Often, little attention is paid to critical ac motor protection factors, such as thermal limit curves and their relation to winding temperatures in an induction motor, which can result in premature motor and system failures that are costly and avoidable. To overcome those problems and improve the protection of the vast population of industrial ac motors, Stanley Zocholl, Distinguished Engineer with Schweitzer Engineering Laboratories (SEL) has authored a 90-page illustrated handbook, "AC Motor Protection" that is now available through SEL's Web site.
Comprehensive motor protection requires knowledge of all the characteristics of the motor in operation, Zocholl points out. Providing optimized thermal and fault protection for ac motors require electrical, mechanical, and thermal models to determine the motor characteristics. Written for the professional engineer, all of the steps necessary to develop this vital information are included in this concise "AC Motor Protection" publication.
"AC Motor Protection" includes a review of the principles of synchronous and induction motors, as well as motor characteristics and electrical, mechanical and thermal models needed to provide proper relay protection for various ac motors operating under various conditions.
A section of the handbook is devoted to a variety of motor protection requirements, such as pullout or stall protection, high-inertia starting, phase and ground protection, differential protection, running overload protection, drive protection and other requirements.
A summary of guidelines for calculating settings for motor protection relays, including motor data, selecting CTs and setting guidelines, will help power systems protection, maintenance and facility engineers successfully establish and apply appropriate relay protection to provide optimum service life from AC motors.
For more information, visit www.selinc.com/zocholl/index.html.
