Lessons Learned Commissioning a Relay-Based Synchronous Motor Excitation Control System

Synchronous motors are a vital asset in many industrial processes. Although typically requiring 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 paper presents a practical example of a control solution that enables automatic excitation regulation of a synchronous motor field winding – a microprocessor-based motor protection relay that provides a closed-loop feedback control signal to the silicon-controlled rectifier (SCR) exciter to automatically regulate the excitation supply current, which in-turn enables automatic regulation of the motor power factor (PF) and efficiency. In addition, this paper will discuss the various lessons learned during the update and associated startup commissioning of an aged excitation control system to the above solution for two synchronous motors driving ball mills in a large cement plant.