Selecting Torque for Top Motor Efficiency - (EC&M) Magazine
description
Transcript of Selecting Torque for Top Motor Efficiency - (EC&M) Magazine
![Page 1: Selecting Torque for Top Motor Efficiency - (EC&M) Magazine](https://reader035.fdocuments.in/reader035/viewer/2022081006/563dbad1550346aa9aa84aba/html5/thumbnails/1.jpg)
Forum Subscribe About Us Magazine Issues Newsletters Advertise Shop
Jan 1, 1999
Tweet COMMENTS 0
Selecting Torque for Top Motor EfficiencyRobert J. Lawrie | Electrical Construction and Maintenance
Sure, horsepower is an important motor parameter. However, torque is just as important. That said, what
exactly is torque? It really depends on your point of view. If you're the motor, your shaft exerts the torque's
turning effort. As such, we call it motor torque. We commonly measure it in pounds-feet (lb-ft.). If you're
the load, torque is the turning effort you require at your input shaft for your
Sure, horsepower is an important motor parameter.
However, torque is just as important. That said, what
exactly is torque? It really depends on your point of view.
If you're the motor, your shaft exerts the torque's turning
effort. As such, we call it motor torque. We commonly
measure it in pounds-feet (lb-ft.). If you're the load, torque
is the turning effort you require at your input shaft for your
proper operation. In this context, we call it load torque, also measured in lb-ft. Basically,
you should consider torque both as it pertains to the demands of the load you want to
drive, and as it applies to the capabilities of the driving motor.
Regardless of your point of view, selecting the best and most efficient motor for the job
(based on first-cost and operating costs) depends directly on its torque. Remember, a
motor's operating efficiency falls off rapidly at lower values of torque loading.
Motor ratings and nameplates are standardized in terms of horsepower and speed,
with no mention of torque. However, you can relate horsepower and torque with the
following equation: Horsepower = Torque (lb-ft) x rpm/5250
Cost differentials.
Up-front cost. It's the design torque rating of the motor that most directly affects its
material cost. For example, a 10-hp, 1200-rpm motor costs more than a 10-hp, 1800-
rpm motor, because the former's rated torque is nearly 50% greater. Likewise, a 10-hp,
900-rpm motor costs even more, because its rated torque is almost 100% greater than
that of an 1800-rpm motor.
This also helps explain why you don't see motors with synchronous speeds lower than
900 rpm very often; it's usually more economical to use an 1800-rpm motor instead, and
add any necessary gearing or pulleys to obtain the desired speed.
Operating cost. The operating cost of a motor depends on its efficiency at a given
condition of loading. This applies to existing standard induction motors as well as energy-
efficient (EE) motors.
Hot Topics Comments New Topics
Tip of the Week: Don’t Blow it on the
Measurement Front
Tip of the Week: The Practical Safeguarding of
Persons and Property
Electrical Troubleshooting Quiz - June 23,
2015
Curing Customer Confusion, Part 2
Tip of the Week: Play it Safe with a Divide and
Conquer Strategy
Jo in the Discussion on EC&M Talk
New 3,000 Amp Service 1
la st r eply by Pa u l A bern a t h y in Power
Dist ribu t ion
T12 Electronic Ballast Resetting Problem 3
la st r eply by T odd H. in Gen era l Elect rica l
T a lk Discu ssion
LED Office Lighting 6
la st r eply by Nilsson 121 in Ligh t in g &
Ligh t in g Con t rols
HOME > CONTENT > SELECTING TORQUE FOR TOP MOTOR EFFICIENCY
SHARE 0Recommend
Photo Galleries
7 Things You Probably
Didn’t Know About
Solar Power 1
Think you're up to date on
solar pow er? You might
be surprised to learn
these seven facts.
EC&M White Papers
Know Your TCO: A
Look at Medium
NEC Design Ops & Maintenance Contractor Safety Power Quality T raining Basics
Products
Electrical Construction & Maintenance (EC&M)
REGISTER LOG IN
![Page 2: Selecting Torque for Top Motor Efficiency - (EC&M) Magazine](https://reader035.fdocuments.in/reader035/viewer/2022081006/563dbad1550346aa9aa84aba/html5/thumbnails/2.jpg)
Tweet
For competitive manufacturing-cost reasons, manufacturers generally design motors to
have peak efficiency at or near the full-load nameplate rating. You can see this in the
accompanying diagram, on page 44. Notice how rapidly efficiency deteriorates below the
approximate 50% level of nameplate load. The reason for this decline is: About one-third
of the losses in a typical motor will vary with load torque, while the remaining losses are
essentially constant.
