# The influence of motor re-acceleration on voltage sags

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## Abstract

The influence of motor reacceleration on voltage sags - Industry Applications, IEEE Transactions on IEEE RANSACTIONS ON IKDUSTRY APPLICATIONS, VOL. 31. NC) 4, JULYIAUGUST 1995 The Influence of Motor Reacceleration on Voltage Sags Math H. J. Bollen, Member, IEEE Abstract-The assumption that a voltage sag is rectangular is not correct in a system with large induction motor loads. The motors decelerate during the short circuit. After fault-clearing they will accelerate again, drawing a high reactive current from the supply, causing a prolonged postfault voltage sag. This is aggravated by the removal of branches by the protection. The resulting shape of some voltage sags in an example system is shown and discussed. For the example system, a stochastic voltage sag table is determined. This table gives the expected number of sags of different depth and duration. The influence of faster protection and of reduced transformer impedance on the table is presented. A simple motor model is implemented in a method for including interruptions due to voltage sags in the reliability analysis of power systems. This model is presented hriefly and used to show the influence of motor parameters on the number of sags that lead to an interruption of plant operation. I . INTRODUCTION HORT-DURATION voltage sags due to short circuits are S recognized as an important power quality problem. In par- ticular, electronic equipment like computers, adjustable-speed drives and process-control systems are extremely sensitive. Despite this recognition, not much work has been published on the shape of voltage sag\, nor on their stochastic assessment. A simple method for ascessing the number of sags expe- rienced by a customer is presented in [ l I. This method is proposed to become part of thc IEEE Recommended Practice for the Design of Reliable Industrial and ('ommercial Power Systems 121. A detailed stochastical method for including interruptions due to voltage sags in the relia

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