Optimal håndtering av utfordringer i lavspenningsnett

In many places, the low-voltage grid in Norway is so weak that secure disconnection in the case of short circuits in the network or in the customer's installations cannot be guaranteed. The consequence of the protection not being released during short circuiting is hot conductors and components, which in turn could cause fire. The cost of strengthening the network to a sufficient grid strength is estimated at between 9 and 33 billion NOK. The main idea behind the OptiNett project is to reduce costs by facilitating new methods that guarantee safe disconnection of short circuits in weak low voltage networks and the connected customer installations. Cost estimates show that the use of alternative solutions can reduce the investment requirement by up to 80% in some cases.The network company manages a socially critical infrastructure and therefore places high demands on safety and reliability when introducing new products or methods. For the grid companies to be able to use alternative solutions that ensure safe disconnection, it is therefore necessary that the equipment is tested, verified and documented. This will be done in the project through detailed risk analyses, simulations and experiments carried out in the national smart grid laboratory.The project will help to increase the safety of the low-voltage grid and in the customers' low-voltage installations by ensuring that areas where it is not possible to guarantee safe disconnection can be remedied more quickly than using current solutions. The planning methodology that will be developed will enable network planners to make more optimal investment decisions. This will result in a socio-economic benefit. A study of alternative measures has been carried out, which is described with advantages and disadvantages in a project memo. There is very limited international literature available on the subject. Simulations have been performed with asynchronous and synchronous motors located in different places in a model of a real low-voltage network. Simulations show that asynchronous motor is best suited in relation to short-circuit contribution / motor rating. This solution is also verified through tests in the physical network. The disadvantage of an asynchronous motor is that it can not contribute to improved voltage quality. Rather the opposite as it increases the voltage drop in the mains due to its reactive power requirement. The simulations also show that secure disconnection depends on the type of fuse and its producer. For the same fuse type and nominal performance, there is a significant difference in trip characteristics. Therefore, a new analysis methodology has been developed and documented, including the tripping characteristics of the fuses, for assessing the need for measures for safe disconnection. REN AS has implemented the fuse tripping characteristics in its design tool for network companies, albeit limited to the network company's own short-circuit protection. REN will consider further developing its products with the analysis methodology with connected installations later. The analysis methodology includes a risk analysis for the various alternative measures. Simulation and testing of battery system shows promising results with the ability to both provide safe disconnection of minimum shortcircuit current and mitigate poor voltage quality. However, its price level is still relatively high. Furthermore, voltage upgrade to 1000 V has been tested. This measure also provides increased short-circuit current and improved voltage quality, but at a lower cost than a battery system today. But the measure is only suitable in cases where the customers are not evenly distributed along a radial. Alternatives to the reinforcement of weak low-voltage networks in order to secure disconnection of fault currents are: * Switch to protection with other fuse characteristics, if feasable. * Upgrade voltage to 1000 V, if feasable. * Battery system, if feasable. The project has developed an analysis tool which calulates the minimum fault current and its appropriate standard fuse in order to secure disconnection within 5 sec. The tool also includes a Net Present Value calculation of the alternatives together with traditional grid reinforcement.

Prosjektet vil bidra til å øke sikkerheten i lavspenningsnettet og lavspenningsinstallasjoner gjennom at områder hvor det i dag ikke er mulig å garantere sikker utkobling av feilstrømmer kan identifiseres enklere og utbedres raskere enn ved bruk av dagens metoder og løsninger. Alternative løsninger vil kunne redusere nettselskapenes kostnader knyttet til utbedring av svake lavspenningsnett. Prosjektet har dokumentert og utviklet et enkelt analyseverktøy som skal bidra til at nettselskapene bedre gjøres i stand til å avdekke et behov for tiltak og velge det hensiktsmessige tiltak. På lenger sikt vil REN AS også kunne utvikle veiledere og videreutvikle sine prosjekteringsverktøy som så godt som alle norske distribusjonsselskaper benytter. Dette vil bidra til økt anvendelse av resultatene.

Lavspenningsnettet i Norge er mange steder så svakt at sikker utkobling ved kortslutninger i nettet eller i kundens installasjoner ikke kan garanteres. Konsekvensen av at vern ikke løser ut ved kortslutning er varmgang i ledere og komponenter, som igjen vil kunne medføre brann. Kostnadene for å forsterke nettet til tilstrekkelig nettstyrke er estimert til mellom 9 og 33 milliarder kroner. Hovedidéen bak OptiNett-prosjektet er å redusere kostnader gjennom å legge til rette for at nye metoder som garanterer sikker utkobling ved kortslutninger i svake lavspenningsnett og lavspenningsinstallasjoner tas i bruk av nettselskapene. Kostnadsestimater viser at bruk av alternative løsninger kan redusere investeringsbehovet med opptil 80 % i enkelte tilfeller. Nettselskap forvalter en samfunnskritisk infrastruktur og stiller derfor høye krav til sikkerhet og pålitelighet ved innføring av nye produkter eller metoder. For at nettselskapene skal kunne ta i bruk alternative løsninger som sørger for sikker utkobling er det derfor nødvendig at utstyret testes, verifiseres og dokumenteres. Dette vil gjøre i prosjektet gjennom detaljerte simuleringer og forsøk utført i det nasjonale smartgridlaboratoriet. Prosjektet vil også utføre risikovurdering og dokumentere at løsningene oppfyller de strenge kravene til sikkerhet i forskriftene. Verifisering av alternative løsninger er tid- og kompetansekrevende og krever verktøy nettselskapene normalt ikke har tilgang til. Prosjektet skal derfor utvikle prestandarder for å gjøre det enklere for nettselskapene å ta i bruk alternative løsninger til nettforsterkning for å garantere sikker utkobling.