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Electric Motors and VFDs: How the Work, When they Don't!


This presentation will describe the basics of electric motors and variable frequency drives (VFD). A VFD (also termed adjustable-frequency drive, variable-speed drive, AC drive, micro drive or inverter drive) is a type of adjustable-speed drive used in electromechanical drive systems to control electric motor speed and torque by varying motor input frequency. VFDs have been a big hit in the industry for providing excellent speed control and thereby taking advantage of the Affinity Laws to achieve significant gains energy efficiency. However, there are issues that need to be understood when considering or specifying VFDs. VFDs can cause an increase in temperature rise in motors leading to early failure. They can also cause insulation breakdown and accelerated bearing wear, both of which can lead to early and unexpected motor failure. The presentation will cover most of the technical issues when employing a VFD by looking at root causes and reviewing their solution.



Thomas Sherman, CEM, CEA, CDSM, CCASS
Sustainable Energy Services, Inc

Tom is the founder and president of Sustainable Energy Services, Inc., an unbiased and independent energy management services company that serves non-residential customers throughout the U.S. Services include ASHRAE Level I, II & III Energy Audits, Energy Procurement, Demand Response, Energy Project Management, Post Project Measurement and Verification, Utility Rebates, and other energy related services.

Prior to Sustainable Energy Services, Tom was co-founder of PCX Energy Services where he conducted industrial and commercial energy audits. He was also a member of the energy consulting practice at FirstEnergy Corporation, and held senior management positions at Buschman Corporation, Enersys and Sola Electric.

Tom has been a regular speaker on energy efficiency at regional and national energy conferences including the Annual Ohio Energy Conference, GlobalCON and the World Energy Engineering Congress.  He has also been a past speaker at the National Retail Construction Conference, National Restaurant Association Conference, National Grocers Association Conference, AEP Conference on Compressed Air, and is a speaker/trainer for the Operator Training Committee of Ohio.  Tom serves on the Policy Board of Advanced Energy Economy Ohio and the Environmental Task Force of the Ohio Grocers Association.  He is a member of the Association of Energy Engineers, and is a Certified Energy Manager (C.E.M.), Certified Energy Auditor, (C.E.A.) and Certified Demand Side Manager (C.D.S.M.).  Tom earned his BS in Physics from Northeastern Illinois University and an MBA from Lake Forest Graduate School of Management.