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Dynamic Rating with Applications to Renewable Energy
KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering. (QED Asset Management)ORCID iD: 0000-0002-4065-715x
2020 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Abstract [sv]

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.

Place, publisher, year, edition, pages
Stockholm,: KTH Royal Institute of Technology, 2020. , p. 84
Series
TRITA-EECS-AVL ; 2020:3
Keywords [en]
dynamic rating, dynamic line rating, dynamic transformer rating, power transformers, power system optimization, wind farm planning
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electrical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-266363ISBN: 978-91-7873-390-3 (print)OAI: oai:DiVA.org:kth-266363DiVA, id: diva2:1383904
Public defence
2020-01-31, Kollegiesalen, Brinellvägen 8, Stockholm, 14:00 (English)
Opponent
Supervisors
Funder
Swedish Energy AgencySweGRIDS - Swedish Centre for Smart Grids and Energy Storage, FPS18StandUp for Wind
Note

QC 20200109

Available from: 2020-01-09 Created: 2020-01-09 Last updated: 2020-01-09Bibliographically approved
List of papers
1. A framework for application of dynamic line rating to aluminum conductor steel reinforced cables based on mechanical strength and durability
Open this publication in new window or tab >>A framework for application of dynamic line rating to aluminum conductor steel reinforced cables based on mechanical strength and durability
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2020 (English)In: International Journal of Electrical Power & Energy Systems, ISSN 0142-0615, E-ISSN 1879-3517, Vol. 116, article id 105491Article in journal (Refereed) Published
Abstract [en]

Dynamic line rating can be described as a method of overloading the power line within reliability and safety limits. Power line's loading limits can be increased, if its temperature is controlled to be below the maximum allowable conductor temperature, which is defined by the grid regulations. Dynamic rating brings additional uncertainties and risks to the grid operation due to high variability of weather conditions, which plays an essential role in determining real-time capacity limits. Power lines often are under the influence of risk factors related to power system performance, however, they could also be subjected to additional risks related to their mechanical structure. Overhead lines, which are composed of more than one stranded material, are exposed to increasing mechanical stress due to differences in thermal expansion characteristics of different materials. The reliability analysis of transient expansion/shrinkage of the material has identified the risks to the conductor mechanical strength that are associated with dynamic heating and cooling. This study determines an optimal dynamic line rating application, which not only would take into account electrical properties of the system and economic benefits, but would also minimize the aging of steel reinforced aluminum overhead lines. Alternatively to hourly line rating adjustment, 2 h, 3 h and 4 h ratings are suggested as possible way to decrease impact of DLR on conductor mechanical durability. Comparing the mechanical durability and cost benefits between different frequencies of loading limit adjustments, allows suggesting improvements to dynamic line rating application. 

Place, publisher, year, edition, pages
Elsevier, 2020
Keywords
Aluminum conductor steel reinforced, Conductor mechanical strength, Dynamic line rating, Power line durability, Durability, Electric power system control, Overhead lines, Reinforcement, Reliability analysis, Risk assessment, Thermal expansion, Dynamic line ratings, Maximum allowable conductor temperature, Mechanical durability, Power lines, Power system performance, Reliability and safeties, Thermal expansion characteristics, Dynamics
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-262058 (URN)10.1016/j.ijepes.2019.105491 (DOI)000499733200009 ()2-s2.0-85072543859 (Scopus ID)
Note

QC 20191122

Available from: 2019-11-22 Created: 2019-11-22 Last updated: 2020-01-13Bibliographically approved
2. Effects of Dynamic Line Rating on the Durability and Mechanical Strength of Aluminum Cable Steel Reinforced (ACSR) Conductors
Open this publication in new window or tab >>Effects of Dynamic Line Rating on the Durability and Mechanical Strength of Aluminum Cable Steel Reinforced (ACSR) Conductors
2019 (English)In: Innovative Solutions for Energy Transitions, Elsevier, 2019, Vol. 158, p. 3164-3169Conference paper, Published paper (Refereed)
Abstract [en]

Dynamic Line Rating (DLR) is an emerging technology, which provides better utilization of power lines, by using real-time information on the weather parameters to dynamically adjust line rating limits. The power line capacity is highly dependent on its heat balance. The heat balance is influenced by external factors such as wind speed, ambient temperature, humidity, solar radiation and load. DLR analyses have shown high economical and reliability benefits from power system perspective. However, the mechanical stress on the conductor due to differences in thermal expansion characteristics of Aluminum and Steel materials could lead to faster ageing and mechanical damages. The study aims to provide better understanding of the risks associated with DLR application, which can affect conductor's mechanical lifetime. The reliability analysis of transient expansion and shrinkage of the material has identified the risks to the conductor mechanical strength that are associated with dynamic heating and cooling.

