Critical insulation fault revealed during a online PD survey
During a PD survey there were detected critical PD activity at one of the cables in a 24 kV substation. After analyzing the data ( PRPD, PD pulse, FFT and pulse rate) we recommended that measures had be taken.
The PRPD, PD pulse and FFT of the measurement
Three moths later the cable failed
The fault was located approx 500 meters from the substation. When the cable were cut, water poured out of the cable. This was an early generation XLPE, and the cable had severe watertreeing in the insulation. Watertreeing do not generate PD activity, but when the watertrees gets severe enough, electrical trees will start.
Benefits of PD survey
No need for service interruption
Fast measurements on site
Needs only access to the outherjacket of the cable or earthings
One measurement provides all the necessary data to determine the condition
Suitable for cablesystems, transformers, switchgear and electrical machines