We’ve covered how to assess impeller damage in a previous webinar. Now learn how to fix that damage. This webinar recording covers:
- Replacing/repairing wear rings
- Repairing cavitation damage
- Impeller replacement options
- Dynamic balancing impellers
We’ve covered how to assess impeller damage in a previous webinar. Now learn how to fix that damage. This webinar recording covers:
This 12-part recording covers a wide range of topics on vibration.
Members rely on EASA to provide technical assistance and training in all areas related to machinery repair. In the area of machinery vibration, there are training providers that offer general classes in vibration analysis and balancing, but the content is geared to plant maintenance personnel who would be conducting in-plant predictive maintenance services. Some key areas important to EASA service center technicians is not covered adequately, and much of the content does not apply to vibration testing conducted in the service center. This course is designed to address those shortcomings and provide fundamental training in vibration analysis and balancing that directly applies to technicians working in the service center.
Available as a printed booklet or as a downloadable PDF.
This webinar series was designed to:
Service center technicians who measure and analyze machinery vibration, and those who must evaluate the vibration data will benefit greatly from the fundamental understanding and knowledge provided by this training series. Service center engineers who may be involved in writing, interpreting and applying vibration and balancing specifications and tolerances will gain a practical understanding of the terms, definitions and parameters encountered in those specifications.
As with any technical subject, fundamental math skills will allow attendees to quickly comprehend concepts and apply techniques. Vibration results from the mechanical and electrical forces at work in machinery, and a fundamental understanding of those forces, and machine components that cause them, will aid in the understanding and application of the subject matter.
Downloadable version - $745 for members, $1,885 for non-members
DVD-ROM version (for viewing on a computer) - $795 for members, $1,985 for non-members
Introduction and Overview
Amplitude, Frequency and Phase
Basic Vibration Analysis (Part 1)
Basic Vibration Analysis (Part 2)
Dynamic Balancing Basics
Time and Speed Transient Analysis
Rolling Element Bearing Vibration
Demodulation and High Frequency Band Measurements
Field Analysis Techniques
Field Balancing—Problems and Solutions
A condensed outline of the review and approval process for AR100 is as follows: The EASA Technical Services Committee (TSC) reviews the Recommended Practice and proposes changes; then a canvass group approves and often comments on the TSC proposals. The canvass group has representation from service centers, end users, testing laboratories, government and those having a general interest. Per ANSI requirements, there must be balanced representation among the canvass group representatives. After the canvass group and the TSC find consensus agreement, the revised document is submitted for approval to the EASA Board of Directors. Following Board approval, ANSI is requested to approve the revision as an American National Standard. The entire process must be completed within five years following the previous revision.
The 2015 edition of AR100 contains nearly 100 revisions from the previous version. A PDF version of AR100 with the changes highlighted is available. The focus of this article will be on the more significant changes, noted in clause order, and some of the reasons for making these changes. Also noted will be explanations of the effects on the EASA Accreditation Program.
1.12 Authorization to Ship (new clause): Added a recommendation to indicate an authorization to ship for a completed repair, e.g., “OK to ship.” It is a good practice to have someone “sign off” on a repair to indicate that all repairs are complete and the finished machine is ready to be returned to the customer. The EASA Accreditation Program Checklist already included this step as a requirement.
2.6 Balancing: Changed balance quality level for machines rated above 2500 rpm to balance quality grade level G1.0; machines rated 2500 rpm and below remain at the grade level of G2.5. This change reflects an indus.try trend of both service centers and end users to provide more precise dynamic balance levels for rotating elements that operate at higher speeds. This change will affect service centers that are EASA accredited or are considering accreditation. Effective August 2016, the balance level of G1.0 for motors rated above 2500 rpm will be a requirement for the EASA Accreditation Program.
2.7 Slip Rings: Added a specific tolerance for slip ring surface finish to be between 40 and 60 micro-inches (1.02 and 1.52 microns). The previous guidance was somewhat subjective, calling for the finish to be smooth and polished.
2.8.1 Machining (of commutators): Added a specific tolerance for commutator surface finishto be between 40 and 60 micro-inches (1.02 and 1.52 microns). As with the slip ring finish, the previous guidance for com.mutators was somewhat subjective, calling for the finish to be smooth and burnished.
2.12 Air Gap of Machines: Expanded the scope of air gap tolerances. The previous edition only addressed DC machines. The revised clause provides a 10% tolerance for variation from the average for all machines.
3.1.1 Core Laminations: Clarifies that stators and armatures should be core tested before and after winding removal. Further, the revision states that cores should be tested for hot spots and losses. The primary change is the expansion in scope to include armatures; the reason is that armature cores are part of an AC circuit and may have frequencies up to and above typical AC motor frequencies. Thus the core condition can significantly affect heating and losses.
3.3 Stripping of Windings: Added temperature limits of 700°F (370°C) for cores with organic coreplate and 750°F (400°C) for inorganic coreplate. These temperature limits have been in the Technical Manual for many years. Since they have been, or should have been, standard practice, they were adopted into AR100. Also, a good practice is to assume the coreplate is organic un.less it is known to be inorganic. Thus the 700°F (370°C) should be used in almost all cases. Further, as a conservative approach, the EASA Accreditation Program prescribes using the 700°F (370°C) limit.