Place, publisher, year, edition, pages
Elsevier, 2019
Series
Energy Procedia, ISSN 1876-6102 ; 158
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-239530 (URN)10.1016/j.egypro.2019.01.1019 (DOI)000471031703082 ()2-s2.0-85063912210 (Scopus ID)
Conference
10th International Conference on Applied Energy, ICAE 2018; Hong Kong; China; 22 August 2018 through 25 August 2018
Projects
Dynamic rating with applications to renewable energy
Funder
SweGRIDS - Swedish Centre for Smart Grids and Energy Storage, FPS18StandUp for WindSwedish Energy Agency
Note

QC 20181126

Available from: 2018-11-23 Created: 2018-11-23 Last updated: 2020-01-09Bibliographically approved
3. Reliability considerations and economic benefits of dynamic transformer rating for wind energy integration
Open this publication in new window or tab >>Reliability considerations and economic benefits of dynamic transformer rating for wind energy integration
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2019 (English)In: International Journal of Electrical Power & Energy Systems, ISSN 0142-0615, E-ISSN 1879-3517, Vol. 106, p. 598-606Article in journal (Refereed) Published
Abstract [en]

An increasing share of renewable energy on the electricity market creates the need for economic and efficient production, operation and integration technologies, associated with the specific behavior of renewable energy sources (RES). Dynamic rating (DR) provides a possibility to apply improvements to the system both during planning and operation stages. The DR benefits are well described in various literature sources. However, DR is often focused on more efficient exploitation of power lines, not power transformers. Power transformers are costly equipment and their efficient usage and planning can have drastic effect on total costs.

Our analysis focuses on the dynamic transformer rating (DTR) for wind energy applications. The main objective is to study reliability effects of DTR from the component perspective. We utilize existing knowledge about transformer heat balance models from IEC and IEEE standards to obtain information on the loss of life (LOL) of the transformer under investigation and propose possible improvements for the system in question. The method can be employed for identifying the appropriate transformer size by taking into account ambient temperature and load variations and then overloading the transformer beyond nameplate ratings. The reliability of the proposed application is ensured by calculating the risk of overloading the transformer for each day of the year. A risk of overloading is quantified as LOL of the transformer. The risk is presented as a function of ambient temperature and duration of an overload. The final step consists of an economic analysis, which demonstrates economic benefits of DTR application.

Keywords
Dynamic transformer rating, Loss of life, Heat balance, Wind energy
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electrical Engineering
Identifiers
urn:nbn:se:kth:diva-239531 (URN)10.1016/j.ijepes.2018.09.038 (DOI)000454377000055 ()2-s2.0-85056630521 (Scopus ID)
Projects
Dynamic rating with applications to renewable energy
Funder
SweGRIDS - Swedish Centre for Smart Grids and Energy Storage, FPS18Swedish Energy AgencyStandUp for Wind
Note

QC 20181130

Available from: 2018-11-23 Created: 2018-11-23 Last updated: 2020-01-09Bibliographically approved
4. Dynamic rating assists cost-effective expansion of wind farms byutilizing hidden capacity of transformers
Open this publication in new window or tab >>Dynamic rating assists cost-effective expansion of wind farms byutilizing hidden capacity of transformers
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Dynamic rating of power transmission devices is a technology that allows better equipment utilization through real-time information about the system state. Dynamic rating of transformers is a fairly new technology if compared to dynamic rating of power lines, and has high potential for significantly improving component utilization while lowering investment costs on installing new transformers.

Dynamic transformer rating increases the rating of the transformer considering load and temperature variations without affecting safe operation. Dynamic rating is highly suitable for being used in conjunction with renewable energy generation, specifically wind power. The following work investigates how to utilize existing transformers, which are under exploitation at wind farms, for expanding wind generation capacity. Also, this paper shows improvements that dynamic rating can bring to both power grid operators and wind farm owners by exploring the economic benefits of expanding wind parks while using dynamic rating. Connecting additional wind turbines with the same transformer at sites with high wind capacity after the wind park is already in exploitation can assist in lowering electricity price and provide a possibility of less risky investment in wind power.

