Protection of Induction Motors Against Unbalanced Voltage Operation

The results are presented of a computer study to determine various operating quantities of squirrel-cage induction motors as a function of unbalanced voltage and mechanical loading utilizing a new analytical technique. A similar study with the extreme unbalance of single phasing was reported elsewhere. The operating characteristics of various motor protective devices are then superimposed on the motor operating curves to evaluate the effectiveness of the specific relay. The results of this study will aid in selecting and setting relays to provide protection against voltage unbalance and may possibly provide an engineering rationale for the development of future protective devices.