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  • 1. Arifianto, I.
    et al.
    Josue, F.
    Saers, R.
    Rosenlind, Johanna
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Hilber, Patrik
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Suwarno,
    Investigation of transformer top-oil temperature considering external factors2012In: Condition Monitoring and Diagnosis (CMD), 2012 International Conference on, IEEE , 2012, p. 198-201Conference paper (Refereed)
    Abstract [en]

    Standard estimation of top-oil temperature uses a thermal model related to load changes and variation of ambient temperature. Attempts have been done to improve the accuracy of top-oil temperature calculations by introducing internal properties into the model i.e. oil viscosity and winding resistance. The interest of this paper is to investigate the effect of external factors on top-oil temperature by looking into the weather, i.e. wind velocity. The results are compared with measurements on a 63MVA-ONAF 55/140 kV transformer unit, which is operated in ONAN cooling mode. The unit is located in subarctic climate, and it is equipped with a monitoring system and a weather station.

  • 2.
    Ariza Rocha, Oscar David
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS). ABB Power Grids Research.
    Morozovska, Kateryna
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Laneryd, Tor
    ABB Power Grids Research.
    Ivarsson, Ola
    E.ON Energidistribution AB.
    Ahlrot, Claes
    E.ON Energidistribution AB.
    Hilber, Patrik
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Dynamic rating assists cost-effective expansion of wind farms by utilizing the hidden capacity of transformers2020In: International Journal of Electrical Power & Energy Systems, ISSN 0142-0615, E-ISSN 1879-3517, Vol. 123, article id 106188Article in journal (Refereed)
    Abstract [en]

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

    The following work investigates how to utilize already operational transformers, which are used for wind farm connection, for expanding wind generation capacity. Also, this paper shows improvements that dynamic transformer rating can bring to both power grid operators and wind farm owners by exploring the economic benefits of expanding wind parks without investing in new power transformers. Connecting additional wind turbines at sites with high wind potential after the wind park is already in exploitation can assist in lowering electricity price and provide a possibility of less risky investment in the wind energy sector. This paper uses transformer thermal modelling and wind farm expansion techniques such as convolution method and product method to investigate to which extent existing wind farms can be expanded using already installed transformer units.

    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%" role="presentation" style="box-sizing: border-box; margin: 0px; padding: 0px; display: inline-block; line-height: normal; font-size: 16.2px; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; position: relative;">% to 50%" role="presentation" style="box-sizing: border-box; margin: 0px; padding: 0px; display: inline-block; line-height: normal; font-size: 16.2px; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; position: relative;">%, although, it can be limited further by network restrictions. A possibility to use a large component, such as 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.

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    Dynamic rating for wind power
  • 3.
    Ariza Rocha, Oscar David
    et al.
    ABB Corporate Research, Västerås, Sweden. E.ON. Energidistribution AB, Malmö, Sweden.
    Morozovska, Kateryna
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Laneryd, Tor
    ABB Corporate Research.
    Ivarsson, Ola
    E.ON. Energidistribution AB, .
    Ahlrot, Claes
    E.ON. Energidistribution AB, .
    Hilber, Patrik
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Dynamic rating assists cost-effective expansion of wind farms byutilizing hidden capacity of transformersManuscript (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.

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    fulltext
  • 4.
    Babu, Sajeesh
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Hilber, Patrik
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Reliability and Sensitivity Analysis of Substation and Feeder DesignConsidering Correlated Failures2017Conference paper (Refereed)
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    Reliability and Sensitivity Analysis of Substation and Feeder Design Considering Correlated Failures
  • 5.
    Babu, Sajeesh
    et al.
    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.
    On the status of reliability studies involving primary and secondary equipment applied to power system2014In: 2014 International Conference on Probabilistic Methods Applied to Power Systems, PMAPS 2014 - Conference Proceedings, IEEE , 2014, p. 6960653-Conference paper (Refereed)
    Abstract [en]

    Growth in infrastructure and energy utilization consistently put forward the demand for added quality and quantity of electric power. Reliability concerns over power systems are widespread within its different associated divisions like 'primary' power system structure, protection system, control equipment, ICT (Information and Communication Technologies) etc. This paper is a review of the present status of practices regarding reliability analysis in these divisions and works towards collectively assessing some of the studies in the respective areas. The idea of integrating reliability analysis from the above areas is introduced along with pointing out the major challenges associated. A set of tools for operators to make use in these reliability evaluations and modelling are mentioned. The earlier attempts towards combined overall system reliability analysis are discussed and the approach in this regard with the help of 'control functions' is emphasised. The paper includes works dealing with theory, different methodologies and data associated with power system reliability.

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    On the Status of Reliability Studies Involving Primary and Secondary Equipment Applied to Power System
  • 6.
    Babu, Sajeesh
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Hilber, Patrik
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Shayesteh, Ebrahim
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Enarsson, Lars Einar
    Reliability Evaluation of Distribution Structures Considering the Presence of False Trips2018In: IEEE Transactions on Smart Grid, ISSN 1949-3053, E-ISSN 1949-3061Article in journal (Refereed)
    Abstract [en]

    This paper presents a method for modelling the different modes of failures in a substation and feeder architecture along with updating the possible false tripping scenarios in it. A traditional approach to collectively assess the failure modes using reliability block diagram is reviewed, and the method is updated to count in the unaccounted false tripping scenarios. A generalizable radial feeder branching structure is adopted and the effect of total feeder length and number of feeders from each busbar is examined and modelled with the help of the updated reliability block diagram. The modelled trends are also studied from real-world substation architectures. Thus, the analysis attains an improved estimation of the complex hidden failure probabilities combining theoretical and practical models.

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    fulltext
  • 7.
    Babu, Sajeesh
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Jürgensen, Jan Henning
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Wallnerström, Carl Johan
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Hilber, Patrik
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Tjernberg, Lina Bertling
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Analyses of Smart Grid Technologies and Solutions from a System Perspective2015In: Smart Grid Technologies - Asia (ISGT ASIA), 2015 IEEE Innovative, IEEE conference proceedings, 2015, p. 1-5, article id 7387089Conference paper (Refereed)
    Abstract [en]

    This paper consolidates the data, analysis andobservations from a case study conducted in cooperation withthe Smart Grid Gotland project. The analysis identifies howelectrical power consumption interacts with distributedelectricity generation such as wind and solar power andpresents how it correlates to weather data and smart gridsolutions. The analysis model developed based on the Gotlandnetwork is generic and hence can be functional in investigatingother power networks of different size, voltage level andstructures. The key observations from the study of smart gridsolutions such as dynamic load capacity and energy storagesolutions are specified. Based on the project, an overview offuture risks and opportunities of smart grid systems is presented.

    Download (pdf)
    Analyses of Smart Grid Technologies and Solutions from a System Perspective
  • 8.
    Babu, Sajeesh
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Shayesteh, Ebrahim
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Hilber, Patrik
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Analysing Correlated Events in Power System Using Fault Statistics2016In: Probabilistic Methods Applied to Power Systems (PMAPS), 2016 International Conference on, IEEE, 2016Conference paper (Other academic)
    Abstract [en]

    Power system automation requires logical presumptions made on practical grids to correctly comprehend and manage complex and correlated faults occurring in real world systems. Traditional grid fault analysis methods lack in-depth understanding of these complex events and demand development of approaches that make use of available data to address this problem. Here, the traditional classification approach and challenges relating control equipment in power system are reviewed and a method observing the affected customers during faults along with grid design is discussed based on Swedish case study data. Various contrasting observations are made on the data recorded over two time periods to understand the trend developing over years. Moreover, it will be shown that the classification method also has potential in identifying weak spots in the grid when it comes to the reliability of control equipment.

