Voltage sag and recovery time in repetitive events

Thunderstorms and lightning are large contributors to fault occurrence due to the fact that the spark stroke is repeated several times during a very short time interval. Lightning bolts are not the only origin for repetitive faults. Reclosers and recloser circuit breakers are among several types of cyclic loads that submit the system to a similar current pattern. The connected equipment may be able to withstand the first voltage sag but will drop out with the following one, if it arrives before the equipment reaches a stable situation or if the equipment self-recovers. The concept of recovering time was originally presented ten years ago without further development. The Computer Business Equipment Manufacturing Association (CBEMA) curve is the most widespread power acceptability or equipment sensitivity graph; however, its values are given in a one-event base so they cannot be applied for repetitive sag studies. The undervoltage part of the CBEMA curve follows very closely the expression ∫ υ² dt=k, which allows the extension of this criterion to repetitive sags. Results obtained are in good agreement with those previously published.