3.7 Field Coils: For clarity, the text of the main clause was deleted. The text was moved to the appropriate location in clauses 3.7.1 and 3.7.2.
4.2.5 Winding Surge Test (previously 4.2.6): Clarified that the winding surge test, formerly termed “surge comparison test,” applies to complete new or used windings. Previously the reference of applicability was to “winding circuits.” The recommended test level was not changed, but the applicability was clarified.
4.2.6 Interlaminar Insulation Test (previously 4.2.7): The content of this clause regarding interlaminar insulation testing was expanded to include the types of tests and parameters for evaluating cores, including maintain.ing the same test flux level within 5% for the after-winding removal test versus the before-winding removal test. The reasons for these changes were to make the clause more specific and less subjective.
4.2.7 Bearing Insulation Test (previously 4.2.8): Changed evaluation criteria for the bearing insulation test (see Figure 2), noting that there is no industry consensus for bearing insulation in motors supplied by variable frequency drives (VFDs). Although the 1 megohm minimum from the previous edition still applies to motors operating from sinusoidal (e.g., utility line) or DC power supplies, the change reflects the uncertainty regard.ing a bearing insulation test for motors supplied by variable frequency drives (VFDs). If and when there is industry consensus on a bearing insulation test for VFD supplied motors, the Recommended Practice will consider adopting such a test.
Clauses 4.2.8 through 4.2.11: All of the clauses in main clause 4.2 describe tests that are used in AR100. Clauses 4.2.8 through 4.2.11 were added to provide descriptions of the phase balance (4.2.8), polarity (4.2.9) and the dummy rotor [previously ball rotation] (4.2.10) tests (see Figure 3) that had not been previously described; and to describe the new impedance (4.2.11) test.
4.3.1 Stator and Wound-Rotor Windings: Winding resistance and surge tests should now be performed on every repair; previously they were optional. Insulation resistance testing also should be performed on every repair. This “tightening” of the recommendation brings AR100 in line with generally accept.ed industry practice. That is, almost all service centers perform insulation resistance tests and many perform winding resistance tests. Although not all service centers have surge testers, the surge test is the only winding test that checks for turn-to-turn, coil-to-coil and phase-to-phase defects or anomalies. This change will affect service centers that are EASA accredited or are considering accreditation. Effective August 2016, a calibrated surge tester will be required equipment for the EASA Accreditation Program.
Clauses 4.3.3 and 4.3.4: Insulation resistance testing should now be per.formed on every repair; previously it was an option for armatures (4.3.3) and shunt, interpole, series, compensating and synchronous rotor windings (4.3.4). The reasoning for the change to these test clauses is the same as for the insulation resistance test change in clause 4.3.1.
4.4 High-Potential Tests: As a further step toward internationalizing AR100, the term “earth(ed)” or “earthing” has been added whenever “ground(ed)” or “grounding” is referenced. This change applies throughout the document and is mentioned here because this clause contains many references to these terms.
126.96.36.199 Accessories of Machines with Windings Not Reconditioned: Added to this subclause was an acceptance criterion for insulation resistance testing of accessories. The previous text was somewhat subjective, indicating only that an insulation resistance test be performed. It is noteworthy to mention that other standards do not address a specific insulation resistance level for accessories, which this clause now provides.
4.5 No-Load Tests: Added that motors should be secured on a base plate or on a resilient pad for the no-load test. Also, added recommendations for testing AC and DC motors that operate at above base speed. The reason for the first change in this clause was to clearly bring AR100 in line with existing NEMA and IEC requirements. The second change applies to motors that are operated above base speed, such as some AC motors on VFDs with output frequencies above line frequency and DC motors with field weakening. The primary reason for checking the operation of AC motors on VFDs at their maximum rated frequency (and speed) is to confirm that vibration levels are acceptable. For DC motors with field weakening, the primary reasons are to check for acceptable (sparkless) commutation and to check that vibration is acceptable.
Table 4-5 Unfiltered Vibration Limits: Unfiltered vibration limits were revised to conform to current NEMA and IEC standards values. Further, the changes simplify and clarify the information in the table. The table continues to provide levels for resilient mounting and notes that a 0.8 multiplier is to be used for rigid mounting conditions.
As time goes on, the Technical Services Committee will continue to revise and improve AR100. Within a few years the revision process will become an active agenda item for the committee. One of the foremost goals with AR100 is to include as many good practices in it as possible. Further, when it is desired or necessary to add new good practices to the EASA Accreditation Program, AR100 is the conduit since it is the primary source document for the EASA Accreditation Program. Because AR100 is revised periodically, it is a “living document.” Changes to AR100 not only aid with the EASA Accreditation Program, its good practices and other guidance help enable service centers that use it to provide quality repairs that maintain or sometimes even improve rotating electrical apparatus reliability and efficiency.
This valuable instructional/resource manual is available in printed, downloadable and CD-ROM versions.
