kth.sePublications
Change search
Refine search result
1 - 23 of 23
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 1.
    Hu, Wei
    et al.
    Jilin Univ, Sch Mech & Aerosp Engn, Key Lab CNC Equipment Reliabil, Minist Educ, Changchun 130025, Peoples R China..
    Westerlund, Per
    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.
    Chen, Chuanhai
    Jilin Univ, Sch Mech & Aerosp Engn, Key Lab CNC Equipment Reliabil, Minist Educ, Changchun 130025, Peoples R China..
    Yang, Zhaojun
    Jilin Univ, Sch Mech & Aerosp Engn, Key Lab CNC Equipment Reliabil, Minist Educ, Changchun 130025, Peoples R China..
    A general model, estimation, and procedure for modeling recurrent failure process of high-voltage circuit breakers considering multivariate impacts2022In: Reliability Engineering & System Safety, ISSN 0951-8320, E-ISSN 1879-0836, Vol. 220, article id 108276Article in journal (Refereed)
    Abstract [en]

    The high-voltage circuit breaker (HV CB) constitutes an important repairable asset in power systems. Due to its great number in the power network and strategic role in the successful operation of power systems, it is important to ensure its reliability. This paper deals with the estimation of the failure process of CBs considering the impact of age, operation intensity, corrective maintenance, and examination. A general model that integrates the above factors' effects is proposed, which can be reduced to many specific models like virtual age models, scale models, the two combinations, and their regression analysis. The model estimation under the condition of random censoring population data is illustrated, including parameters, reliability indicators, the cumulative intensity function, and goodness-of-fit tests. Moreover, a general procedure to stepwise select valuable effect functions into the general model is presented, thereby obtaining a specific formulation fitting the given data. The above works are applied to a real case to discuss the most probable failure process of the given HV CBs.

  • 2.
    Koziel, Sylvie Evelyne
    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.
    Westerlund, Per
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering.
    Shayesteh, Ebrahim
    Vattenfall Serv Nordic AB, Evenemangsgatan 13C, S-16956 Solna, Sweden..
    Investments in data quality: Evaluating impacts of faulty data on asset management in power systems2021In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 281, article id 116057Article in journal (Refereed)
    Abstract [en]

    Data play an essential role in asset management decisions. The amount of data is increasing through accumu-lating historical data records, new measuring devices, and communication technology, notably with the evolution toward smart grids. Consequently, the management of data quantity and quality is becoming even more relevant for asset managers to meet efficiency and reliability requirements for power grids. In this work, we propose an innovative data quality management framework enabling asset managers (i) to quantify the impact of poor data quality, and (ii) to determine the conditions under which an investment in data quality improvement is required. To this end, an algorithm is used to determine the optimal year for component replacement based on three scenarios, a Reference scenario, an Imperfect information scenario, and an Investment in higher data quality scenario. Our results indicate that (i) the impact on the optimal year of replacement is the highest for middleaged components; (ii) the profitability of investments in data quality improvement depends on various factors, including data quality, and the cost of investment in data quality improvement. Finally, we discuss the implementation of the proposed models to control data quality in practice, while taking into account real-world technological and economic limitations.

  • 3.
    Gariboldi, Nicola
    et al.
    Qualitrol LCC.
    Mantilla, Javier
    Hyundai Electric.
    Catanese, Dan
    ESB.
    Poirier, Sébastien
    IREQ.
    Pater, Ryszard
    IREQ.
    Herrera, Alexander
    Omicron Electronics.
    Nenning, Andreas
    Omicron Electronics.
    Westerlund, Per
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    CIGRE JWG A3.43 progress report “Tools for lifecycle management of T&D switchgear based on data from condition monitoring systems"2020Conference paper (Other academic)
    Abstract [en]

    In March 2019 the joint working group A3.43 "Tools for lifecycle management of T&D switchgear based on data from condition monitoring systems" started its activities with the goal to provide inside three years a guide on how to use the data from monitoring activities of switchgear.

