The results are based on literature surveys covering a total of about 130 publications. In addition, a questionnaire survey was performed among TSOs providing information on reliability management in practice. The responses cover 9 TSOs in total from the Nordic countries and the Continental Europe. These represent different system sizes, characteristics and control zones. Despite the limited number, the responses are regarded sufficiently representative for Europe.
Assessing power system reliability is a complex and comprehensive task involving a multitude of factors, dimensions and uncertainties. Due to the complexity and different needs in different decision contexts and time horizons, it is necessary to decompose the problem into sub problems. Various methodologies for reliability assessment have been developed over decades, each solving a specific part of the overall problem and there are different indicators in use to describe reliability.
The results of the literature survey on reliability assessment are presented for two main areas: reliability indicators and reliability methods. Indicators are separated in deterministic and probabilistic reliability indicators. In the area of reliability analysis, a distinction is made between the two main approaches to probabilistic reliability assessment, namely analytical and Monte Carlo simulation methods. Both online and offline tools found in the literature are also presented.
The literature survey on socio-economic impact assessment mainly deals with value of lost load (VOLL) or customer interruption costs, and how to estimate such costs. A lot of different methods exist for estimation of VOLL. Examples of applications of VOLL estimates are given in the report, such as, cost-benefit studies of probabilistic reliability criteria compared to the N-1 criterion and the use in quality of supply regulation of the network companies.
Most of the TSOs in the questionnaire survey reported that they use the N-1 criterion strictly. However, the majority also reports that they sometimes apply the N-0 criterion, meaning that they accept more severe consequences when the probability is regarded small.
The synthesis of the literature survey and responses to the questionnaire indicates that there is a gap between the existing research literature and what is practiced by TSOs. Probabilistic methods, including socio-economic impact assessment, seem to be used to some extent in long-term planning and in mid-term planning and asset management, while almost absent in the short-term operation of the power system. The TSOs are, however, already collecting reliability data for primary equipment.
A few lessons can be learned from air traffic management and sectors such as nuclear power, gas supply, water supply, and railway, amongst other: reliable infrastructures result from complex interactions between multiple human operators, procedures and technical systems. Traditional indicators fall short in covering these complex interactions. Thus, there is a need for novel probabilistic assessment methodologies.