| 1. |
- Arifianto, I., et al.
(author)
-
Investigation of transformer top-oil temperature considering external factors
- 2012
-
In: Condition Monitoring and Diagnosis (CMD), 2012 International Conference on. - : IEEE. - 9781467310208 ; , s. 198-201
-
Conference paper (peer-reviewed)abstract
- 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.
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| 2. |
- Ariza Rocha, Oscar David, et al.
(author)
-
Dynamic rating assists cost-effective expansion of wind farms by utilizing the hidden capacity of transformers
- 2020
-
In: International Journal of Electrical Power & Energy Systems. - : Elsevier. - 0142-0615 .- 1879-3517. ; 123
-
Journal article (peer-reviewed)abstract
- 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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| 3. |
- Ariza Rocha, Oscar David, et al.
(author)
-
Dynamic rating assists cost-effective expansion of wind farms byutilizing hidden capacity of transformers
-
Other publication (other academic/artistic)abstract
- 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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| 4. |
- Babu, Sajeesh, 1987-, et al.
(author)
-
Analyses of Smart Grid Technologies and Solutions from a System Perspective
- 2015
-
In: Smart Grid Technologies - Asia (ISGT ASIA), 2015 IEEE Innovative. - : IEEE conference proceedings. - 9781509012374 ; , s. 1-5
-
Conference paper (peer-reviewed)abstract
- 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.
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| 5. |
- Babu, Sajeesh, et al.
(author)
-
Analysing Correlated Events in Power System Using Fault Statistics
- 2016
-
In: Probabilistic Methods Applied to Power Systems (PMAPS), 2016 International Conference on. - : IEEE. - 9781509019700
-
Conference paper (other academic/artistic)abstract
- 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.
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| 6. |
- Babu, Sajeesh, et al.
(author)
-
On the status of reliability studies involving primary and secondary equipment applied to power system
- 2014
-
In: 2014 International Conference on Probabilistic Methods Applied to Power Systems, PMAPS 2014 - Conference Proceedings. - : IEEE. - 9781479935611 ; , s. 6960653-
-
Conference paper (peer-reviewed)abstract
- 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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| 7. |
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| 8. |
- Babu, Sajeesh, 1987-
(author)
-
Reliability Evaluation of Distribution ArchitecturesConsidering Failure Modes and Correlated Events
- 2015
-
Licentiate thesis (other academic/artistic)abstract
- Power systems are in a phase of automation where intelligent components and sub-systems are employed to monitor, control and manage the grid. Quantifying the complex consequences on system reliability, from the integration of such automated and semi-automated equipment into the existing grid is important for maintenance optimisation and fault mitigation. This thesis identifies the advanced approaches in power system reliability analysis with the potential to capture the complications and correlations in modern power grid after reviewing the traditional reliability evaluation methods.A method for modelling the different modes of failures, possible in a substation and feeder architecture along with the probable false tripping scenarios was developed. An improved Reliability Block Diagram based approach was designed to count in the traditionally unaccounted failure cases affecting both the primary grid and the protectionand control equipment. The effect and corresponding trend of additional feeder lines in a radial distribution system on the net interruption rate experienced at load ends of feeders are derived and modelled. Such real-world substation architectures are analysed and the aforementioned trends are compared with those from the practical grid. Thus, the analysis was able to identify and measure the complex hidden failure probabilities due to both unwanted operation of breakers and functional failure of protection systems.The measured probabilities were used to calculate the impact of protection and control equipment on system reliability. The obtained results were verified by comparing it with the observations by energy researchers on ten years of protection system failure statistics. The application of the model and results, in optimal maintenance planning and power network optimisation are identified as the next step.
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| 9. |
- Babu, Sajeesh, et al.
(author)
-
Reliability Evaluation of Distribution Structures Considering the Presence of False Trips
- 2018
-
In: IEEE Transactions on Smart Grid. - : IEEE. - 1949-3053 .- 1949-3061.
