Design features and protection of valve actuator motors in nuclear power plants

A status report on an effort of the Working Group IEEE-NPEC-SC4.7 is presented and the performance requirements, selection, design, and protection of valve actuator motors (VAMs) commonly used as components in direct gear driven valve actuator assemblies in nuclear power plants are discussed. VAMs are short-time-rated, high torque-to-inertial ratio motors. The actuator manufacturer selects the performance parameters for the VAM based on the maximum thrust required by the valve for tight shutoff. Since valve actuators require a high starting torque, the rating system begins with the assignment of nominal starting torque. The requirement of minimum frame size dictates a minimal (running) torque and a minimum run time. Design features of the VAM leading up to its design as a short-time-duty rated motor are described and compared with a continuous-duty motor designed to NEMA MG1. The unique features of the speed-torque characteristics and performance at varying voltages and temperatures are described