Here You Go.

When it comes to inspecting electric motors, it’s not just the electrical components that are important. The mechanical aspects of a motor are extremely important to its performance, which is why mechanical inspection of electric motors is so important.

Critical Fits for Electric Motors

Electric motor inspection, when done correctly, always includes a mechanical inspection. As the motor is carefully dismantled, critical fits are measured. These critical fits include …

• Bearings fits
• Journal fits
• Housings
• Seal fits
• Keyway
• Shaft extension size
• Etc.

For an electric motor to run efficiently and productively, attention must be paid to the often mundane aspects of mechanical fits and tolerances.

After you’ve approved an electric motor for repairs, certain components may go through various machining processes to bring them back to tolerance. And in some cases, new parts need to be manufactured to duplicate the original.

What is Machining?

Machining is a material removal process: the final part is created by removing material using cutting tools. Both metals and plastics can be machined, but not all materials are well adapted for machining. Steel and aluminum are far easier to machine than cast iron, though it certainly can be done. One of the key benefits of machining lies in the extremely tight tolerances that can be achieved by skilled machinists working with quality tools.

Everyone agrees that proper testing is vital, and initial test runs--when performed correctly--help electric motor repair technicians get a head start on troubleshooting electric motor problems. But what exactly do these initial test runs involve?

When Initial AC Motor Test Runs are Needed?

For most electric motor repair shops, an incoming test run is only performed for a few specific reasons such as if (1) the customer requests it (which is common), (2) if it is a 2-pole motor, or (3) if the motor has a particular problem that can be observed (e.g., vibration).  Beyond those situations, most shops only test run the electric motor, after repairs are completed, as a final quality assurance check of their repair.

Keep in mind there are many times when you cannot run a motor on arrival due to the condition of the unit. If the motor is grounded, shorted, locked up or has a bearing issue, it may not be safe to test it prior to repair. Think of driving a car after an accident - sometimes it can be safe and other times the vehicle must be fixed before it can be safely driven.

Why Initial Motor Test Runs are Important

Initial test runs give insight into the condition and performance of the motor before anything else takes place (e.g., cleaning, disassembly, repairs). The results of initial testing will better inform the troubleshooting process, which can shorten the lead time for getting your motor back. Which tests a motor fails and which tests it passes are key to narrowing down the cause of problems. 

Two-pole motors can be more challenging to repair because of the vibration issues that can be related to the units operating at higher speeds, which means there are special tests that need to be performed on them. Without checking characteristics such as runout and roundness, there is a chance that vibration won’t show up until you get your two-pole induction motor back and running.

Here is a Quick Review of Two-Pole Motors

Two-pole induction motors are just like other induction motors but they operate at 3600RPM versus 1800RPM, 1200RPM, or even slower. These motors are most often found in applications that need higher speeds such as conveyor belt systems, pumps, and air compressors.  And the major issue with two-pole motors involves two things: speed and vibration.

At 60 Hz, a two-pole induction motor will operate at a synchronous speed of 3,600 rpm. At those speeds, everything is amplified, which means there are tighter tolerances involved for bearings, shafts, housing fits, etc. Any dimensional variations or frame distortions will play a significant role in how these motors perform.

You hear the world "quality" all the time. Many times its one of those words that you ignore. I always think of it as a word that is used so frequently that it doesn't mean much anymore.

However, when it comes to having your electric motor's repaired, the word quality really does have a meaning and there are many ways to verify and ensure quality repairs are done properly. Here are a few of the bullet points to consider:

1. Documented data & images during inspection
2. Inspection/incoming report
3. Formal quotation/estimate
4. Calibration program and calibrated equipment
5. Modern technology (where appropriate)
6. Documented procedures/processes
7. Final report

Your plant or industrial facilities have spare electric motors. They sitting on a shelf in your warehouse "ready to go" in the event you need them. However... how do you know for sure they are "ready to go"? 

One of the first steps we take in our repair process here at HECO is steam cleaning your electric motor. Electric motor parts can get extremely dirty and the interior of the motor is often covered in dirt and dust (on DC motors: carbon dust). Sometimes technicians can’t visually check for signs of wear or damage -- or accurately troubleshoot the motor, for that matter --  when the motor is still dirty.  

Dirty Motors

We all know electric motors get dirty -- and don’t worry: we won’t judge you if your motors look filthy. Depending on the environment and motor enclosure, we usually expect to open one up and see a significant buildup of dust and other debris. Sand, fly ash, cement, paper pulp, carbon black, etc. buildup alone can impact motor performance and efficiency, causing areas to overheat, contaminate lubricants, accelerate wear, and damage the windings. Carbon dust is conductive, which means it can cause shorts if they get in the wrong area. However, accumulations like this are natural, but that doesn’t mean your motor has to stay that way.

You sent an electric motor out for repair. Now it is back.

What are all these tags that were not there before?

Good question! 

The idea of this article came to me when I walked past the motor shown in the image. I noticed lots of tags and badging on the motor. For a simple 125HP, 1800RPM Siemens motor we had a lot of visual aids on the motor. Many of these aids are standard from HECO. Others are a result of working with a specific client. So, who benefits from all these visual aids, or tags as we call them?

Are your electric motor bearings wearing out long before they should? The problem might be bearing fluting … and the good news is that there are ways to prevent it.

What is Fluting?

Fluting is a form of electrical damage suffered by electric motor bearings when alternating (AC) or direct (DC) current actually passes through the metal bearing. As the currents pass through the bearings, they can leave behind surface damage that results in premature bearing failure.

Electric motor bearings are supposed to provide support, reduce friction, and constrain motion so that it only occurs in certain directions (e.g., radial, axial). When they can't do that anymore, they need to be replaced. However, before replacing a bearing in one the electric motors or drive trains you are responsible for, you need to be aware of certain key factors that affect bearing suitability and have an understanding of the different types of bearings you may encounter.