-
Journal article (peer-reviewed)abstract
- 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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| 10. |
- Babu, Sajeesh, 1987-
(author)
-
Reliability Evaluation of Distribution Systems Considering Failure Modes and Network Configuration
- 2017
-
Doctoral thesis (other academic/artistic)abstract
- Power distribution networks are recognized as the constituent part of power systems with the highest concentration of failure events. Even though the faults in distribution networks have a local effect when compared to the generation and transmission sides, major contingency escalation events are being more frequently reported from this section. The various aspects regarding the reliability and performance of distribution networks are identified as an important topic. Integration of new technologies, automation and increased penetration of distributed generation is expected to make improving and even sustaining high reliability standards a complex task. This thesis presents developed approaches to quantify and analyze the complex correlated failure probabilities of different failure modes in distribution networks. A theoretical simulation model that relates to real world data to measure false tripping probabilities is developed and tested. More simplified approaches that utilities can exercise with readily available data in fault registers are also established. Optimal configurations that could improve system performance and respective investment costs are analyzed and savings in system reliability at the cost of grid investments are modelled. The optimization helps in prioritizing the most critical investments by considering the system impact of reconfigurations focusing on meeting customer demands and respecting transfer capacities of weak links. The value of existing networks and willingness of the grid owner in investing can be integrated into suggestive alterations to assist decision making in planning and maintenance allocation. The thesis makes both system specific and generalizable observations from detailed data collection from power utilities. The observations and results have potential in aiding future research by giving important understanding of the reliability impacts of network structures and of control and protection equipment.
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| 11. |
- Berg, Petra, et al.
(author)
-
Towards a Model for Assessing the Effects of Social-Cyber-Physical Threats on the Future Power Grid - Review and Workshop Results
- 2024
-
In: 2024 International Workshop on Artificial Intelligence and Machine Learning for Energy Transformation, AIE 2024. - : Institute of Electrical and Electronics Engineers (IEEE).
-
Conference paper (peer-reviewed)abstract
- The energy system, including the electrical power system, is currently undergoing major changes to meet increased demands and climate target plans, and to stand against potential malicious activities and all sorts of disruptions. Specifically, the electrical power system is drastically changing with regards to consumption, production, transmission, control, monitoring, markets, and digitalization. Such a change, however, makes the power system an attractive and vulnerable target to all kinds of disruptive events and social-cyber-physical attacks since the system is crucial for the functioning of the society and economy. In this work, to act against such events and to study the future power system's susceptibility and resilience towards social-cyber-physical attacks, the Resilient Digital Sustainable Energy Transition (REDISET) project has shown the need for a new model that is able to describe the future electrical power system in a way that reflects the future reality. In this paper, existing power system models, the changing landscape of power systems, the drivers for a new model, the suggested model that comprises 7 building blocks instead of today's 3, and finally a direction of future related work are presented.
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| 12. |
- Bergerland, Sune, et al.
(author)
-
Summary of the Swedish tariff regulation and impact of changes on investment strategies
- 2015
-
Conference paper (peer-reviewed)abstract
- 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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| 13. |
- Bertling, Lina, et al.
(author)
-
RADPOW development and documentation
- 2008
-
Reports (pop. science, debate, etc.)abstract
- 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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| 14. |
- Bragone, Federica, et al.
(author)
-
Physics-informed neural networks for modelling power transformer’s dynamic thermal behaviour
- 2022
-
In: Electric power systems research. - : Elsevier. - 0378-7796 .- 1873-2046. ; 211, s. 108447-108447
-
Journal article (peer-reviewed)abstract
- 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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| 15. |
- Brodersson, Anna Lilly, et al.
(author)
-
Towards health assessment : Failure analysis and recommendation of condition monitoring techniques for large disconnector populations
- 2016
-
In: CIRED Workshop -. - Helsinki : Institution of Engineering and Technology. ; , s. 4-
-
Conference paper (peer-reviewed)abstract
- 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.
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| 16. |
- Chakrapani Manakari, Vageesh, et al.
(author)
-
Minimization of Wind Power Curtailment using Dynamic Line Rating
- 2020
-
In: 2020 IEEE PES Innovative Smart Grid Technologies Europe (ISGT-Europe).
-
Conference paper (peer-reviewed)abstract
- 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.
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| 17. |
- Cheng, Jialu, et al.
(author)
-
Impact of Advanced Bushing Diagnostic Techniques on Operation Reliability and Maintenance Strategy
- 2022
-
In: Proceedings 2022 IEEE International Conference on High Voltage Engineering and Applications, ICHVE 2022. - : Institute of Electrical and Electronics Engineers (IEEE).