  • 9.
    Bergerland, Sune
    et al.
    Karlstads El- och Stadsnät.
    Wallnerström, Carl Johan
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Hilber, Patrik
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Summary of the Swedish tariff regulation and impact of changes on investment strategies2015Conference paper (Refereed)
    Abstract [en]

    This paper evaluates how upcoming changes in the Swedish tariff regulation could affect distribution system operators (DSOs), with focus on reinvestment planning. This is done by general analyses as well as by authentic calculation examples of a real power distribution system. The paper describes the Swedish tariff regulation with expected changes, provides a summary of changes in Swedish laws and regulation affecting DSOs between 1996 and 2016, describes how a DSO at local distribution level conduct their reinvestments, illustrates economic calculation examples and finally presents analyses and conclude the results. Analysis results presented show that the outcome from the regulation is sensitive towards relatively small changes in WACC and age structure. The tariff cap allowed will however be significantly reduced for all tested scenarios. A reinvestment rate of in average~10 % regarding meters and IT and ~2.5 % regarding all other categories could be a rough guideline to meet the new incentives, but that could differ depending on the actual age structure of the DSO.

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    fulltext
  • 10.
    Bertling, Lina
    et al.
    Chalmers.
    Hilber, Patrik
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Jensen, Jolanta
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Setreus, Johan
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Wallnerström, Carl Johan
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    RADPOW development and documentation2008Report (Other (popular science, discussion, etc.))
    Abstract [en]

    This report summarizes the status of the computer program RADPOW. RADPOW is a program for Reliability Assessment of electrical Distribution POWer systems. It was developed at KTH School of Electrical Engineering, within the research program EKC and the research project on reliability of new electrical distribution systems. Further on, RADPOW has been used and further developed within the RCAM research group at KTH School of Electrical Engineering.

    This status report contains a brief description of the RADPOW_2006 version, the Loadflow module from the RADPOW_1999_PH version and a description of the work done in the resulting RADPOW_2007 version. This version now includes a tested load flow module and the ability to calculate the latest component importance indices developed within the RCAM research group. The source code for the program has also been restructured and commented in a more detailed level than before.

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    fulltext
  • 11.
    Bragone, Federica
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Computational Science and Technology (CST).
    Morozovska, Kateryna
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Computational Science and Technology (CST).
    Hilber, Patrik
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Laneryd, Tor
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering.
    Luvisotto, Michele
    Hitachi Energy.
    Physics-informed neural networks for modelling power transformer’s dynamic thermal behaviour2022In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 211, p. 108447-108447, article id 108447Article in journal (Refereed)
    Abstract [en]

    This paper focuses on the thermal modelling of power transformers using physics-informed neural networks (PINNs). PINNs are neural networks trained to consider the physical laws provided by the general nonlinear partial differential equations (PDEs). The PDE considered for the study of power transformer’s thermal behaviour is the heat diffusion equation provided with boundary conditions given by the ambient temperature at the bottom and the top-oil temperature at the top. The model is one dimensional along the transformer height. The top-oil temperature and the transformer’s temperature distribution are estimated using field measurements of ambient temperature, top-oil temperature and the load factor. The measurements from a real transformer provide more realistic solution, but also an additional challenge. The Finite Volume Method (FVM) is used to calculate the solution of the equation and further to benchmark the predictions obtained by PINNs. The results obtained by PINNs for estimating the top-oil temperature and the transformer’s thermal distribution show high accuracy and almost exactly mimic FVM solution.

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  • 12. Brodersson, Anna Lilly
    et al.
    Hilber, Patrik
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Jürgensen, Jan Henning
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Towards health assessment: Failure analysis and recommendation of condition monitoring techniques for large disconnector populations2016In: CIRED Workshop -, Helsinki, 2016, p. 4-Conference paper (Refereed)
    Abstract [en]

    Condition monitoring of power system equipment is an important part of asset management. Hence, health indices were developed to describe the equipment condition in a linguistic form with the obtained data. The development of health indices requires knowledge about the equipment population under investigation to consider all important factors. Therefore, this paper investigates the failure data of a large disconnector population to identify population characteristics such as failure modes and failure locations. The analysis showed that the functions maneuverability and current carrying are essential to monitor. Moreover, this paper discusses condition monitoring techniques for disconnector and their applicability in large populations. The paper concludes that even without cost intensive investments in condition measurements or higher preventive maintenance costs, a condition evaluation can be performed.

  • 13.
    Chakrapani Manakari, Vageesh
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electric Power and Energy Systems.
    Thengius, Sandra
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electric Power and Energy Systems.
    Tammanur Ravi, Akshaya
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electric Power and Energy Systems.
    Morozovska, Kateryna
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Hilber, Patrik
    Heimdall Power AS, Oslo, Norway.
    Minimization of Wind Power Curtailment using Dynamic Line Rating2020In: 2020 IEEE PES Innovative Smart Grid Technologies Europe (ISGT-Europe), 2020Conference paper (Refereed)
    Abstract [en]

    Large scale penetration of wind power to the grid and unevenly spread power demand can result in the transmission system not being able to dispatch all the produced wind power, causing in wind power curtailment.Dynamic line rating (DLR) is a technology which uses thermal properties of overhead conductors and weather data to determine the real-time ampacity limits of transmission lines. In general, dynamic rating allows extending capacity limits of power lines and helps to remove congestion in the grid.(/p)(p This study looks into the possibility of using dynamic line rating for removing congestion in the power system to allow dispatching more wind power and minimize the need for curtailment. The results of case-studies have shown that DLR allows to significantly reduce the curtailment of generation, especially during winter, when wind production is highest and day time, when the power demand is the highest.

  • 14.
    Cheng, Jialu
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Taylor, Nathaniel
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Hilber, Patrik
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Impact of Advanced Bushing Diagnostic Techniques on Operation Reliability and Maintenance Strategy2022In: Proceedings 2022 IEEE International Conference on High Voltage Engineering and Applications, ICHVE 2022, Institute of Electrical and Electronics Engineers (IEEE) , 2022Conference paper (Refereed)
    Abstract [en]

    The reliability of power transformers is crucial for the safety operation of the power system. Detection of incipient faults, as well as natural aging, is the key to reduce the failure risk, which gives the operators adequate margin to perform maintenance before reaching a critical failure. Routine maintenance consists of a few testing techniques to check whether mechanical and electrical components fulfill the minimum threshold requirement. In addition, there are various advanced diagnostic testings that are capable of giving more precise condition indications of a transformer in thermal, electrical, and mechanical aspects. The reliability of transformers can thus be enhanced with the help of advanced diagnostic testings. However, in practice, it is often costly to perform the advanced testings and the effectiveness is hard to verify due to the lack of relevant cases and case studies. According to the published statistics, the failure rate is only around 0.1% - 0.2% per year. In this project, a widely accepted insulation condition diagnostic method, Dielectric Frequency Response, DFR was investigated in aspects of cost and return. Testing objects were a group of transformer bushings in three HVDC substations. Reliability is enhanced by identifying incipient bushing defects that cannot be detected by other routine testing techniques. By analyzing the cost and return of the DFR testing, the transition of the current maintenance strategy towards reliability-centered is in position.

