Voltage sags and swells are power quality disturbances characterized by temporary reductions or increases in the root mean square (RMS) voltage from its nominal value. In microgrids, these voltage variations can disrupt the operation of sensitive equipment and negatively impact overall system stability. Primary causes and mitigation techniques are:
Voltage Sags (Undervoltages):
1. Faults: Short circuits (line-to-ground, line-to-line, three-phase) cause a sudden increase in current demand, leading to a voltage drop at the fault location and throughout the microgrid. The severity depends on the fault impedance and location.
2. Starting Large Motors: The inrush current drawn by induction motors during startup is several times their full-load current, causing a temporary voltage sag, especially on weaker parts of the distribution network.
3. Transformer Energization: When a transformer is switched on, it draws a large magnetizing inrush current, creating a voltage dip.
4. Sudden Load Increase: A large, abrupt increase in load demand can overwhelm the available generation capacity, leading to a voltage sag until generation can respond.
5. Intermittent Renewable Generation: Rapid drops in renewable generati....
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