Efficient method for power quality surveying in distribution networks

In the future the importance of methods for an overall power quality rating of distribution networks will increase continuously. Utilities become more and more interested in knowledge about the average levels of power quality as well as the distances between actual levels of power quality and corresponding limits in their distribution networks. Reporting power quality in accordance with DIN EN 50160 leads to simple qualitative results only. However the measurement data contain much more information about the time- and site-dependent behaviour of power quality. Therefore enhanced quantitative calculation methods are needed for additional in-detail-analyses of the measurement data. The results can be reasonably used e.g. for estimating an overall performance of power quality, benchmarking power quality between networks or planning purposes. The paper describes a method of power quality surveying in distribution networks by several performance indices. Their values are direct proportional to the actual reserve of power quality at the measured sites. Considering statistical aspects already during the measurement site selection results in performance indices, that give a good estimation of average power quality levels in the analysed distribution networks. Finally the paper applies the new method to different medium voltage networks of two German distribution system operators (DSO A and DSO B).