  • 15.
    Colmenares, Juan
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Sadik, Diane-Perle
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Hilber, Patrik
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Reliability Analysis of a High-Efficiency SiC Three-Phase Inverter2016In: IEEE Journal of Emerging and Selected Topics in Power Electronics, ISSN 2168-6777, E-ISSN 2168-6785, Vol. 4, no 3, p. 996-1006Article in journal (Refereed)
    Abstract [en]

    Silicon carbide as an emerging technology offers potential benefits compared with the currently used silicon. One of these advantages is higher efficiency. If this is targeted, reducing the on-state losses is a possibility to achieve it. Parallel-connecting devices decrease the on-state resistance and therefore reduce the losses. Furthermore, increasing the amount of components such as parallel connection of devices introduces an undesired tradeoff between efficiency and reliability, since an increased component count increases the probability of failure. A reliability analysis has been performed on a three-phase inverter rated at 312 kVA, using parallel-connected power modules. This analysis shows that the gate voltage stress has a high impact on the reliability of the complete system. Decreasing the positive gate-source voltage could, therefore, increase the reliability of the system approximately three times without affecting the efficiency significantly. Moreover, adding redundancy in the system could also increase the mean time to failure by approximately five times.

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  • 16.
    Colmenares, Juan
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Sadik, Diane-Perle
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Hilber, Patrik
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Reliability analysis of a high-efficiency SiC three-phase inverter for motor drive applications2016In: 2016 IEEE Applied Power Electronics Conference and Exposition (APEC), Institute of Electrical and Electronics Engineers (IEEE), 2016, p. 746-753, article id 7467955Conference paper (Refereed)
    Abstract [en]

    Silicon Carbide as an emerging technology offers potential benefits compared to the currently used Silicon. One of these advantages is higher efficiency. If this is targeted, reducing the on-state losses is a possibility to achieve it. Parallel-connecting devices decrease the on-state resistance and therefore reducing the losses. Furthermore, increasing the amount of components introduces an undesired tradeoff between efficiency and reliability. A reliability analysis has been performed on a three-phase inverter for motor drive applications rated at 312 kVA. This analysis has shown that the gate voltage stress determines the reliability of the complete system. Nevertheless, decreasing the positive gate-source voltage could increase the reliability of the system approximately 8 times without affecting the efficiency significantly. Moreover, adding redundancy in the system could also increase the mean time to failure approximately 5 times.

  • 17.
    Duvnjak Zarkovic, Sanja
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering and Fusion Science.
    Hilber, Patrik
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering and Fusion Science.
    Shayesteh, Ebrahim
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering and Fusion Science.
    Defining Power System Health: Framework and Process towards a System Health IndexManuscript (preprint) (Other academic)
    Abstract [en]

    The health index has traditionally been devised and calculated for individual assets within a power system. This index provides vital details about an asset’s overall health and allows for a standardized comparison among various assets. However, the intricate nature of power systems poses significant challenges when trying to adapt this methodology for a broader, global power system health index. To tackle this obstacle, this paper proposes an innovative framework for evaluating power system health. The framework’s primary purpose is either to monitor the performance of a power system within a defined jurisdiction (such as a country, region, or utility) over time and identify trends/changes or to compare the performance across various jurisdictions. This paper further presents a comprehensive overview of key concepts that play a vital role in determining power system health. These include the driving factors, performance metrics, and associated costs, all of which are under the careful supervision of asset management. Special attention is given to the physical dimensions of the security of electricity supply, which represent the performance-based aspect of power system health and constitute the foundation for the power system health index. Each performance-based dimension is thoroughly reviewed, and a list of relevant key performance indicators is provided for every dimension. 

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  • 18.
    Duvnjak Zarkovic, Sanja
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Hilber, Patrik
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Shayesteh, Ebrahim
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    On the Security of Electricity Supply in Power Distribution Systems2018In: 2018 IEEE International Conference on Probabilistic Methods Applied to Power Systems (PMAPS), IEEE conference proceedings, 2018, article id 8440489Conference paper (Refereed)
    Abstract [en]

    Security of electricity supply has become a fundamental requirement for modern societies. However, attempts to define and evaluate security of supply have differed from one another. This paper reviews relevant studies in order to give a comprehensive explanation of the security of supply concept. The paper includes theory, assessment, methodology, regulations, data and practical issues associated with the security of supply and power system reliability. Special focus is given to the methodologies used for improving the reliability and security of supply in power distribution systems.

  • 19.
    Duvnjak Zarkovic, Sanja
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering and Fusion Science.
    Hilber, Patrik
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering and Fusion Science.
    Shayesteh, Ebrahim
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering and Fusion Science.
    Outage Statistics and Trends in Sweden – What does data tell us?2023In: Energy Proceedings / [ed] Prof. Jinyue Yan, 2023Conference paper (Refereed)
    Abstract [en]

    Data analysis plays a pivotal role in identifying patterns and relationships within data sets. By examining historical outage statistics in power systems, trends in system performance can be revealed, contributing to a better understanding of its behavior. Furthermore, by understanding the past performance of the power system, utility companies can make better decisions to enhance system reliability and resilience. This study investigates outage statistics in the Swedish power system from 2009 to 2019 and examines in depth the reporting mechanism. The data is clustered and analyzed according to three different criteria: voltage level of the breaking device, cause of the failure, and faulty equipment. Although the presented overview highlights key trends in system performance, the analysis has uncovered issues related to data quality and availability, such as missing values and inconsistencies that require further attention.

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    fulltext
  • 20.
    Duvnjak Zarkovic, Sanja
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Shayesteh, Ebrahim
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Hilber, Patrik
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Integrated reliability centered distribution system planning — Cable routing and switch placement2021In: Energy Reports, E-ISSN 2352-4847, Vol. 7, p. 3099-3115Article in journal (Refereed)
    Abstract [en]

    Distribution utilities aim to operate and plan their network in a secure and economical way. The prime focus of this work is to assist utilities by developing a new integrated approach which considers the impacts of system reliability in distribution system planning (DSP). This approach merges different problems together and solves them in a two-stage process, as follows: 1. cable routing and optimal location and number of switching devices (circuit breakers and reclosers); 2. optimal location and number of tie switches. Moreover, the possibility of installing different cable options, with different prices and capacities, is included. The optimization algorithm is designed using mixed-integer programming (MIP). The developed algorithm analytically evaluates relationships between different components in the system and dynamically updates reliability indices, failure rate and restoration time, of every node in the system. This approach has been tested on two distribution systems. Despite the complexity and the exhaustiveness of the problem, MIP converges and provides the optimal solution for every studied scenario. The results show that an integrated approach enables utilities to obtain more comprehensive solutions. Moreover, by understanding the impact of parameter variation enables utilities to categorize their priorities in the decision making process and optimally invest in distribution network with respect to reliability.

