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  • 51.
    Mazidi, Peyman
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems. Comillas Pontifical University.
    Bertling Tjernberg, Lina
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Sanz Bobi, Miguel Angel
    Comillas Pontifical University.
    Wind Turbine Prognostics and Maintenance Management based on a Hybrid Approach of Neural Networks and Proportional Hazards Model2016In: Journal of Risk and Reliability, ISSN 1748-006X, E-ISSN 1748-0078Article in journal (Refereed)
    Abstract [en]

    This paper proposes an approach for stress condition monitoring and maintenance assessment in wind turbines (WTs) through large amounts of collected data from the supervisory control and data acquisition (SCADA) system. The objectives of the proposed approach are to provide a stress condition model for health monitoring, to assess the WT’s maintenance strategies, and to provide recommendations on current maintenance schemes for future operations of the wind farm. At first, several statistical techniques, namely principal component analysis, Pearson, Spearman and Kendall correlations, mutual information, regressional ReliefF and decision trees are used and compared to assess the data for dimensionality reduction and parameter selection. Next, a normal behavior model is constructed by an artificial neural network which performs condition monitoring analysis. Then, a model based on the mathematical form of a proportional hazards model is developed where it represents the stress condition of the WT. Finally, those two models are jointly employed in order to analyze the overall performance of the WT over the study period. Several cases are analyzed with five-year SCADA data and maintenance information is utilized to develop and validate the proposed approach.

  • 52.
    Mazidi, Peyman
    et al.
    KTH, School of Electrical Engineering (EES), Electric power and energy systems.
    Bertling Tjernberg, Lina
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Sanz-Bobi, Miguel A.
    Comillas Pontifical University.
    Anomaly Detection and Performance Analysis in Wind Turbines through Neural Networks2015Conference paper (Other academic)
  • 53.
    Mazidi, Peyman
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems. Comillas Pontifical University.
    Bertling Tjernberg, Lina
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Sanz-Bobi, Miguel A.
    Comillas Pontifical University.
    Wind Turbine Prognostics and Maintenance Management based on a Hybrid Approach of Neural Networks and Proportional Hazards Model2017In: Journal of Risk and Reliability, ISSN 1748-006X, E-ISSN 1748-0078, Vol. 231, no 2, p. 121-129Article, review/survey (Refereed)
    Abstract [en]

    This paper proposes an approach for stress condition monitoring and maintenance assessment in wind turbines(WT) through large amounts of collected data from supervisory control and data acquisition (SCADA) system. Theobjectives of the proposed approach are: to provide a stress condition model for health monitoring, to assess the WT’smaintenance strategies, and to provide recommendations on current maintenance schemes for future operations ofthe wind farm. At first, several statistical techniques, namely Principal component analysis, Pearson, Spearman andKendall correlations, mutual information, regressional ReliefF and decision trees are used and compared to assessthe data for dimensionality reduction and parameter selection. Next, a normal behavior model is constructed by anartificial neural network which performs condition monitoring analysis. Then, a model based on mathematical form ofProportional hazards model is developed where it represents stress condition of the WT. Finally, those two modelsare jointly employed in order to analyze the overall performance of the WT over the study period. Several cases areanalyzed with a five-year SCADA data and maintenance information is utilized to develop and validate the proposedapproach.

  • 54.
    Mazidi, Peyman
    et al.
    KTH, School of Electrical Engineering (EES).
    Du, Mian
    KTH. China Electric Power Research Institute.
    Bertling Tjernberg, Lina
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Sanz Bobi, Miguel A.
    Comillas Pontificia Universidad.
    A Performance and Maintenance Evaluation Framework for Wind Turbines2016Conference paper (Refereed)
    Abstract [en]

    In this paper, a data driven framework forperformance and maintenance evaluation (PAME) of windturbines (WT) is proposed. To develop the framework, SCADAdata of WTs are adopted and several parameters are carefullyselected to create a normal behavior model. This model which isbased on Neural Networks estimates operation of WT andaberrations are collected as deviations. Afterwards, in order tocapture patterns of deviations, self-organizing map is applied tocluster the deviations. From investigations on deviations andclustering results, a time-discrete finite state space Markov chainis built for mid-term operation and maintenance evaluation.With the purpose of performance and maintenance assessment,two anomaly indexes are defined and mathematically formulated.Moreover, Production Loss Profit is defined for PreventiveMaintenance efficiency assessment. By comparing the indexescalculated for 9 WTs, current performance and maintenancestrategies can be evaluated, and results demonstrate capabilityand effectiveness of the proposed framework.

