Master thesis in cooperation with High Voltage Valley (Ludvika) and VB Energi (Ludvika)

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. / 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.

Detta arbete undersöker temperaturdynamiken och sluttemperaturen hos ledare iinstallationskablar för olika fall av belastningsström. En laborativ model och entidsstegande numerisk modell har skapats och jämförts. Resultaten jämförs med denmärkström som ges i installationsstandarder, och även med de överlastnivåer somkan tolereras av säkringar och strömbrytare enlig Europeiska standarder.Exempel på användningsområden för studiens resultat är kabelklassificeringar medtillfälliga laster, och potentiell överlast på grund av tung belastning kombineratmed extra matningar till en krets (t.ex. inkopplad solkraft). De studerade kablarnavar fyllda och ofyllda 3-ledarkablar (varav 2 belastade) med PEX-isolering, allamed 1,5 mm2 kopparledare (EQLQ 3G 1,5 mm2). De testades fritt i luft och i ensektion av värmeisolerad vägg. Strömmar applicerades från en styrbar likströmskälla.Ledarens temperatur mättes genom att logga spänningsfallet över en cirka 10 cmlång ledarsektion, med tanke på resistansens temperaturkoefficient. Denna metodverifierades genom tester i ett värmeskåp.Resultaten visade att ledarna maximalt nådde 92 % av den tillåtna drifttemperaturen(90 ◦C) vid 150 % belastning av typisk säkringsstorlek. Kombinerat med extramatningar nådde den maximala temperaturen 118 % av drifttemperaturen vid 170 %belastning av typisk säkringsstorlek. Resultaten visade också en temperaturskillnadmellan horisontella och vertikala förläggningar, som varierade från 3-10 ◦C högre idet vertikala fallet, beroende på belastning och kabel. / This work examines the temperature dynamics and final temperature of conductorsin electrical installation cables, for various cases of load current. A laboratory modeland a time-stepping numerical model have been made and compared. Results arecompared with the ampacity given in installation standards, and also with theoverload levels that could be sustained by fuses and circuit breakers, followingEuropean standards.Examples of use-cases for the study’s results are cable ratings with intermittentloads, and potential overload due to heavy load combined with extra infeeds intoa circuit (e.g. plug-in solar power). The studied cables were filled and non filled 3-conductor (of which 2 loaded) PEX insulated installation cables, all with 1.5 mm2copper conductors (EQLQ 3G 1.5mm2). They were tested in open air and in a sectionof insulated cavity wall. Currents were applied from a controlled dc current source.The conductor temperature was measured by logging the voltage drop across a 10 cmlength of conductor, bearing in mind the temperature coefficient of resistance. Thismethod was verified by tests in a heating chamber.Results showed that conductors reached a maximum of 92 % of the permissibleoperating temperature (90 ◦C) at 150 % load of typical fuse-size. Combined withextra infeeds the maximum temperature reached 118 % of operating temperatureat 170 % load of typical fuse-size. The results also showed a temperature differencebetween horizontal and vertical orientations, varying from 3-10 ◦C higher in thevertical scenario, depending on load and cable

Based on conventional static line rating method, the actual current carrying capability of overheadconductors cannot be judged. Due to continuous increment in electricity demand and the difficultiesassociated with new line constructions, the overhead lines are therefore required to be rated based on amethod that should establish their real-time capability in terms of electricity transmission. The methodused to determine the real-time ampacity of overhead conductors not only can enhance their transmissioncapacity but can also help in allowing excessive renewable generation in the electricity network. In thisdiploma work, the issues related to analyzing an impact of wind power on periodical loading of overheadline as well as finding its static and dynamic ampacities with line current are investigated in detail.Initially, in this project, the investigation related to finding a suitable location for the construction of a 60MW wind farm is taken on board. Thereafter, the wind park is integrated with a regional grid, owned byFortum Distribution AB. In addition to that, the electricity generated from the wind park is also calculatedin this project. Later on, the work is devoted to finding the static and dynamic line ratings for‘VL3’overhead conductor by using IEEE-738-2006 standard.Furthermore, the project also deals with finding the line current and making its comparison withmaximum capacity of overhead conductor (VL3) for loading it in such a way that no any violation of safeground clearance requirements is observed at all. Besides, the line current, knowing the conductortemperature when it transmits the required electricity in the presence of wind power generation is also animportant factor to be taken into consideration. Therefore, based on real-time ambient conditions withactual line loading and with the help of IEEE-738-2006 standard, the conductor temperature is alsocalculated in this project.At the end, an economic analysis is performed to evaluate the financial advantages related to applying thedynamic line ratings approach in place of traditional static line ratings technique across an overheadconductor (VL3) and to know how much beneficial it is to temporarily postpone the rebuilding and/orconstruction of a new transmission line. Furthermore, an economic analysis related to wind power systemis taken into consideration as well to get familiar with the costs related to building and connecting a 60MW wind farm with the regional grid.