NEMA Motor Standards Provide Foundation for Industry

NEMA Motor Standards Provide Foundation for Industry

This piece was originally published in the June 2016 issue of ei, the magazine of the electroindustry.

John Malinowski, Senior Manager of Industry Affairs, Baldor Electric Company, a Member of the ABB Group

At one time, there was no industry standard for integral horsepower severe-duty AC induction motors. Each manufacturer had a product line with features that it believed enhanced performance and reliability in a particular process industry. Thus, feature sets varied from manufacturer to manufacturer.

Manufacturers in these industries often developed their own specifications for motors they wanted in their facilities. Sometimes the specifications and the severe-duty motors matched, but usually there were features missing. In most cases, orders required building a customized motor. This made it difficult to purchase a compliant motor from stock inventory whenever there was an outage.

Within the IEEE Petroleum and Chemical Industry Committee, a working group (WG) was formed to help resolve this dilemma. IEEE 841 Standard for Petroleum and Chemical Industry—Severe-Duty, Totally Enclosed Fan-Cooled (TEFC) Squirrel Cage Induction Motors—Up to and including 370 kW (500 hp) was first developed as a recommended practice in 1986; it became a standard in 1994.

Over the years, the standard has been updated, adopting tables from NEMA MG 1 Motors and Generators as the U.S. Department of Energy established minimum efficiency levels for motors. IEEE 841 always seems to be ahead of government regulations, because process industries understand the life cost of motors.

Usual and unusual service conditions have been adjusted over the years and have NEMA references. IEEE 841 motors are rated for Division 2/Zone 2 use as a normal condition. As more motors were used with adjustable speed drives, manufacturers began to rate the motors for allowable speed range in variable and constant torque use. The IEEE Guide for the Application of Electric Motors in Class I, Division 2 and Class I, Zone 2 Hazardous (Classified) Locations was developed for use in the petrochemical industry by many professionals who also served in the IEEE 841 WG.

The insulation system definition comes from NEMA MG 1, along with some additional IEEE standards. Motor frame designations also are from MG 1, and NEMA vibration and noise standards are referenced.

Once the standard was developed, multiple manufacturers built motors to comply with it and inventoried motors, usually in the 1–250 horsepower range with 2, 4, and 6 pole speeds in 460- and 575-volt designs. Most not only offered rigid base mounted motors but were also designed with a C-face with and without the base. Additional variants for API 661 vertical heat exchangers are available from some manufacturers.

A working group of users, consultants, academics, manufacturers, and others is updating IEEE Standard 841-2009. It evolved from its petrochemical roots to be adopted by most IEEE process industry committees, including Portland cement, metals, mining, petroleum and chemical refining, and pulp, paper, and forest products. Automobile manufacturers, brewers, and others appreciate the robust motor provided when made to comply with the 841 standard.

Embedded in this IEEE standard are many elements of NEMA MG 1-2014, NEMA MG 10-2013 Energy Management Guide for Selection and Use of Polyphase Motors, and NEMA Application Guide for AC Adjustable Speed Drive Systems.

IEEE Standard 841-2009 primarily covers low-voltage motors to 600 volts but also allows medium-voltage motors with anti-friction bearings. Just as IEEE 841 defines 1–500-horsepower motors, other American Petroleum Institute (API) standards define larger induction motors (API 547), critical service motors (API 541), and synchronous motors (API 546). These API standards also rely on certain aspects of NEMA MG 1 in their definitions.

NEMA standards are prevalent in all of these motor standards. Moving forward in response to user requests, there will be a version of IEEE 841 developed to define a similar motor standard for IEC metric motors in the 0.75–370 kW range. The IEC 60034 series of standards is expected to support that version rather than NEMA standards.

NEMA and CEMEP (European Committee of Manufacturers of Electrical Machines and Power Electronics) often collaborate on such projects. Like NEMA, CEMEP represents motors and drives.

Mr. Malinowski is immediate past chairman of the NEMA Motor and Generator Section.

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