  • 55.
    Mazidi, Peyman
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems. Comillas Pontifical Unviersity.
    Mian, Du
    Bertling, Lina
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Sanz Bobi, Miguel Angel
    Comillas Pontifical University.
    Health Condition Model for Wind Turbine Monitoring through Neural Networks and Proportional Hazard Models2017In: Journal of Risk and Reliability, ISSN 1748-006X, E-ISSN 1748-0078Article in journal (Refereed)
    Abstract [en]

    In this article, a parametric model for health condition monitoring of wind turbines is developed. The study is based on the assumption that a wind turbine’s health condition can be modeled through three features: rotor speed, gearbox temperature and generator winding temperature. At first, three neural network models are created to simulate normal behavior of each feature. Deviation signals are then defined and calculated as accumulated time-series of differences between neural network predictions and actual measurements. These cumulative signals carry health condition–related information. Next, through nonlinear regression technique, the signals are used to produce individual models for considered features, which mathematically have the form of proportional hazard models. Finally, they are combined to construct an overall parametric health condition model which partially represents health condition of the wind turbine. In addition, a dynamic threshold for the model is developed to facilitate and add more insight in performance monitoring aspect. The health condition monitoring of wind turbine model has capability of evaluating real-time and overall health condition of a wind turbine which can also be used with regard to maintenance in electricity generation in electric power systems. The model also has flexibility to overcome current challenges such as scalability and adaptability. The model is verified in illustrating changes in real-time and overall health condition with respect to considered anomalies by testing through actual and artificial data.

  • 56.
    Nilsson, Julia
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Bertling, Lina M.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Maintenance management of wind power systems using condition monitoring systems - Life cycle cost analysis for two case studies2007In: IEEE transactions on energy conversion, ISSN 0885-8969, E-ISSN 1558-0059, Vol. 22, no 1, p. 223-229Article in journal (Refereed)
    Abstract [en]

    The large growth in the wind power industry in the past years. mainly focuses on a growing market and the development of large turbines and offshore farms. The high technical availability of wind turbines comes with a greater need for frequent maintenance. Current maintenance planning is not optimized, and it is possible to make maintenance more efficient. Condition monitoring systems (CMS) could resolve the growing wind power industry's need for better maintenance management and increased reliability. Such systems are commonly used in other industries. CMS could continuously monitor the performance of the wind turbine parts and could help determine specific maintenance timing. This paper presents a life cycle cost (LCC), analysis with strategies where CMS improved maintenance planning for a single wind turbine onshore and a wind farm offshore. Case studies are based on real data from Olsvenne2 at Nasudden (Gotland, Sweden) and Kentish Flats, in the U.K. The main conclusion is that CMS benefits maintenance management of wind power systems. Improvements can be especially shown for offshore wind farm maintenance planning.

  • 57. Pinares, G.
    et al.
    Tuan, L. A.
    Bertling-Tjernberg, Lina
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Breitholtz, C.
    Analysis of the dc dynamics of VSC-HVDC systems using a frequency domain approach2013In: 2013 IEEE PES Asia-Pacific Power and Energy Engineering Conference (APPEEC), IEEE Computer Society, 2013, p. 6837285-Conference paper (Refereed)
    Abstract [en]

    In this paper, the dc dynamic performance of VSC-HVDC systems is investigated using the frequency domain approach. In a previous work, it has been found through the eigenvalue analysis that, in some situations, the VSC-HVDC system becomes unstable when the converter which controls the direct-voltage injects power exceeding a certain value. However, the cause of the instability was not addressed. This paper attempts to answer some of the remaining questions in the previous work through the frequency response of the elements that compose the system. In order to facilitate the analysis, appropriate assumptions have been made. The transfer function of both, dc grid and the converter which controls the direct-voltage, are derived. The results from the analysis show that, depending on the direction of the power, the frequency response of the converter has a negative resistance characteristic which amplifies resonances in the dc grid.

