Archives for 2016

Resonance is a condition that can occur in mechanical structures and can be described as sensitivity to a certain vibration frequency. Resonance occurs when a natural frequency is at or close to a forcing frequency, such as rotor speed. For machinery—such as pumps, turbines and electric motors—resonance can amplify the small vibratory forces from machine operation, and severe vibration levels can result. Such problems often develop after a speed change has been implemented, as with retrofitting a machine with an adjustable-speed drive (ASD) or operating a 50-hertz motor on 60 hertz of power.

The solution to these problems frequently depends on distinguishing between structural resonance and a rotor critical speed. Structural resonance refers to excessive vibrations of non-rotating components, usually machine components or supporting structures. Rotor critical speed refers to a condition in which the speed of the rotating element of the machine matches the rotor’s natural frequency

Many of you have good in-house predictive maintenance departments, and others outsource that work to others. Either way, you routinely know when a bearing is deteriorating, and remove the motor from service before it turns into a catastrophic failure. That saves a lot of maintenance dollars, which is great. But if you stop there — without discovering why that bearing is faulty — you could be facing the same problem again in a few short weeks or months. Bad bearings often hold a great deal of evidence, if you know what items to focus on.  Click here to learn more and read the complete article.

From Electrical Construction & Maintenance Magazine

By Chuck Young, Senior Technical Support Specialist, Electrical Apparatus Service Association

Right-sizing of three-phase induction motors for different applications – and striking a balance between reliability and efficiency – isn’t always easy, but it can be cost-effective. Before the days of comprehensive predictive and preventive maintenance programs, the conventional approach to reliability was conservatism, both in design and in application. That’s to say that on a 25 hp application, you’d find a very conservatively designed 60 hp motor that was really 75 hp “under the hood.” And yes, the motor would last a very long time, but it would have an inflated (and often ignored) operational cost. Many of these robustly engineered applications are still out there, and it can be well worth the effort to identify and correct them.

By Mike Howell, Electrical Apparatus Service Association (EASA)
Careful evaluation of motor load requirements could yield long-term savings. To learn more, click here.