Apples, Oranges, and Above-NEMA (A-NEMA) Large Electric Motors - HECO

Large electric motors, those of 400HP or more, are typically referred to as Above-NEMA or A-NEMA electric motors. When it comes time to purchase one (either new or previously owned), it’s vitally important that when bidding manufacturer to manufacturer, they are all given the same parameters.

There is tremendous value in saying “This is what I want.” Without specifying, “what you want” you will simply get what each manufacturer builds. It’s like the old saying “apples vs. oranges”. If you don’t specify that everybody quote an “apple” and you just say you want a piece of fruit, you might get an apple, an orange, or even a banana!

By specifying exactly what you want, you will have leveled the playing field and stand a much better chance of getting precisely the right motor for the job.

Following are some guidelines to follow when requesting bids for an A-NEMA large electric motor. These might not all pertain to your situation, but make sure the ones that do matter are specified in the bid. 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
• Vibration levels to be within API 541
• Copper-bar type rotor construction
• Sleeve bearings to be split for ease of maintenance
• Opposite drive end bearing housing to be insulated
• Jacking bolts for alignment purposes
• Specific electrical testing
• Hold points at certain steps of the manufacturing process
• Witness testing of certain tests by plant personnel
• Specific reporting of tests done
• A certain warranty

There are also specifications that you can require manufacturers to meet, such as:

• API 541 (Form Wound SCIM’s 350HP+)
• IEEE 429 (Evaluation of Sealed Insulation Systems)
• IEEE 112 (Test Procedures for Induction Motors)
• IEEE 275 (Recommended Practice for Thermal Evaluation)
• IEEE 522 (Surge Comparison Testing)
• NEMA MG1 (Standards for Motors & Generators)
• ANSI C50.41 (Polyphase Induction Motors for Generating Stations)
• CSA C22.2100 (Motors & Generators)

Beyond these “basic parameters” you should consider the individual motor’s situation, application, and history when selecting a replacement or a new build.

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

There are also specifications that you can require manufacturers to meet, such as:

• API 541 (Form Wound SCIM’s 350HP+)
• IEEE 429 (Evaluation of Sealed Insulation Systems)
• IEEE 112 (Test Procedures for Induction Motors)
• IEEE 275 (Recommended Practice for Thermal Evaluation)
• IEEE 522 (Surge Comparison Testing)
• NEMA MG1 (Standards for Motors & Generators)
• ANSI C50.41 (Polyphase Induction Motors for Generating Stations)
• CSA C22.2100 (Motors & Generators)

Beyond these “basic parameters” you should consider the individual motor’s situation, application, and history when selecting a replacement or a new build.

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

• Horsepower – Measurement of the motor’s designed output rating.
• Speed – The revolutions per minute (RPM) of the motor at the nameplate rated voltage and frequency.
• Voltage – The rated voltage at which the motor is designed to operate –changes in voltage directly affect motor performance and reliability.
• Full Load Amps – The amperage that the motor will draw at full load/torque – this is used in selecting motor starter, which if not considered, could cause starting issues.
• Enclosure – The degree of protection the motor has from the environment as well as the method of cooling.
• Frame – In motors 500HP+ there are still some NEMA standard frames, but there are also odd, manufacturer specific frames. This is not always available, and if not, an outline drawing becomes very important.
• Mounting – The method in which the motor is secured/fastened to the base. Typically, rigid foot design or using a flange.
• Frequency – Generally given in Hertz (Hz) – this is the frequency the motor is designed to operate at. Generally, 60Hz in the US & Canada, 50Hz or 60Hz in other countries.
• Service Factor – Multiple of rated horsepower at which the motor can be allowed to operate continuously.
• Ambient Temperature – The maximum temperature of the area around and in which the motor will operate.
• Altitude – Only an issue in higher elevation areas: Air density decreases with increasing elevation – Motors do not cool as efficiently.
• Temperature Rise – The increase in temperature above ambient that a motor is designed for.
• Bearing Type – Two main types: Anti-friction (Ball or Roller Bearings) or Sleeve (Babbit).
• NEMA Design – NEMA defines 4 basic types of speed/torque characteristics for induction motors:
  • Design A: Similar to Design B except higher breakdown torque and starting current
  • Design B: Standard general purpose design for fans, blowers, pumps, etc.
  • Design C: High locked rotor torque for harder to start applications (Conveyors, Compressors)
  • Design D: High breakaway torque (275%+ of full load torque) with high slip. (Stamping, Cranes)
• KVA Code – Locked rotor kVA per horsepower per NEMA MG1 – a letter ranging from A to V – The higher the letter, the higher the inrush current per horsepower.
• Starting Method – Method in which motor is started: across the line (direct online “DOL”), variable frequency drive (VFD), soft starter, etc.
• Accessories – Any non-normal features such as RTD’s (bearing and/or winding), thermocouples, heaters, accelerometers, shaft grounding devices, special seals, proximity probes, filters, etc. You should specify what is required in an RFQ.
• Environment – Consider what environment the motor is exposed to: Indoor or Outdoor? Classified or non-classified area? Subject to saltwater/coastal concerns? Vaport, abrasive airborne particles? High humidity? Does the area the motor resided in get cleaned by sprayed water (washdown)?

Help is available

Many of the previous items, if not factored in when finding a replacement, can cause issues. The best way to determine which items you need to include is to ask someone who deals with such matters on a daily basis.

HECO can help with any questions you may have about electric motor repair. Of course, before we give you any answers, we’ll ask you some questions. Most will begin with “why.” Looking at the motor as part of the entire system, and determining “why” the failure occurred, makes HECO a little different than other electric motor shops. Our customers appreciate the difference. We think you will to.

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