    The working group counts presently 34 members, from 17 different countries met already five times and work is ongoing on the main Technical Brochure (TB) structure as follows: 

     

    1. Executive summary 

    2. Introduction

    3. Literature Review

    4. Condition indicators of T&D switchgear

    5. Tools and Criteria for lifecycle management and Switchgear Health Index

    6. Compliance with digital substation for data management

    7. User’s experiences of end-of-life of T&D switchgear: survey, case studies and interviews

    8. Future needs and trends

    A literature review offers a glimpse into state of the art tools and techniques for lifecycle management and the equipment used. A very steep increase of publications on this matter is observed in the last years with implications in other aspects beyond lifecycle management.  Second, the condition indicators as determined in the TB737 are taken over and used in this work as proxies for the switchgear variables evaluation.

    The main part of the work concentrates on the tools and techniques their framework established. The works from other WG’s on substation level on B3 study committees are introduced as an organic part of the activities. A fundamental decision has been made to follow Health Index concepts as defined in B3.48 concentrating on providing valuable inputs specifically for switchgear. The main focus is on Tools and Criteria for lifecycle management for which the target is to propose models which can condense the specific and deep knowledge of the members to arrive to an advanced and reliable assessment. Some concrete examples are planned to act as guidelines on how to apply the theory to real life scenarios. 

    The digitization of substation equipment is an ongoing process, which is radically changing how assets will be controlled in the substation.  IEC 61850 is today the followed standard on which this automation revolution is based for operation and protection.  Four members from study committee B5 are part of the group specifically to identify the potential benefit of a technology which has not been driven by monitoring.  User experiences are under evaluation. Preliminary results, not presented here, have shown mixed opinions between use and necessity.

    Finally, the future trends identified so far are discussed.  The role of condition monitoring systems as enablers for future developments in the networks is discussed. 

  • 4.
    Westerlund, Per
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Naim, Wadih
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Extreme Value Analysis of Power System Data2019In: ITISE 2019 International Conference on Time Series and Forecasting: Proceedings of Abstract 25-27 September 2019 Granada (Spain) / [ed] Ignacio Rojas, 2019, Vol. 1, p. 322-327Conference paper (Refereed)
    Abstract [en]

    In the electric system, the consumption varies throughout the year, during the week and during the day. The consumption should be balanced by the production, which is not easy with solar power and wind power, as they lack storage like the dams for hydropower. Then these sources should be modelled as time series. The time series analyzed is the solar and wind power production in Sweden during 5 months. The method is called Peaks over Threshold or POT and it calculates the frequency of peaks above a certain threshold. It also determines the distribution of the size of the peaks, which is the generalized Pareto distribution in this case. Two different clustering methods are tried; one by Lindgren and the other one a modification of Leadbetter's method. The latter one gives the best fit. However, some ten years of data should be analyzed in order to include the seasonal effects.

  • 5.
    Koziel, Sylvie Evelyne
    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.
    Westerlund, Per
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Shayesteh, E.
    Forecasting cross-border power exchanges through an HVDC line using dynamic modelling2019In: Proceedings - 2019 IEEE International Conference on Big Data, Big Data 2019, Institute of Electrical and Electronics Engineers Inc. , 2019, p. 4390-4394Conference paper (Refereed)
    Abstract [en]

    As smart grids develop, power systems become more complex, and the role of data gain considerable importance for the reliability of power supply. Thus, data processing techniques have to be investigated and compared to increase the efficiency of asset management decisions. In this paper, we explore several black-box models in order to predict power exchanges through a high-voltage direct-current line between Sweden and Denmark, using publicly available data on loads and power prices. An auto-regressive moving average with external input model based on load data provides the most accurate forecasts according to mean square error and other selected criteria. This is the first step to build a more comprehensive model that will also include other technical data such as maintenance and unplanned outages, but also macroeconomic factors. The final goal is to provide network operators with a parsimonious sequential model composed of several modules giving accurate predictions that support efficient asset management decisions. 

  • 6.
    Boričić, Aleksandar
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering.
    Bhatt, Dhruv
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering.
    Westerlund, Per
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering.
    Reliability and Cost-Effectiveness Analysis of Various HV Substation Configurations2019Conference paper (Refereed)
    Abstract [en]

    Reliable power supply is one of the crucial factors for the development of any industry. Different technologies as well as configurations are available when it comes to investing in new electrical assets. According to [1], the circuit configurations of high voltage substations are strongly influenced by many factors, such as operational requirements, security standards, availability, maintainability, etc. There is always a trade-off between the technical requirements and the cost of investment. This paper aims to quantify the availability of a switchyard with two lines and two transformer bays for various switching configurations. Once the overall availability is determined, the decision for the selection of a switching configuration is made based on the cost-benefit analysis.

