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AC Induction Electric Motor Retrofit Guideline


PA_Fan.pngThere are not many new plants being built these days. Yes, there are some but most of what takes place today is retrofitting of older, existing equipment in plants that already exist. This process of retrofitting older equipment to new, modern, technology can be complex. We see many instances where someone replaces without considering all of the aspects of a replacement and the motor ends up not working. This article should serve as a guide for doing retrofits on large electric motors, focusing on AC Induction motors. We also want to give credit for a lot of this information from our friends at Siemens. They do many retrofits every year with us as well as their other channel partners.

Before we move forward, we must ask, What a-nema electric motor is best for you? Check out the linked article for some additional information.

Download How To Get The Righ Electric Motor

Key Issues for Retrofits:

  • Main Terminal Box Location
  • Shaft Height & Extension (Adapter Base)
  • Vertical Motors (P-Base/Shaft, Thrust Requirements, Bearing arrangement).
  • Application – Compressors (3600RPM), Fan Drives (High Inertia), Conveyors/Crushers (High Torque)

Applications Considerations:

  • Compressors – 2 Pole, 3600RPM, precision balance
  • I.D./F.D./P.A. Fans – Horizontal, High Inertia, Large H.P.
  • Coal Crushers/Pulverizers – High Torque, WK2
  • Circulating Water Pumps – Slow Speed, Horizontal/Vertical
  • Condensate Pumps – Vertical P-Base
  • Coal Conveyors – High Torque

Motor Design Requirements based on the Application

  • Motor must accelerate the driven equipment
  • Load curve of driven equipment is needed
  • Reduced inrush requirements
  • Reduced Voltage Starting
  • High/Low ambient temperatures
  • High Torque applications (Crushers and Conveyors)
  • High Inertia applications (Fan Drives)
  • Slow speed applications (Circ Water Pumps, ID Fans)
  • High Speed applications (Compressors, Boiler Feed Pumps)
  • Adapter Bases utilized to increase horizontal motor shaft height to match existing motors “D” dimension as well as other critical mounting dimensions.
  • Motor must be properly framed to meet temperature requirements as defined by plant or industry standards
  • Efficiency, noise level, etc. per customer requirements
  • Special Shaft extensions to match existing motors
  • Special Main Terminal Box location to match existing incoming power cables
  • Special P-base to match existing Vertical motors

Critical Dimensions for Retrofits:

All of the dimensions shown below need to be factored in when decided a retrofit motor for an application. The left side


Retrofit Examples (From Siemens):

Primary Air Fan Motor (PA Fan) 6000HP, 1200RPM, 6600Volt


Induced Draft Fan Motor (ID Fan) 3000HP


To learn more about Siemens Electric Motors and HECO - All Systems Go, please consider attending the 2016 RPM Symposium located in Kalamazoo, MI on September 13 & 14, 2016. To learn more please visit







To learn more about what our “All Systems Go” approach, please contact:

Justin Hatfield

HECO - All Systems Go



About the author:

Justin Hatfield is Vice President of Operations of HECO, Inc. He is responsible for Electric Motor & Drive Sales, Electric Motor & Generator Repairs, and Predictive Services. Justin was instrumental in developing HECO MAPPS (Motor And Powertrain Performance Systems) which focuses on “why” you have a motor problem instead of simply “What” product or service should be recommended. HECO is an EASA Accredited Service Center.

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