Lina Bertling Tjernberg

KTH Royal Institute of Technology | KTH · School of Electrical Engineering (EE)

From October 2012, electricity customers in Sweden have the possibility to pay their electricity consumption based on the hourly spot prices on the day-ahead electricity market, Nordpool spot. Customers will know the electricity prices 12-36 hours in advance and will have the possibility to schedule their electricity usage in order to reduce their...

The introduction of Smart Meter (SM) is a first stage towards Smart Grid to develop future energy system. The main difference of a SM with a traditional meter is that instead of only showing the current usage on the meter itself, it can also communicate the usage details directly to a Distribution System Operator. In order to make overall reduction...

In a power system with high renewable power penetration, uncertain and intermittent characteristics of renewable energy resources become major concerns of system planning and operation. In such a power system, conventional thermal or hydro units have to be dispatched, shut down or started up more frequently to incorporate load, renewable resource v...

With the advent of plug-in electric vehicles (EV), it becomes increasingly important to study the impact of charge scheduling of a large number of EVs on the day-ahead electricity market price. In this paper, two scheduling models are proposed-joint scheduling model and aggregator scheduling model. They are used to study the effects of scheduling o...

A massive introduction of plug-in electric vehicles (PEVs) in the transportation sector would likely increase the total electricity consumption. Depending on how and when the PEVs are charged, the effects on the power demand will vary. Previous studies have shown that uncontrolled charge of PEVs can cause problems for the distribution system in som...

High Voltage Direct Current (HVDC) seems going into another booming time since the first test line was developed by Dr. Uno Lamm about seventy years ago in Sweden. The boom of this time can be seen from not only fast increased project number but significant research interests around whole world as well. The major motivation behind comes from new ch...

The concept of reliability-centered maintenance (RCM) is applied to the two wind-turbine models Vestas V44-600 kW and V90-2MW. The executing RCM workgroup includes an owner and operator of the analyzed wind turbines, a maintenance service provider, a provider of condition-monitoring services, and wind-turbine component supplier as well as researche...

An important component in the modernization of electrical grid infrastructure is the increasing production of energy from renewable distributed generation sources. However, the intermittency of this generation motivates stochastic optimization to address uncertainty, and an adequate system of reserves. This paper investigates the stochastic optimiz...

The electrical distribution system is facing major challenges in the near future related to increased electricity consumption, increased amount of distributed generation (DG) and the introduction of plug-in electric vehicles (PEVs). These could require large investments in the distribution system to maintain and operate the system in a secure way....

Over the years the electric power system has seen an exponential growth in terms of size and technology. A similar growth and development has taken place in the terms of probabilistic applications used to analyze the power systems. A literature survey was done to analyze the existing widely used test systems; IEEE RTS and RBTS [5]. Conclusions were...

Denna rapport presenterar resultat från en studie där inverkan av så kallade smartaelnäts¬teknologier/lösningar har analyserats. Utöver egna analysresultat identifieras behov av framtida forskning, detta kompletteras med hänvisningar till fördjupningsmaterial Smarta¬elnätsteknologier innebär nya möjligheter, men också nya utmaningar och risker. Ett...

The aim of this paper is to incorporate reliability aspects in the transmission planning process presented in previous work. The decision maker has to consider many different aspects during the definition of transmission planning strategy, that sometimes might be contradicting. In the whole planning framework the decision is made by combining econo...

Over the years the reliability test systems such as the IEEE Reliability Test System (RTS) and Roy Billinton Test System (RBTS) have been used extensively by researchers, as a bench mark system, for reliability assessment and other developments in the field of probabilistic applications in power systems. This paper presents an extensive literature...

Wind power has emerged as a promising and feasible resource to provide clean energy. The intermittent and uncontrollable characteristics of wind power yet create many stability and reliability issues in power system planning and operation. Battery energy storage systems (BESSs) have been broadly used to solve the problems. Reliability cost and wort...

A sound maintenance planning is of crucial importance for wind power farms, and especially for offshore locations. This paper presents a stochastic optimization model for opportunistic service maintenance of offshore wind farms. The model takes advantage of 7 days wind production ensemble forecast and opportunities at corrective maintenance activit...

