Establish Motor-VFD PM
EP Editorial Staff | April 1, 2020
By Howard Penrose
All types of electric motors remain the prime movers of industrial and commercial applications, efficiently converting more than 68% of electrical energy to mechanical energy. While sometimes identified as the energy consumer in electrically driven equipment, they actually consume very little. Primary electrical consumption occurs with the driven load and related processes.
Adjusting and tuning these systems is often done with variable-frequency drives. If the overall system is not properly maintained, efficiency drops and it becomes difficult to match motor output speed with fluid flow, gas flow, or pressure.
Scaling a program around just the motor and drive can still be a significant undertaking, depending on the size and voltage of the motor and drive combination. It involves understanding the context of the application and the overall impact of defects surrounding the energy converter. There are times when a 50-hp motor and drive can be considered run to failure and times when a 1-hp setup can be considered critical equipment.
The single most important question is “Where do I start?”
Most often a motor-system maintenance and management program can be a significant investment to start from scratch. When beginning with a clean slate, the first step is to know what you own by surveying your electrically driven equipment. In a successful program, start small with a department or single building. Then perform a simple analysis to determine the safety, regulatory, and financial impact of each system and select those that will have the largest impact first.
Chances are, as you develop the condition-based maintenance program,
electric motor repairs will be necessary. Address this by developing or adopting motor-repair specifications and repair-versus-replace decision trees. If you do not already have a repair specification prepared, consider either a simple specification such as the ANSI/EASA AR100 or the more robust IEEE Standard 1068.
Once the rules for repair are established, the program may be developed around the motors and drives. The U.S. Department of Energy Office of Industrial Technologies, Washington (energy.gov), has resources in these areas, including the online book, Improving Motor and Drive System Performance Sourcebook, which was developed by industry and is available here. While this document will provide some ideas and guidelines, a motors program should consider, at a minimum:
• A lubrication program that includes an understanding of what grease is being used for grease-lubricated motors and what oil is being used for oil-lubricated bearings. For ball and roller bearings, the proper selection of grease and compatibility needs to be understood.
• Cleaning cooling passages and replacing or cleaning any filters or external fans. This will help the motor and drive stay cool. Within a VFD, an annual vacuuming (de-energized) and tightening of power-related connections is recommended.
• Develop a system of purchasing and tracking spare parts. EP
Contact Howard W. Penrose, PhD, CMRP; MotorDoc LLC, at email@example.com.