Reliability is an important issue in power systems and historically has been assessed using deterministic criteria and indexes. However, these approaches can be, and in many cases have been, replaced by probabilistic methods that are able to respond to the actual stochastic factors that influence the reliability of the system. In the days of global, completely integrated and/or nationalized electricity supply industries, the only significant objective was the reliability seen by actual end users. Also, the system was structured in a relatively simple way such that generation, transmission, and distribution could be assessed as a series of sequential hierarchical levels. Failures at any level could cause interruptions of supply to the end user. All planning and operational criteria were intended to minimize such interruptions within economic limits. The system has been, or is being, restructured and now many individual parties are involved, often competitively, including generators, network owners, network operators, energy suppliers, regulators, as well as the end users. Each of these parties has a need to know the quality and performance of the system sector or subsector for which they are responsible. Therefore, there is now a need for a range of reliability measures; the actual measure(s) needed varying between the different system parties. This paper addresses these issues and, in particular, reviews existing approaches and how these may be used and/or adapted to suit the needs and the required indexes of the new competitive industry and the different parties associated with it.

http://home.eng.iastate.edu/~jdm/ee653/BasicConcept_ReliabilityEvaluation.pdf

Probabilistic assessment of power systems

A probabilistic model for the active power produced and the reactive power absorbed by wind turbines (WTs) equipped with induction generators is developed which takes into account the probabilistic nature of short-term wind velocity forecasts. The model is incorporated in a radial distribution load flow program which allows probabilistic modeling of loads at the MV/LV substation level and of voltage regulator effects at the beginning of the MV distribution feeder. Using this program probabilistic short- and medium-term predictions of the power flows at the various sections of the feeder and of voltage profiles at all nodes of the network are obtained. >

Probabilistic load flow in distribution systems containing dispersed wind power generation

Use of the wind for electric power generation is increasingly being considered as a possible generation alternative due to the rising interest in sources of energy that are renewable and without harmful environmental effects. Furthermore, difficult global economic and political conditions are tending to make countries depend more on their own resources and rely less on imported fuels. Wind is, however, not always available, and conventional generation sources must provide power to meet demands in these calm periods. It is therefore necessary to include energy limitations in the reliability evaluation of wind energy conversation systems (WECS). The paper presents energy-based models that permit the assimilation of wind energy sources in conventional generation system adequacy evaluation.

Incorporation of wind energy conversion systems in conventional generating capacity adequacy assessment

The authors study the long-term competitiveness of introducing renewable energy sources alongside the conventional generating units in a generation expansion plan by linking a short-term study and a long-term planning model. The short-term study is an extensive examination of the different combinations of the renewable energy sources which can operate with the conventional generating system for different objectives. These objectives are varied between two general strategies: the fuel-saver strategy and the peak-shaving strategy. In long-term planning, these combinations are considered as decision variables. For this purpose, a long-term generation expansion planning model is used to decide which strategy can be used and the capacity as well as the time of addition. >

Generation expansion planning including the renewable energy sources

An availability index, Generation Ratio Availability (GRA), is proposed to evaluate the electrical system of offshore wind farms (OWF). The GRA is the probability that at least a certain percent of wind power could be transferred to the grid system through the concerned electrical system. The GRA does not depend on the load demand and has weaker correlation with the wind speed in comparison with other reliability indices, such as loss-of-load probability, expected energy not supplied, etc. On the basis of the particular characteristics of the OWFs, the algorithm to compute the GRA is proposed. Comprehensive studies have been conducted to investigate the influence of the network design, component parameters, and wind-speed regimes on the GRA. The analysis presented in this paper is useful for both future wind farm planning and existing OWF evaluation.

Generation Ratio Availability Assessment of Electrical Systems for Offshore Wind Farms

There is much interest in using renewable energy sources, such as wind, wave and solar, to generate electrical energy. Unfortunately, such energy sources are intermittent, and, therefore, conventional sources must still be available to meet the demand during quiescent periods. Hence, the reliability and economic assessment of these novel sources cannot be made using standard capacity-replacement-based methods; instead, energyreplacement methods are required. The paper extends the loss-of-energy-expectation method to evaluate the generation reliability including novel energy sources. These results are then used to calculate the economic benefits of such sources. The approach is illustrated using the IEEE reliability test system. Although the paper concentrates on wind energy sources, the technique and approach are applicable to a generation system containing any type of intermittent energy source.

P. Corredor Avella

Papers

Reliability and economic assessment of generating systems containing wind energy sources

Modelling wind energy sources in generating reliability evaluation