A method for characterisation of three-phase unbalanced dips (sags) from recorded voltage waveshapes

A proposal is presented for characterisation of voltage dips as experienced by three-phase loads. The method is based on the well-proven theory of symmetrical components. The primary result of the method is a so-called "characteristic magnitude" which corresponds to the dip magnitude (remaining voltage) as used for the existing methods to characterise dips experienced by single-phase load. The proposed method may be extended by adding additional parameters including the zero-sequence voltage. For three-phase balanced dips the proposed method corresponds to the methods currently in use and recommended by international standards. The method has been applied to individual dips and to the results of a power quality survey.