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Application of dynamic rating to improve transportation capability of the power systems connected to wind power plants
KTH, School of Electrical Engineering (EES).
2016 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

Current flow in the electrical grid is changing due to the introduction of new generators and loads.Specifically, weak Overhead lines, are a constraint for the introduction of wind farms located farfrom the central network. The current situation requires smart solutions to improve the transportationcapabilities of these grid’s components. Among the different possibilities, Dynamic Line Rating(DLR), is emerging as the most interesting solution from both the economic and technical points ofview. The presented Thesis work investigates the performance of DLR from both the theoretical andpractical perspectives.The theory behind DLR is based on the development of a thermal model able to estimate the precisetemperature experienced by OHLs conductor under different climate conditions. Since 1972, whenthe first investigation on DLR have been published, different thermal models have been developed,each with a different precision level. The first part of the thesis concerns the investigation of IEEE738 standard accuracy.The standard analysis highlighted weaknesses on the theoretical approach employed on the forcedconvective cooling calculation. Specifically the wind direction effect is estimated as the conductorwas a perfect cylinder. A wind tunnel test has been performed in order to verify the effect of theconductor’s strands on the total thermal equilibrium. The results show that an inclined wind-conductor relative direction can have a more important impacton the line rating than foreseen with the IEEE thermal model. Since the wind tunnel test has been thefirst experience of this kind pursued at KTH, the presence of few different laboratory set-updeficiencies did not allow to draw a definitive and precise conclusion on the necessary IEEE formulacorrection.The practical side of the Thesis project includes an extensive literature research on the differentdevices that can be employed for dynamic line rating and a real-case study analysis. The analysis isperformed in order to evaluate which can be the best solution when the introduction of new windenergy supply increase the load on a pre-existent OHL. Results show that, in the selected region,Värmland, in the southwestern Sweden, DLR has the prerequisites to allow the exploitation of thehigh wind energy resource at the lower expenses. Wind energy production is often associated with anincreased cooling on the line’s conductors. This means that higher current levels can be withstoodavoiding the need for expensive lines’ upgrading. For the selected hot-spot, in 2015, DLR wouldhave allowed a transport capability improvement of 69.6% during the summer and of 26.7% duringthe winter. It is also reported that a load equal to the SLR during the winter period would have causedserious overheating transients of the conductor. Overall DLR proved to allow technical and economicbenefit for the system operator.

Abstract [sv]

Flödet genom elnätet förändras på grund av införandet av ny generering och nya typer av laster.Specifikt är svaga luftledningar en begränsning för installation av vindkraft som ligger långt fråndet centrala nätet. Den nuvarande situationen kräver smarta lösningar för att förbättratransportkapaciteten i elnätet. Bland de olika möjligheterna finns Dynamic Line Rating (DLR) somframstår som den mest intressanta lösningen från både ekonomiska och tekniska synvinklar. Det härexamensarbetet behandlar resultatet av DLR från både teoretiska och praktiska perspektiv.Den teoretiska grunden för DLR är baserad på utvecklingen av en termisk modell som kan skattatemperaturen i luftledningar under olika klimatförhållanden. Examensarbetets första del behandlaren undersökning av IEEE 738 standarden (DLR standard). IEEE 738 standarden utgår från ledarensom en perfekt cylinder. Något som har en effekt bland annat i effekten av vindriktning. Ettvindtunnel test har utförts för att verifiera effekten av fler kardelers effekt på den totala termiskajämvikten. Resultaten visar att antalet kardeler har en betydande effekt på den termiska jämviktenoch då alltså även på DLR.Den andra delen av examensarbetet innehåller en omfattande litteratursökning på de olikaapparaterna som kan användas till DLR samt en praktik undersökning/analys. Analysen utförs föratt utvärdera vilken lösning som kan vara den bästa vid införandet av mer vindkraft, som ökarbelastningen på en redan existerande luftledning. Resultaten visar att, i det valda området,Värmland, i sydvästra Sverige, har DLR förutsättningar för att medge ökat utnyttjandet av den storavindkraft resurs som finns där till relativt låga kostnader. Slutsatsen av examensarbetet är att DLR ger tekniska och ekonomiska fördelar tillsystemoperatören.

Place, publisher, year, edition, pages
2016.
Series
TRITA-EE, ISSN 1653-5146 ; 2016:095
Keyword [en]
dynamic line rating, overhead lines, conductor temperature model, wind energy
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:kth:diva-200930OAI: oai:DiVA.org:kth-200930DiVA: diva2:1071664
Available from: 2017-02-06 Created: 2017-02-06 Last updated: 2017-02-06Bibliographically approved

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