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  • 21.
    Duvnjak Zarkovic, Sanja
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Shayesteh, Ebrahim
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Hilber, Patrik
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Onshore wind farm - Reliability centered cable routing2021In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 196, p. 107201-Article in journal (Refereed)
    Abstract [en]

    Designing an onshore wind farm is a complex planning process that requires various stages to be completed. The prime focus of this work is to assist planners and experts in finding the optimal cable layout of the onshore wind farm. The optimization algorithm is designed using mixed integer linear programming (MILP). The MILP algorithm takes into account system reliability, power transfer capacities and power quality issue. The novelty in this optimization algorithm is to simultaneously minimize cable installation cost and the cost of lost energy production and therefore maximize the reliability of the system. Additionally, the algorithm supports the optimal selection among different cable options, with different features, prices and capacities. By calculating voltage increase at the point of connection (POC), power quality issue is considered as well. The designed algorithm provides optimal results for four different wind farm layouts. Every layout is tested for three different case scenarios, where different number and type of cables are considered. The results show that more cable options contribute in lowering the total costs. Moreover, cables with higher capacity can help in improving the power quality issue.

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  • 22.
    Duvnjak Zarkovic, Sanja
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering. KTH Royal Institute of Technology.
    Shayesteh, Ebrahim
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering. KTH Royal Institute of Technology.
    Hilber, Patrik
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering. KTH Royal Institute of Technology.
    Onshore Wind Farm - Reliability Centered Cable RoutingManuscript (preprint) (Other academic)
    Abstract [en]

    Onshore wind farm design requires various stages to be completed. Due to complexity, these stages can not be unified as one planning process. Rather, every design step is considered separately. The prime focus of this work is to assist planners and experts in finding the optimal cable layout of the onshore wind farm. The optimization algorithm is designed using a mixed integer linear programming (MILP). The MILP algorithm takes into account system relia- bility, power transfer capacities and power quality issue. Beside minimizing cable installation cost, the novelty in this optimization algorithm is to mini- mize the cost of lost energy production and therefore maximize the reliability of the system. Additionally, the algorithm supports the optimal selection among different cable options, with different features, prices and capacities. By calcu- lating voltage increase at the point of connection (POC), power quality issue is considered as well. The designed algorithm provides optimal results for four different wind farm layouts. Every layout is tested for three different case sce- narios, where different number and type of cables are considered. The results show that more cable options contribute in lowering the total costs. Moreover, cables with higher capacity can help in improving the power quality issue.

  • 23.
    Duvnjak Zarkovic, Sanja
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering. KTH Royal Institute of Technology.
    Shayesteh, Ebrahim
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering. KTH Royal Institute of Technology.
    Hilber, Patrik
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering. KTH Royal Institute of Technology.
    Reliability Centered Distribution System Planning - Cable Routing and Switch PlacementManuscript (preprint) (Other academic)
    Abstract [en]

    Distribution utilities aim to operate and plan their network in a secure and economical way. The prime focus of this work is to assist utilities by developing a new integrated approach which considers the impacts of system reliability in distribution system planning (DSP). This approach merges different problems together and solves them in a two-stage process, as follows: 1. cable routing and optimal location and number of reclosers; 2. optimal location and number of tie switches. The optimization algorithm is designed using a mixed integer programming (MIP). The developed approach has been tested on 2 distribution systems and for each system 18 different case scenarios have been conducted, making an overall of 36 simulations. Despite the complexity and the exhaustiveness of the problem, MIP converges and provides optimal solution within reasonable time for every scenario. The results show that without sufficient number of reclosers, drastically changing the cable layout can worsen the reliability. Moreover, the benefit of tie switch placement is very susceptible to the network outline (cable layout and number and position of reclosers). With more layout changes and bigger number of reclosers, the benefit of tie switches becomes more significant.

  • 24.
    Duvnjak Zarkovic, Sanja
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Stankovic, Stefan
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electric Power and Energy Systems.
    Shayesteh, Ebrahim
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Hilber, Patrik
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Reliability improvement of distribution system through distribution system planning: MILP vs. GA2019In: 2019 IEEE Milan PowerTech, 2019Conference paper (Refereed)
    Abstract [en]

    Distribution system planning (DSP) is very important because it can result in reliability enhancement and large cost savings for both utilities and consumers. DSP is a complex nonlinear problem, which can be solved with different optimization methods. This paper compares two such optimization methods, conventional (mixed-integer linear programming - MILP) and meta-heuristic (genetic algorithm - GA), applied to the DSP problem: construction of feeders in distribution power system from scratch. The main objective of DSP is to minimize the total cost, where both the investment and operational outage costs are considered, while the reliability of the whole system is maximized. DSP problem is applied to an actual distribution system. Solution methods are outlined, and computational results show that even though GA gives reasonably good results in faster computation time, MILP provides a better optimal solution with simpler implementation.

  • 25. Duvnjak Zarkovic, Sanja
    et al.
    Weiss, Xavier
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electric Power and Energy Systems.
    Hilber, Patrik
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering and Fusion Science.
    Addressing Data Deficiencies in Outage Reports: A Qualitative and Machine Learning Approach2024Conference paper (Other academic)
    Abstract [en]

    This study investigates outage statistics in the Swedish power system. More specifically, this paper delves into the critical analysis and enhancement of data quality, focusing on inconsistencies and missing values, i.e. unknown outage causes and unidentified faulty equipment. By carefully examining the data, noticeable gaps and deficiencies are revealed. Thus, a format for improving outage reporting using a database with 3 relations (outage summary, outage breakdown and customer breakdown) is proposed. In addition to a qualitative analysis of the data, various machine learning algorithms are explored and tested for their capability to predict the unknown values within the dataset, thereby offering a twofold solution: enhancing the accuracy of outage data and facilitating deeper, more accurate analytical capabilities. The findings and proposals within this work not only illuminate the current challenges within outage data management but also pave the way for more robust, data-driven decision-making in outage management and policy formation. 

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  • 26.
    Edström, Fredrik
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Rosenlind, Johanna
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Alvehag, Karin
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Hilber, Patrik
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Influence of Ambient Temperature on Transformer Overloading During Cold Load Pickup2013In: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208, Vol. 28, no 1, p. 153-161Article in journal (Refereed)
    Abstract [en]

    This paper proposes a method to investigate the socioeconomical aspects of transformer overloading during a cold load pickup (CLPU) in residential areas. The method uses customer damage functions to estimate the cost for their power interruption and a deterioration model to estimate the cost for transformer wear due to the CLPU. A thermodynamic model is implemented to estimate the peak and the duration of cold residential load. A stochastic differential equation is used to capture the volatility of the load and to estimate the probability for transformer overloading. In a numerical example, an optimal cold load pickup for a two-area system is demonstrated where transformer overloading is allowed. In this example, an ambient temperature threshold is identified, where transformer overloading is socioeconomically beneficial.