For this second edition, the manual has been reorganized, updated with new information, including revised standards and published articles, and edited extensively. The manual includes drawings, photos and extensive text and documentation on AC motors, including how they work, specific information on enclosures, construction of components and applications. Many of the principles included apply to all AC motors, especially those with accessories that were associated with larger machines in the past (such as encoders, RTDs, thermostats, space heaters, vibration sensors, etc.).
While the manual covers horizontal and vertical squirrel-cage induction motors in the 300 to 5,000 horsepower range, low- and medium-voltage, most of the principles covered apply to other sizes as well. This manual focuses primarily on NEMA motors.
Sections in the manual include:
On occasion, service centers are asked to balance fan blades that are designed for an overhung mounting. The fan blade may be received mounted on the shaft, or without any shaft. The decision has to be made about how to mount the rotor in the balancing machine. One solution is to fabricate a mandrel to balance the fan blade between the machine pedestals. The other alternative is to mount the fan blade on the end of the shaft in an overhung configuration, with the fan blade outboard of both balancing machine pedestals. This would be the more expedient method if the fan blade is already mounted on the shaft in the overhung configuration.
How the fan blade is mounted doesn’t change the balance, as long as the fit to the shaft doesn’t change. So the question is, “Which is easiest?” Often it is easiest to mount the rotor in the overhung configuration, but balancing in that configuration presents some challenges. Those challenges are addressed here.
This presentation examines:
Often an overhung fan is balanced in a single plane, only to find that the vibration has shifted to the outboard bearing. Attempts to use standard two-plane techniques may result in calculated correction weights that are very large and produce poor results. There are more effective ways to approach this common problem. This presentation shows a methodical approach and techniques for tackling this difficult balancing problem.
This presentation is intended for field service balancing technicians, supervisors and managers.
Fundamental to every good mechanical repair is the ability to disassemble, repair and reassemble the motor correctly without unnecessary damage to any of the motor parts. This sounds simple, and yet too many costly mistakes are made in this process of taking things apart. If every motor repaired was in “as new” condition, the task would be much simpler. But this would be no guarantee that the reassembly would be correct.
There is usually an easy way and a hard way to remove and install parts. Brute force is seldom the easiest or the correct way. The old saying of “don’t force it, get a bigger hammer” is seldom the best way.
When a service center is paid to repair equipment, the service center wants it to stay in operation. If the equipment fails again—within the warranty period—the service center pays to repair it again. It makes sense to repair it correctly the first time.
In order to improve equipment, it is important to know how and where it operates. Without understanding why a motor fails, it is impossible to deliberately improve its mean time between failures.
To do this, there must be communication between the service center and the motor user. Not only does this help the repairer decide the best course of action, but it helps the user appreciate the professionalism of the service center.
Repair procedures, like motors themselves, are affected by changes in technology. This book attempts to include the latest proven technologies. Time-honored methods of repair, in many cases, may still be the most practical option. Options presented throughout this book are intended to help the technician select the appropriate repair method, recognizing that the ultimate decision rests with the equipment owner.
Repair methods sometimes fall into disfavor, not because better methods are introduced, but because of poor techniques. Other repair methods are well-suited to some applications but not to others. It is the job of the repairer to decide what is the best method for each case.
This book is divided into sections for basic motor components with repair methods and tips dispersed throughout. Where practical, reasons for failures are also discussed. These will aid the technician in selecting the most appropriate method of repair for each unique application.
The information presented draws from EASA publications, IEEE publications, technical journals and literature supplied by vendors, motor manufacturers and established service centers.
This book contains many suggestions on how to correctly handle the various parts of a motor during the repair process so as to minimize damage. However, it is impossible to develop an all-inclusive list. Instead, the basic principle of taking the time to use the correct tool and correct procedure will usually lead the technician down the right path. Always remember, if it has to be forced beyond reason, it might be that neither the proper tool or procedure is being used or something is wrong with the parts. Step back and ask “What am I overlooking?”
Table of Contents
This book is available as part of EASA's Fundamentals of Mechanical Repair seminar.
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:
The purpose of this book is to address the lack of experience in identifying the root cause of motor failures. By using a proven methodology combined with extensive lists of known causes of failures, one can identify the actual cause of failure without being an “industry expert.” In fact, when properly used, this material, will polish one’s diagnostic skills that would qualify one as an industry expert.
The book is divided into the various components of an electric motor. In addition to a brief explanation of the function of each component and the stresses that act upon them, numerous examples of the most common causes of failure are also presented.
Since it is not always possible to pinpoint the exact cause of failure, some examples are used more than once. Due to a lack of all the necessary facts associated with the application and history of a given machine, it is only possible to assign the root cause to the most probable scenario.
A reference section is included at the back of this book for those wanting to further research root cause failure analysis.
The book is available only in black & white. Photographs in the CD-ROM version are in color, where available.
Table of Contents - (Download the complete Table of Contents)
This book and it's companion CD-ROM is available as part of EASA's Root Cause Failure Analysis seminar or it may be purchased in EASA online store. This product is also available as a download.