Starting Large Synchronous Motors in Weak Power Systems

Utility company standards for power quality are making it difficult for industrial users to start large induction and synchronous motors due to high inrush current. This paper will present a large oil company's challenges in starting large motors driven by the utility company in a relatively weak power system in East Texas while not violating the utility company's standards. A workable solution is an air-cooled pulsewidth-modulated voltage source variable-frequency drive system designed to start multiple large-horsepower medium-voltage synchronous motors without any measurable voltage flicker. Various combinations of motor design (induction versus synchronous) and starting methods are reviewed, and final design schematic diagrams are documented. Challenges encountered during the design and start-up are described, and solutions with final performance details are provided.