Here You Go.

If you have a specific NEMA-T frame motor, you can be assured that, regardless of manufacturer, that specific T frame (for example, a 324T) will have the same shaft length, shaft diameter, and bolt hole mounting dimensions. What too many people don't realize, however, is that the physical size of specific T frame motors can vary greatly. That means you could buy what you are assuming is a simple drop-in replacement that doesn't quite fit in the space allotted for it.

NEMA Class Designations

NEMA, which stands for National Electrical Manufacturers Association, revolutionized electric motor manufacturing by using a motors's starting-torque and accelerating load to categorize it into specific classes. NEMA standard motors make it much easier for you to find the right one for your particular application.

The four standard classes they developed are NEMA A, NEMA B, NEMA C, and NEMA D (and very large motors classified as Above-NEMA). Each classification has certain applications they are well-adapted for (e.g., NEMA C is for situations that require high starting torque while NEMA A motors lend themselves to applications that require a high speed at full load).

Reliability and electric motors do not always seem to go hand-in-hand. There is electrical reliability and mechanical reliability, but what about electro-mechanical reliability? This can exist, and it does for many plants across the country! This presentation covers how to create a reliable electric motor driven powertrain over the entire lifecycle of the electric motor.

Starting with selecting and purchasing the correct motor, having a general specification for general motor purchases and creating custom specifications for large/critical motor purchases. We then transition into how motors are tracked and maintained while in-operation, including the variety of condition monitoring techniques that can be used. Eventually, even a well-planned, sourced, and maintained electric motor will have an issue of some kind and must go out for repair.

The 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.

There is more than one way to change the speed of your electric AC motor, and some of the most commonly used methods are eddy current drives and variable frequency drives (VFDs).

The Need for Adjusting Speed

Not all electric motor applications need to run at motor's standard speed. An application may need more torque (which requires a reduction in speed) or more additional speed (which in turns means a reduction in torque). A motors' speed really should match what the application needs, and when they do not, there are significant losses in efficiency. When you consider some experts' estimate that 65% of industrial power consumption comes from electric motors, you realize how much of an impact this can have on your overall plant efficiency and energy consumption.

However, if a motor is not a perfect match to the loading needs of the application, the speed and torque can be adjusted through the use of system devices (valves, dampers, etc.). That approach, however, is not ideal and still leads to wasted power and inefficiency -- which is something you normally try to avoid. An alternate, more effective solution is the use of eddy current drives or variable frequency drives (VFDs).

You are responsible for getting as much as possible out of the electric motors in your facility -- and you know that proper lubrication for your electric motors is a big part of that equation. You've heard that there can be issues with too much grease, but how much is too much? And how do you know when grease needs to be added?

The Purpose of Grease

Grease is a semisolid lubricating material comprised of oil suspended in a thickener. Grease does more than just reduce friction in bearings: it helps conduct heat away from the bearing, protects it from contaminants such as dust or moisture, and protects the surface finish by preventing corrosion. The thickener in grease helps it to stay in place and act as a seal for the bearings. Basically, the oil is held within the grease until the motor begins to operate. Once it starts to operate, the oil begins to flow and compress between the various bearing surfaces.

The Results of Too Much Grease

There's an old saying about how you can never have too much of a good thing. Grease is a good thing, but too much grease can result in several issues, starting with an increase in friction -- the very thing that grease is supposed to reduce. This friction leads to elevated temperatures which can cause the oil in the grease to begin to separate from the thickener and lead to premature bearing failure. Overheating will lead to a reduction in the overall effectiveness of the grease. In addition, the presence of too much grease means that the anti-friction bearing elements have to push through this excess grease, making it harder for the bearing to do its job. That means more losses and even less efficiency.

Do you know what equipment you have in your plant? The unfortunate truth is that if you are like many others, you don't!

True story!

