A study of voltage sags generated by induction motor starting

Voltage sag produced by induction motor starting current is one of the main causes of sensitive equipment (SE) dropout. The use of motor starter reduces the voltage sag depth but increases its duration. The subsequent connection to full voltage originates a new sag separated from the first one by a few seconds. An extensive experimental research that aimed at determining the effect of assisted starting characteristics on the generated voltage sag is reported. Results show the existence of critical combinations of commutation time and assisted starting voltage from the SE dropout susceptibility point-of-view. Voltage drop and consequent specific energy of the assisted starting is compared with values corresponding to both direct on-line starting and direct at-reduced-voltage starting.