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The electricity cost from offshore wind turbines has significantly declined over the past decade.However, in the context of energy transition, the further reduction in electricity generation costs remainsa forefront subject. One possibility is to enable offshore wind farms to have a greater installed capacitythan their transmission infrastructure, known as “overplanting”. This allows increasing their energygeneration revenues while requiring some curtailments of their power output during the most energy-rich periods of the year. Also, export cables may have a high thermal inertia, so they can be fully loadedfor several days before the cable reaches the maximum permissible temperature (usually 90℃ for XLPEcables). Hence, some Transmission System Operators (TSOs) have recently allowed offshore wind farmoperators to export more power than the transmission infrastructure may deliver in the steady-stateconditions. This is known as the «dynamic thermal rating» (DTR). DTR combined with overplantingcan lead to a significant reduction in the Levelized Cost Of Energy (LCOE) of offshore wind farms.This paper examines the benefits of improving the electricity production commitment strategiesagainst business-as-usual approaches based on the 50% quantile, called P50. In this perspective, atheoretical case is investigated, where the day-ahead and imbalance prices would be known in advancein order to define an optimized power production commitment. This theoretical case intends to definethe upper bound on the annual revenue that could be gained by enhanced forecasts on both theproduction and the day-ahead and real-time energy prices. The study is based on a thermal model of ageneric export cable, built per IEC standards 60287 and 60853-2, with data provided by the French TSO.The model was validated against simulation results provided by the French TSO. Historical day-aheadand imbalance prices are considered, as well as forecast and actual measured production profiles fromoffshore wind farms provided by the Belgian TSO. The source code developed in the project describedin this paper, along with relevant data, and a related documentation will soon be provided in open-accessrepositories available from the project official webpage

Increased consumption and increased use of renewable energy make overhead lines and transformers more often congested. Dynamic rating (DR) uses a time-depending maximum permissible current instead of a long-term-fixed rating; it is an effective solution to upgrade the capacity of existing grid assets to minimize this congestion. Dynamic line rating (DLR) considers how the weather affects the thermal behavior of the conductor and therewith its rating; environmental parameters as well as conductor characteristics have to be considered. Likewise, dynamic rating of transformers (DTR) relies on a thermal assessment of the hottest spot in the transformer windings. The hot-spot temperature is dependent on the ambient temperature, loading, and transformer’s cooling system. In this thesis, a number of lesser-studied aspects of DR are studied: stochastic modeling of the rating; relations between protection, reliability and rating; risk assessment for line selection when using DLR; and increased transformer hosting capacity (HC) in the presence of solar photovoltaic (PV). In the first part of the work, the focus is on the stochastic modeling of DLR and its relation to the protection operation. Actual line rating is considered a random variable in the protection system for a more flexible decision-making. Different sources of uncertainties are modeled using suitable probability density functions. The method allows for a transparent trade-off between the risk of failure to take measures and the risk of unnecessary measures against overload. The results depicts that deterministic DLR could result in high probabilities of overloading or would require large safety margins. While, a stochastic approach will allow for both small margins and appropriate risks. A generic model is introduced to consider DLR reliability from two different viewpoints: errors and failures of components that would affect the calculation of the rating; and the impact of a DLR failure on the power system. The qualitative reliability study highlights that it is important to update the protection settings on a real-time basis. In the second part of the work, a risk assessment framework is proposed to select the minimum set of overhead lines for DLR implementation. Results show a possible increase of permissible hosting capacity (HC) for electric-vehicle charging by up to 80% (depending on the test system and initial data) with low interruption costs and reduced risk of congestion. Furthermore, the improvement in the transformer HC by using DTR has been quantified. The results indicate that depending on the HC performance indices, the transformer can be loaded beyond the normal operational limits up to 35% to host PV and up to 100% for increased consumption.

