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This paper addresses the problem of estimating the characteristics of three-phase unbalanced voltage dips from measured phase voltages. This is important for obtaining statistics on voltage dips and for obtaining information about the underlying event (e.g., the fault type). Two different algorithms are compared. The "six-phase algorithm" is computationally simple and easy to interpret. However, large phase-angle jumps lead to wrong estimations. The "symmetrical component algorithm" gives a correct value in almost all cases. Exceptions are events with very severe load influence on the voltages during the fault. The latter algorithm is studied in more detail: through a measurement example and through a study of a range of synthetic events. The conclusion is that both algorithms have their specific application areas.
Date of Publication: July 2003