    The voltage rating of a primary substation is decided based on the scale of an industry. Switching configuration is one of the major factors affecting the overall availability of the substation. Each switching configuration has its own pros and cons in terms of its operation, reliability and investment cost. It is impossible to achieve 100% availability of a substation with any kind of switching scheme. Availability and investment cost of a substation vary with the choice of the configuration and substation technology. There are mainly three available technologies - Air Insulated Switchgear (AIS), Gas Insulated Switchgear (GIS) and Mixed Technology Switchgear (MTS).

    This paper evaluates possible choices for an example of supply which is very often seen in practice, providing guidelines for decision-making process in order to optimize profit of an industry, from the supply-reliability point of view. In this paper, a 220/66kV AIS substation for an upcoming process plant is under consideration. The scope of this paper is limited to assess the availability of primary side of the substation. There are two-line bays and two transformer bays in the 220kV switchyard. Down-stream to the 66kV side is not taken into consideration for the analysis purpose.

  • 7.
    Uzelac, Nenad
    et al.
    G & W Electric.
    Heinrich, Christian
    Siemens.
    Pater, Ryszard
    Hydro-Québec.
    Arnold, Jack
    National Instruments.
    Eichhoff, Daniel
    Amprion.
    Ferraro, Venanzio
    Schneider Electric.
    Gariboldi, Nicola
    Qualitrol.
    Germain, Mario
    Hydro-Québec.
    Gioseffi, Alejandro
    Edesur.
    Ito, Takashi
    Mitsubishi Electric.
    Kopejtko, Petr
    Livshitz, Albert
    CE Power.
    López-Roldán, José
    MacLeod, Jason
    Burns and McDonnell .
    Mantilla, Javier
    ABB.
    Milosevic, Ana
    Poirier, Sébastien
    Hydro-Québec.
    Schuepferling, Bernd
    Siemens.
    Smeets, Rene
    DNV GL.
    Smit, Johan
    TU Delft.
    Taylor, Erik
    Siemens.
    van Rijn, Theo
    Alliander.
    Wang, Xiaohua
    Xi'an Jiaotong University.
    Westerlund, Per
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Non-intrusive methods for condition assessment of distribution and transmission switchgear2018Report (Other academic)
    Abstract [en]

    JWG A3.32 with CIRED completed the Technical Brochure, which provides comprehensive information on Non-Intrusive Condition assessment of the T&D switchgear that can be applied on HV and MV circuit breakers, HV and MV switching equipment, MV reclosers and fault interrupters. Many emerging non-intrusive techniques were reported in the literature, most of them allowing in service evaluation. The JWG reviewed the current and future trends of non-intrusive, especially in service, diagnostic methods completing the work on Condition Assessment of Switchgears dealt in TB 167 and on Online Monitoring HV Substations available in TB 462. The brochure will provide useful information for everybody who is going to apply or improve Condition Assessment Methods to Switchgears.

     

  • 8.
    Westerlund, Per
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Dimoulkas, Ilias
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electric Power and Energy Systems.
    Prediction of Current by Artificial Neural \\ Networks in a Substation in order \\ to Schedule Thermography2018In: ITISE, Granada, 2018Conference paper (Other academic)
    Abstract [en]

    Thermography or infra-red imaging is a method that measures the temperature of a surface by receiving the infra-red radiation that the surface emits. Thermography is used in, for example, condition measuring of electrical equipment. It shows which parts are heated more than normally due to a higher resistance. Those parts will need maintenance.

    In order to get accurate values, thermography needs a high current in the equipment. Thus it is necessary to predict when the current will be high throughout the year. Here a neural network with two layers is used for the prediction. The data set consists of the hourly currents at a point in a Swedish substation from a period of ten years.

    \\

    The purpose is to plan when to go to a substation to do thermography. As the prediction is done several months ahead, the outdoor temperature cannot be used. Hence only the time expressed as week, day and hour with different resolutions in the discretization, is used as an explanatory variable. With increasing resolutions in the discretization, the prediction error decreases. Adding inputs based on interaction does not improve the prediction. The results are however not satisfactory as the prediction error is large in comparison with the predicted values of the current and the prediction is biased. One reason is that the prediction should be several months ahead, so the actual temperature cannot be used.