  • 58.
    Puglia, Gloria
    et al.
    Chalmers, Sweden.
    Bangalore, Pramod
    Chalmers, Sweden.
    Bertling Tjernberg, Lina
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Cost Efficient Maintenance Strategies for Wind Power Systems Using LCC2014In: International Conference on Probabilistic Methods Applied to Power Systems (PMAPS), 2014Conference paper (Refereed)
    Abstract [en]

    Maintenance costs for wind power plants are a significant part of the total life cycle cost, especially for offshore wind power plants, situated at remote sites. In order to decrease the cost of maintenance, monitoring systems have been used to estimate the condition of critical components in wind turbines. This paper proposes Life Cycle Cost analysis (LCC) approach for maintenance management of wind turbines. The LCC approach for maintenance management presented in this paper is an extension on previous work by J. Nilsson and L. Bertling, where a comparison has been made with this previous work and the same is extended with new data and models. Case studies are presented based on data from three different wind turbinesrated 3 and 6MW. Three different scenarios have been studied and the effect of condition monitoring system (CMS) has been analysed. For any chosen value the CMS proves to be a profitable option.

  • 59.
    Ribrant, Johan
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Bertling, Lina M.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Survey of failures in wind power systems with focus on Swedish wind power plants during 1997-20052007In: 2007 IEEE POWER ENGINEERING SOCIETY GENERAL MEETING, 2007, p. 3896-3903Conference paper (Refereed)
    Abstract [en]

    The wind power industry has expanded greatly during the past few years, has served a growing market, and has spawned the development of larger wind turbines. Different designs and technical advances now make it possible to put wind turbines off shore. The fast expansion of the wind power market comes with problems. The new designs are not always fully tested, and the designed 20 year lifetime is typically never achieved before the next generation of turbines is erected. This paper presents results from an investigation of failure statistics from four sources, i.e. two separate sources from Sweden, one from Finland, and one from Germany. Statistics reveal reliability performance of the different components within the wind turbine. The gearbox is the most critical because downtime, per failure, is high compared to the other components in the wind power turbine. The statistical data for larger turbines also show trends toward higher, ever increasing failure frequency when compared to small turbines, which have a decreasing failure rate over the operational years.

  • 60.
    Setréus, Johan
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Arnborg, Stefan
    KTH, School of Electrical Engineering (EES).
    Eriksson, Roland
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Bertling, Lina
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Components' Impact on Critical Transfer Section for Risk Based Transmission System Planning2009In: 2009 IEEE Bucharest PowerTech: Innovative Ideas Toward the Electrical Grid of the Future / [ed] Toma L; Otomega B, IEEE , 2009, p. 368-375Conference paper (Refereed)
    Abstract [en]

    In the planning of the electrical transmission system it is of greatest concern to quantify the security margin for unwanted conditions in the system. This paper proposes an approach based on quantifying the risk of insufficient transmission capacity in bottlenecks in the system. Stresses in these critical transfer sections (CTS) provide a potential risk to corrective actions, or worst, load curtailments. The proposed method provides a general screening of component outages in order to find potential risk events for the CTS. Furthermore, the severity of each risk event is quantified based on the likelihood of the event and the consequence on the section's transmission capacity. The components' contribution to the risk of insufficient capacity in the CTS is then based on these risk events' severity. The method investigates several forecasted load levels during the year and consequently gives an input to a scheme for a risk based transmission system planning. The method is demonstrated on the reliability test system RBTS.