  • 27.
    Edström, Fredrik
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Rosenlind, Johanna
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Hilber, Patrik
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Modeling Impact of Cold Load Pickup on Transformer Aging Using Ornstein-Uhlenbeck Process2012In: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208, Vol. 27, no 2, p. 590-595Article in journal (Refereed)
    Abstract [en]

    Thermostatically controlled devices, such as air conditioners, heaters, and heat pumps may cause cold load pickup (CLPU) problems after a prolonged blackout. This causes an increased load on the power components in the electrical grid. The result is unpredictable aging and increased risk of failure. Quantifying this risk is crucial for efficient asset management for cost-intensive components such as the transformer. This paper presents a new approach to model the loading profile of a CLPU using stochastic differential equations. The realization of the loading profile is used to determine the aging of a transformer. Two models for the deterioration of transformer solid insulation represent the loss of life due to the CLPU. A comparison between two models for the aging of the solid insulation in the transformer is made in a case study. Due to the stochastic behavior of the load, there is a probability for loading the transformer above the recommended ratings, and this probability is estimated with Monte Carlo simulations.

  • 28.
    Ekstedt, Niklas
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Babu, Sajeesh
    Hilber, Patrik
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Failure Rate Trends in an Aging Population - Monte Carlo Approach2015In: 23rd International Conference on Electricity Distribution - CIRED 2015, CIRED - Congrès International des Réseaux Electriques de Distribution, 2015Conference paper (Refereed)
    Abstract [en]

    This paper proposes a method to make future failure predictions from input data on population age distribution and failure rates, using a Monte Carlo approach. In contrast to many methods used today, the method in this paper is designed to address multiple properties and assumptions simultaneously, which makes the task complicated. For example, the component population is allowed to be divided into both age and different types. The time-dependent failure rates are defined separately for each individual type, can consist of a combination of multiple different failure rates for separate modes, and can be of practically any shape. Furthermore, a volatility measure for the failure rates is introduced and used to model the uncertainties in failure rate estimates. The method handles investment and reinvestment scenarios as well as different restoration models, such as replacing a failed component with a new component of a different type. As a part of the project, a stand-alone software tool was developed and presented in the paper. In the included case study, the method and the tool are shown to be useful when investigating reinvestment strategies to renew the population and decrease the expected number of future failures. The paper gives the reader useful information and understanding on how the problem of predicting the reliability of the future power system can be addressed and solved.

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  • 29.
    Ekstedt, Niklas
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Hilber, Patrik
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Categorization and Review of Failure Rate Factors Used in Power Systems2014In: 2014 International Conference on Probabilistic Methods Applied to Power Systems, PMAPS 2014 - Conference Proceedings, 2014, IEEE Press, 2014Conference paper (Refereed)
    Abstract [en]

    To evaluate the reliability of power systems, good estimates of the failure rates of the included components are needed. Better predictions can be performed if relevant factors that affect the failure rates are used, and an increasing number of models that include different types of factors have been presented recently. This paper proposes a categorization of failure rate factors into seven categories, based on the type of information for the factors. The categorization can be used to map future studies in the context of similar work.  Furthermore, the paper presents a review of a number of publications that uses different factors to model the failure rate of different power system components. The failure rate factors used in the reviewed publications are categorized into the proposed seven categories and a comprehensive summary table is included. The used models and methods to estimate the failure rate in the reviewed publications are also noted in the summary table.

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    Categorization and Review of Failure Rate Factors Used in Power Systems
  • 30.
    Ekstedt, Niklas
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Wallnerström, Carl Johan
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Babu, Sajeesh
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Hilber, Patrik
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Westerlund, Per
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Jürgensen, Jan Henning
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Lindquist, Tommie
    Svenska kraftnät.
    Reliability Data: A Review of Importance, Use, and Availability2014Conference paper (Refereed)
    Abstract [en]

    For reliability studies of power distribution systems availability and collection of data on reliability is a key aspect. The acquirement of data can be challenging, because it endures effort and experience to know where to obtain accessible types of data. This paper gives the reader a guide to why input data to reliability analyses and asset management are useful, which data that can be obtained, and how to access the different types of data. Also, how to measure data accurately and the quality needed are discussed in the paper.

    After a general discussion on the benefits of data, we discuss the importance of knowing exactly what the data are measurements of. Furthermore, we argue that data from different contexts, even if seemingly similar, should be used with care. We also state and explain that the amount data restrict the type of analysis that can be conducted. The paper continues with a description of some examples of (to different degrees) open accessible data. Nationally collected reliability data from Swedish utilities, reported to authorities and interest organizations, are described and discussed. We discuss how Swedish weather data, which recently have become free and open, enable more studies on the weather related reliability effects, and some existing test systems are mentioned. A section follows that describes how failure and condition data are typically stored and utilized internally in organizations. Finally, we conclude that the paper is a potential guide and inspiration for anyone planning to conduct a reliability study in the future.

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  • 31.
    Estanqueiro, Ana
    et al.
    National Laboratory on Energy and Geology (LNEG).
    Ahlrot, Claes
    E.ON AB.
    Duque, Joaquim
    National Laboratory on Energy and Geology (LNEG).
    Santos, Duarte
    National Laboratory on Energy and Geology (LNEG).
    Gentle, Jake P.
    Idaho National Laboratory (INL).
    Abboud, Alexander W.
    Idaho National Laboratory (INL).
    Morozovska, Kateryna
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Hilber, Patrik
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Söder, Lennart
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electric Power and Energy Systems.
    Kanefendt, Thomas
    Fraunhofer IEE.
    DLR use for optimization of network design withvery large wind (and VRE) penetration2018Conference paper (Refereed)
    Abstract [en]

    Due to the stochastic nature of wind and clouds,the integration of wind and PV generation in the powersystem poses serious challenges to the long-term planning oftransmission systems. Grid reinforcements always involverelevant direct costs while the average load factor of the windand solar PV dedicated transmission lines is usually low.Additionally, in very windy sites, the same high windresource that produces large amounts of wind generation andmay congest the transmission lines transporting it to distantconsumption centres may also have a beneficial effect inincreasing the transmission capacity of those lines. In fact, theoccurrence of wind not only contributes to the loading of theconnecting line, but also increases the line capacity, via theconvective cooling of the cables - one of the main heattransfer mechanisms in conductor heat balance; in otherwords, higher winds speeds contribute to faster cooling ofconductor and therefore higher conductor’s capacitypotential. In this paper the existing methodologies tocharacterize those thermal effects in electrical cables - usuallyreferred as dynamic line rating (DLR) - are applied to severalIEA Task 25 countries case studies to characterize thetechnical value of the dynamic operation of thermallycongested lines, as well as its potential economic benefits.

