Characterisation of voltage sags experienced by three-phase adjustable-speed drives

It is shown in this paper that voltage sags experienced by three-phase loads like adjustable-speed drives, can be classified into four types. Each sag can further be characterized by a magnitude and a phase-angle jump. Relations between fault type, sag type, and load connection are presented. The transfer of sags through transformers is discussed. Magnitude and phase-angle jump of sags are directly related to the voltage in the faulted phase, or between the faulted phases, at the point-of-common coupling between the load and the fault.