This presentation examines:
- How the spectrum is generated from the vibration signal
- The effect of f-max ad resolution settings
- Averaging techniques
- Scaling and demodulation
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.
This book covers low- and medium-voltage horizontal and vertical squirrel-cage induction motors in the 300 to 5000 horsepower range. Many of the principles discussed also apply to motors of all sizes and technologies. Although the focus is on motors built to standards of the National Electrical Manufacturers Association (NEMA), much of the material applies to motors designed according to standards of the International Electrotechnical Commission (IEC).
This book is designed primarily as a training manual for EASA’s seminar Principles of Large AC Motors. Since it contains reference materials, graphics and visual aids for both the instructor and the student, it also makes an excellent “on the job” shop reference and training guide.
As shown below, the manual is organized in 24 sections or modules, complete with a table of contents to guide users to appropriate sections. The material is configured for use with students having various levels of knowledge and experience, from technicians to engineers. The entire course can be presented in one or two days, depending on the time available. Individual sections can also be presented as stand-alone training modules.
Table of Contents
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 Pump 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 Falure Analysis seminar or it may be purchased in EASA online store.
A customer specifies that the rotor is to be balanced to 4W/N. Is that the 4W/N Military specification, or the 4W/N API specification?It could make a big difference. And, how do they compare to the ISO 1940/1 specification (G2.5, G1, etc.)? Fortunately, for symmetrical rotors, comparing the various standards is only a matter of a bit of easy algebra. For non-symmetrical rotors, the process gets a little more difficult because each of the specifications handles these cases differently. The other good news is that there are on-line references that provide graphic and tabulated comparisons.
Most service centers balance rotors routinely, with few surprises in the process. There are even technicians who balance rotors so well that the highest velocity readings on the test bed are normally under 0.01 inch/second. It is a great indication of quality when a customer swears that a motor has never run that smoothly. Most of us do not balance fans nearly as often as rotors. The fan balancing tips in this article should be helpful. We'll start with a basic explanation of balancing and then get into balancing tips for fans. Many of these are also applicable to impellers, large sheaves and other rotating parts our customers may ask us to balance.
This article describes machine balancing of the rotating components of motors and generators, primarily rotors and armatures. The methods described here, in general, can be applied to on-site balancing if the rotating component is accessible. The intent is to describe the methods of attaching balance weights, not determining acceptable balance level or the location and amount of correction weight.