Consider these real examples of what a facility told us about how many electric motors were in their plant, versus what they really had:

• Power plant: Told us they had 6,000, Reality: 9,000 (+50%)
• Power plant: Told us they had 5,000, Reality: 11,000 (+120%)
• Paper mill: Told us they had 300, Reality: 800 (+166%)
• Steel mill: Told us they had 15,000, Reality: 27,000 (+80%) and had 3000 spare motors with no matching applications

So, let us ask again ... are you really sure you know what you have on hand in the way of equipment?

Performing an Equipment Survey

Here at HECO, we perform equipment surveys so that you know exactly what you have on hand. We will help you establish your minimum and maximum stock levels based on technical data, not a stock number. You will be able to identify areas of excess or insufficient coverage so you can make sure your critical application needs are met. And the results of our equipment surveys contain much more information than a list of electric motors in a spreadsheet -- these surveys include both the driver of the equipment and the driven equipment.

As part of this asset survey, we will record all nameplate and critical data for all your plant locations along with application information. Each asset is tagged with a unique identifying number to allow it to be tracked throughout the remainder of its life. This information is then entered into the TracRat Repairable Asset Management Software.

Once everything has been entered into TracRat, an Inventory Analysis Report is generated that includes information on in-service to spares comparisons, obsolete inventory, in-service reports sorted by equipment type or application, and custom reports that can be sorted by nameplate data.

Our team can also help you standardize your equipment where possible, as well as reduce your inventory to get rid of obsolete assets. HECO will help you deal with those obsolete assets through scrapping them or selling them through consignment or attrition.

Purpose of Sleeve Bearings

Sleeve bearings go by several different names, including Babbitt bearings, bushings, journal bearings and plain bearings, and are crucial to the correct operation of rotating equipment that they are part of. They can serve multiple purposes at the same time: constrain motion, serve as a guide, provide support, and reduce friction. They work with linear, rotating, and oscillating motion. Sleeve bearings are cylindrical in shape and are straight, as opposed to tapered or conical.

For some reason, you've found yourself in a position where you need to purchase a large electric motor -- as in a motor that is not a standard "NEMA" electric motor. It may be that some new equipment is being installed at your location, you may be in search of a surplus motor, or the time has come to replace one. Regardless of why you need a large electric motor, there are some key things to keep in mind. But first, let's define what we mean by large.

Large Electric Motors

These are not your everyday, on-the-shelf motors that every PT (Power Train) house and motor shop has in stock.

The kind of motors under discussion here are typically built specifically for your application and although some large motors may provide hundreds of horsepower (400+ hp), the kind I'm talking provide thousands of horsepower. These are typically referred to Above-NEMA or A-NEMA motors and they can be far more challenging to purchase than a standard motor.

The Basics of Bidding Out an ANEMA Motor

First, start with the basics which include information such as ...

• Horsepower
• Speed
• Voltage
• Full load amps
• Enclosure
• Frame
• Mounting
• Bearing type
• NEMA design
• KVA code
• and quite a few more!

You also want to include any other information you have about the original motor and its application. This can include frame dimensions, speed vs. torque curves, data packets, and schematics.

There is so much more to the electric motor repair industry than just repairing motors. Some repair professionals go above and beyond the status quo by associating with EASA and seeking accreditation to affirm their commitment to reliability, efficiency, and performance.

What is EASA?

You may have run across the acronym EASA when looking for electric motor dealers or repair services. EASA stands for Electrical Apparatus Service Association. EASA is a formal association that motor repair shops can utilize to remain actively involved in their industry.

EASA is an international trade organization and a recognized leader in sales, repair, and service of electro-mechanical systems (which includes electric motors, generators, pumps, and powertrains). According to EASA, they "[provide] an ongoing flow of industry information and education that helps members worldwide serve as total solution providers for electrical and mechanical equipment and system."

There have been many advances in technology that allow us to gather, analyze, and visualize data. Remote condition monitoring and data communication has evolved over the years to allow massive amounts of information about machinery performance to be transmitted wirelessly and automatically . New developments in artificial intelligence and machine learning have made it possible to even automate the interpretation of data. But where does that leave the human element?