The purpose of this article is to provide the information you need to get the most effective and useful information from EASA’s Technical Support Department. This in turn helps you serve your customers quickly and efficiently. 

High vibration is a common problem for motors that are installed on top of vertical pumps. Its source can be a mechanical issue with the pump, motor or coupling or even hydraulic forces from the pump.

An important step when selecting a centrifugal pump and an electric motor for an application or when troubleshooting operation issues is to determine how much power the pump should be using.

In a previous article in Plant Engineering ("A systematic approach to AC motor repair," Plant Engineering, April 2015), EASA highlighted the good practices for electrical repair found in ANSI/EASA Standard AR100 Recommended Practice for the Repair of Rotating Electrical Apparatus, and the significant impact they can have on motor efficiency and reliability. But that was only part of the story, because mechanical repairs—and even documentation, cleaning, and inspection—can also markedly affect motor reliability and efficiency.

This article provides a look at one service centers work at troubleshooting drive units on stamping presses. Topics covered include:

• On-site tests
• Fact finding
• Effects of contamination
• Verifying DC portion of eddy current drive
• Tachometer signal
• The job performed by the press

When a motor fails to perform, we know what to check: the voltage, whether it's balanced, the current, whether there is a ground, etc. When a pump fails to perform, many service centers are at a loss on how to troubleshoot it. If the pump has just been repaired and fails to perform, it will be hard to convince the customer that the pump is not the problem. The fact is, there are three areas of possibilities: It could be the pump, or it could be the fluid that is being pumped (the pumpage), or it could be the system of vessels, pipe and fittings connected to the pump (the system). Understanding a little bit about pump curves and pump performance parameters, and using the process of elimination, will allow the service center technician to narrow the possibilities - especially those that are pump related.

Has this ever happened to you? You have rewound a motor without changing the design at all; you tested the motor before you sent it out, and everything appeared to be fine. But now your customer wants you to figure out what is wrong, or rewind the motor again. Before you consider this, there are a few things to check to see if the motor is, in fact, running properly. It is quite possible that the motor ran "hot" before it failed, but what are the chances that someone on-site put their hand to the frame before it had to be rewound?

There are a number of different types of DC generators: shunt, series and compound, each of which can be separately or self-excited. A DC generator is built and designed exactly the same as a DC motor,and can be run as such. Regardless of the type, there are a number of reasons why a generator won't produce the correct voltage, or any voltage at all.

Shaft failures are not an everyday occurrence, but when they come in, it can be an interesting challenge to determine the cause of failure. Regardless of what caused the shaft to fail, what actually happens when it bends or breaks? To understand shafts and why they fail, you need to understand the relationship between stress and strain for steel.

When an armature is rewound, there is always a slim chance that it may be connected incorrectly. If two coil leads are switched, or if the error results in an armature where each coil closes on itself, normal tests will detect the problem. The trouble arises when the misconnection results in a uniform winding. When that happens, the result may be—in effect—an accidental redesign for a different voltage.