Stochastic assessment of voltage dips (Sags): The method of fault positions versus a Monte Carlo simulation approach

Two methods for stochastic assessment of voltage dips (sags) are compared. The method of fault positions and a Monte Carlo simulation approach are utilized to stochastically describe the expected dip performance at some sites of a large transmission system. Fault scenarios are created and pseudo measurements are obtained in order to compare stochastic assessment with simulated measurements. It is shown that the method of fault positions cannot be used to predict the performance of a particular year, unless correcting factors are used to adjust the assessment. A Monte Carlo simulation approach is suggested to better describe the expected dip performance. Whereas the method of fault positions gives long- term mean values, the Monte Carlo approach provides the complete frequency distribution function of selected sag indices (SARFI-X).