A System On Voltage Sag Analysis Based On Virtual Instrument

The fact that automatic production lines have been used in more and more modern high-tech enterprises requires a more strict standard for power supply sustainability. The drop of voltage amplitude in an extremely short-time can result in poor quality productions even scrap ones, which not only brings huge economic loss to high-tech enterprises but induces contradictions between power utility and power customers. As a result, voltage sag has been a power quality problem concerned greatly by both power utility and power customers. How to determine the enterprises inducing voltage sags (i.e. voltage sag source) may help solve the contradiction and take effective measures to improve power quality.Actually, voltage sag is mainly caused by all kinds of system short circuit faults, induction motor starting and transformer energizing. Initially the paper simulates the three voltage sags in Matlab/Simulink. The simulation result shows that voltage sag caused by short circuit faults has a much deeper sag depth and a wider influence scope in power system. In the case of transformer energizing, three-phase voltage sag depths are different and the voltage amplitude drops suddenly when sag begins and restores gradually to normal level, the wave of which has no mutation but includes a large amount of harmonic components. For the third case, three-phase voltage sags happen at the same time with a sudden but identical degree amplitude drop, and when reaching the valley floor, the voltages restore immediately and slowly to normal level with constant phase angles.Following that, the voltage sag amplitude is obtained by calculating the RMS curve of voltage sag by sliding the curve point by point. The DB Morlet complex wavelet is used to detect the starting time and ending time and a new method to location the voltage sag source based on the positive sequence power of fault component is advanced. Finally, a voltage sag analysis system is developed based on LabVIEW.