Dynamic rating (DR) of power components is a method for assessing real-time capacity of large scale power transmission and distribution devices (commonly: transmission lines, power transformers, underground cables) and using this knowledge for adjusting loading limits of these components. Dynamic rating of power lines or dynamic line rating (DLR) is a pioneering technology in the area of dynamic rating. Heat balance of an overhead conductor is a defining factor when designing capacity limits for power lines. The maximum ampacity of the power line depends on the factors, such as ambient temperature, wind speed, wind direction, solar radiation, humidity, location, height above the sea level and conductor dimensions and material properties. Dynamic transformer rating (DTR) is a new emerging technology with high interest from industry and academia. Similarly to DLR, the dynamic rating of transformers relies on a thermal assessment of the device by locating the hottest spot in the transformer windings. The hot-spot temperature is the limiting factor for determining the maximum allowable ampacity. By shifting from the power-constrained the loading limits to the temperature-constrained, it is possible to achieve much better utilization of power transformer. Recently, DLR became a recognizable concept in the power systems research community; DTR is also slowly gaining its popularity among researchers. At the same time, the industry begins to recognize DR benefits and invest in dynamic rating technologies. However, there exist many unanswered questions to the technology's reliability, applicability and safe operation. One of the central questions is: how to integrate dynamic rating into short term and long term planning decisions? he results of the work presented in this thesis show that dynamic rating has high potential to improve power system performance and reduce the costs for power dispatch and increase the share of the renewable energy in the electricity mix. Together with that dynamic rating can help to make renewable energy more accessible by decrease the investment needed for supplying the electricity demand and providing cheaper and faster grid connection. Dynamisk rating (DR) av elkraftkomponenter syftar till tekniker för att uppskatta kapaciteten hos komponenter för storskalig överföring av elkraft (vanligtvis: kraftledningar, transformatorer, underjordiska kablar) i realtid och använda denna information för att justera belastningsgränserna för dessa. Dynamisk rating av kraftledningar (DLR) är en nydanande teknik inom detta område. Värmebalansen för en kraftledning är en viktig faktor för att bestämma dess överföringskapacitet. En kraftlednings maximala strömledningsförmåga beror därför på faktorer så som temperatur, vindhastighet, vindriktning, solstrålning, fuktighet, geografiskt läge, höjd över havet och ledarens dimensioner och materialegenskaper. Dynamisk rating av transformatorer (DTR) är en ny teknik med stort intresse från industri och akademi. Liknande som för DLR använder sig DTR av en uppskattning av den hot-spot temperaturen, hos komponenten genom att hitta den varmaste punkten i transformatorlindningarna. Hot-spot temperaturen är den begränsande faktorn för att avgöra transformatorns överföringskapacitet. Genom att låta den maximalt tillåtna belastningen bero på temperaturen istället för effekten kan utnyttjandet av transformatorn förbättras väsentligt. Nyligen har DLR blivit ett erkänt koncept inom forskningen för elkraft och DTR har också börjat bli populärt bland forskare. Samtidigt har industrin börjat se fördelarna av DR och investera i dessa tekniker. Det finns dock fortfarande många frågor kring teknikern som rör tillförlitlighet, applicerbarhet och säkerhet. En av de viktigaste frågorna är hur man bäst kan integrera dynamisk rating i kort- och långtidsplaneringen av elkraftsystem. Resultaten av arbetet som presenteras i denna avhandling visar att dynamisk rating har en stor potential att minska kostnaderna för driften av elnätet och tillåta integrering av mer förnybara energikällor. Dessutom kan dynamisk rating göra förnybar energi mer tillgänglig genom att minska de investeringar som krävs för att tillgodose efterfrågan på elektricitet och möjliggöra snabbare och billigare anslutning till elnätet. QC 20200109

The increase of global energy demand and new ways of electricity production are two of the main challenges for the power sector. The electric market has to address the addition of new and renewable sources of energy to the energy mix and to be able to integrate them into the grid, while maintaining the principles of robustness, security and reliability [1] . All of these changes point to the creation of smart grids, in which advanced generation, information and communication technologies are needed. An accurate knowledge of the electric grid state is crucial for operating the line as efficiently as possible and one of the most important grid parameters to be measured and controlled is the temperature of the overhead conductors due to their relation with the maximum allowable sag of the line and its thermal limit (annealing). This paper presents the results of real-time monitoring of an overhead power line using a distributed temperature sensing system (DTS) and compares these results with spot temperature measurements in order to estimate the loss of accuracy of having less thermal information. This comparison has been carried out in a 30 km long distributed temperature sensing system with fiber optic inside a LA-455 conductor and 6 weather stations placed along the line. An area of influence is defined for each weather station corresponding to the orography of the surroundings. The spot temperatures are obtained from the DTS in the nearest point from the weather stations assuming these six locations to be the ones where the spot temperature measurement equipment would be located. The main conclusion is that, in the case of study, spot measurements are enough to obtain a good approximation of the average temperature of the line conductor.