  • 61.
    Setréus, Johan
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Bertling, Lina
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Introduction to HVDC Technology for Reliable Electrical Power Systems2008In: Proceedings of the 10th International Conference on Probabilistic Methods Applied to Power Systems, PMAPS 2008, NEW YORK: IEEE , 2008, p. 560-567Conference paper (Refereed)
    Abstract [en]

    The transmission system is becoming ever more complex. Furthermore, demand for reliable supply of electricity is growing, increasing the need for a higher level of system reliability. A solution might be to incorporate controllable power components within the system. One such component is the HVDC link. However, in the domain of reliability models for HVDC and the component's impact on the overall transmission system reliability, there is still much work to be done. This is an important issue in future grid planning, especially with an increasing penetration of HVDC links within synchronous transmission systems acting as "firewalls". These links may prevent disturbances propagating in the system, which is a common cause of blackouts. This paper provides a broad introduction to the HVDC technology and a literature review of reliability assessments published within this area. It gives a background to and motivation for the technology. Published reliability assessments of the HVDC technology have been reviewed and categorized. One conclusion is that a large number of models and methods for the reliability evaluation of the HVDC system itself have been published, but very few on its impact on the composite system reliability. One future challenge to be solved is how the "firewall" properties of the HVDC can be quantified in a reliability assessment.

  • 62.
    Setréus, Johan
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Wallnerström, Carl Johan
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Bertling, Lina
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    A Comparative Study of Regulation Policies for Interruption of Supply of Electrical Distribution Systems in Sweden and UK2007In: 19th International Conference on Electricity Distribution (CIRED), CIRED , 2007, p. 1-4Conference paper (Other academic)
    Abstract [en]

    This paper presents a comparative study of regulating policies for interruption of supply in Sweden and UK. The two regulating regimes have been applied for a case study with a real rural electrical distribution system in Sweden, Flymen. The Swedish and UK regulations state that the distribution system operators (DSO) should restore power delivery to customers within 12 and 18 hours respectively for normal weather conditions. If this could not be fulfilled the DSOs are opposed to different predetermined penalty payments to the customers.

    In a comparative case study of Flymen the Swedish model (GL) gives a 68% higher compensation to customers than the UK model (GS) for a 30 hours interruption of supply during normal weather conditions. Historical interruption data for the same system gives a 75% higher compensation with the Swedish model (GL) than the UK model (GS). The main conclusion from the comparative study is that the Swedish GL model provides a higher compensation for interruptions of supply to customers than the UK GS model.

  • 63.
    Shafiee, Mahmood
    et al.
    Cranfield University, UK.
    Patriksson, Michael
    Chalmers.
    Strömberg, Ann-Brith
    Chalmers.
    Bertling Tjernberg, Lina
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Optimal Redundancy and Maintenance Strategy Decisions for Offshore Wind Power Converters2015In: International Journal of Reliability, Quality and Safety Engineering (IJRQSE), ISSN 0218-5393, Vol. 22, no 3, p. 1550015-1-1550015-24, article id 1550015Article in journal (Refereed)
    Abstract [en]

    Analysis of field failure data collected from various wind farm databases indicates that the power converters are among the most critical components in offshore wind turbines, since they suffer from a high failure rate. One efficient approach to enhance the reliability and availability of the wind power systems is through using a redundant converter design, in which a set of power converters is placed together in parallel. The main advantage of a multiple parallel converter system is that the failure of one converter will not necessarily lead to the failure of the entire system. It may however increase the wind turbine’s acquisition cost, volume, and weight. In this paper, we propose an approach of joint redundancy and maintenance strategy optimization for offshore wind power converters, aiming to simultaneously determine the “optimal allocation of redundant converters” and the “optimal threshold number of converters that are allowed to fail before sending a maintenance crew to the offshore platform”. The optimal solution under various system- level constraints (such as reliability, weight, and the available space in nacelle) is derived and the conditions required to make using a redundant system beneficial are discussed. The proposed design is applied to an offshore wind turbine system and its performance is evaluated using a Monte-Carlo simulation technique. Finally, the results are compared with the conventional power converter system and a sensitivity analysis is conducted in order to make the proposed approach applicable for the next generation of wind turbines. 