This paper presents results from a limited-scope Reliability-Centred Maintenance (RCM) analysis of the wind turbines Vestas V44-600kW and V90-2MW. The RCM analysis has been carried out within a workgroup involving a wind turbine owner and operator, a maintenance service provider, a provider of condition-monitoring services and wind turbine componen...

The electric power system is under an extensive development phase. This change is today normally expressed in the concept of Smart Grid. It captures different developments for a sustainable electric power system, e.g. including large changes at the electrical distribution level with new features for electricity customers. One move in these changes...

A typical power system voltage collapse scenarios is often ended with the undesirable operation of the Zone-3 distance relay of the transmission lines. This paper presents a protection scheme to avoid power system voltage collapse using a combined method of distance relay's Zone-3 blocking scheme and a sensitivity-based load shedding selection. The...

Wind power is expanding in Sweden as in many other countries. Varying wind power production may be a challenge for the electric power system to balance due to the intermittency. The paper studies three future scenarios of wind power expansion in Sweden and relates that to the current system power reserves located in each congestion area. Production...

The electric power system is changing and, especially, the electrical distribution system will meet new features. One of the large changes is a transformation of the transportation sector with the use of electricity, with introduction of Plug-in Electric Vehicles (PEVs). This will pose new challenges and opportunities for the electric distribution...

The current transition from passive to active electric distribution networks comes with problems and challenges on bi-directional power flow in the network and the uncertainty in the forecast of power generation from grid-connected renewable and distributed energy sources. The power flow management would need to be distributed, flexible, and intell...

Reliability and availability are key issues for the implementation of future sustainable power systems. This paper discusses the need, methods and challenges for maintenance optimization to improve the reliability, availability, and profitability of wind power plants being a major source of renewable energy today and in future “smart grids”. The pr...

Nuclear power constitutes one of the main electricity production sources in several countries, e.g. in Sweden, with about half of today's electricity production. Driving forces for cost-efficiency have pushed the development of new methods for maintenance planning and optimization forward. Reliability Centered Asset Management (RCAM) is one of thes...

This paper assesses the effects of the future European power generation system with strict CO₂ emission reduction targets on the planning of cross-border interconnection lines. Results from a techno-economic energy systems model have been used as input to this work, regarding the development of the European power generation system until...

Integration of plug in hybrid electric vehicles and electric vehicles (PHEVs and EVs) includes a wide area of topics like grid effects, different charging concepts, charger designs, harmonics from the charger etc. This short paper gives an introduction to ongoing work within this field in Sweden, and shows on research work within the topic at Chalm...

The introduction of performance based tariff regulations, and higher media and political pressure have increased the need for well-performed asset management in the operation and planning of electrical distribution systems. In this paper quantitative reliability assessment methods are proposed as a tool to meet these new incentives. Electrical dist...

A sound maintenance planning is of crucial importance for wind power systems. There is a large potential in cost savings by optimizing maintenance decisions to make the projects more cost-efficient. This paper presents an approach to optimize condition-based maintenance strategies for components which degradation can be classified according to the...

Load forecasting is important in the operation of power systems. The characteristics of the electrical energy consumption are analyzed and its variation as an effect of several weather parameters is studied. Based on historical weather and consumption data received from a distribution system operator (DSO), numerical models of load forecasting are...

The large growth in the wind power industry in the past years mainly focuses on a growing market and the development of large turbines and offshore farms. The high technical availability of wind turbines comes with a high need for frequent maintenance. Current maintenance planning is generally not optimized, and it is possible to make maintenance m...

This paper gives an overview of a turbulent time for the regulator and distribution system operators (DSO) in Sweden since the de-regulation of the electricity market in 1996. A performance based ex-post model was introduced 2003 as a tool to judge distribution system tariffs. This model is since 2009 formally abandoned and a new exante regulation...

