This article addresses a wide three-phase voltage sag characterisation, including sag magnitude, phase-angle jump, and duration. A signal-processing algorithm is proposed to obtain voltage sag characteristics for phase voltages and positive sequence voltage. The proposed methodology is applied to a set of actual measurements obtained from a power quality monitor and from a synchrophasor measurement unit (PMU). Sag characterisation from both data sources are compared, indicating advantages and drawbacks of each device. Results show that data from PQ-monitors permit a more complete disturbance characterisation, however results from data obtained by PMUs are promissory for sag characterisation when the recording frequency of the PMU is increased.
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