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Root Cause Failure Analysis Introduction Root Cause Failure Analysis This book was developed to help electric motor technicians and engineers prevent repeated failures because the root cause of failure was never determined. There are numerous reasons for not pursuing the actual cause of failure including: ã A lack of time. ã Failure to understand the total cost. ã A lack of experience. ã A lack of useful facts needed to determine the root cause. The purpose of this book is to address the lack
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  Copyright © 2002, Electrical Apparatus Service Association, Inc. (Version 502CI-502) Root Cause Failure Analysis Introduction Root Cause Failure Analysis This book was developed to help electric motor techni-cians and engineers prevent repeated failures because theroot cause of failure was never determined. There arenumerous reasons for not pursuing the actual cause offailure including:ãA lack of time.ãFailure to understand the total cost.ãA lack of experience.ãA lack of useful facts needed to determine the rootcause.The purpose of this book is to address the lack ofexperience in identifying the root cause of motor failures. Byusing a proven methodology combined with extensive listsof known causes of failures, one can identify the actualcause of failure without being an “industry expert.” In fact,Electrical Apparatus Service Association, Inc.1331 Baur Boulevard ã St. Louis, Missouri 63132 ã USA314-993-2220 ã Engineering Fax 314-993-2998 ã www.easa.comThe information in this book was carefully prepared and is believed to be correct,but EASA makes no warranties respecting it and disclaims any responsibility or liability of any kindfor any loss or damage as a consequence of anyone’s use of or reliance upon such information. Many of the pictures in this book are of failures thathave occurred where the actual cause was identified.However, in some cases the exact cause was neververified, nonetheless they are included along with theauthor’s opinion of the most likely cause. In othercases, the pictures are of parts that have not failed, butthe pictures are useful in illustrating how and where thepart could fail.It is difficult to segregate each type of failure into nicedistinct categories and to do so would require jumpingback and forth from section to section which wouldcause some amount of discontinuity. Hence, there is acertain amount of overlap and duplication of photos toclarify specific points.There is no attempt to single out a particular motormanufacturer or to suggest that one product has moredefects or failures than another. For this reason, wehave not identified the manufacturer of the parts ormotors. In some cases, the failed part is not even ansrcinal equipment part. Also, we have made no effortto identify whom may have repaired a particular motor.The intent of this book is not to place blame but to assistin a correct diagnostic procedure that will preventrepetitive failures.The authors would like to express our appreciation toall those who have donated pictures for this edition andhope that we will continue to receive more pictures ofunique types of failures to fill the gaps. EDITOR’S NOTE when properly used, this material, will polish one’s diagnos-tic skills that would qualify one as an industry expert.The book is divided into the various components of anelectric motor. In addition to a brief explanation of thefunction of each component and the stresses that act uponthem, numerous examples of the most common causes offailure are also presented.Since it is not always possible to pinpoint the exact causeof failure, some examples are used more than once. Due toa lack of all the necessary facts associated with the applica-tion and history of a given machine, it is only possible toassign the root cause to the most probable scenario.A reference section is included at the back of this book forthose wanting to further research root cause failure analy-sis.  Copyright © 2002, Electrical Apparatus Service Association, Inc. (Version 502CI-502) Root Cause Failure Analysis Table of Contents Table of Contents Section Root Cause Methodology................................................................................................................................... 1Bearing Failures................................................................................................................................................. 2Winding Failures ................................................................................................................................................ 3Shaft Failures..................................................................................................................................................... 4Rotor Failures..................................................................................................................................................... 5Mechanical Failures ........................................................................................................................................... 6DC Motor Failures.............................................................................................................................................. 7Accessory Failures............................................................................................................................................. 8Case Studies...................................................................................................................................................... 9Reference Materials......................................................................................................................................... 10  Copyright © 2002, Electrical Apparatus Service Association, Inc. (Version 502CI-502) 1 - 1 Root Cause Failure Analysis Root Cause Methodology — Section 1 1 Root Cause Methodology Section OutlinePage Introduction to failure surveys .........................................................................................................................1-2Root cause methodology ................................................................................................................................1-2Summary of motor stresses ............................................................................................................................1-3Analysis of the motor and system ...................................................................................................................1-4Arriving at the correct conclusion....................................................................................................................1-5Basic AC motor nomenclature and common alternatives ...............................................................................1-6Basic DC motor nomenclature and common alternatives...............................................................................1-7Methodology formsAppearance of motor and system.............................................................................................................1-8Application considerations........................................................................................................................1-9Maintenance history ...............................................................................................................................1-10Motor system and environment checklist ...............................................................................................1-11Stator coil layout for location and identification of fault...........................................................................1-12Inspection reports ...................................................................................................................................1-13

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