  • 9.
    Westerlund, Per
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Rydén, Jesper
    Sveriges lantbruksuniversitet.
    Hilber, Patrik
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Lindquist, Tommie
    Prediction of high current for thermography in maintenance of electrical networks2018In: Nordstat, Tartu, 2018Conference paper (Other academic)
  • 10.
    Westerlund, Per
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Condition measuring and lifetime modelling of disconnectors, circuit breakers and other electrical power transmission equipment2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The supply of electricity is important in modern society, so the outages of the electric grid should be few and short, especially for the transmission grid. A summary of the history of the Swedish electrical system is presented. The objective is to be able to plan the maintenance better by following the condition of the equipment.

    The risk matrix can be used to choose which component to be maintained. The risk matrix is improved by adding a dimension, the uncertainty of the probability. The risk can be reduced along any dimension: better measurements, preventive maintenance or more redundancy. The number of dimensions can be reduced to two by following iso-risk lines calculated for the beta distribution.

    This thesis lists twenty surveys about circuit breakers and disconnectors, with statistics about the failures and the lifetime. It also presents about forty condition-measuring methods for circuit breakers and disconnectors, mostly applicable to the electric contacts and the mechanical parts.

    A method for scheduling thermography based on analysis of variance of the current is tried. Its aim is to reduce the uncertainty of thermography and it is able to explain two thirds of the variation using the time of the day, the day of the week and the week number as explanatory variables. However, the main problem remains as the current is in general too low.

    A system with IR sensors has been installed at the nine contacts of six disconnectors with the purpose of avoiding outages for maintenance if the contacts are in a good condition. The measured temperatures are sent by radio and regressed against the square of the current, the best exponent found. The coefficient of determination $R^2$ is high, greater than 0.9. The higher the regression coefficient is, the more heat is produced at the contact. So this ranks the different contacts.

    Finally a framework for lifetime modelling and condition measuring is presented. Lifetime modelling consists in associating a distribution of time to failure with each subpopulation. Condition measuring means measuring a parameter and estimating its value in the future. If it exceeds a threshold, maintenance should be carried out. The effect of maintenance of the contacts is shown for four disconnectors.

    An extension of the risk matrix with uncertainty, a survey of statistics and condition monitoring methods, a system with IR sensors at contacts, a thermography scheduling method and a framework for lifetime modelling and condition measuring are presented. They can improve the planning of outages for maintenance.

    Finally a framework for lifetime modelling and condition measuring is presented. Lifetime modelling consists in associating a distribution of time to failure with each subpopulation. Condition measuring means measuring a parameter and estimating its value in the future. If it exceeds a threshold, maintenance should be carried out. The effect of maintenance of the contacts is shown for four disconnectors.

    An extension of the risk matrix with uncertainty, a survey of statistics and condition monitoring methods, a system with IR sensors at contacts, a thermography scheduling method and a framework for lifetime modelling and condition measuring are presented. They can improve the planning of outages for maintenance.

    Download full text (pdf)
    Westerlund_doktorsavhandling
  • 11.
    Westerlund, Per
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Hilber, Patrik
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Lindquist, Tommie
    Svenska kraftnät (Swedish National Grid), Sweden.
    Condition monitoring of disconnectors in the electric power transmission grid with temperature sensors2016In: International Journal of Industrial and Systems Engineering, ISSN 1748-5045, Vol. 23, no 1, p. 90-110Article in journal (Refereed)
    Abstract [en]

    This paper presents a method that can be used to rank disconnectors in the electric power system, according to the condition of one of the most critical parts, the contacts. The temperature of the contacts can be continuously measured by a new type of infrared sensor. For the case study, 54 sensors were placed on six disconnectors together with reference sensors measuring the ambient temperature. The measured temperature at each contact is then regressed against the ambient temperature and the current through the disconnector. Both a linear and a quadratic dependency of the current are tested and the quadratic one explains the data best. The coefficient of the current serves as a measure of the condition of the contact. Then, it becomes possible to identify in which contacts the resistance has increased the most. As a consequence, it is possible to make better maintenance decisions for the disconnectors.

