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What A-NEMA Large Electric Motor is Best for You?

02/18/2016

 YOU NEED A MOTOR. NOW WHAT?

large electric motor

Maybe you need a new NEMA standard electric motor. Maybe you need a previously owned one. In either case, there are some important questions to ask before placing the order. If you make the wrong call, it can cost you — big time.

The following will give you some tips to help make sure you don’t make that costly mistake.

OK, you need another motor – why?

This is the most important question of all. Exactly why do you need one?  Was there a failure with a current motor? Has this exact same failure or one very similar occurred before?  If so, maybe the motor was not the best available motor for the application. Here are some things to ask yourself in that regard:

  • Did the motor have the wrong enclosure?
  • Did the motor have the wrong horsepower?
  • Is the motor on a VFD?
  • What else? There are a variety of items that can be mishandled or misapplied. Go over them all to get a handle on the situation when the motor went down.

If you don’t figure out why it happened – how on earth can you prevent it from happening again?

You’ve decided on a motor. Sure it's the right one?

Before that piece of equipment arrives on your doorstep, it’s good to do some double-checking. Who is supplying the motor? To what spec? How has the motor been sized? How have you decided what features are required? Which manufacturer makes that motor? Is it is one-off motor or a stocked catalog motor?

These aren’t easy questions to answer. It all depends on your situation, your plant floor, your industry, your company.

So… where to start?

DO YOU NEED A LARGE ELECTRIC MOTORs (400HP+)?

For ease of discussion, these motors are typically referred to Above-NEMA or A-NEMA motors. Typically, the approach that makes the most sense is to have some basic parameters that must be met by every A-NEMA motor you purchase. For instance, do you require:

  • Any fans/baffle arrangements to be non-sparking
  • Screens/filters to be re-useable and washable
  • L-10 bearing life (100,000 hours)
  • High permeability M19 silicon steel and C-5 insulation for laminations
  • Core-loss test with thermal images with a temperature difference not greater than 5C.
  • Class F insulation system or better

Of course, there are many other parameters that should also be taken into account.

There are also specifications that you can require manufacturers to meet. Here are but a few:

  • API 541 (Form Wound SCIM’s 350HP+)
  • IEEE 429 (Evaluation of Sealed Insulation Systems)
  • NEMA MG1 (Standards for Motors & Generators)
  • ANSI C50.41 (Polyphase Induction Motors for Generating Stations)
  • CSA C22.2100 (Motors & Generators)

However many you choose, you will have leveled the playing field when you bid manufacturer to manufacturer. Just make sure the parameters that matter the most to you are specified! Beyond these “basic parameters” you should consider the individual motor’s situation, application, and history when selecting a replacement or a new build.

First, be sure that the following nameplate listed and application requirement items are recorded and specified in your request for quote:

    • Horsepower
    • Speed
    • Voltage
    • Full Load Amps
    • Enclosure
    • Frame
    • Mounting
    • Frequency.
    • Service Factor
    • Ambient Temperature
    • Altitude
    • Temperature Rise
    • Bearing Type
  • NEMA Design
  • KVA Code
  • Starting Method
  • Accessories
  • Environment

WHY SPEC PARAMETERS ARE IMPORTANT

One parameter that is not discussed very often is the KVA Code. This is the inrush current that the motor will draw when it is first started, assuming across-the-line start. Many times, KVA Code is not even considered in replacing a motor, but if you don’t, there is a chance the motor will not be able to start.

A common misperception

One common misperception is that if you start the motor under no load, the inrush current will be less. This is incorrect. Without a load, the motor will see the same inrush current as what it does with the load. The only difference is that the motor will draw the inrush current for a longer period of time, due to the load.

Between this common misperception and a misunderstanding of what the KVA code actually is. You could buy a motor that will do everything your application demands, but due to not factoring in one small factor, the motor may not work.

There is still more information that should be reviewed and provided to manufacturers, even after you have specified everything already discussed:

  • Drawings: Any drawings that you have can provide tremendous value — especially an outline drawing of the original motor.
  • Drawing of Connection box locations – a drawing of your connection box locations can help ensure you do not have to do re-wiring when trying to install your replacement.
  • Speed v/s Torque Curve: Providing a speed versus torque curve (that also shows Inertia WK2) for the load/ allows for double checking if the motor will be able to start the load.

IS A NEW MOTOR REALLY YOUR BEST OPTION?

Motor manufacturers sell on the fact that motors are getting smaller and smaller. Is this better for you? The simple fact is that motors were designed to last 25 to 35 years in the past, and were over-designed for what they were required to do. Modern-day, smaller, more efficient motors are designed to last 15-20 years. They are engineered with little to no leeway on what they are required to do.

The question: is it possible that you could purchase an older motor and have it re-manufactured in order to get that 25-35 years of life versus the 15-20 years out of a modern day motor? It may be possible, but it depends on the availability of an older motor, and the capability of a repair center to re-manufacture or re-engineer it for use in your application…. But it IS possible.

WHAT IF YOU DON’T HAVE ALL THE INFO AND NEED TO REPLACE A MOTOR?

There are other options that can be considered, but each path forward will be unique to what information is missing and/or available. For example, if you do not have an outline drawing of the original motor but would like to have a drop in-replacement, measurements can be taken onsite. These options exist dependent upon the missing information – but there are still options available so that you are not stuck without a replacement.

Help is available

HECO can help you with any questions you may have about whether you should get a new or used motor, and which manufacturer offers the motor best suited to your needs. We’ll begin by asking “Why?”  Why do you need a motor? How will it be used? Where? Is it a replacement or an addition? What about spares?

Then we’ll use our problem solving and engineering expertise to keep your plant up and running. To learn more about what our “All Systems Go” approach can mean to you, please contact:

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About the author:

Justin Hatfield is Vice President of Operations of HECO, Inc. He is responsible for Electric Motor & Drive Sales, Electric Motor & Generator Repairs, and Predictive Services. Justin was instrumental in developing HECO MAPPS (Motor And Powertrain Performance Systems) which focuses on “why” you have a motor problem instead of simply “What” product or service should be recommended.

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