  • 64. Steen, D.
    et al.
    Balram, P.
    Tuan, L. A.
    Reichenberg, L.
    Bertling Tjernberg, Lina
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Impact assessment of wind power and demand side management on day-ahead market prices2015In: IEEE PES Innovative Smart Grid Technologies Conference Europe, IEEE Computer Society, 2015, no JanuaryConference paper (Refereed)
    Abstract [en]

    This paper provides an approach to investigate the impacts of wind power (WP) and demand side management (DSM) on the day-ahead electricity market prices. A market model incorporating demand scheduling has been developed for the study, to assess whether there are any mutual economic benefits between WP and scheduling of electric heating demand. A case study performed on a representative Nordic system with a scenario for future WP development in the Nordic electricity market has been carried out. The study results show that DSM could reduce the revenue for the WP producers, up to 2%. On the other hand, WP could result in reduced heating cost, up to 10%, for the customers. However, with an objective of reducing the total system cost, customers in some areas could experience an increase in electricity price even after providing their flexible demand to the market.

  • 65.
    Wallnerström, Carl Johan
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Bertling, Lina
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    A Sensitivity Study of the Swedish Network Performance Assessment Model Investigating the Effects of Changes in Input Data2007In: 19th International Conference on Electricity Distribution (CIRED), CIRED , 2007, p. 1-4Conference paper (Other academic)
    Abstract [en]

    This paper present results from a sensitivity study of the Network Performance Assessment Model (NPAM) as an effect of changes in input data. The NPAM estimates a cost corresponding to operate a fictive reference network, so called network performance assessment (NPA). This value is then compared with the revenue. Small changes have been implemented at the customer data level for real electrical distribution systems e.g. moving a low-voltage customer a few meters. Results show on that the NPA could differ up to 7 million Euros. The main conclusion is that a small divergence in input data could result in significant differences in the output data from the NPAM.

  • 66.
    Wallnerström, Carl Johan
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Bertling, Lina
    Chalmers.
    Känslighetsanalys av Nätnyttomodellens indata: En analys av 2005 års version av Nätnyttomodellen och dess parametrar för autentiska indata2005Report (Other academic)
  • 67.
    Wallnerström, Carl Johan
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Bertling, Lina
    Chalmers.
    Laws And Regulations Of Swedish Power Distribution Systems 1996-2012: learning from novel approaches such as less good experiences2010Conference paper (Refereed)
    Abstract [en]

    This paper gives an overview of a turbulent time for the regulator and distribution system operators (DSO) in Sweden since the de-regulation of the electricity market in 1996. A performance based ex-post model was introduced 2003 as a tool to judge distribution system tariffs. This model is since 2009 formally abandoned and a new exante regulation will be introduced in 2012. The aim of this paper is to learn from both unique and novel approaches such as less good experiences. The paper desccribes the history, the current situation and planed future regulations and desccribes additional relevant laws.

  • 68.
    Wallnerström, Carl Johan
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Bertling, Lina
    Chalmers.
    Learning from Experiences of the prior Swedish Electrical Distribution System Regulation: Reference Material when Developing the Future Regulatory Incentives2010In: Innovative Smart Grid Technologies Conference Europe (ISGT Europe), 2010 IEEE PES, IEEE , 2010Conference paper (Refereed)
    Abstract [en]

    The electric power system is under an extensive development phase. This change is today normally expressed in the concept of Smart Grid. It captures different developments for a sustainable electric power system, e.g. including large changes at the electrical distribution level with new features for electricity customers. One move in these changes is the larger role of the regulator. In Sweden, a performance based regulatory model was introduced in 2003 as a tool to support in judging if the distribution system operators (DSOs) was charging the customers the right level of tariffs. The model was referred to as the Network Performance Assessment Model (NPAM). The NPAM was an international unique and innovative regulatory tool. The model evaluated tariffs by enter several system data to a computer program which produce a fictive network with the aim of having the same objective conditions as the real system. However, the NPAM was strongly criticized and since 2009 formally abandoned and a new regulation will be introduced 2012. Moreover, the NPAM not support climate incentives such as low losses, which will be a challenge when adopting a smart grid perspective into the regulation of distribution system tariffs in the future. The authors of this paper have followed the development of this model, and have a unique insight in the complexity behind the model. No stringent description of the NPAM is available. This paper aims to fill this gap by providing an overall picture of the NPAM including hitherto unpublished details on underlying theory. This could hopefully inspire and give a reference when developing regulations in different countries in the future by learning from its novelties as well as from its drawbacks.

