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How to Test an Electric Motor: Techniques, Part 2

07/16/2020

In part 1 of How to Test an Electric Motor, we talked about the importance of testing and different types of tests that you can perform. In part 2, we are going to talk about more of these tests and how you can put test data to good use.

Shaft Current Test

When you suspect that the motor bearings have suffered electrical damage, then you likely need to perform a shaft current test.

So how can bearings experience electrical damage? When capacitive coupling exists between the motors and the windings, it can create a voltage on the shaft that can be discharged through the motor bearings. When that happens, it leaves behind surface damage like pitting, fluting, and craters. This type of damage shortens the useful life of the motor bearings and can lead to premature motor failure.

You can detect and measure shaft voltage (and bearing currents that result from it) by either using an oscilloscope with special voltage probes or a shaft voltage tester such as the one made by Aegis . If you're wondering why you can't use a multimeter, it's because the voltages occur too quickly for it to capture. The oscilloscope, on the other hand, allows you to observe those changes over time despite this.

How to Test an Electric Motor: Techniques, Part 1

07/07/2020

There are so many different tests that you can perform on an electric motor -- and that's why it's key that you know what the purpose is of these tests, how they work, and what the data means. This blog post is the first in a two-part series on the subject of electric motor testing.

We'll start with a quick review of why testing is important followed by a discussion of rotor bar, hipot, surge, and motor winding resistance as well as a discussion of vibration analysis.

Importance of Testing

Bearing problems may be the number one cause of electric motor failure, but electrical faults are a close second. And electrical failures require your maintenance group to go about testing the motors in your care.

The most obvious benefit of testing is troubleshooting. When a motor isn't working right or fails, you can use testing to track down the most probable cause of the problem. You can also use test results as a measure of a motor's performance. That data, in turn, can inform decisions about repairs, maintenance, rebuilds, and replacements.

Regular testing is key to your maintenance program and contributes to the performance and reliability of the motors in your care. For example, you can detect minor problems before they become expensive failures. And remember, well maintained motors have much higher reliability, and both the M&O costs and energy costs for them are lower.

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.

I don't care why it failed - Just get production running again!

12/17/2019

A piece of equipment in your plant just failed. You didn't see it coming. You aren't prepared for this. Management is demanding that production starts again. Sound familiar?

STOP!    STOP!    STOP!

You may be caught in an endless cycle of failure after failure. You continually look for "who to blame" versus figuring out what actually happened.

Failure, Rinse, Repeat! Isn't it time to do something different? Let's look at the entire picture to see this... Ever heard of the Uptime® Elements?

Don't Forget About the Base! Your Equipment's Base Could be Causing you Issues.

06/27/2019

There appears to be a trend happening in industry that needs to be looked at in greater detail and I hope to shed some light on this subject.

We are all so quick to repair the motor, pump, gearbox, or fan when a failure occurs; however, we hardly ever spend time looking at what the equipment is attached to…the base.

                                                                                                                                 Picture 1

What Is Our Predictive Maintenance World Coming To? - The History of PdM

06/13/2019

There are a few of us “old timers” left around who can remember our first analyzer. It was free, and we thought we could solve anything. It was our very own brain. With the touch of the hand, chunk of broomstick, or long screwdriver, by listening we could solve any issue and predict an impending failure. For the most part, this system worked pretty well and to this day, listening and feeling plays a very integral role in PdM (Predictive Maintenance). The biggest downfall of this method is that same ear and same touch can’t always be there and can’t log or trend what you are feeling and hearing, nor could we actually measure that feel to determine and trend precise changes.

IIoT vs. PdM (Internet of Things Vs. Predictive Maintenance)

06/27/2018

When you start a compare and contrast with Predictive Maintenance and the Internet of Things within the industrial maintenance world; you may have some people scratch their head and say, “are they not the same thing?”.  Well, the easy answer is a simple answer of yes and no.  Yes, they are both moving towards a new way of understanding maintenance and maintenance needs.  No, they are not the same because different tools and technologies are being used to assess equipment and assets. 

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:

Maintenance Philosophies: Breakdown Maintenance, Preventive Maintenance, Predictive Maintenance

01/16/2018

The below video is a 7 minute segment of a 30 minute long presentation given by Adam Smith and Jacob Bell of HECO PSG at the 2017 Reliability, Process, and Maintenance (RPM) Symposium. This presentation discusses three different maintenance philosophies: breakdown maintenance, preventive maintenance, and predictive maintenance.

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