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Resource Library

Shaft and Bearing Currents

  • March 2020
  • Number of views: 1286
  • Article rating: 5.0
FREE for Members of EASA
Webinar recording

This webinar explains what shaft currents are, what causes them, and differentiate between the two common causes. It also discusses and compares methods to mitigate shaft currents and explains why the different causes of shaft currents require different solutions.

Considerations for using VFDs with standard motors

  • December 2016
  • Number of views: 991
  • Article rating: No rating
Trade press article — Plant Engineering

There are a few areas of concern involving the misapplication variable frequency drives (VFDs) on a standard induction motor. This article looks at some of those.

Identifying and getting to root cause of shaft currents

  • February 2015
  • Number of views: 470
  • Article rating: No rating

Shaft currents have always been a concern for large motors due to magnetic asymmetries within the motor. Manufacturers strive to keep these to a minimum.  With the widespread use of Variable Frequency Drives (VFDs), shaft current issues have become a concern in all sizes of motors. If these currents are discharged through the bearings, electrical discharge machining (EDM) occurs. Proper installation of VFDs can play a large part in mitigating issues with shaft currents. 

Demagnetizing motor shafts to prevent bearing failures

  • October 2005
  • Number of views: 886
  • Article rating: 2.5

There are a number of ways that the shaft of an electric motor can become magnetized in service. The most likely culprit is electric current through the motor and shaft, either from internal dissymmetry, welding or from a variable frequency drive. It can also be caused by electrical faults in the system, or even a lightning strike. If enough current does pass through the shaft, then it can remain magnetized, even after it is taken off line. The problem is that when a shaft is magnetized, it can further lead to bearing failures, unless something is done to eliminate the residual magnetism. The first reason for bearing failures is that the residual magnetism can cause shaft currents, which can quickly lead to bearing failures. But in addition, a magnetized shaft will attract bits of metal to the bearings. This reduces bearing life because it damages the bearing surfaces.

An update on causes of, solutions for shaft currents

  • April 2004
  • Number of views: 509
  • Article rating: No rating

While shaft currents are not a new problem (papers on the subject date back prior to 1930), what is "new" is our understanding of how to solve the problem. Shaft currents have been described as shaft voltages, circulating currents, bearing currents and circulating voltages. This article will refer to the phenomenon as "shaft currents" because it is the current that causes the damage.

Getting The Most From Your Electric Motors

Getting The Most From Your Electric Motors - coverThis 40-page booklet provides a great marketing tool for your service center! Use it to provide end users with information that will help them obtain the longest, most efficient and cost-effective operation from general and definite purpose electric motors.

This booklet covers topics such as:

  • Installation, startup and baseline information
  • Operational monitoring and maintenance
  • Motor and baseline installation data
  • How to read a motor nameplate
  • Motor storage recommendations



EASA Technical Manual

EASA Technical Manual cover

The EASA Technical Manual is the association's definitive and most complete publication. It's available FREE to members in an online format. Members can also download PDFs of the entire manual or individual sections.


ANSI/EASA AR100-2015

ANSI/EASA AR100-2015 cover

Recommended Practice for the Repair of Rotating Electrical Apparatus
This is a must-have guide to the repair of rotating electrical machines. Its purpose is to establish recommended practices in each step of the rotating electrical apparatus rewinding and rebuilding processes.




EASA AR200: Guide for the Repair of Power and Distribution Transformers cover

Guide for the Repair of Power and Distribution Transformers
This document establishes guidelines for each step of the repair of power transformers, describing record keeping, tests, analysis, and general guidelines for the repair of power transformers.