    Download full text (pdf)
    fulltext
  • 12.
    Westerlund, Per
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Hilber, Patrik
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Lindquist, Tommie
    Prediction of current in a substation in order to schedule thermography2016In: 2016 INTERNATIONAL CONFERENCE ON PROBABILISTIC METHODS APPLIED TO POWER SYSTEMS (PMAPS), IEEE, 2016Conference paper (Refereed)
    Abstract [en]

    It is important to predict the current in a line in the electrical grid for example when planning thermography or handling dynamic rating. This paper takes data from a Swedish substation from 10 years and applies analysis of variance (ANOVA) to construct a linear model. The factors are the time of the day, the day of the week and the week number.

    About two thirds of the variance in the data can be explained by the model, but the means are too low to attain a current of at least one third of the current for which the equipment is rated. Thus the model is not good enough to plan thermography for the studied bay in the substation.

    However the model is able to predict the current and can also be used to predict power flows in the electric network.

    Download full text (pdf)
    fulltext
  • 13.
    Westerlund, Per
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Hilber, Patrik
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Lindquist, Tommie
    Prediction of time for preventive maintenance2016In: The Nordic Conference in Mathematical Statistics, Köpenhamn, 2016Conference paper (Refereed)
    Abstract [en]

    In maintenance planning a crucial question is when some asset should be maintained. As preventive maintenance often needs outages it is necessary to predict the condition of an asset until the next possible outage. The degradation of the condition can be modelled by a linear function. One method of estimating the condition is linear regression, which requires a number of measured values for different times and gives an interval within which the asset will reach a condition when it should be maintained [1]. A more sophisticated calculation of the uncertainty of the regression is presented based on [2, section 9.1].

     

    Another method is martingale theory [3, chapter 24], which serves to deduce a formula for the time such that there is a probability of less than a given $\alpha$ that the condition has reached 0 before that time. The formula contains an integral, which is evaluated numerically for different values of the measurement variance and the variance of the Brownian motion, which must be estimated by knowing the maximum and the minimum degradation per time interval. Then just one measured value is needed together with an estimate of the variance.

     

    The two methods are compared, especially with regard to the size of the confidence interval of the time when the condition reaches a predefined level. The application for the methods is the development of so called health indices for the assets in an engineering system, which should tell which asset need maintenance first. We present some requirements for a health index and check how the different predictions fulfil these requirements.

    References

    [1] S.E. Rudd, V.M. Catterson, S.D.J. McArthur, and C. Johnstone. Circuit breaker prognostics using SF6 data. In IEEE Power and Energy Society General Meeting, Detroit, MI, United States, 2011.

    [2] Bernard W. Lindgren. Statistical theory. Macmillan, New York, 2nd edition, 1968.

    [3] Jean Jacod and Philip Protter. Probability essentials. Springer-Verlag, Berlin, 2000.

  • 14.
    Westerlund, Per
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Condition measuring and lifetime modelling of electrical power transmission equipment2015Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The electric grid is important in modern society, so the outages should be few. The transmission grid should have a real high availability, since it transports electrical energy across the country. Then, it is difficult to plan outages for maintenance and installation. This thesis lists twenty surveys about failures of circuit breakers and disconnectors, with data about the cause and the lifetime. It also contains a survey of about forty condition-measuring methods for circuit breakers and disconnectors, mostly applicable to the electric contacts and the mechanical parts.

    As there is no published method to monitor the electric contacts at voltages around 400 kV, a system with IR sensors has been installed at the nine contacts of six disconnectors. The purpose is to avoid outages for maintenance by estimating the condition of the contacts while the disconnectors are still connected to high voltage. The measured temperatures are collected by radio and regressed against the square of the current, since the best exponent for the current was found to be 2.0. The coefficient of determination $R^2$ is high, greater than 0.9. This gives for each contact a regression coefficient, which can serve as an estimate of the condition of the contact. The higher the coefficient is, the more heat is produced at the contact, which can damage the material. This enables a ranking of the different contacts and shows which the worst ones are. This coefficient can also give a dynamic rating of the disconnector.