In the present thesis an investigation is performed for the effect of moisture contenton the aging of the solid insulation for transformers that are dynamically loaded. Theinvestigation is based on a theoretical analysis and a model.First, a literature review is conducted on the basics of transformer operation, transformerinsulation and moisture in oil-paper systems. Furthermore, a model is developedbased on moisture equilibrium curves created by Oommen and MIT, moisture diffusionprocesses in oil-paper insulation systems and calculations for the aging of cellulose insulationfrom IEC 60076-7. The model represents an experimental system which is loadedon different load patterns that simulate dynamic loading. The aim of the model is toconclude whether the load patterns will cause the paper to age differently dependingon the frequency that the moisture migration phenomenon between paper and oil occurs.The result of the modeling part is that the aging process is affected by the load pattern,and that the higher the frequency the moisture migration phenomenon occurs within aloading cycle, the larger the impact on insulation degradation. This difference, though,is too small to be measured experimentally in terms of DP and it is suggested thatdifferent load patterns are used in the experiment than those used in the model, whichwill amplify the effect of moisture migration even further.Finally, experimental work is conducted in the thesis, which focuses on implementingthe LabVIEW design from previous work into hardware, debugging the system andpreparing the experimental set-up on practical matters that occurred in the lab. Somefinal work is required before the experiment is able to run, such as preparation of theexperimental units. I detta examensarbete undersöks effekten av fuktinnehåll på åldring av fast isolationsmateriali transformatorer med dynamisk last. Arbetet är baserat på en teoretisk analysoch en modell.Först genomförs en litteraturstudie på grundläggande transformatorfunktion, transformatorisolationoch fukt i oljeimpregnerade papperssystem. Vidare utvecklas en modellbaserad på jämviktskurvor for fukt skapade av Oommen och MIT, fuktdifussionsprocesseri isolationssystem baserade på oljeimpregnerat papper och beräkning av åldringav cellulosaisolation från IEC 60076-7. Modellen representerar ett experimentellt systemsom lastas för att simulera dynamisk last. Målet med modellen är att avgörahuruvida lastprofilen påverkar åldrandet av pappret beroende på frekvensen av fuktmigrationenmellan papper och olja.Resultatet av modelleringen är att åldrandet påverkas av lastprofilen och desto oftarefuktmigrationen sker inom en lastcykel, desto större är effekten på isolationsdegraderingen.Skillnaden är dock för liten att mäta experimentellt med avseende på DP och andralastprofiler föreslås i framtida experiment, för att förstärka effekten av fuktmigration.Slutligen utförs experimentellt arbete som fokuserar på implementation av LabVIEWdesignenfrån tidigare arbete i hårdvara, felsökning av systemet samt förberedelse av denexperimentella installationen för praktiska bekymmer som uppstått i laboratoriemiljön.En liten mängd arbete återstår före experimentet kan utföras, såsom förberedelse av deexperimentella enheterna.

Appropriate forecasts of the dynamic rating of buried cables can be exploited by networks operators to significantly increase the power transport capacity of medium voltage and low voltage distribution systems, without sacrificing the normal life of the cables. However, forecasting the effects of the soil conditions on the dynamic rating of the buried cable is not an easy task. In this paper, a detailed procedure is proposed to deal with this problem. The proposed procedure handles the changing environmental conditions by exploiting a thermal-hydraulic model of the soil and a model for the thermal exchange between the buried cable and the surrounding soil. The forecasts of external influencing variables, such as precipitations and soil temperature, and of cable currents, needed as inputs of the proposed procedure, are obtained by means of a Support Vector Regression technique. Numerical applications based on actual load and weather data confirmed the suitability of the procedure, encouraging for further research on the topic.

