DGnett - Alternative løsninger for integrasjon av distribuert produksjon

The overall goal of the DGnett project is to reduce costs related to grid connection and operation of distributed generation through facilitating that new technologies and new methods are adopted by the utility companies. There has been an increase in the amount of small scale power production in recent years. Connecting large amounts of generation to the distribution grid, previously used exclusively to serve consumption, challenges the grid companies in new ways. An examination of Norwegian utility companies revealed that there are differences in how the utility companies handle grid connection of distributed generation, and what requirements are posed to new producers to day. Limitations in the hosting capacity is today to a large extent handled by building new connections or upgrading the grid and the examination revealed that there is a need for testing and documentation of alternative methods to make them more accessible. A study of different technologies and methods for increasing hosting capacity showed that three methods are particularly interesting from a Norwegian perspective: voltage regulated transformers, reactive power control, and active power control. Analysis performed in the project have revealed that it is possible to increase the hosting capacity through better utilization of available resources for voltage regulation in the distribution grid. The project has developed guidelines of choosing regulation mode and set point in the voltage regulators in the power transformers and in the DG-units that will assure that the voltage stays within the boundaries in the regulation and transmission losses are minimized. New methods for voltage regulation, which utilizes more communication and integration, have been evaluated through an assessment of a selection of international demo projects. A simulation study illustrating the potential to increase the hosting capacity in a real case through voltage regulation with reactive power and tap changing of the power transformer based on distributed voltage measurements has been performed. The use of distribution transformers with on load tap changers, are increasing in Europe. In Norway, no such transformers have been used until now. Helgeland Kraft have in association with the DGnett project invested in a distribution transformer with on load tap changer. The transformer was put into operation in December 2016 in an area where distributed generation leads to large voltage variations through the year. Measurements shows that the transformer seems to solve the problems with large voltage variations. Based on the results of the testing and experience gained through specifying and purchasing the transformer the project has developed a guideline for acquiring and operation voltage regulated distribution transformers. This guide is intended to help network companies when considering the use of such transformers. A measure that has not been applied on a permanent basis in Norway is generation curtailment. A cases study performed in the project revealed that generation curtailment is socio-economically profitable in certain cases compared to grid investments. The project has also studied how systems for generation curtailment are implemented in other countries, in addition to opportunities and challenges regarding implementation of such a system in Norway. These results will provide a better basis for assessing whether generation curtailment should be allowed as a permanent alternative to network upgrading in Norway. During 2017 new network codes from EU posing requirements to fault-ride-through capabilities for all generators over 1.5 MW which is to be connected to the grid, will with all likelihood be introduced in Norway. It will be up to the DSOs to make sure the generators comply with the network code and post requirements on what models to be used. This will require that the DSO have knowledge on dynamic modelling. A workshop has been arranged with the different relevant actors to discuss the implementation of the network code and the consequences of implementing FRT requirements to distributed generation. The project results will be implemented during a major revision of the REN 3000 series, including three new RENblad. This will expand the tool box available to grid companies in handling the connection of new distributed generation and increase flexibility and the capability to handle uncertainties in the planning phase, and reduce connection costs. A course on grid connection of small hydro power plants has also been arranged for the grid companies that participated in the project.

DGnett-prosjektets overordnede mål er å stimulere til verdiskapning gjennom å redusere kostnader forbundet med tilknytning og drift av distribuert produksjon. Prosjektet skal utvide verktøykassen som er tilgjengelig for nettselskap i håndteringen av dist ribuert produksjon, og gjennom det øke fleksibiliteten og evnen til å håndtere usikkerhet i planleggingsfasen, og redusere kostnadene ved tilknytning av distribuert produksjon. En håndbok fra prosjektet skal gjøre veien til anvendelse i nettselskapene kor t. Det vil være fokus på riktig beregning av "hosting capacity", altså hvor mye kapasitet nettet har til å integrere ny distribuert produksjon. Det er i hovedsak tre produktgrupper som er av spesiell interesse; regulerbare transformatorer, styring av rea ktiv effekt, og energilagring. Det vil bli utført tester av de mest aktuelle teknologiene. Det skal gis ny kunnskap om nytteverdien av ulike tiltak. Et verktøy som ikke har vært tatt i bruk som permanent tiltak i Norge til nå er produksjonsbegrensning. Ho sting capacity tar høyde for at nettet må være i stand til å håndtere maksimal belastning, selv om denne bare opptrer noen få timer i løpet av et år. Det er derfor interessant å se på muligheter for en dynamisk produksjonsbegrensning, som kan bidra til å øke kapasiteten i enkelte deler av nettet og dermed gjøre flere DG-prosjekter økonomisk realiserbare. En annen viktig faktor er økt kunnskap om stabilitetsgrensene til småkraftverk, og hvilke krav som må stilles til den enkelte enhet for å oppnå tilfreds stillende systemsikkerhet. Måten dette skal oppnås er verifisering av de simuleringsmodeller som benyttes i dag gjennom kortslutningstester av produksjonsenheter. Resultatene vil gi en indikasjon på hvorvidt dagens krav til transient stabilitet i distribu sjonsnettet er riktige, og ikke minst hvordan de kan følges opp.