Tilstandsovervåkning av spenningssatte kabler med LIRA (Line Resonance Analysis)

Electrical cables for power distribution can be considered as the arteries in any power network delivering energy from power generation plants to oil and gas installations, public infrastructure and consumer households. The condition of a vast part of these cables are unknown and they represent a significant risk with regards to security of supply. By knowing more about the condition of these cables, one can e.g. predict the cable residual lifetime. With such information the cable owners and operators can reduce their supply risk significantly. Line Resonance Analysis (LIRA), an already established technology, can contribute to reduction of this risk by gathering measurement data from a cable and perfrom a series analysis based on those data which can say something about the condition of the cable. Today, these measurements has to be performed manually, which implies that the cable is out of service. The LIRA Power project has developed a method enabling LIRA measurements on cables without putting them out of service. This enables cable owners and operators to monitor the condition of their cables without any service disruptions. Performing measurements on on-line and energized cables are not considered trivial, and challenges such as large currents, high voltage noise, network structure and signal injection and retrieval are considered the major technological barriers the project has to overcome. Since startup, the project has developed a technology and a prototype for LIRA based measurements on power cables in operation. Simulations and laboratory testing of the solution has produced good results. The solution is also tested in SINTEF Energys high voltage laboratory in Trondheim, Norway, where the target for the testing was to reveal any operational issues related to the safety, installation and operation of the system. Wirescan has currently a patent pending for the solution. In the spring 2017 the project verified the principles in the technology allowing injection and extraction of measurement signals without the need of a galvanic connection to the cable. This was regarded as a particularly important milestone in the project, and further work focused on optimization of the coupling mechanism and the surrounding infrastructure. Further optimization of signal processing in both hardware and software have resulted in valuable results to the customer. In December of 2017 SINTEF and Wirescan executed two field trials based on the world's first LIRA-based cable condition monitoring system for cables in operation. One of these trials is a permanent installation of the system on a 1850 kVA distribution net line in Denmark. The results are very promising and they show good correlation between conventional LIRA measurements and the results from the online system. The project is working to write an informative presentation of the technology and the results for presentations at conventions and conferences, and as presentations for potential new partners.

I Norge er det idag mer enn 36.000km PEX isolert jordkabel i overførings- og distribusjonsnettet (NVE 2014). Slik jordkabel ble gravd ned tidlig på 1970-tallet og disse kablene nærmer seg 50 år med økende feilrate. Idag er også belastningen større og er forventet å øke i takt med at grønn energi gjør inntog og antall elektriske biler øker. Idag går i stor grad utviklingen av "smarte nett" ut på utvikle intelligente komponenter og brytere. For også å få med tilstanden til kablene som binder nettet sammen, ser man at en kontinuerlig overvåkning kan være med å skifte fra reparasjonsbasert vedlikehold der kablene feiler til tilstandsovervåket vedlikehold. Dette vil hindre kost, nedetid og uforutsett belastning på distribusjonsnettet. Et sanntids monitoreringssystem har også anvendelse innenfor kritisk infrastruktur som eksportkabler, offshore vind og oljeplattformer, samt prosessindustri. I prosjektet LIRA Power vil man utvikle en løsning som kontinuerlig kan måle på strømførende kabler, gi estimater på hvordan kabelisolasjonen aldres, og samtidig ikke ødelegge kabelen som følge av høye spenninger. Et slikt system vil gi forbrukere større forsyningssikkerhet, nettselskapene kan planlegge nødvendig vedlikehold og kan dermed utvide levetid for kabler og redusere risiko og kost.