DNV GL China

Partial discharges in underground cables

Compared to offline protection systems, DNV GL's Smart Cable Guard uses online monitoring to ensure even irregular partial discharge activity is detected in time to act proactively

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Partial discharge activity is a good indicator of weak spots in underground cable networks - but its irregular nature means constant monitoring is vital

Partial discharges (PD) are small electrical breakdowns in a power cable's insulation which can degrade the insulation to the point of short circuit. Therefore cables with high PD activity have a greater risk of failure than cables with low or no activity. Partial discharges affect all cables and cable accessories above 6.6 kV.

PD activity is not continuously present. It can disappear for hours or days before starting again - some cables have a "self-healing" effect caused by migrating oil. It also changes due to loads and cable temperatures, while other cables can show PD activity rising to critical levels within days.

This makes PD activity difficult to detect. Preventive measurements using occasional offline 'snapshots' are no use. Due to the irregular nature of PD, a snapshot can easily miss the activity. The online monitoring of Smart Cable Guard provides constant surveillance, giving operators a much better picture of the health of their cable network.

Smart Cable Guard is the most efficient solution to provide you with a clear overview of the health of the MV cable circuit, it helps to proactively act upon weakness in the cable and it operates 24/7 on live cables.