  • 69.
    Wallnerström, Carl Johan
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Bertling, Lina
    Chalmers.
    Risk Management Applied to Electrical Distribution Systems2009Conference paper (Refereed)
    Abstract [en]

    This paper summarizes results from a research project investigating risk management applied to electrical distribution systems (EDS) in Sweden. New incentives have motivated the distribution system operators (DSOs) to consider more comprehensive analysis methods. The project focuses on investigating long term consequences of different project- and maintenance plans. This paper shortly desccribes related research, incentives, results from an application study and future work. The main conclusion is that there is a trend that DSOs use more complex risk management approaches as a result of new incentives.

  • 70.
    Wallnerström, Carl Johan
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Bertling, Lina M.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Investigation of the robustness of the Swedish network performance assessment model2008In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 23, no 2, p. 773-780Article in journal (Refereed)
    Abstract [en]

    The Swedish energy agency (STEM) has developed a regulatory model to supervise the revenues of the distribution system operators (DSO). The model is referred to as the network performance assessment model (NPAM). The NPAM calculates customer values for a fictive electrical distribution system, with a total cost referred to as the network performance assessment (NPA). The debiting rate for a DSO is defined by the quotient of the revenue and the NPA. If the debiting rate is higher than a certain value, the DSO is placed under review and could be forced to pay back revenue to customers. A lawsuit is currently in progress on this use of the NPAM. This paper shows results from a comprehensive sensitiveness study of the NPAM investigating the robustness of the model. The investigation shows that the model is not robust, since small stochastic variations in input data could lead to larger differences in the results than those from the model. For example, it is shown that a five-meter difference in the coordinates of the nodes in the reference system could result in a difference of 5 million Euros, i.e., approximately US $6.5 million. The understanding of weaknesses in the NPAM presented in this paper provides an important means for future developments of regulatory models in the world.

  • 71.
    Wallnerström, Carl Johan
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Bertling, Lina
    Chalmers.
    Tuan, Le Anh
    Risk and reliability assessment for electrical distribution systems and impacts of regulations with examples from Sweden2010In: International Journal of Systems Assurance Engineering and Management, ISSN 0975-6809, Vol. 1, no 2, p. 87-95Article in journal (Refereed)
    Abstract [en]

    The introduction of performance based tariff regulations, and higher media and political pressure have increased the need for well-performed asset management in the operation and planning of electrical distribution systems. In this paper quantitative reliability assessment methods are proposed as a tool to meet these new incentives. Electrical distribution systems have compared to other technical systems several special characteristics which are important to take into consideration when introducing reliability analysis methods. Moreover, the paper gives a brief discussion on the effects and the importance of customer participation in improving system reliability by providing additional system operating reserve from the market perspective. Finally, the paper discusses the reliability analysis with the reliability test systems, and stresses the usefulness of generally known test systems for such assessments. The ideas of future work on development of these test systems to address the changing power systems are presented.

  • 72.
    Wallnerström, Carl Johan
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Bertling Tjernberg, Lina
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Hilber, Patrik
    KTH, School of Electrical Engineering (EES).
    Babu, Sajeesh
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Jürgensen, Jan Henning
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Analys av smartaelnätsteknologier inom kategorin elnätslösningar2014Report (Other academic)
    Abstract [sv]

    Denna rapport presenterar resultat från en studie där inverkan av så kallade smartaelnäts­teknologier/lösningar har analyserats. Utöver egna analysresultat identifieras behov av framtida forskning, detta kompletteras med hänvisningar till fördjupningsmaterial Smarta­elnätsteknologier innebär nya möjligheter, men också nya utmaningar och risker. Ett behov av att utveckla nya metoder för tillförlitlighetsberäkningar och riskanalys har identifieras. På grund av bristande erfarenhet gällande många nya tekniker och lösningar av smartaelnäts­teknologier är det värdefullt med demonstrationsanläggningar såsom Smart Grid Gotland, varifrån indata har erhållits. Information om Smart Grid Gotland och Gotlands elkraftsystem sammanfattas i rapporten. Gotlands regionnät har även implementerats i datorverktyget NEPLAN. En visuell modell av ett elnät med integrerade smartaelnätsteknologier som kan illustrera möjligheter och utmaningar ur ett systemperspektiv. I rapporten behandlas även frågan om framtida kompetensbehov till följd av smarta elnät ur ett riskperspektiv.

