In English

Using PMU and PQ monitor for voltage sag extended-characterization

Peiyuan Chen
Göteborg : Chalmers tekniska högskola, 2006. 122 s.
[Examensarbete på avancerad nivå]

Modern industrial processes are sensitive to power quality problems, due to the use of power electronic equipment in the power systems. For example, rolling mills are sensitive to voltage disturbances, due to the use of converter drive systems, which trip due to voltage sags. Voltage sag (dip) is one of the most severe power quality problems. The root cause of voltage sag is a short circuit in the power system, e.g., due to lightning. The consequence of voltage sag may be that expensive power electronic devices are damaged, and the industrial products are scrapped. In order to evaluate the impact of different voltage sags and accompanying economic losses on the industrial processes, a detailed study of characterization of voltage sags is needed. In this thesis, different methods for the characterization of voltage sags in the single-phase events and three-phase events are studied. The indices for characterizing voltage sags are discussed in terms of voltage magnitude, sag duration, and phase-angle jump, for both the single-phase events and the three-phase events. For the latter case, the characteristic voltage, the ABC classification and the symmetrical component classification are also analyzed. Theoretical, simulation and experimental studies have been done to compare the results from different indices, based on four generic configurations constructed in the analog network. The simulation tool is PSCAD/EMTDC. The simulation results have shown accordance with the theoretical and experimental results with an acceptable error. It also has been shown in the three-phase events that the results of the minimum retained voltage and the magnitude of the characteristic voltage are identical for the sag type A and E, but not for the sag type B and C. The results also indicate that for the ideal sag type A, B, C and E, the phase-angle jump of the characteristic voltage is equal to that of the symmetrical phase voltage. However, this equivalence will not be valid if there is asymmetry of the other two phases with respect to the symmetrical phase. The effect of induction machine on voltage sags in terms of sag magnitude, phase-angle jump, and jump of the transmission angle is discussed intensively. The voltage data recorded by phasor measurement unit (PMU) and power quality monitor (PQ monitor) are analyzed and compared. The results of the voltage magnitude recorded by PMU are in accordance with those recorded by PQ monitor. However, the results of phase-angle jump are not in accordance with each other, due to the low sampling frequency of PMU. Finally, the voltages sag types are summarized according to the ABC classification and the symmetrical component classification. However, the algorithm of the latter classification may lead to erroneous results due to the impact of the load condition.

Publikationen registrerades 2013-02-27. Den ändrades senast 2013-04-04

CPL ID: 174161

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