulnerable parts of the cable system, i.e. in the HV cable accessories. High voltage cables and accessories have to be designed to withstand certain types of transients, such as lightning impulses or switching impulses. However, there are some defects in the insulation that cannot be detected during commissioning tests. At the same time, the combined line- cable system will generate superimposed transients, which may trigger and accelerate partial discharge activities in the non-detectable defects in cable insulation, especially in cable accessories. In case the partial discharge activities remain even after the transient has disappeared, a degradation process becomes active, which may finally lead to insulation failure. Currently, we have insufficient knowledge about the effect of transient voltages on incipient routes to failure.
The goal of this PhD project is to determine which transient situations may lead to a sustained degradation process of the insulation system, in particular the high voltage cable accessories. New knowledge rules are expected to be created from the above studies. Next, the created knowledge rules are to be adopted with the settings of the TenneT cable monitoring system, so that potentially dangerous transients are singled out and proper warning signals are given.