A Penetrating Gaze at One Open Phase: Analyzing the Polyphase Induction Motor Dilemma

Portions of the material proposed for a chapter in a new IEEE Standard (#399-the ``Brown Book´´) being prepared by the Power System Analysis Subcommittee of the I & CPS Committee are presented. In order to establish a library of approved analytical methods, the material provides a review of the more important basic electrical circuit analysis techniques used for determining the voltage and current relationships which describe various power system network events and operating conditions. Certain simplified circuit arrangements are examined. They illustrate the power and merit of the analytical methods that evolve, as well as the errors that can occur because of improper regard for the restraints that apply. Using the analytical methods, the classical problem of a three-phase induction motor operating with one phase of the supply line open-circuited is studied in considerable detail. Finally, important observations and conclusions are presented regarding the motor protection requirements.