Customers all over the world experience problems due to voltage sags. Computers, industrial control systems, and adjustable-speed drives are especially notorious for their sensitivity. Tripping of high-power adjustable-speed drives is probably the main voltage sag problem. The number of trips depends strongly on the equipment sensitivity. Prediction methods are needed to quantify this aspect of the quality of the supply. From utility and manufacturer＇s data, a customer can assess the compatibility between a piece of equipment and the electricity supply.