This paper is based on a project work of the course ldquoPower Engineering Design Projectrdquo given by the Division of Electric Power Engineering, Chalmers University of Technology in Sweden in Fall semester, 2008. The project has focused on simulating power system voltage collapse scenarios using Advanced Real-Time Interactive Simulator for Train...

A sound maintenance planning is of crucial importance for wind power farms, and especially for offshore locations. There is a large potential in cost savings by maintenance optimization to make the projects more cost-efficient. This paper presents an opportunistic maintenance optimization model for offshore wind power system. The model takes advant...

Nuclear power is one of the main electricity production sources in Sweden today. Maintenance management is one tool for reducing the costs for operation of a power plant. Driving forces for cost-efficiency has pushed the development of new methods for maintenance planning and optimization forward. Reliability Centered Asset Management (RCAM) is one...

In the planning of the electrical transmission system it is of greatest concern to quantify the security margin for unwanted conditions in the system. This paper proposes an approach based on quantifying the risk of insufficient transmission capacity in bottlenecks in the system. Stresses in these critical transfer sections (CTS) provide a potentia...

This paper summarizes results from a research project investigating risk management applied to electrical distribution systems (EDS) in Sweden. New incentives have motivated the distribution system operators (DSOs) to consider more comprehensive analysis methods. The project focuses on investigating long term consequences of different project- and...

The results from an extensive study of SF₆ and minimum-oil circuit breaker failures in the Swedish and Finnish transmission systems are presented. The study includes 1546 breakers with a total operating history of 16 384 years. In the study, a detailed analysis of a specific SF₆ type of breaker revealed which parts caused the...

Sweden was re-regulated in 1996 followed by new laws and regulations. These new circumstances have become incentives to adopt more comprehensive and quantitative analysis methods applied on Electrical Distribution Systems (EDS). This paper provides a systematic presentation of the current risk management at a Distribution System Operator (DSO) as a...

This paper discusses a number of aspects of operational-risk assessment of transmission systems, operational-risk assessment uses techniques developed from reliability analysis to predict the performance of the transmission system during a short period of time (several hours) starting from a well-defined operational state. The influence of weather...

Maintenance managers of today's electrical distribution systems are faced with the problem of where their maintenance resources will be utilized best. In previous work the authors have developed a method for maintenance policy optimization for electrical networks. This paper presents results from an application study performed for a distribution sy...

The transmission system is becoming ever more complex. Furthermore, demand for reliable supply of electricity is growing, increasing the need for a higher level of system reliability. A solution might be to incorporate controllable power components within the system. One such component is the HVDC link. However, in the domain of reliability models...

This paper presents a reliability assessment of the HVDC converter transformer system (CTS) comparing different component models and configurations. The CTS model is based on the Markov modelling approach, which is shown to be well suited for these relatively small systems. The failure rate data in the models is based on statistical surveys by OGRE...

The Swedish energy agency (STEM) has developed a regulatory model to supervise the revenues of the distribution system operators (DSO). The model is referred to as the network performance assessment model (NPAM). The NPAM calculates customer values for a fictive electrical distribution system, with a total cost referred to as the network performanc...

The Swedish energy agency (STEM), has developed a new regulatory model to supervise the revenues of the Distribution System Operators (DSO), referred to as the Network Performance Assessment Model (NPAM). The fundamental idea of the NPAM is that the electrical distribution system provides customer values, and the DSO is allowed to collect revenue c...

Infrared thermography is the most common way to assess the condition of high-voltage electrical contacts in electric distribution and transmission systems. However, thermography has one major drawback as contacts carrying low or no load may not be assessed. This paper proposes a method to save and make use of thermography measurements to estimate s...

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 indic...

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

The wind power industry has expanded greatly during the past few years, has served a growing market, and has spawned the development of larger wind turbines. Different designs and technical advances now make it possible to put wind turbines off shore. The fast expansion of the wind power market comes with problems. The new designs are not always fu...

This paper presents a comparative study of regulating policies for interruption of supply in Sweden and UK. The two regulating regimes have been applied for a case study with a real rural electrical distribution system in Sweden, Flymen. The Swedish and UK regulations state that the distribution system operators (DSO) should restore power delivery...

