Utfordring med spolejordet nett

Abstract

Formålet med prosjektet er å undersøke og utføre analyser av jordfeilstrømmer i 22 kV blandet distribusjonsnett som består av høyspentkabler og luftlinjer. Distribusjonsnettet kompenseres av sentrale og distribuerte spoler. Plassening av ekstra distribuerte spoler i distribusjonsnettet er evaluert til å være en god løsning for å redusere jordfeilstrømmer og sikre et feilfritt system i nettet. Basert på resultater og analysere av enlinjeskjema vil det anbefales for plassering av distribuerte spolet i nettet i tillegg til de eksisterende.

Den vitenskapelige litteraturen, publiserte artikler og informasjon gitt av veileder, oppdragsgiveren og bedrifter har blitt brukt under prosjektet som grunnlag for en løsning. Manglende tilgang for Netbas og nettdata til nettsystemet pga. smitteverntiltak som ble iverksatt av myndighetene, umuliggjorde utføring av noen form for simulering hos oppdragsgiver. Alle beregninger og målinger ble gjort for hånd. Resultater er brukt som en del av grunnlaget for forslag til plassering av distribuerte spoler i nettet.

Rapporten konkluderes med anbefaling for plassering av distribuerte spoler i nettet for kompensering av jordfeilstrømmer i distribusjonsnettet. Det anbefales og byttet to av de 15 A distribuerte spoler i blå sonen og heller bruke de to 15 A i den grønne sonen der det er planlagt for framtidig reinvestering av nettet. Distribuerte spolene vil holde nettverket overkompensert og ta seg av påløpende feil.

The purpose of the project is to research and analyze the ground fault currents in 22 kV distribution power network with mixed layout of power transmission that consists of ground and overhead lines. Distribution network is compensated by central and distributed coils. The placement of additional distributed coils in distribution network is evaluated to be a good solution to reduce the amount of ground fault currents in the networks and secure the safe and uninterrupted operation of the system. Based on the results and analysis of the single line diagram there will be formed a recommendation for the placement of additional distributed coils in the power network.

The scientific literature, published articles, provided paper literature, and information by project supervisor together with professional contacts from Glitre Energi AS and Valdres Energi AS, have been used in the project research as the basis for the solution. The lack of access to Netbas and extended amount of live data from distribution network due to restrictions imposed by the government to limit the contact and spread of ongoing pandemic, the ability to perform simulations at the power station were not possible. All the measurements and calculations were done by hand. The results were used as part of the basis to assist the placement of distributed coils within the network.

The paragraphs about arc suppression coils, ground fault protection and high voltage cables are described in the theory part of the report and were used as part of the solution basis for the project. During the research it was discovered that the placement distance of distributed coils from the centralized coil together with the distance between distributed coils play a big role in how high voltage protection relay behave. This information was used to decide an appropriate placement of additional distributed coils within the network.

The report concludes with the recommendation for placement of distributed coils to compensate for the ground fault currents in the 22 kV distribution network. It is recommended to displacetwo of the distributed coils to the area with high amount of overhead power lines. The area is the subject for future reinvestment of distribution network with ground cables. The presence of distributed coils will keep the network overcompensated and take care of accruing ground faults.