AC Large Motor Maintenance

Course Description

EASA’S newest technical seminar covers horizontal and vertical squirrel cage induction motors in the 300 to 5,000 horsepower range, low and medium voltage. Many of the principles covered will apply to other sizes and technologies, as well. While the focus primarily is on motors built to NEMA standards, much of the material is also applicable to IEC motors. This seminar was produced by Austin Bonnett, EASA’s education and technology consultant.

Seminar Leader

Chuck Yung is a technical support specialist at EASA Headquarters in St. Louis. Prior to joining EASA, he held various positions in the electrical apparatus sales and repair industry for 25 years. He regularly contributes technical articles to EASA’s newsletter, CURRENTS, and various trade publications.

Partial List Of Topics

Motor Basics

  • Motor theory
  • Equations


  • Pumps
  • Compressors
  • Fans/Blowers
  • Material handling

Motor Manufacturers

  • Domestic
  • Foreign

Motor Types

  • Enclosure
  • Custom
  • Functions

Large Motor Standards

  • NEMA
  • IEC
  • IEEE
  • API

Safety Considerations

Root Cause Failure Analysis

Test & Inspection Procudures

  • De-energized and energized
  • Loaded
  • Locked rotor

Motor Starting

  • Across the line
  • Part winding
  • Reduced voltage
  • Wye-Delta


  • Windings
  • Vibration monitoring
  • Surge protection
  • Current differential transformers
  • Power factor correction

Stator Construction

Rotor Construction

Bearing Types and Lubrication Systems

Shaft Construction

Motor Geometry and Alignment

Repair Procedures