-
Conference paper (peer-reviewed)abstract
- 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.
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| 18. |
- Colmenares, Juan, 1989-, et al.
(author)
-
Reliability Analysis of a High-Efficiency SiC Three-Phase Inverter
- 2016
-
In: IEEE Journal of Emerging and Selected Topics in Power Electronics. - : IEEE. - 2168-6777 .- 2168-6785. ; 4:3, s. 996-1006
-
Journal article (peer-reviewed)abstract
- 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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| 19. |
- Colmenares, Juan, 1989-, et al.
(author)
-
Reliability analysis of a high-efficiency SiC three-phase inverter for motor drive applications
- 2016
-
In: 2016 IEEE Applied Power Electronics Conference and Exposition (APEC). - : Institute of Electrical and Electronics Engineers (IEEE). - 9781467395502 ; , s. 746-753
-
Conference paper (peer-reviewed)abstract
- 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.
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| 20. |
- Duvnjak Zarkovic, Sanja, 1989-, et al.
(author)
-
Addressing Data Deficiencies in Outage Reports : A Qualitative and Machine Learning Approach
- 2024
-
Conference paper (other academic/artistic)abstract
- 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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| 21. |
- Duvnjak Zarkovic, Sanja, 1989-, et al.
(author)
-
Defining Power System Health : Framework and Process towards a System Health Index
-
Other publication (other academic/artistic)abstract
- 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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| 22. |
- Duvnjak Zarkovic, Sanja, 1989-, et al.
(author)
-
Integrated reliability centered distribution system planning — Cable routing and switch placement
- 2021
-
In: Energy Reports. - : Elsevier BV. - 2352-4847. ; 7, s. 3099-3115
-
Journal article (peer-reviewed)abstract
- 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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| 23. |
- Duvnjak Zarkovic, Sanja, 1989-, et al.
(author)
-
On the Security of Electricity Supply in Power Distribution Systems
- 2018
-
In: 2018 IEEE International Conference on Probabilistic Methods Applied to Power Systems (PMAPS). - : IEEE conference proceedings.
-
Conference paper (peer-reviewed)abstract
- 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.
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| 24. |
- Duvnjak Zarkovic, Sanja, 1989-, et al.
(author)
-
Onshore Wind Farm - Reliability Centered Cable Routing
-
Other publication (other academic/artistic)abstract
- 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.
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| 25. |
- Duvnjak Zarkovic, Sanja, 1989-, et al.
(author)
-
Onshore wind farm - Reliability centered cable routing
- 2021
-
In: Electric power systems research. - : Elsevier BV. - 0378-7796 .- 1873-2046. ; 196, s. 107201-
-
Journal article (peer-reviewed)abstract
- 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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| 26. |
- Duvnjak Zarkovic, Sanja, 1989-, et al.
(author)
-
Outage Statistics and Trends in Sweden – What does data tell us?
- 2023
-
In: Energy Proceedings.
-
Conference paper (peer-reviewed)abstract
- 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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| 27. |
- Duvnjak Zarkovic, Sanja, 1989-, et al.
(author)
-
Reliability Centered Distribution System Planning - Cable Routing and Switch Placement
-
Other publication (other academic/artistic)abstract
- 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.
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| 28. |
- Duvnjak Zarkovic, Sanja, 1989-, et al.
(author)
-
Reliability improvement of distribution system through distribution system planning: MILP vs. GA
- 2019
-
In: 2019 IEEE Milan PowerTech.
-
Conference paper (peer-reviewed)abstract
- 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.