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    DLR use for optimization of network design with very large wind (and VRE) penetration
  • 32.
    Fam, Mei Ling
    et al.
    KTH. Lloyds Register Global Technol Ctr, Singapore, Singapore.;Nanyang Technol Univ, Singapore, Singapore..
    He, X. H.
    Lloyds Register Global Technol Ctr, Singapore, Singapore..
    Hilber, Patrik
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Ong, L. S.
    Nanyang Technol Univ, Singapore, Singapore..
    Konovessis, D.
    Singapore Inst Technol, Singapore, Singapore..
    Tan, H. K.
    Lloyds Register Global Technol Ctr, Singapore, Singapore..
    Data learning and expert judgment in a bayesian belief network for offshore decommissioning risk assessment2018In: Safety and Reliability - Safe Societies in a Changing World: Proceedings of the 28th International European Safety and Reliability Conference, ESREL 2018, CRC Press/Balkema , 2018, p. 397-406Conference paper (Refereed)
    Abstract [en]

    Decommissioning of offshore facilities involve changing risk profiles at different decommissioning phases. Bayesian Belief networks (BBNs) are used as part of the proposed risk assessment method to capture the multiple interactions of a decommissioning activity. The Bayesian Belief network is structured from the data learning of an accident database and a modification of the BBN nodes to incorporate human factors and barrier performance modelling. The analysis covers one case study of one area of decommissioning operations by extrapolating well workover data to well plugging and abandonment. Initial analysis from well workover data, of a 5-node BBN provided insights on two different levels of severity of an accident, the “Accident” and “Incident” level, and on its respective profiles of the initiating events and the investigation-reported human causes. The initial results demonstrate that the data learnt from the database can be used to structure the BBN, and give insights on how human factors pertaining to well activities can be modelled, and that the relative frequencies can act as initial data input for the proposed nodes. It is also proposed that the integrated treatment of various sources of information (database and expert judgement) through a BBN model can support the risk assessment of a dynamic situation such as offshore decommissioning. 

  • 33.
    Fazlagic, Berina
    et al.
    KTH.
    Wallnerström, C. J.
    Shayesteh, Ebrahim
    KTH.
    Hilber, Patrik
    KTH.
    Development of the utilisation and smart grid incentive scheme within the Swedish revenue cap regulation2017In: CIRED - Open Access Proceedings Journal, Institution of Engineering and Technology, 2017, Vol. 2017, no 1, p. 2696-2699, article id 1Conference paper (Refereed)
    Abstract [en]

    This study provides a summary on how Swedish distribution system operators (DSO) are regulated after a revenue cap model, and describes a potential development on the current utilization incentive scheme within this regulation. The analyses are based on data from a Swedish DSO, which have been elaborated with the use of demand response program. The outcome of the demand response simulation has in a later step been applied to calculate the incentive in the revenue cap regulation. Two different calculation approaches are used and compared in order to calculate the load factor in the revenue cap regulation. The results of the case study show that by applying a weighted daily load factor, the DSO in the case study can receive ~3% additional economic income compared to applying an average daily load factor in the incentive calculation. The motivation behind applying weighted load factor is to prioritize days with high energy consumption since those days have more impact on the costs. Most important, the analysis display that replacing the average load factor with a weighted load factor have a non-negligible impact on the incentive calculation and hence if the change fulfill its purpose enough.

  • 34.
    Giesecke, Oskar
    et al.
    KTH, School of Electrical Engineering (EES).
    Karlsson, Rikard
    KTH, School of Electrical Engineering (EES).
    Morozovska, Kateryna
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Hilber, Patrik
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Reliability study of two offshore wind farm topologies: Radial and ring connection2016In: PROCEEDINGS 15th Wind Integration Workshop: International Workshop on Large-Scale Integration of Wind Power into Power Systems as well as on Transmission Networks for Offshore Wind Power Plants / [ed] Uta Betancourt / Thomas Ackermann, Darmstadt: Energynautics GmbH, 2016Conference paper (Refereed)
    Abstract [en]

    Reliable electrical infrastructure in offshore wind farms (OWF) is a key to maintenance cost minimization. Due to the difficult environment and distance to shore reliability is crucial for the feasibility of the OWF. In this study, two different topologies of OWF designs were investigated and compared. An algorithm was established to estimate reliability and economic profit of the two systems. The two topologies under investigation were the radial and ring system configuration. A radial system has in general less components, but the ring configuration provides redundancy. For the particular case studied, with its assumptions, a threshold of 18 turbines was identified. From this level and above the ring configuration is beneficial.

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  • 35.
    Grahn, Pia
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Rosenlind, Johanna
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Hilber, Patrik
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Alvehag, Karin
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    A method for evaluating the impact of electric vehicle charging on transformer hotspot temperature2011In: 2011 2nd IEEE PES International Conference and Exhibition on Innovative Smart Grid Technologies (ISGT Europe), IEEE, 2011Conference paper (Refereed)
    Abstract [en]

    The expected increasing market share of electric vehicles is a response to the combination of new technological developments, governmental financial control, and an attitude shift of residents to a more environmentally friendly lifestyle. The expected capacity required for charging, imposes changes in the load to the already existing components in the electric power grid. In order to continue managing these existing assets efficiently during this load change, it is important to evaluate the impact imposed by the battery charging.

  • 36.
    Habib, Md Zakaria
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering. Swedish Energy Agency (SWEGRIDS).
    Duvnjak Zarkovic, Sanja
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Taylor, Nathaniel
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Hilber, Patrik
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Shayesteh, Ebrahim
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Distributed fault-passage indicators versus central fault location: comparison for reliability centered planning of resonant-earthed distribution systemsManuscript (preprint) (Other academic)
    Abstract [en]

    Fault location methods are crucial for reducing fault restoration time, and thus improving a network's system average interruption duration index (SAIDI) and customer outage cost. Resonant-earthed systems pose problems for traditional fault location methods, leading to poor accuracy and a need for additional complexity. In this context, methods that detect fault direction (fault-passage indicators, FPI) at multiple points in the network may show advantages over a central distance-estimation method using fault locators (FL) of poor accuracy. This paper includes a comparative study of these two major fault location methods, comparing the reliability benefit from a varied number of FPIs or a central method. The optimal placement of the fault locating devices is found by formulating a mixed-integer linear programming (MILP) optimization approach that minimizes both outage and investment costs and assesses SAIDI. This approach has been tested on an example distribution system. However, to justify the universality of the algorithm, the RBTS reliability test system has also been analysed. The comparison of location methods and placement method of FPIs are useful for reliability centred planning of resonant-earthed distribution systems where fault location is to be used. Results show that a small number of FPIs that give accurate identification of direction may give more cost effective increase in reliability than a distance estimate by FL with typical levels of inaccuracy.

  • 37.
    Habib, Md Zakaria
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Duvnjak Zarkovic, Sanja
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Taylor, Nathaniel
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Hilber, Patrik
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Shayesteh, Ebrahim
    Swedish Natl Grid Svenska Kraftnät, Sundbyberg, Sweden..
    Distributed fault-passage indicators versus central fault location: Comparison for reliability centred planning of resonant-earthed distribution systems2023In: Energy Reports, E-ISSN 2352-4847, Vol. 9, p. 1731-1742Article in journal (Refereed)
    Abstract [en]

    Fault location methods are crucial for reducing fault restoration time, and thus improving a network's system average interruption duration index (SAIDI) and customer outage cost. Resonant-earthed systems pose problems for traditional fault location methods, leading to poor accuracy and a need for additional complexity. In this context, methods that detect fault direction (fault-passage indicators, FPI) at multiple points in the network may show advantages over a central distance-estimation method using fault locators (FL) of poor accuracy. This paper includes a comparative study of these two major fault location methods, comparing the reliability benefit from a varied number of FPIs or a central method. The optimal placement of the fault locating devices is found by formulating a mixed-integer linear programming (MILP) optimization approach that minimizes both outage and investment costs and assesses SAIDI. This approach has been tested on an example distribution system. However, to justify the universality of the algorithm, the RBTS reliability test system has also been analysed. The comparison of location methods and placement method of FPIs are useful for reliability centred planning of resonant-earthed distribution systems where fault location is to be used. Results show that a small number of FPIs that give accurate identification of direction may give more cost effective increase in reliability than a distance estimate by FL with typical levels of inaccuracy.