The wind power industry has expanded greatly during the past few years, has served a growing market, and has spawned the development of larger wind turbines. Different designs and technical advances now make it possible to erect wind turbines offshore. The fast expansion of the wind power market faces some problems. The new designs are not always f...

The large growth in the wind power industry in the past years mainly focuses on a growing market and the development of large turbines and offshore farms. The high technical availability of wind turbines comes with a greater need for frequent maintenance. Current maintenance planning is not optimized, and it is possible to make maintenance more eff...

This paper present results from a sensitivity study of the Network Performance Assessment Model (NPAM) as an effect of changes in input data. The NPAM estimates a cost corresponding to operate a fictive reference network, so called network performance assessment (NPA). This value is then compared with the revenue. Small changes have been implemente...

This compendium is collection of exercises for the course on reliability assessment of electric power systems. The course has been developed within the RCAM group at KTH School of Electrical Engineering. The first version of the compendium was prepared in 2005, with examples made by master theses students Carl Johan Wallnerström and Otto Wilhelmss...

This paper presents a practical method of quantifying and evaluating changes to existing thermography inspection schemes for disconnector contacts. The inspection interval availability is used to calculate disconnector contact average maintenance costs. Any changes to existing thermography schemes regarding load or inspection intervals are subseque...

Tidigare studier har visat att resultat från Nätnyttomodellen (NNM) är känsliga för förändringar i indata. Exempelvis kan en mindre justering av indata förändra nätnyttan med över åtta procent [1], ändringar som för större nät i tidigare studie motsvarar ca 60 miljoner svenska kronor (SEK) per år. Mot bakgrund av detta är det angeläget att utreda t...

The methodology used to assess the historical reliability performance of a Canadian Utility's electric distribution system is outlined. Included is an overview of the process used to collect and organize the required interruption data as well as a description of the performance indices calculated for use in the causal assessment. The various compon...

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 assu...

This paper presents a novel reliability cost-benefit approach, taking into account customer value of reliability, to compare different transformer loading philosophies while concurrently considering varying levels of transformer emergency capability. Using this cost benefit approach, guidelines for loading existing transformers can be determined. T...

This paper describes the Mid-Continent Area Power Pool (MAPP) transmission equipment outage data collection scheme and presents bulk transmission line average outage statistics for forced outage category for the 230 kV and above systems computed using the data for the ten-year operating period from 1991 to 2000. In addition, a causal and seasonal c...

Power system reliability assessment methods can be categorized either analytical or as Monte Carlo simulation. Analytical methods represent the power system by a mathematical model and assess the reliability performance indices from the model utilizing mathematical solutions. On the other hand, Monte Carlo simulation methods, compute the reliabilit...

Nätnyttomodellen är ett hjälpmedel för Statens Energimyndighet (STEM) att bedöma skälighet i eldistributionsföretagens tariffer och huruvida deras distributionsnät upprätthåller en fullgod leveranskvalitet. Nätägarna skall enligt ellagen årligen skicka in data om sina nät till STEM; indata som Nätnyttomodellen sedan använder till att bygga upp ett...

A new regulatory model for the Swedish electrical distribution system operators has been proposed, and is now being implemented. The model is referred to as the network performance assessment model (NPAM). The NPAM is based on fictive reference networks. These emanate from a radial network that is reinforced with redundant components if it increase...

In order to optimize the maintenance of electric power equipment, models of equipment reliability as a function of age and maintenance are necessary. As a first step towards the development of these kinds of models, this paper proposes a quantitative method for establishing the condition of disconnector contacts by the use of thermography, which is...

This panel presentation aims to propose a possible solution for how to evaluate the effect of RCM as a tool for maintenance management. The starting point is a general understanding of the RCM methodology. Further on, a quantitative approach for relating the impact of component maintenance on system reliability and total cost is introduced. The met...

In this paper we present a method for establishing the value of a network's components from a reliability worth perspective. The method can be applied to a general distribution system i.e. both for radial and meshed network systems. Moreover, this paper shows results from an application study for a rural network system that is dominated by overhead...