“Whatever the nature of the fault, if an underground cable fails, the necessary repairs take around 20 days on average. Six days alone are taken up with searching for and pinpointing the location of the actual cable fault. This leads to high downtime costs”, explains Dan Keller, Sales Manager Utility Business at HIGHVOLT. This is exactly where HiMON^® comes in. The modular service package for quality assurance and condition assessments of HVDC underground cables provides a perfect combination of sensors and software that complement each other. HiMAG^® sensors and the corresponding digitalizsation unit HiRES Locator are installed at every cable station that connects the individual cable sub-sections. Thanks to the way the sensors are distributed all along the entire cable section, faults can be immediately detected and localised. So, if a customer has chosen to use this new system, their service engineers are able to quickly and accurately pinpoint where the repairs need to be carried out.

HIGHVOLT is currently testing the second feature of the service package, which will be used to identify potential problem areas before failure of the cable system occurs. Although partial discharges do not always cause the cable system to fail, they often indicate sources of faults. Consequently, the second feature also includes special sensors capable of detecting even the tiniest partial discharges. These sensors are installed at distances of 12 km along the length of the cable, resulting in minimal installation requirements. The corresponding digitalization unit and the TruePD software employ intelligent algorithms to calculate the likelihood of failures from the sensor data and offer forward-looking service recommendations even before a problem occurs. HiMON^® also includes an Intelligence Cluster – an expert system in which all the data is pulled together ready for checking and analysis at any time. “In terms of the HVDC projects that are planned, we are looking at cables that are several thousands of kilometres long. The need to be able to centrally monitor as closely as possible such huge distances with minimal installation effort is completely new for the market”, emphasises Keller.

At present, several major HVDC projects are at the planning stage in Germany. The SuedOstLink project alone, which is being built in a cooperation with the transmission system operators 50Hertz and TenneT, will be around 540 km long once it is completed. These underground cables are many times longer than the ones used previously. Keller explains why continuous monitoring and maintenance of these electricity links is so important: “Availability tells us how often a cable works perfectly, i.e. with no problems. Statistically speaking, we are expecting at around the 95 percent mark for the Project SuedOstLink. This sounds solid but looking at it the other way around it means a failure rate of 15 to 20 days per year. And the longer the cables become, the more metres of cable there are where failure can occur, which – when using conventional sensor systems – would have taken a great deal of time and effort to determine the exact location of.“ In addition, most failures are attributed to faults on the cable joints that connect the cable sections, the quantity of which cannot be reduced. Since underground cables need to be transported to the installation site, the maximum length of each cable section is limited by the maximum permitted transport weight. Accurate localisation of the defective joints alone therefore makes repairs significantly more efficient.