  • 38.
    Habib, Md Zakaria
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Duvnjak Zarkovic, Sanja
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering. KTH Royal Institute of Technology.
    Taylor, Nathaniel
    KTH, Superseded Departments (pre-2005), Electrical Systems. KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Hilber, Patrik
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering. KTH Royal Institute of Technology.
    Shayesteh, Ebrahim
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering. KTH Royal Institute of Technology.
    Reliability Centered Planning of a Resonant-earthed Distribution System with Focus on the Fault Location MethodsManuscript (preprint) (Other academic)
    Abstract [en]

    Fault location methods help to reduce the restoration time and thus improve the SAIDI (System average interruption duration index) of the network. Besides that, restoration time has a direct impact on customer outage cost. Traditional fault location methods struggle to perform adequately and need additional features for a resonant-earthed system. This paper assists in the reliability centred planning of such a system with the focus on fault location methods. Two major fault location methods are modelled for the study. The optimal placement of the fault locating devices is found by formulating a MILP optimization approach that minimizes both outage and investment cost and asses SAIDI. Moreover, a comparative study among the fault location methods is done to find the best case for an actual resonant-earthed distribution system.

  • 39.
    Hilber, Patrik
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Cable Segment Replacement Optimization2014In: Reliability Modeling and Analysis of Smart Power Systems / [ed] Rajesh Karki, Roy Billinton, Ajit Kumar Verma, New Delhi Heidelberg New York Dordrecht London: Springer London, 2014, 1, p. 195-202Chapter in book (Refereed)
  • 40.
    Hilber, Patrik
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Component reliability importance indices for maintenance optimization of electrical networks2005Licentiate thesis, comprehensive summary (Other scientific)
    Abstract [en]

    Maximum asset performance is one of the major goals for electric power system managers. To reach this goal minimal life cycle cost and maintenance optimization become crucial while meeting demands from customers and regulators. One of the fundamental objectives is therefore to relate maintenance and reliability in an efficiently and effectively way, which is the aim of several maintenance methods such as the Reliability Centered Maintenance method (RCM). Furthermore, this necessitates the determination of the optimal balance between preventive and corrective maintenance to obtain the lowest total cost.

    This thesis proposes methods for defining the importance of individual components in a network with respect to total interruption cost. This is a first step in obtaining an optimal maintenance solution. Since the methods consider several customer nodes simultaneously, they are especially suitable for network structures that serve many purposes/customers e.g. transmission and distribution networks with more than one load point. The major results are three component reliability importance indices, which are applied in two case studies. The first case study is based on a network in the Stockholm area. The second case study is performed for one overhead line system in the rural parts of Kristinehamn. The application studies demonstrate that the indices are possible to implement for existing electrical networks and that they can be used for maintenance prioritization. Consequently these indices constitute a first step in the overall objective of a maintenance optimization method.

    The computations of the indices are performed both with analytical and simulation based techniques. Furthermore, the indices can be used to calculate the component contribution to the total system interruption cost. The approach developed for the importance indices can be utilized in any multi-state network that can be measured with one performance indicator.

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  • 41.
    Hilber, Patrik
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Maintenance optimization for power distribution systems2008Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    Maximum asset performance is one of the major goals for electric power distribution system operators (DSOs). To reach this goal minimal life cycle cost and maintenance optimization become crucial while meeting demands from customers and regulators. One of the fundamental objectives is therefore to relate maintenance and reliability in an efficient and effective way. Furthermore, this necessitates the determination of the optimal balance between pre¬ventive and corrective maintenance, which is the main problem addressed in the thesis.

    The balance between preventive and corrective maintenance is approached as a multiobjective optimization problem, with the customer interruption costs on one hand and the maintenance budget of the DSO on the other. Solutions are obtained with meta-heuristics, developed for the specific problem, as well as with an Evolutionary Particle Swarm Optimization algorithm. The methods deliver a Pareto border, a set of several solutions, which the operator can choose between, depending on preferences. The optimization is built on component reliability importance indices, developed specifically for power systems. One vital aspect of the indices is that they work with several supply and load points simultaneously, addressing the multistate-reliability of power systems. For the computation of the indices both analytical and simulation based techniques are used. The indices constitute the connection between component reliability performance and system performance and so enable the maintenance optimization.

    The developed methods have been tested and improved in two case studies, based on real systems and data, proving the methods’ usefulness and showing that they are ready to be applied to power distribution systems. It is in addition noted that the methods could, with some modifications, be applied to other types of infrastructures. However, in order to perform the optimization, a reliability model of the studied power system is required, as well as estimates on effects of maintenance actions (changes in failure rate) and their related costs. Given this, a generally decreased level of total maintenance cost and a better system reliability performance can be given to the DSO and customers respectively. This is achieved by focusing the preventive maintenance to components with a high potential for improvement from system perspective.

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  • 42.
    Hilber, Patrik
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Bertling, Lina
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    A Method for Extracting Reliability Importance Indices from Reliability Simulations of Electrical Networks2005In: 15th Power Systems Computation Conference, PSCC 2005, Power Systems Computation Conference ( PSCC ) , 2005Conference paper (Refereed)
    Abstract [en]

    This paper proposes a reliability importance index that is possible to extract from existing reliability simulations at a low additional computational cost. The index utilizes the concept of reliability worth as a measure of system reliability in order to establish the importance of components in systems with several load points. Since the method is based on simulations, it is suitable for large networks with a high level of detail. The index can be used as decision support for asset management, for example where maintenance actions will become most beneficial. The index is evaluated against the background of a number of analytically calculated indices. Furthermore, the index is applied to a network in the Stockholm area. The conclusion of the paper is that the proposed simulation based importance index provides a means of improving analysis of electrical network reliability.

  • 43.
    Hilber, Patrik
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Bertling, Lina
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Component Reliability Importance Indices for Electrical Networks2007In: 2007 CONFERENCE PROCEEDINGS IPEC, VOLS 1-3, NEW YORK: IEEE , 2007, p. 257-263Conference paper (Refereed)
    Abstract [en]

    This paper presents three new component reliability importance indices, developed for electrical networks. Component reliability importance indices are useful for prioritization of components as part of a system, especially when considering maintenance activities and/or investment in new equipment. Traditional component reliability importance indices were developed for systems with one input and one output point, which not captures the general function of electrical networks. The proposed indices utilize the concept of reliability worth as a single measure of system reliability in order to establish the importance of the components. This single measure of reliability works over several supply and load points and does for example enable comparisons between components decicated to different load points as well as components from different systems. Furthermore this paper presents data from application studies, which shows on some of the possibilities with the indices. The conclusion of the paper is that the proposed indices provide means of improving analysis of electrical network reliability.