The overall growth of electrical energy consumption and the spread of distributed generation pose severe problems to system planners and operators, mainly due to the difficulties in expanding and upgrading electrical distribution systems. These problems can be partially overcome through the smart operation of power system components. In particular, under the new smart grid paradigm, lines and transformers could be loaded beyond their nameplate rating in favorable thermal conditions, without loss of rated life or breakdown. This paper deals with the loading of oil-immersed distribution transformers, and it proposes a probabilistic approach based on the monitoring of electrical and environmental conditions. The approach consists in forecasting the predictive distribution of the transformer dynamic rating, and then in forecasting the transformer allowable current. The probabilistic approach takes into account the unavoidable uncertainties involved in the thermal modeling of the transformer; indeed, it selects the allowable current through an index that takes into account both the probability of the allowable current to be higher than the predicted dynamic rating and the corresponding expected load curtailment. Numerical applications are performed on real data to evaluate the effectiveness of the proposed procedure.

It is anticipated that with the thrust towards use of clean energy resources such as electric vehicles, future distribution grids will face a steep increase in power demand, forcing the utility operators to invest in enhancing the power delivering capacity of the grid infrastructure. It is identified that the critical 5–20 km medium voltage (MV) underground ac distribution cable link, responsible for bulk power delivery to the inner urban city substation, can benefit the most with capacity and efficiency enhancement, if the existing infrastructure is reused and operated under dc. Quantification of the same is offered in this paper by incorporating all influencing factors like voltage regulation, dc voltage rating enhancement, capacitive leakage currents, skin and magnetic proximity effect, thermal proximity effect and load power factor. Results are presented for three different ac and dc system topologies for varying cable lengths and conductor cross-sections. The computed system efficiency is enhanced with use of modular multilevel converters that have lower losses due to lower switching frequency. A justified expectation of 50–60% capacity gains is proved along with a generalized insight on its variations that can be extrapolated for different network parameters and configurations. Conditions for achieving payback time of 5 years or lower due to energy savings are identified, while the socio-economic benefits of avoiding digging and installing new cable infrastructure are highlighted. The technical implications of refurbishing cables designed for ac to operate under dc conditions is discussed in terms of imposed electric fields, thermal profile and lifetime. A novel opportunity of temperature dependent dynamic dc voltage rating to achieve additional capacity and efficiency gains is presented.

In this project dynamic thermal rating for transformers and its effect on transformer reliability are investigated. A literature review is done on different thermal models used for this purpose and at the end differential equations model from IEC 60076-7 and bottom oil model from IEEE C57.91-1995 standard are selected to calculate hot spot temperature. A wind farm connected transformer is selected to implement the models. This transformer belongs to Ellevio AB and manufactured by ABB AB. Load data are gathered for every 5 minutes during 2016. Loss of life of transformer is calculated and it is concluded that by considering this factor, the transformer is overdesigned. The optimum size of transformer by utilizing dynamic rating is selected which results in a reduction in investment cost. This method can be used to select the appropriate size oft ransformer by taking advantages of ambient temperature variations and overload the transformer beyond nameplate ratings without exceeding transformer temperature limitations. Moreover, the risk of overloading the transformer at any time during 2016 is calculated. The risk of overloading is quantified as loss of life of transformer. It is shown that this risk is a function of ambient temperature and the duration of overloading. Finally, an economic analysis is done to demonstrate economic benefit of expanding wind farm by overloading the existing transformer by reducing the transformer life expectancy while keeping it in a safe limit. I detta projekt undersoks dynamisk varmeklassicering for transformatorer ochdess eekt pa transformatorns tillforlitlighet. En litteraturoversikt gors pa olikatermiska modeller som anvands for detta andamal och i slutet av dierentialekvationsmodellenfran IEC 60076-7 och bottenoljemodellen fran IEEE C57.91-1995 standard valjes for att berakna varmpunktstemperatur. En transformatormed vindkraftpark valjs for att genomfora modellerna. Denna transformatortillhor Ellevio AB och tillverkas av ABB AB. Lastdata samlas in for var 5: eminut under 2016. Transformatorns livslangd beraknas och det slutsatsen atttransformatorn ar overdesignad med hansyn till denna faktor. Den optimalastorleken pa transformatorn genom att anvanda dynamisk rating valjs vilket resulterari en minskning av investeringskostnaden. Denna metod kan anvandasfor att valja lamplig storlek for transformatorn genom att dra fordel av omgivandetemperaturvariationer och overbelasta transformatorn bortom markskyltarutan att overskrida transformatortemperaturbegransningar. Dessutomberaknas risken for overbelastning av transformatorn nar som helst under 2016.Risken for overbelastning kvantieras som forlust av livslangd for transformatorn.Det visas att denna risk ar en funktion av omgivande temperatur ochvaraktigheten av overbelastning. Slutligen gors en ekonomisk analys for attvisa ekonomisk nytta av att expandera vindkraftparken genom att overbelastaden bentliga transformatorn genom att minska transformatorens livslangd samtidigtsom den halls i en saker grans.