     

    En stor mängd timvis väderdata har bearbetats och analyserats tillsammans med timvis data för elkonsumtion och lokal elproduktion. Samband mellan olika parametrar har identifierats, vilka kan vara värdefulla att använda sig av vid utvecklandet av smarta lösningar i elnätet. Resultat från denna initiala analys av indata har använts i genomförda analyser, men kan även vara användbarts referensmaterial i andra studier. Ett analysverktyg har tagits fram för att analysera integrering av elproduktion från både vindkraftturbiner och solkraft, analys av acceptgränser, dynamisk belastningsförmåga och energilager. Hänsyn tas till vädrets påverkan på elproduktions- och elkonsumtionsmönster samt överföringskapacitet.

     

    Dynamisk belastningsförmåga innebär att systemets överföringskapacitet varierar dynamiskt med avseende på externa parametrar såsom väder, vilket ökar möjligheten att nyttja ekraft­system mer effektivt. Analysresultat från flera olika scenarion presenteras i rapporten, vilka visar på olika exempel avseende hur elnätet kan hantera högre maxnivå av elkonsumtion och/eller elproduktion utan fysiska nätförstärkningar. I rapporten presenteras även exempel på hur denna lösning i vissa fall kan öka leveranssäkerhet. Potential av att använda sammanlagring mellan elkonsumtion och lokal elproduktion har analyserats, det vill säga hur dessa tar ut varandra. Även resultat för olika risknivåer med avseende på överlast har analyserats för flera olika scenarier, med och utan dynamisk belastningsförmåga. Om över­last endast medför ökat slitage går det att tänka sig att det kan tillåtas under korta perioder.

     

    Energilagring har analyserats ur ett teknikneutralt perspektiv och resultat redovisas som kravlistor. Av elproduktion från vindkraftturbiner respektive solkraft och elkonsumtion kan ett lika stort energilager höja maxeffekten av solkraft mer jämfört med övriga analyserade kategorier. Även energilager i systemdel innehållendes både elkonsumtion och elproduktion, vilken har problem med både import- och exportbegränsningar, har analyserats. Denna kombination balanserar ofta varandra så att överlast undviks; energilagret tar hand om de två ytterligheterna: export- respektive importtoppar. Hur energilager potentiellt kan användas för att höja leveranskvalitet har också analyserats. Energilager som hanterar överföringstoppar behöver endast användas under en liten period av årets timmar och skulle därför kunna användas för flera olika saker såsom att öka leverenssäkerhet.

     

    I ett appendix till rapporten görs en ansats till att koppla studiens innehåll till rekommendationer presenterade i Samordningsrådet för smarta elnäts handlingsplan.

  • 73.
    Wallnerström, Carl Johan
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Bertling Tjernberg, Lina
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Hilber, Patrik
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Jürgensen, Jan Henning
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Framework for System Analyses of Smart Grid Solutions with Examples from the Gotland Case2016In: 2016 International Conference on Probabilistic Methods Applied to Power Systems (PMAPS), IEEE, 2016Conference paper (Refereed)
    Abstract [en]

    This paper presents results from a study on the impact of smart grid solutions, which includes development of a generic framework for power system analyses. The study has been performed as one of several independent studies, part of a national governmental task on smart grid in Sweden. A large amount of weather data, along with electricity consumption and wind power generation data, have been analyzed. Achieved results from these initial analyses can be used as reference material and have also been used within case studies presented. The proposed framework is flexible and numerous combinations of scenarios are possible to define. Integration of wind and solar power, analyses of transfer limits using static or dynamic rating and energy storage can be considered as well as weather effects. Results show how power systems can handle more electricity consumption and generation. The study shows that Smart Grid solutions are beneficial for resource efficient electricity grids. Moreover, different risk levels with respect to increased load can be included. Case study results show that energy storages most of the time will be unused, but that they can be used to increase the system reliability.

