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

This paper proposes a method to allocate resources in power distribution planning and also introduces a new reliability index category, R_T, flexibility to adjust to different laws or DSO policies of long outages. Possible legal consequences for distribution system operators are first identified and studied. A vulnerability-analysis method is introduced, including a statistical validation. The overall idea is to identify and evaluate possible states of power distribution systems using quantitative reliability analyses. Results should thus indicate how available resources (both human recourses and equipment) could be better utilized, e.g. in maintenance and holiday scheduling and in evaluating whether additional security should be deployed for certain forecasted weather conditions.

To evaluate the method, an application study has been performed based on hourly weather measurements and about 65 000 detailed failure reports over eight years for two distribution systems in Sweden. Months, weekdays and hours have been compared and the vulnerability of several weather phenomena in these areas has been evaluated. Of the weather phenomena studied, only heavy snowfall and strong winds, especially in combination, significantly affect the reliability. Temperature (frost), rain and snow depth have a relatively low or no impact. 

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

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

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

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

Sweden will implement a new tariff regulation from 2012. This paper presents results from a project initiated by the Swedish regulator, performed by the RCAM (Reliability Centered Asset Management) research group aimed to review the potential of using equivalent comparison standards to judge effectible costs. The study includes interviews and surveys distributed to every Swedish distribution system operator (DSO). However, no sharp proposal on units appropriate to use in the first regulatory period (2012-2015) could be provided, due to e.g. large variations in response from the DSOs. The study provides several results such as enabling for all parties to contribute their views before implementation; indication of how current units should be modified; increased knowledge for involved parties and an action plan for future work. The regulator’s initial idea was to apply this kind of model to 25 % of the effectible cost part during the first regulatory period, but based on this study the regulator changed this plan.

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

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

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