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