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Importance of Air Gap in Electric Motors

05/19/2020

air gap for electric motorsThe air gap refers to an actual physical gap in an electric motor that separates the moving rotor and the stator core. This gap is a necessary part of motor design and the size of the air gap is one of the keys to motor performance and reliability.

The Case for a Correct Air Gap

The air gap needs to be large enough to prevent contact between the rotor and stator, taking into account tolerances related to their respective dimensions, loose bearings, and movement that results from deflection during operation. In addition, if the rotor is eccentric relative to the stator and the air gap is too small, the stiffness of the shaft might be overcome by the resulting unbalanced magnetic pull. This, in turn, leads to damage resulting from the rotor striking the stator as it is pulled out of place by the magnetic forces.

At the same time, the motor's air gap needs to be as small as possible because wider air gaps require more power to achieve magnetization. In short, in air gap that is wider than necessary could have a negative impact on the efficiency and performance of your motor.

Air Gap Eccentricity

We just talked about how important it is for the air gap to be the right size -- it is also extremely important that the air gap be uniform. When the air gap is eccentric, the motor is going to vibrate and make noise. While noise in and of itself is not a big deal, it is important to realize that both noise and vibration (relying on vibration analysis) reduce motor performance and can lead to components wearing out faster than normal. This leads to higher M&O costs and more downtime.

But noise and vibration aren't the only issues with an eccentric air gap. It can also lead to increased coil movement which can speed up how fast the coil insulation degrades. If the eccentricity is large rough, the magnetic pull can become unbalanced and lead to rubbing between the rotor and stator, which is never a good thing.

So how is a uniform gap defined? Obviously, perfect uniformity is ideal but not very realistic. Most motor design and repair professionals recommend that air gap variation should never exceed +/- 10% of the average air gap.

A Picture Says a Thousand Words, or in the Case of IRIS M, Millions of Enhanced Pixels

08/22/2019

Far more than a data collection tool, IRIS M is RDI’s patented technology that turns millions of pixels from a camera image into millions of data points that can be monitored, read, and analyzed for critical manufacturing machinery, operations, quality control and other factors that affect plant reliability and productivity. For the first time ever, you can now see movement that is invisible during real time. 

How Does Vibration Analysis Work?

05/08/2019

In recent years, companies have entered the transition from reactive maintenance, to planned maintenance, and into the most efficient method found in predictive maintenance. While the first two methods have dominated in the past, they have been found to be costly, inefficient in time, and sometimes result in over-maintenance of machines. 

In predictive maintenance, machine downtime, cost for spare parts, and overtime are all held to a minimum. With all of these benefits, you may be asking - “What is the best implementation of predictive maintenance in my workplace?"

One of the most effective ways of predictive services is Vibration Analysis.

What is Vibration Analysis? Time Waveform and FFT Spectrum Analysis

03/08/2018

The below video is a 5 minute segment of a 30 minute long presentation given by Adam Smith, CMRT and Jacob Bell of HECO PSG at the 2017 Reliability, Process, and Maintenance (RPM) Symposium. This presentation discusses the basics of vibration analysis as a predictive maintenance tool. This presentation covers:

What is Vibration Analysis? The Basics

02/13/2018

The below video is a 11 minute segment of a 30 minute long presentation given by Adam Smith, CMRT and Jacob Bell of HECO PSG at the 2017 Reliability, Process, and Maintenance (RPM) Symposium. This presentation discusses the basics of vibration analysis as a predictive maintenance tool. This presentation covers:

Are your vendors holding you hostage?

12/19/2017

During a recent plant survey we encountered several motors that were suspiciously missing the manufacturer’s data plate but miraculously had a data plate from the last repair vendor. These “vendor” data plates usually only have the vendors job number and of course their logo and contact phone number. This is an old trick that forces the customer to call the last vendor for a replacement motor or a motor repair. 

How did you choose your vibration route & vibration analysis company?

11/28/2017

A common situation... 20 years ago someone decided that utilizing vibration analysis was a good idea in your plant. Maybe the idea came from a vendor or an internal Predictive Maintenance (PdM) guru. Either way you evaluated it and it just didnt make sense to have an internal team dedicated to this so you decided to outsource it.

How did you choose which company to use?

Was it  a simple decision and go with the person who was bringing the idea to your plant? Did you develop a specification and go out for bid? How you made this determination is something to review down the road.

How important is certification for vibration analysis?

07/06/2017

Category I, Category II, Category III and Category IV - What are they and what do they have to do with vibration analysis? Why should they matter to my corporation?

Through The Vibration Institute, Mobius Institute, Technical Associates of Charlotte, and various other groups offer certification in vibration analysis. More importantly, they are certification to ISO 18436-2 Vibration Condition Monitoring and Diagnostics.

Imbalance and Vibration in your fan are not the same!

05/25/2017

It is very regularly that we receive a call from a client that a fan is vibrating and that we need to send someone out there to balance the fan! A good portion of the time when we arrive, it is indeed a balance issue, where the fan has had a buildup of material on it. Many times this throws off the balance but simply cleaning the fan blades can resolve the issue. Sometimes it can't which is when the actual process of balancing comes into play.

Considering buying a vibration condition monitoring system? Here are the various types of systems and technologies

03/21/2017

The world of vibration condition monitoring is quickly and constantly changing. New products and technologies are coming out regularly from a variety of manufacturers.

There are data collector applications for iPads, Bluetooth sensors such as the iALERT2 Equipment Health Monitor, wireless continuous monitoring solutions, etc. With so many options out there, where do they all fit? The purpose of this article is to discuss the basic types of solutions that are out there and where they may fit you and your plant's needs. 

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