  • 74.
    Wallnerström, Carl Johan
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Hasselström, Jörgen
    Fortum Distribution, Karlstad, Sweden.
    Bengtsson, Per
    Fortum Distribution, Karlstad, Sweden.
    Bertling, Lina
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Review of the Risk Management at a Distribution System Operator2008In: 2008 10TH INTERNATIONAL CONFERENCE ON PROBABILISTIC METHODS APPLIED TO POWER SYSTEMS, IEEE , 2008, p. 90-97Conference paper (Refereed)
    Abstract [en]

    Sweden was re-regulated in 1996 followed by new laws and regulations. These new circumstances have become incentives to adopt more comprehensive and quantitative analysis methods applied on Electrical Distribution Systems (EDS). This paper provides a systematic presentation of the current risk management at a Distribution System Operator (DSO) as an integrated part of the net planning process. The description is complemented by an example and an evaluation including ideas of future developments. Furthermore, the paper gives a definition on the risk concept; investigates how different incentives affect the risk management; describes and discusses similarities and differences between voltage levels. The main objective is to support DSOs in the work of developing risk management and to give academic reference material to utilize industry experience.

  • 75.
    Wallnerström, Carl Johan
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Setreus, Johan
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Hilber, Patrik
    KTH, School of Electrical Engineering (EES).
    Tong, Fan
    Bertling, Lina
    Chalmers.
    Model of Capacity Demand under uncertain Weather2010In: Proceedings IEEE International Conference on Probabilistic Methods Applied to Power Systems (PMAPS), IEEE , 2010, p. 314-318Conference paper (Refereed)
    Abstract [en]

    Load forecasting is important in the operation of power systems. The characteristics of the electrical energy consumption are analyzed and its variation as an effect of several weather parameters is studied. Based on historical weather and consumption data received from a distribution system operator (DSO), numerical models of load forecasting are suggested according to electrical power consumption and on daily peak power respectively. Two linear regression models are presented: simple linear regression (SLR) with one input variable (temperature) and multiple linear regressions (MLR) with several input variables. The models are validated with historical data from other years. For daily peak power demand a MLR model has the lowest error, but for prediction of energy demand a SLR model is more accurate.

  • 76.
    Yuan, Zhao
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Hesamzadeh, Mohammad Reza
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Cui, Yue
    KTH, School of Electrical Engineering (EES).
    Bertling Tjernberg, Lina
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Applying High Performance Computing to Probabilistic Convex Optimal Power Flow2016In: 2016 INTERNATIONAL CONFERENCE ON PROBABILISTIC METHODS APPLIED TO POWER SYSTEMS (PMAPS), IEEE, 2016Conference paper (Refereed)
    Abstract [en]

    The issue of applying high performance computing (HPC) techniques to computation-intensive probabilistic optimal power flow has not been well discussed in literature. In this paper, the probabilistic convex AC OPF based on second order cone programming (P-SOCPF) is formulated. The application of P-SOCPF is demonstrated by accounting uncertainties of loads. To estimate the distributions of nodal prices calculated from PSOCPF, two point estimation method (2PEM) is deployed. By comparing with Monte Carlo (MC) method, the accuracy of 2PEM is proved numerically. The computation efficiency of 2PEM outperforms MC significantly. In the context of large scale estimation, we propose to apply high performance computing (HPC) to P-SOCPF. The HPC accelerated P-SOCPF is implemented in GAMS grid computing environment. A flexible parallel management algorithm is designed to assign execution threads to different CPUs and then collect completed solutions. Numerical results from IEEE 118-bus and modified 1354pegase case network demonstrate that grid computing is effective means to speed up large scale P-SOCPF computation. The speed up of P-SOCPF computation is approximately equal to the number of cores in the computation node.

12 51 - 76 of 76
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