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| 29. |
- Duvnjak Zarkovic, Sanja, 1989-
(author)
-
Security of Electricity Supply in Power Distribution System : Optimization Algorithms for Reliability Centered Distribution System Planning
- 2020
-
Licentiate thesis (other academic/artistic)abstract
- The importance of electricity in everyday life and demands to improve the reliability of distribution systems force utilities to operate and plan their networks in a more secure and economical manner. With higher demands on reliability from both customers and regulators, a big pressure has been put on the security of electricity supply which is considered as a fundamental requirement for modern societies. Thus, efficient solutions for reliability and security of supply improvements are not just of increasing interest, but also have significant socio-economic relevance. Distribution system planning (DSP) is one of the major activities of distribution utilities to deal with reliability enhancement.This thesis deals with developing optimization algorithms, which aim is to min- imize customer interruption costs, and thus maximize the reliability of the system. This is implemented either by decreasing customer interruption duration, frequency of customer interruptions or both. The algorithms are applied on a single or multi- ple DSP problems. Mixed-integer programming has been used as an optimization approach.It has been shown that solving and optimizing each one of the DSP problems contributes greatly to the reliability improvement, but brings certain challenges. Moreover, applying algorithms on multiple and integrated DSP problems together leads to even bigger complexity and burdensome. However, going toward this inte- grated approach results in a more appropriate and realistic DSP model.The idea behind the optimization is to achieve balance between reliability and the means to achieve this reliability. It is a decision making process, i.e. a trade-off between physical and pricing dimension of security of supply.
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| 30. |
- Duvnjak Zarkovic, Sanja, 1989-
(author)
-
Security of Electricity Supply in Power Systems : Establishing a Global Framework for Assessing Power System Health and Analyzing Outage Statistics in Sweden
- 2024
-
Doctoral thesis (other academic/artistic)abstract
- The primary objective of this thesis is to enhance the security of electricity supply by providing a holistic perspective and introducing a comprehensive framework for assessing power system health. This novel approach aims for a thorough evaluation of the system’s overall performance and well-being, using the physical dimensions of the security of supply as the foundation for a power system health index. After establishing the theoretical framework, relevant and available data is collected in order to analyze and understand the system’s performance. By analyzing outage statistics in Sweden, the research identifies specific trends and performance metrics that can be further investigated and segmented according to various criteria. The insights gained from this research can, in turn, be used to inform proactive maintenance strategies and capacity planning, ultimately mitigating the risks of outages and ensuring a more reliable electricity supply. Outage statistics are furthermore analyzed from the aspect of data quality, focusing on inconsistencies and missing values in the outage reports, 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 highlight the current challenges within outage data management and also lay the groundwork for a more comprehensive, data-driven approach in outage management and policy development.
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| 31. |
- Edström, Fredrik, et al.
(author)
-
Influence of Ambient Temperature on Transformer Overloading During Cold Load Pickup
- 2013
-
In: IEEE Transactions on Power Delivery. - 0885-8977 .- 1937-4208. ; 28:1, s. 153-161
-
Journal article (peer-reviewed)abstract
- 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.
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| 32. |
- Edström, Fredrik, et al.
(author)
-
Modeling Impact of Cold Load Pickup on Transformer Aging Using Ornstein-Uhlenbeck Process
- 2012
-
In: IEEE Transactions on Power Delivery. - 0885-8977 .- 1937-4208. ; 27:2, s. 590-595
-
Journal article (peer-reviewed)abstract
- 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.
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| 33. |
- Ekstedt, Niklas, 1979-, et al.
(author)
-
Categorization and Review of Failure Rate Factors Used in Power Systems
- 2014
-
In: 2014 International Conference on Probabilistic Methods Applied to Power Systems, PMAPS 2014 - Conference Proceedings, 2014. - : IEEE Press. - 9781479935611
-
Conference paper (peer-reviewed)abstract
- 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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| 34. |
- Ekstedt, Niklas, 1979-, et al.
(author)
-
Failure Rate Trends in an Aging Population - Monte Carlo Approach
- 2015
-
In: 23rd International Conference on Electricity Distribution - CIRED 2015. - : CIRED - Congrès International des Réseaux Electriques de Distribution.
-
Conference paper (peer-reviewed)abstract
- 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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| 35. |
- Ekstedt, Niklas, et al.
(author)
-
Reliability Data : A Review of Importance, Use, and Availability
- 2014
-
Conference paper (peer-reviewed)abstract
- 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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| 36. |
- Estanqueiro, Ana, et al.
(author)
-
DLR use for optimization of network design withvery large wind (and VRE) penetration
- 2018
-
Conference paper (peer-reviewed)abstract
- 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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| 37. |
- Fam, Mei Ling, et al.
(author)
-
Data learning and expert judgment in a bayesian belief network for offshore decommissioning risk assessment
- 2018
-
In: Safety and Reliability - Safe Societies in a Changing World. - : CRC Press/Balkema. ; , s. 397-406
-
Conference paper (peer-reviewed)abstract
- 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.
