Aleatory and Epistemic Uncertainty Considerations in Power System Reliability Evaluation

There are two fundamentally different forms of uncertainty in power system reliability assessment. Aleatory uncertainty arises because the study system can potentially behave in many different ways. The component failure and repair processes are random and create variability known as aleatory uncertainty. There are also limitations in assessing the actual parameters of the key elements in a reliability assessment. This is known as epistemic uncertainty and is knowledge based and therefore can be reduced by better information. Load forecast uncertainty belongs in this category. Load forecast uncertainty is an important factor in long range system planning and has been shown to have a significant impact on the calculated reliability indices in power system reliability evaluation. Generally, a higher capacity reserve is required in order to maintain a specified level of reliability for an uncertainty load than for a known load. It is important to recognize the differences in aleatory and epistemic uncertainty and appropriately incorporate and appreciate the implications of these uncertainties in system analyses. Two developed Monte Carlo simulation programs including aleatory and epistemic uncertainties are applied in this paper to a study system and the impacts of load forecast uncertainty, wind power and their interactive effects on the system reliability are examined. The basic indices of loss of load expectation (LOLE), loss of energy expectation (LOEE) and the index probability distributions are used to illustrate the effects.