Lessons Learned Commissioning A Relay-Based Synchronous Motor Excitation Control System: A Case Study

Synchronous motors are vital assets in many industrial processes. Although they typically require more complex controls and maintenance than standard induction motors, synchronous motors provide operational benefits that often render them the preferred driver for numerous specialized manufacturing and processing applications. This article presents a practical example of a control solution that enables automatic excitation regulation of a synchronous motor field winding. That is, a microprocessor-based motor protection relay that provides a closed-loop feedback control signal to a silicon-controlled rectifier (SCR) exciter to automatically regulate the excitation supply current, enabling automatic regulation of the motor’s power factor (PF) and efficiency. In addition, this article discusses the various lessons learned during the update as well as the associated start-up commissioning of an aged excitation control system to the aforementioned solution for two synchronous motors driving ball mills in a large cement plant.