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| 38. |
- Fazlagic, Berina, et al.
(author)
-
Development of the utilisation and smart grid incentive scheme within the Swedish revenue cap regulation
- 2017
-
In: CIRED - Open Access Proceedings Journal. - : Institution of Engineering and Technology. ; , s. 2696-2699
-
Conference paper (peer-reviewed)abstract
- 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.
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| 39. |
- Giesecke, Oskar, et al.
(author)
-
Reliability study of two offshore wind farm topologies : Radial and ring connection
- 2016
-
In: PROCEEDINGS 15<sup>th</sup> Wind Integration Workshop. - Darmstadt : Energynautics GmbH. - 9783981654943
-
Conference paper (peer-reviewed)abstract
- 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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| 40. |
- Grahn, Pia, et al.
(author)
-
A method for evaluating the impact of electric vehicle charging on transformer hotspot temperature
- 2011
-
In: 2011 2nd IEEE PES International Conference and Exhibition on Innovative Smart Grid Technologies (ISGT Europe). - : IEEE.
-
Conference paper (peer-reviewed)abstract
- 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.
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| 41. |
- Habib, Md Zakaria, et al.
(author)
-
Distributed fault-passage indicators versus central fault location : comparison for reliability centered planning of resonant-earthed distribution systems
-
Other publication (other academic/artistic)abstract
- 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.
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| 42. |
- Habib, Md Zakaria, et al.
(author)
-
Distributed fault-passage indicators versus central fault location : Comparison for reliability centred planning of resonant-earthed distribution systems
- 2023
-
In: Energy Reports. - : Elsevier BV. - 2352-4847. ; 9, s. 1731-1742
-
Journal article (peer-reviewed)abstract
- 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.
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| 43. |
- Habib, Md Zakaria, et al.
(author)
-
Reliability Centered Planning of a Resonant-earthed Distribution System with Focus on the Fault Location Methods
-
Other publication (other academic/artistic)abstract
- 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.
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| 44. |
- Hilber, Patrik, et al.
(author)
-
A Method for Extracting Reliability Importance Indices from Reliability Simulations of Electrical Networks
- 2005
-
In: 15th Power Systems Computation Conference, PSCC 2005. - : Power Systems Computation Conference ( PSCC ).
-
Conference paper (peer-reviewed)abstract
- 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.
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| 45. |
- Hilber, Patrik, et al.
(author)
-
Benefits of Reliability Centred Asset Management
- 2013
-
In: 22nd International Conference and Exhibition on Electricity Distribution (CIRED 2013). - : Institution of Engineering and Technology. - 9781849197328 ; , s. 0668-
-
Conference paper (peer-reviewed)abstract
- 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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| 46. |
- Hilber, Patrik, 1975-
(author)
-
Cable Segment Replacement Optimization
- 2014. - 1
-
In: Reliability Modeling and Analysis of Smart Power Systems. - New Delhi Heidelberg New York Dordrecht London : Springer London. - 9788132217978 - 9788132217985 ; , s. 195-202
-
Book chapter (peer-reviewed)
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| 47. |
- Hilber, Patrik, et al.
(author)
-
Component Reliability Importance Indices for Electrical Networks
- 2007
-
In: 2007 CONFERENCE PROCEEDINGS IPEC, VOLS 1-3. - NEW YORK : IEEE. - 9789810594237 ; , s. 257-263
-
Conference paper (peer-reviewed)abstract
- 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.
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| 48. |
- Hilber, Patrik, 1975-
(author)
-
Component reliability importance indices for maintenance optimization of electrical networks
- 2005
-
Licentiate thesis (other academic/artistic)abstract
- 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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| 49. |
- Hilber, Patrik, et al.
(author)
-
Effects of Correlation between Failures and Power Consumption on Customer Interruption Cost
- 2006
-
In: 2006 International Conference on Probabilistic Methods Applied to Power Systems, Vols 1 and 2. - 9789171785855 ; , s. 1120-1123
-
Conference paper (peer-reviewed)abstract
- 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.
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| 50. |
- Hilber, Patrik, 1975-
(author)
-
Maintenance optimization for power distribution systems
- 2008
-
Doctoral thesis (other academic/artistic)abstract
- 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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