Five transformer locations and nine units are studied for finding the potential of dynamic transformer rating for network expansion applications. The analysis shows that the optimal expansion of wind power from a generator perspective is around 30 % to 50 %, although, it can be limited further by network restrictions. A possibility to use a large device, suchas power transformer, closer to its full potential can provide material and cost savings for building new devices and decrease investment costs on manufacturing, transportation and installation of new units. Dynamic rating of power transformers can also increase the socio-economic benefits of renewable energy by lowering electricity price from renewables and incentivize an increased share of green power in electricity markets.

Keywords
dynamic transformer rating, wind energy integration, planning of power systems, reliability of power components
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electrical Engineering
Identifiers
urn:nbn:se:kth:diva-266361 (URN)
Funder
Swedish Energy AgencySweGRIDS - Swedish Centre for Smart Grids and Energy StorageStandUp for Wind
Note

QC 20200109

Available from: 2020-01-08 Created: 2020-01-08 Last updated: 2020-01-09Bibliographically approved
5. Day-ahead dispatch optimization with dynamic thermal rating of transformers and overhead lines
Open this publication in new window or tab >>Day-ahead dispatch optimization with dynamic thermal rating of transformers and overhead lines
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2019 (English)In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 171, p. 194-208Article in journal (Refereed) Published
Abstract [en]

Several studies have demonstrated how Dynamic Line Rating (DLR) could be an effective solution for increasing transmission capacity of existing overhead lines. As opposed to Static Line Ratings (SLR), DLR allows for higher power flows depending on real time thermal state of conductors, which highly depend on actual weather conditions. Similarly, recent advances in transformer thermal modelling revealed the feasibility of Dynamic Transformer Rating (DTR) based on the temporal evolution of top oil and winding hot spot temperatures. However, the joint dynamic thermal rating of both overhead lines and transformers in transmission networks has not been thoroughly addressed yet in the literature. This paper proposes a day-ahead dispatch optimization problem based on DC-Optimal Power Flow, where transformer top oil and hot spot dynamics are directly accounted for together with dynamic line ratings of selected transmission lines. Simulated weather data from an actual power system are mapped to the IEEE RTS 24 bus system thus allowing for the estimation of DLR on several lines and the influence of ambient temperature on transformer rating. Results indicate the potential benefits that using DLR in conjunction with DTR could provide for the optimal power system dispatch. The proposed approach does not only indicate advantages compared to standard rating scenarios, but also shows a positive impact that dynamic line rating has on unlocking transformer constraints and vice versa.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Dynamic line rating, Dynamic transformer rating, Optimal power dispatch, Power system optimization, Wind power integration
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-246409 (URN)10.1016/j.epsr.2019.02.026 (DOI)000464488600019 ()2-s2.0-85062302260 (Scopus ID)
Note

QC 20190402

Available from: 2019-04-02 Created: 2019-04-02 Last updated: 2020-01-09Bibliographically approved
6. Including Dynamic Line Rating into the Optimal Planning of Distributed Energy Resources
Open this publication in new window or tab >>Including Dynamic Line Rating into the Optimal Planning of Distributed Energy Resources
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Dynamic line rating (DLR) is an emerging technology that can remove strict power transmission constraints and potentially reduce investment costs in new generation technologies in microgrid.By implementing dynamic rating into distributed generation sizing and placement problem, it is possible to reduce the investment costs on new distributed energy resources by achieving improved optimal power flow results as compared to planning without considering DLR.

This paper explores the possibility of complementing a model for optimal sitting and placement of the distributed energy resources in microgrids, which has been developed at Berkeley Lab with the dynamic line rating. The comparison of results between a solution with no DLR and solution with DLR has shown a decrease in investment costs as well as reduced number of installed generators.  

Keywords
microgrid design, sizing and placement of generation, optimal power flow, dynamic line rating
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electrical Engineering
Identifiers
urn:nbn:se:kth:diva-266362 (URN)
Funder
SweGRIDS - Swedish Centre for Smart Grids and Energy StorageSwedish Energy AgencyStandUp for Wind
Note

QC 20200109

Available from: 2020-01-08 Created: 2020-01-08 Last updated: 2020-01-09Bibliographically approved

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