Chuck Yung
EASA Technical Support Specialist 

Ever rebuilt a motor, only to have the customer call and complain that the motor "isn't right?"  Maybe it vibrates or draws too many amps, or "It never used to run this hot."

The response is usually a costly trip for a salesman and service technician to check it out. 

When a problem exists, it may be in the motor or the installation.  It may even turn out that the problem caused the initial failure. High current could be the result of a voltage supply problem; vibration may be due to misalignment. 

Documentation makes a big difference in how a situation like this is handled.  The service center with good quality control and solid documentation has a decided advantage. If the test voltage and current were recorded when the motor was final-tested, and vibration readings checked and recorded, it is much easier to pinpoint the problem and help correct it.  The whole episode can serve to reinforce the value of dealing with your service center.

The shop with no recorded results is on the defensive from the start. Even if the repair job is eventually ruled out as the cause of the problem, the bad feelings may linger.  At the least — based on the evident lack of quality controls — the customer wonders about quality.  He may send future work elsewhere. 

Too often (and yes, once is too often) a manager hears excuses as to why that particular reading was not written down.  "It ran fine on the test panel" does not translate well when you're sitting across from a customer armed with printouts indicating that it's not running fine now.  A good set of baseline test data taken in the service center means that you can find the problem.  It could be in the motor. The last thing you need in this situation is uncertainty about how the motor really ran in the shop.

What data should be recorded? If it's important enough to check, it's important enough to write down. Final meg reading and hipot test voltage are first and foremost.  Test voltage and amperage should be measured on all 3 phases.  One without the other is useless.  Bearing temperatures should be recorded, along with running time and ambient temperature. Vibration readings should include all 3 axis (horizontal, vertical & axial) on both ends of the machine.  Keep a printout from the vibration analyzer to document any predominant frequency peaks in the spectrum, with each peak identified and evaluated before the motor leaves.

A standardized repair form is essential. It is hard to convince an employee of the importance of writing everything down when you don't consider it important enough to provide a form.  The basic nameplate information, along with mechanical information (bearing sizes, dimensions, required parts, special instructions), and electrical test information (meg reading, hipot voltage, surge-test results) Ñ all should be documented as part of the most basic quality control program.  Final test results are also essential.

If the motor ran fine in the service center, compare the on-site readings and determine the cause of the problem.  The focus should always be on solving the problem.  It is human nature to remember "the mistake" rather than the years of flawless service. The key is to make sure the customer remembers how you helped solve the problem.

Documentation is an essential part of the quality control process. Interpreting the documentation is equally important.  Dutifully recording a bent shaft is no help if the shaft is not repaired.  High amps during a no-load test, or a high vibration reading, are flags that require attention.  What's worse than missing a problem in the service center?  Explaining to the customer why your documentation indicated the very problem he is reporting, and you didn't catch it.

Categories: Testing, Motor testing

Tags: Motor testing

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