Because of these fixed losses, a large cost penalty occurs if you operate a motor at low
values of loading.
Selection guidelines. From the foregoing cost factors, you should focus on two
important selection and application guidelines:
In some manufacturing plants, preexisting conditions may exist, which may prevent you
from applying these rules. In any case, you must be aware of the cost penalties involved if
you cannot "load-match," size appropriately, or operate the motor you select according to
guidelines.
You can use many different techniques to comply with these two guidelines. It's
important you research the numerous considerations applying to proper motor selection
and operation. We'll cover these in the March issue. Future Motor Facts articles will
discuss how steady-state, acceleration, and starting torque reduce motor operating costs.
Please Log In or Register to post comments.
Related Articles
Matching Motor Torque To Your Load
Guidelines for motor application designs.
Choosing a Motor for Efficient Operation
Effectively applying premium efficiency motors.
Understanding modern motors and controllers.
JUL 2 1 , 2 01 5
JUL 1 4 , 2 01 5
EC&M Webinars
SPONSORED
Mitigation Methods for
Arc Flash Hazards -
Enhancing Personal
Safety
SPONSORED
Understanding the
2015 Edition of NFPA
70E and the Arc Flash
Hazard
VIEW MORE WEBINARS
EC&M Learning Center
Understanding the 2014 NEC,
Volume 1 (Articles 90 to 480)
This resource has proven itself in the
field and in the exam room. This latest
edition w ill provide you w ith a rock-solid
foundation...
Understanding NEC Requirements for Grounding
vs Bonding
One of the most confusing areas of the trade continues
Buy only as much motor as you need: Avoid oversizing.
Minimize prolonged operation at light-load conditions.
SHARE 0Recommend
VIEW MORE WHITE PAPERS
Voltage VFDs
Learn about the intricacies
involved in calculating TCO
and the elements that
affect it....
More
EC&M TV
BROWSE ALL VIDEOS
New Certification
Announcement from
NFPA
...
More
![Page 3: Selecting Torque for Top Motor Efficiency - (EC&M) Magazine](https://reader035.fdocuments.in/reader035/viewer/2022081006/563dbad1550346aa9aa84aba/html5/thumbnails/3.jpg)
Site Features
Author Guidelines
RSS
Sitem ap
EC&M Corporate
Privacy Policy
T erm s of Service
About Us
Search ecmweb.com
Subscribe to the print magazine
Ecmweb.com
NEC Design Ops & Maintenance Contractor Safety Power Quality T raining Basics Products
to be grounding and bonding, w hich is
w hy this book needs to be in the
hands...
Changes to The NEC 2014
Don't let the scale of the code changes
intimidate you, this book w ill get you up
to speed on the most essential...
BROWSE ALL TITLES
COUNTRY*
E-MAIL*
Sign-up to receive our free newsletters
eTrain - (Bi-Weekly) View Sample
Product NewsWire - (Monthly) View
Sample
ElectricalZone - (Weekly) View Sample
MRO Insider - (Bi-Weekly) View Sample
PQ NewsBeat - (Bi-Weekly) View
Sample
Illumination Insider - (Bi-Weekly) View
Sample
CodeWatch - (Bi-Weekly) View Sample
G-Biz - (Varies) View Sample
Electrical Testing - (Monthly) View
Sample
United States
Enter your email above to receive messages about
offerings by Penton, its brands, aff iliates and/or third-
party partners, consistent w ith Penton’s Privacy Policy.
Connect With Us
![Page 4: Selecting Torque for Top Motor Efficiency - (EC&M) Magazine](https://reader035.fdocuments.in/reader035/viewer/2022081006/563dbad1550346aa9aa84aba/html5/thumbnails/4.jpg)
Site Archive
Subscribe
View Mobile Site
Advertise
Contact Us
Follow Us
Electrical Wholesaling Electrical Marketing T ransm ission & Distribution World
Copy right © 201 5 Penton
Related EC&M Sites