Power system components usually have standard static ratings that determine the load constraints. Load constraints are designed for extreme conditions and are one of the reasons, why power systems do not use all of their potential transmission capacity. In the 21st century, efficiency and the cost of energy production and distribution have become a very popular topic, because the energy production and its transmission cost has a direct influence on sustainability. Dynamic Rating is a smart grid application, which allows using more of the system capacity by monitoring system conditions. This paper presents a literature review on the topic of Dynamic Rating. We focus on Dynamic Rating of overhead lines. Overhead lines are of great interest for Dynamic Rating applications, because of their high cost and high potential for further improvement. Different tools for analysis of real time data and ways of application of Dynamic Rating to the power system are taken into consideration. QC 20170629 Dynamic Rating for Wind Power

In this project dynamic thermal rating for transformers and its effect on transformer reliability are investigated. A literature review is done on different thermal models used for this purpose and at the end differential equations model from IEC 60076-7 and bottom oil model from IEEE C57.91-1995 standard are selected to calculate hot spot temperature. A wind farm connected transformer is selected to implement the models. This transformer belongs to Ellevio AB and manufactured by ABB AB. Load data are gathered for every 5 minutes during 2016. Loss of life of transformer is calculated and it is concluded that by considering this factor, the transformer is overdesigned. The optimum size of transformer by utilizing dynamic rating is selected which results in a reduction in investment cost. This method can be used to select the appropriate size oft ransformer by taking advantages of ambient temperature variations and overload the transformer beyond nameplate ratings without exceeding transformer temperature limitations. Moreover, the risk of overloading the transformer at any time during 2016 is calculated. The risk of overloading is quantified as loss of life of transformer. It is shown that this risk is a function of ambient temperature and the duration of overloading. Finally, an economic analysis is done to demonstrate economic benefit of expanding wind farm by overloading the existing transformer by reducing the transformer life expectancy while keeping it in a safe limit. I detta projekt undersoks dynamisk varmeklassicering for transformatorer ochdess eekt pa transformatorns tillforlitlighet. En litteraturoversikt gors pa olikatermiska modeller som anvands for detta andamal och i slutet av dierentialekvationsmodellenfran IEC 60076-7 och bottenoljemodellen fran IEEE C57.91-1995 standard valjes for att berakna varmpunktstemperatur. En transformatormed vindkraftpark valjs for att genomfora modellerna. Denna transformatortillhor Ellevio AB och tillverkas av ABB AB. Lastdata samlas in for var 5: eminut under 2016. Transformatorns livslangd beraknas och det slutsatsen atttransformatorn ar overdesignad med hansyn till denna faktor. Den optimalastorleken pa transformatorn genom att anvanda dynamisk rating valjs vilket resulterari en minskning av investeringskostnaden. Denna metod kan anvandasfor att valja lamplig storlek for transformatorn genom att dra fordel av omgivandetemperaturvariationer och overbelasta transformatorn bortom markskyltarutan att overskrida transformatortemperaturbegransningar. Dessutomberaknas risken for overbelastning av transformatorn nar som helst under 2016.Risken for overbelastning kvantieras som forlust av livslangd for transformatorn.Det visas att denna risk ar en funktion av omgivande temperatur ochvaraktigheten av overbelastning. Slutligen gors en ekonomisk analys for attvisa ekonomisk nytta av att expandera vindkraftparken genom att overbelastaden bentliga transformatorn genom att minska transformatorens livslangd samtidigtsom den halls i en saker grans.