    Download full text (pdf)
    Licentiate Thesis
  • 15.
    Westerlund, Per
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Hilber, Patrik
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Lindquist, Tommie
    Function test and condition test for disconnecting circuit breakers2015Conference paper (Refereed)
    Abstract [en]

    Svenska kraftnät has installed about 300 disconnecting circuit breakers (DCB) in the Swedish 245 and 420 kV transmission network. They are installed without any disconnectors in the substation. The first DCBs were installed in the early 2000s and are approaching the age of 12 years, which is the time for the first scheduled maintenance, a function test that requires de-energising of the breaker. For a shunt reactor breaker in a double-breaker double-busbar configuration this means disconnection of one of the busbars at the substation, whereas for a line breaker it means disconnection of the incoming line, which is often difficult.

     

    Thus for disconnecting circuit breakers especially line breakers, there is need for an in-service condition test, which have been developed and tested at Svenska kraftnät. It requires some modification to the DCBs from the manufacturer and has been a Svenska kraftnät standard for many years.

     

    This paper describes the difference between the conventional off-line function test and the new in-service condition test, mainly regarding the possible failures that can be detected. The failures can be classified in three major types: mechanical, electrical and related to the insulation gas. The present condition test measures the movements during the opening and closing operations and it can assess the condition of the mechanical parts, whereas the condition of breaking chamber and the electrical resistance of the contacts are not possible to measure without disconnecting the circuit breaker. The gas pressure and other parameters can be added separately to the condition test. Also this paper provides normal values of the parameters measured in an in-service condition test, such as coil current, motor current and timing parameters.

  • 16.
    Hilber, Patrik
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Westerlund, Per
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Lindquist, Tommie
    The reliability chain2015Conference paper (Refereed)
    Abstract [en]

    This is a conceptual paper introducing the novel reliability chain as a holistic framework for the asset management process. The main objective of the reliability chain is to give a tool for communication regarding asset management decisions and to visualize the different areas that are important for efficient decisions.

     

    The reliability chain describes the process from data on component and system level to asset management decisions, via steps of information handling. Furthermore a brief outline on how to utilize the concept in order to categorize different asset management strategies is provided.

     

    A main challenge in many maintenance and asset management processes is the risk of putting too much attention to a limited part of the process. One of the main conclusions from the paper is that significant efforts have to be spent on the transitions between the different links in the reliability chain in order to reach an efficient and well-organized asset management.

  • 17.
    Westerlund, Per
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Hilber, Patrik
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Lindquist, Tommie
    Svenska kraftnät.
    A review of methods for condition monitoring, surveys and statistical analyses of disconnectors and circuit breakers2014In: Probabilistic Methods Applied to Power Systems (PMAPS), 2014 International Conference on / [ed] Chris Dent, IEEE conference proceedings, 2014, p. 1-6Conference paper (Refereed)
    Abstract [en]

    There is a need for a new survey of condition-monitoring methods for circuit breakers and disconnectors, since during the last two decades less than ten surveys have been carried out. The paper presents several statistical surveys and analyses. The methods of condition monitoring found are reviewed and classified according to the different types of failure identified in the surveys. Some research gaps are identified, such as the prediction of the degradation of the contacts, the signal processing of coil and motor currents and the switching.

    Download full text (pdf)
    fulltext
  • 18.
    Westerlund, Per
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Hilber, Patrik
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Lindquist, Tommie
    Svenska kraftnät.
    Grade levels for multiple-choice tests2014Conference paper (Refereed)
    Abstract [en]

    In education there is nearly always an evaluation of how much of the course syllabus the student has learnt. The multiple-choice tests are a type of written examination that is easy to use, since the correction is quickly done. The problem with these test is to find a good grading scale, since the students can get more points than what their knowledge indicate, as they can guess.

    There are different approaches to analyze the results of multiple-choice tests. However, the articles that have been found do not discuss the number of grades that a multiple-choice test should be able to differentiate. Also in those articles there are no figures, where the effect of guessing is shown.

    The purpose is to design a multiple-choice test. The inputs are the grade scale and the number of alternatives and the output is the number of questions required for a given level of errors in grading. As an example we consider a multiple-choice test with 40 questions with 4 alternatives. We study the distribution of four students that knows nothing, 25 \%, 50 \% and 75 \%  of the questions. They guess the rest of the questions.

