A critical survey of considerations in maintaining process continuity during voltage dips while protecting motors with reclosing and bus-transfer practices

Plantwide shutdowns can be avoided where voltage dips of short duration on the power distribution system are a primary cause. A voltage dip where contactors drop open and reclose can be very serious because of the nature of motors and their driven loads during voltage transients. The general nature of the problem and criteria for safe reclosing or transfer of several motors on the same bus are presented. The mathematical development and modeling techniques for induction and synchronous motors are indicated, and simple easy-to-use expressions are given for determining the currents and torques due to out-of-phase reclosing. Various protective schemes against out-of-phase reclosing and transfer, as well as methods of riding through voltage dips, are discussed