Experience with new large adjustable speed drive technology for multiple synchronous motors

New voltage source inverter technology now exists with high output voltage (ges11kV) suitable for high power synchronous motor applications. The technology with an advanced control system can be used as a multiple motor soft starter and adjustable speed drive for selected motors with significant benefits. Design, commissioning and operation experience is described for a first of its kind installation with three synchronous motors rated 11 kV 17 MW. The overall control and communication system is described with specific attention to safety, redundancy and process availability. New synchronization and desynchronization scheme experience is described. Unique synchronous motor protection and excitation control schemes for both adjustable speed and line operation are outlined. Site recordings prove system ride-through capability in terms of voltage dips and bypass of internal power cells. Conclusions are given which support new voltage source technology as a viable alternative to conventional load commutated inverter technology for certain large synchronous motor applications. Suggestions are made for additions to present medium voltage adjustable speed drive standards.