  • 44.
    Hilber, Patrik
    et al.
    KTH, Superseded Departments (pre-2005), Electrical Systems.
    Bertling, Lina
    KTH, Superseded Departments (pre-2005), Electrical Systems.
    Monetary Importance of Component Reliability in Electrical Networks for Maintenance Optimization2004In: 8th International Conference on Probabilistic Methods Applied to Power Systems: Iowa State Univ, Ames, IA, SEP 12-16, 2004, 2004, p. 150-155Conference paper (Refereed)
    Abstract [en]

    This paper proposes a method for defining the importance of individual components in a network with respect to total interruption cost. Since the method considers several customer nodes simultaneously, it is especially suitable for network structures that serve many purposes/customers e.g. transmission and distribution networks with more than one load point. The major result is an importance index, I-H, for every component. This index can be used for the evaluation of maintenance actions. Furthermore, the importance index is used to calculate the component contribution to the total system interruption cost. Finally, the goal to reach an optimal maintenance plan is outlined. The methodology is presented together with an application study for an electrical distribution system in-the Stockholm area.

  • 45.
    Hilber, Patrik
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Bertling, Lina
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Multiobjective Maintenance Policy for a Distribution System an Application Study2008In: 10th International Conference On Probabilistic Methods Applied To Power Systems, 2008, p. 229-234Conference paper (Refereed)
    Abstract [en]

    Maintenance managers of today's electrical distribution systems are faced with the problem of where their maintenance resources will be utilized best. In previous work the authors have developed a method for maintenance policy optimization for electrical networks. This paper presents results from an application study performed for a distribution system, including both urban and rural parts, for this method. A basic optimization is performed in order to find the right level of maintenance for the involved components with respect to customer interruption costs and maintenance budget. For the rural parts of the system the conclusion is that intensified tree trimmings is the most beneficial maintenance activity. While for the urban parts the maintenance should be focused towards customer intense areas. Furthermore, it becomes clear, especially for the urban part of the system, that the operation mode of the network becomes important. The method presented helps the managers to prioritize their maintenance to the places where it will result in the best system performance.

  • 46.
    Hilber, Patrik
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Bertling, Lina
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Hällgren, Bengt
    Karlstads Universitet.
    Effects of Correlation between Failures and Power Consumption on Customer Interruption Cost2006In: 2006 International Conference on Probabilistic Methods Applied to Power Systems, Vols 1 and 2: 9th International Conference on Probabilistic Methods Applied to Power Systems. KTH, Stockholm, SWEDEN. JUN 11-15, 2006, 2006, p. 1120-1123Conference paper (Refereed)
    Abstract [en]

    This paper evaluates the correlation between failures and power consumption for a distribution systems operator. This is done in order to scrutinize whether the commonly used assumptions of constant failure rate and constant power consumption is reasonable to use for reliability calculations. The studied entity is energy not supplied, which is assumed to be a good estimate of how customer interruption costs are affected. Three different aspects are studied with respect to energy not supplied; seasonal variations, daily variations and repair time variations (as a function of the hour of day). The conclusion is that by using constant failure rates, repair rates and power consumption the approximation of customer costs becomes somewhat low, i.e. by 7% for the studied case. This result indicates that the assumptions of constant failure rates, repair rates and power consumption are quite sufficient for at least the actual case study. Le. since this error probably is significantly smaller than other types of errors, for example customer outage costs estimates. Nevertheless, having performed these calculations the current results should be applied to further modeling of the studied network.

  • 47.
    Hilber, Patrik
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Hällgren, Bengt
    Karlstads Universitet.
    Bertling, Lina
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Optimizing the replacement of overhead lines in rural distribution systems with respect to reliability and customer value2005In: Eighteenth International Conference and Exhibition on Electricity Distribution, CIRED 2005, 2005, p. 127-131Conference paper (Refereed)
    Abstract [en]

    In this paper we present a method for establishing the value of a network's components from a reliability worth perspective. The method can be applied to a general distribution system i.e. both for radial and meshed network systems. Moreover, this paper shows results from an application study for a rural network system that is dominated by overhead lines. The purpose of the study was to establish the value of a secondary feeding point. Further, the method is used to establish the best replacement strategy for the concerned overhead lines.

  • 48.
    Hilber, Patrik
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Miranda, Vladimiro
    Faculty of Engineering, University of Porto.
    Matos, Manuel A.
    Faculty of Engineering, University of Porto.
    Bertling, Lina
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Multiobjective Optimization Applied to Maintenance Policy for Electrical Networks2007In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 22, no 4, p. 1675-1682Article in journal (Refereed)
    Abstract [en]

    A major goal for managers of electric power networks is maximum asset performance. Minimal life cycle cost and maintenance optimization becomes crucial in reaching this goal, while meeting demands from customers and regulators. This necessitates the determination of the optimal balance between preventive and corrective maintenance in order to obtain the lowest total cost.

    The approach of this paper is to study the problem of balance between preventive and corrective maintenance as a multiobjective optimization problem, with customer interruptions on one hand and the maintenance budget of the network operator on the other. The problem is solved with meta-heuristics developed for the specific problem, in conjunction with an evolutionary particle swarm optimization algorithm.

    The maintenance optimization is applied in a case study to an urban distribution system in Stockholm, Sweden. Despite a general decreased level of maintenance (lower total maintenance cost), better network performance can be offered to the customers. This is achieved by focusing the preventive maintenance on components with a high potential for improvements. Besides this, this paper displays the value of introducing more maintenance alternatives for every component and choosing the right level of maintenance for the components with respect to network performance.

  • 49.
    Hilber, Patrik
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Wallnerström, Carl Johan
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Rosenlind, Johanna
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Babu, Sajeesh
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Westerlund, Per
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Benefits of Reliability Centred Asset Management2013In: 22nd International Conference and Exhibition on Electricity Distribution (CIRED 2013), 2013, p. 0668-Conference paper (Refereed)
    Abstract [en]

    This paper provides an overview of risk and reliability assessment techniques, some which are available for distribution system operators, and others that are in the process of development. The main contribution of this paper is showing the possibilities and benefits of detailed risk and reliability analysis. Six samples of findings from research developed over the last decade within the RCAM group (Reliability Centred Asset Management) at the Royal Institute of Technology, Stockholm Sweden, are presented. The research is directly associated with risk and asset management applied to power systems. The first three examples are within developed research, followed by three areas where great potential is seen: 1) The value of accurate thermal models of transformers; 2) The impact of tariff regulation on asset management decisions; 3) Detailed interruption studies; 4) Dynamic rating; 5) Combined risk and reliability analysis of primary equipment and control equipment; 6) Systematic diagnostic measures for asset management.

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  • 50.
    Hilber, Patrik
    et al.
    KTH, School of Electrical Engineering (EES).
    Wallnerström, Carl Johan
    KTH, School of Electrical Engineering (EES).
    Rosenlind, Johanna
    KTH, School of Electrical Engineering (EES).
    Setréus, Johan
    KTH, School of Electrical Engineering (EES).
    Schönborg, Niclas
    Svenska Kraftnät.
    Risk analysis for power systems: overview and potential benefits2010Conference paper (Refereed)
    Abstract [en]

    This paper provides a mapping and sample of recently developed risk assessment techniques that are available for the distribution system operator. Three estimates on the value of more detailed risk analysis are desccribed. I.e. component reliability importance indices can be used to divversify the maintenance efforts, gaining better expected system performance at no cost. Furthermore, components that are assumed to be relatively harmless (based on average values) are identified as critical for longer interruptions. Finally it is shown that losses in a transformer are critical in the decision on transformer lifetime.

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