Determination of the noise signatures of various sparkover phenomena on the insulated shield wire of long HVDC lines

Noise measurements in the power line carrier (PLC) bands of a long HVDC line using an insulated shield wire were taken over a period of 3 to 4 months at a PLC repeater station and the data was analysed. Analysis showed that on some days, very high noise levels were experienced, thereby causing errors in communication between the two converter stations. It was postulated that spark gaps, used together with the shield wire insulators, could be the cause of this extraneous noise. Laboratory work was undertaken in order to determine what the noise signatures from various sparkover events on the shield wire of a long HVDC line would look like in the frequency spectrum. Tests were conducted under AC and DC voltage stresses. The radiated noise levels due to the sparkovers were measured using an inefficient loop antenna and a selective voltmeter. Various noise signatures for the various flashover phenomenon tested, were identified