Power system owners are facing major challenges, for example with changed electricity consumption and production patterns; more distributed generation and increased demand of cost efficiency while maintaining high reliability. The concept of dynamic rating can act as a part solution and implies that the capacity of a component is dynamically varying as a function of external parameters such as weather and load history. This hence implies that a component can be better utilized. This can have both direct economic benefits for the utility, but also benefits for the society and the environment by lower tariff levels, faster and cheaper connection of local environmentally friendly electricity production and less climate impact associated with component production and installation. This paper gives a brief introduction to the concept of dynamic rating applied to power systems. Furthermore, results and conclusions from two workshops during 2013 are summarized, where representatives from Vattenfall and Fortum (distribution system operators), ABB (producer and developer that work with dynamic rating solutions), Swedish national grid and several persons from the academia contributed. This was complemented by interviews with the involved companies. The result is a mapping of knowledge, research, development interests, current situation and future visions. All parties show a great interest and see potential, but there are also challenges to be solved. QC 20140806

Power system owners are facing major challenges with changed electricity consumption and production patterns; more distributed generation and increased demand of cost efficiency while maintaining high reliability. Today, the capacity of power components often is set with static limits based on simulations of worst case scenarios. This leads to a discrepancy between the actually-available capacity and the rating itself which unfortunately is left unused. The approach of dynamic rating implies that the capacity of a component is dynamically varying as a function of external parameters such as weather, load history and diagnostic indicators. Svenska kraftnät (Swedish national grid) has installed temperature sensors with the purpose of developing condition monitoring methods in another research project. Within this project, the same infrastructure can perhaps be used to also evaluate dynamic rating algorithms of power lines or to develop new algorithms regarding e.g. disconnectors. Also the thermal modelling in that project can be reused. This paper hence exemplifies the possibility to get more applications without additional costly and complicated investments. The aim of the paper is hence to show on future research possibilities and bring ideas to discussion. QC 20140922

As the demand for energy increases, as well as the demand for renewable energy, Vattenfall, as network owner, receives many requests to connect new wind power to the grid. The limiting factor for how much wind power that can be connected to the grid is in this case the maximum current capacity of the overhead lines that is based on a line temperature limit. The temperature limit is set to ensure a safety distance between the lines and the ground. This master thesis project is a part of a research project at Vattenfall Research and Development that is examining the possibilities of increasing the allowed current on overhead lines in order to be able to connect more wind power to the existing network. Measured data from two overhead lines in southern Sweden is analyzed and the internal relations between the measured parameters are examined. The measured parameters are overhead line sag, line temperature, ambient temperature, solar radiation, wind speed and line current. The results indicate that there is a big load margin that could be utilized to increase the maximum current as long as further work could show that low winds at line height correlates with low wind at nacelle height. The results show that the sag versus line temperature is approximately linear within the measured temperature range. This means that a real-time-monitoring system measuring the line temperature should give adequate knowledge of the line position to ensure the safety distance. A model for the line temperature as a function of insolation, current, ambient temperature and wind speed has been estimated for one of the lines. Simulations show that a sudden increase in current at a worst-case scenario would give the operators about ten minutes to react before the line reaches the temperature limit.

Due to the great complexity of VHDL models that are created today, the amount of processing time required to simulate these models and the amount of labor required to develop these models have become critical issues. The amount of processing time required to simulate a model can be directly influenced by the efficient use of VHDL concepts in creating the model. This dissertation presents an approach to aiding the modeler in the development of more efficient VHDL models. This is done by measuring the simulation efficiency of process-level VHDL behavioral models. Research in the determination of what VHDL constructs and modeling styles are most efficient is presented. The development and use of a tool that parses VHDL behavioral models and reveals the efficiency of the code in the form of a numerical efficiency rating is also presented. Ph. D.