Response to Forum: Motor Decisions Matter

March 14, 2001
/ Print / Reprints /
ShareMore
/ Text Size+
LEXINGTON, TN — At the recent ASHRAE 2001 Winter Meeting, a forum focusing on the utilization of high-efficiency electric motors and their potential impact on overall system characteristics was conducted. Participants explored the suggestion that higher transformer losses might well offset the energy savings of the motor, primarily due to lower system power factors. As is most often the case, there is no substitute for an informed buying decision, and that applies to electric motors as well.

High efficiency in an electric motor does not necessarily equate to low power factor. It is true, however, that the use of lower loss electrical-grade steels, larger operating air gaps, and the tendency toward as much locked rotor (inrush) current as possible do dominate motor design decisions at the potential sacrifice of power factor. The designer can compensate for these tendencies through the use of more active material in the motor, achieving power factors at or near Pre-EPAct 92 levels.



Understand The Application

Any motor-buying decision, replacement or new, must be based upon an understanding of the application and what attributes the high-efficiency motor has. A replacement motor with the same rating and footprint as the original is not necessarily identical to it.

Some general-purpose high-efficiency motors are marketed as National Electrical Manufacturers Association (NEMA) Design A in lieu of the more traditional NEMA Design B. Design A motors are permitted to have higher locked rotor currents than Design B motors — sometimes as much as 30% more. The locked rotor code letter on the motor nameplate or the locked rotor current information on the motor data sheet will provide this information. Motors with the same locked rotor code letter will have locked rotor (inrush) currents within 10% of each other.

Likewise, motors with the same design letter have important similarities in output performance characteristics potentially critical to existing applications.

Electric motors most often operate at a load less than the rating on the motor nameplate. An electric motor operating at partial load will have a power factor generally lower than that indicated by the full-load power factor shown on the motor nameplate.

For instance, a 20-hp motor operating at 15 hp will likely have a lower power factor than a 15-hp motor operating at full load. The 20-hp motor will draw 33% more locked rotor current at starting and thereby potentially require a larger starter. The 20-hp motor will cost more as well. Therefore, selecting the correct motor for the load requirement most often dominates system costs and energy consumption considerations.

Parkinson is section manager, Integral Horsepower Motor Engineering, A.O. Smith Electrical Products Co., Lexington, TN. He can be reached at info@aosmith.com (e-mail).

Publication date: 03/19/2001

Did you enjoy this article? Click here to subscribe to The NEWS Magazine

You must login or register in order to post a comment.

Multimedia

Videos

Image Galleries

2014 MCAA Annual Convention

Scenes from the 2014 MCAA Annual Convention in Scottsdale, Ariz.

Podcasts

NEWSmakers: Julian Scadden

Training is an ongoing process. Julian will discuss how you can generate maximum return on time and energy invested training by following a three part process. Listen to this podcast to get expert tips on training, tracking and follow up. 

More Podcasts

THE MAGAZINE

ACHRNEWS

NEWS 04-14-14 cover

2014 April 14

Check out the weekly edition of The NEWS today!

Table Of Contents Subscribe

SERVICE CALLS POLL

Which statement on service calls best applies to your business?
View Results Poll Archive

HVACR INDUSTRY STORE

plumbing-hvac.gif
2014 National Plumbing & HVAC Estimator

Every plumbing and HVAC estimator can use the cost estimates in this practical manual!

More Products

Clear Seas Research

 

Clear Seas ResearchWith access to over one million professionals and more than 60 industry-specific publications, Clear Seas Research offers relevant insights from those who know your industry best. Let us customize a market research solution that exceeds your marketing goals.

DON'T MISS A THING

Magazine image
 
Register today for complete access to ACHRNews.com. Get full access to the latest features, Extra Edition, and more.

STAY CONNECTED

facebook icontwitter iconyoutube iconLinkedIn i con