Evaluation of assessment methods used to analyze measured voltage magnitude performance

Various assessment methods are used for analyzing voltage regulation data when reporting electrical transmission system performance. There is an international debate as to which of these assessment methods are the best. A statistical analysis of measured voltage regulation data for the Eskom transmission network was undertaken to investigate the implication of using the various assessment methods - including the maximum 10-min value, the 95% and 99% weekly methods, and the 95% and 99% daily methods. The 95% weekly assessment method is currently being used within Eskom (as well as standards such as EN 50160). The values obtained from the various assessment methods were compared against the corresponding maximum 10-minute values and against each other. The results show significantly higher 10-minute maximum values than the corresponding 95% or 99% values for a given week.