    It can be observed that the distribution narrows when going from the left to the right. This is due to a smaller variance, since the number of guesses decreases. With a smaller variance, the height of the peak has to increase, in order to get the area below the curve. The overlapping tails are bigger to the left, as the variance is bigger. Thus the risk of putting a student in the wrong category is bigger for the lower grades. The rightmost peak is the least symmetric, with a steeper left-hand side. Then the binomial distribution is not approximated by a normal distribution so well, since the number of trials is lower. With 60 questions instead of 40, the intersection between the curves is at a lower level of probability, which means that the risk of giving a student a wrong grade is lower.

  • 19.
    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.

    Download full text (pdf)
    fulltext
  • 20.
    Wallnerström, Carl Johan
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Westerlund, Per
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Hilber, Patrik
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Using power system temperature sensors for moreuses than originally intended: Exemplified by investigating dynamic rating possibilities2014In: NORDAC 2014 (Eleventh Nordic Conference on Electricity Distribution System Management and Development, Stockholm, 8 - 9 September 2014), Elforsk , 2014Conference paper (Refereed)
    Abstract [en]

    Power system owners are facing major challenges with changed electricity consumption and production patterns; more distributed generation and increased demand of cost efficiency while maintaining high reliability. Today, the capacity of power components often is set with static limits based on simulations of worst case scenarios. This leads to a discrepancy between the actually-available capacity and the rating itself which unfortunately is left unused. The approach of dynamic rating implies that the capacity of a component is dynamically varying as a function of external parameters such as weather, load history and diagnostic indicators.

     

    Svenska kraftnät (Swedish national grid) has installed temperature sensors with the purpose of developing condition monitoring methods in another research project. Within this project, the same infrastructure can perhaps be used to also evaluate dynamic rating algorithms of power lines or to develop new algorithms regarding e.g. disconnectors. Also the thermal modelling in that project can be reused. This paper hence exemplifies the possibility to get more applications without additional costly and complicated investments. The aim of the paper is hence to show on future research possibilities and bring ideas to discussion.

    Download full text (pdf)
    fulltext
  • 21.
    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.

    Download full text (pdf)
    fulltext
  • 22.
    Westerlund, Per
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Hilber, Patrik
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Lindquist, Tommie
    Svenska kraftnät.
    Condition monitoring of the disconnectors in the electric power transmission grid with temperature sensors2013In: Conference proceedings of 3rd International Conference on Maintenance Performance Measurement and Management, Lappeenranta: Lappeenranta University of Technology , 2013Conference paper (Refereed)
    Abstract [en]

    In the electrical substations there are disconnectors, which can be opened to disconnect equipment from high voltage parts. As the disconnectors are normally closed and transfer current owing to their often critical positions in the power grid, it is difficult to maintain them. The purpose is to develop a new online method to monitor disconnectors and a new theory for their ageing, in order to schedule the maintenance better.

    Increasing resistance in the contacts could cause high temperatures and eventually failure. Nine IR temperature sensors have been placed on each of six disconnectors together with reference sensors. After cleaning and interpolation of the data, two regressions are made, first between a sensor at a contact and the reference sensor, then adding the square of the current. The method is promising since it explains most of the variation in temperature with a sensor dependent parameter.

     

  • 23.
    Westerlund, Per
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Hilber, Patrik
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Lindquist, Tommie
    Combining risk and uncertainty in technical systemsManuscript (preprint) (Other academic)
    Abstract [en]

    The risk matrix is tool for making decision about technical system such as prioritising of maintenance. It is used in methods such as FMEA (failure mode and effect analysis) and it is based on the definition of risk as the product of the probability of a certain failure and its consequence.

    The problem with the standard formulation is that the probability is not always completely known. The uncertainty of the probability can be estimated by its variance. %We suggest that the the mean value plus the standard deviation times a factor could be used instead of just the mean value.

    Instead of a specific value for the probability of failure, a beta distribution is used for the probability. The main point is to find a trade-off between mean and variance. In this case we want to avoid probabilities larger than the mean. We use a loss function taking into account only the right tail starting at a factor times the mean. The exponent of the deviation is 0. We have calculated how much a decreasing variance should compensate for an increasing mean. We get an approximate relation between the quotient of variances and the quotient of means.

    The conclusion is that this model should be investigated further.

    Download full text (pdf)
    uncertainty_westerlund_et_al
1 - 23 of 23
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf