motors.
I hope you find them useful and I would appreciate any comments or thoughts you
might have for future improvements, corrections or topics.
If you should have questions on motors not covered by these papers, please give us a
call and we will do our best to handle them for you.
Thank you for buying Baldor motors.
Sincerely,
Edward Cowern, P.E.
EMS, INC.
65 SOUTH TURNPIKE ROAD
WALLINGFORD, CT 06492
PHONE:
(203) 269-1354
FAX:
(203) 269-5485
E N E R G Y S A V I N G I N D U S T R I A L E L E C T R I C M O T O R S ABOUT THE AUTHOR
Edward H. Cowern, P.E.
Ed Cowern is Baldors District Manager in New England, U.S.A. and has been
since1976. Prior to joining Baldor he was employed by another electric motor
company where he gained experience with diversified electric motors and related
products. His Baldor office and warehouse are located in Wallingford, Connecticut,
near I-91, about 1/2 hour south of Connecticuts capital, Hartford, and about
15 miles north of Long Island Sound.
He is a graduate of the University of Massachusetts where he obtained a BS
degree in Electrical Engineering. He is also a registered Professional Engineer in
the state of Connecticut, a member of the Institute of Electrical and Electronic
Engineer (IEEE), and a member of the Engineering Society of Western
Massachusetts.
Ed is an excellent and well-known technical writer, having been published many
times in technical trade journals such as Machine Design, Design News, Power
Transmission Design and Control Engineering. He has also been quoted in
Fortune Magazine. In addition, he has authored many valuable technical papers
for Baldor, used repeatedly by sales and marketing personnel throughout our
company.
Ed lives in North Haven, Connecticut with his wife, Irene.
EMS, INC.
65 SOUTH TURNPIKE ROAD
WALLINGFORD, CONNECTICUT 06492
PHONE (203) 269-1354 TABLE OF CONTENTS
Motor Basics
Glossary of Frequently Occurring Motor Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1
Types of Motors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5
The Mystery of Motor Frame Size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11
A Primer on Two Speed Motors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15
Motor Temperature Ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17
Metric Motors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
23
Locked Rotor Code Letters and Reduced Voltage Starting Methods . . . . . . . . . . . . . . . . . . .
27
Applications
Understanding Torque . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
31
Fans, Blowers, and Other Funny Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
41
RMS Horsepower Loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
43
Power & Energy
Factors That Determine Industrial Electric Bills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
47
Electric Motors and Power Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
53
Electric Motors and Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
59
Unbalanced Currents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
63
Conserving with Premium Efficiency Motors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
65
Premium Efficiency Motors (Q & A) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
75
Amps, Watts, Power Factor and Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
79
Approximate Load Data from Amperage Readings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
83
Power Factor Correction on Single Induction Motors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
85
Convenient Motor & Energy Formulas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
89
Horsepower Calculations for Speed Changes on Variable Torque Loads . . . . . . . . . . . . . . . .
91
Hazardous Location
How to Select Motors for Hazardous Locations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
93
Explosion Proof Motors in Division II Areas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
99
Miscellaneous
DC Drive Fundamentals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
Handling 50 Hertz Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
Operating Motors in Wet and Damp Environments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
1
GLOSSARY OF FREQUENTLY OCCURRING MOTOR TERMS
AMPS
Full Load Amps
The amount of current the motor can be expected to draw under full load (torque)
conditions is called Full Load Amps. it is also know as nameplate amps.
Locked Rotor Amps
Also known as starting inrush, this is the amount of current the motor can be
expected to draw under starting conditions when full voltage is applied.
Service Factor Amps
This is the amount of current the motor will draw when it is subjected to a percentage
of overload equal to the service factor on the nameplate of the motor. For example,
many motors will have a service factor of 1.15, meaning that the motor can handle a
15% overload. The service factor amperage is the amount of current that the motor
will draw under the service factor load condition.
CODE LETTER
The code letter is an indication of the amount of inrush or locked rotor current that is
required by a motor when it is started. (See Locked Rotor Code Letters for more details.)
DESIGN
The design letter is an indication of the shape of the torque speed curve. Figure 1
shows the typical shape of the most commonly used design letters. They are A, B, C,
and D. Design B is the standard industrial duty motor which has reasonable starting
torque with moderate starting current and good
overall performance for most industrial
applications. Design C is used for hard to start
loads and is specifically designed to have high
starting torque. Design D is the so-called high slip
motor which tends to have very high starting
torque but has high slip RPM at full load torque. In
some respects, this motor can be said to have a
spongy characteristic when loads are changing.
Design D motors are particularly suited for low
speed, punch press applications and hoist and
elevator applications. Generally, the efficiency of
Design D motors at full load is rather poor and
thus they are normally used on those applications
where the torque characteristics are of primary
importance. Design A motors are not commonly
specified but specialized motors used on injection
molding applications have characteristics similar to
Design A. The most important characteristic of
Design A is the high pullout torque.
EFFICIENCY
Efficiency is the percentage of the input power that is actually converted to work
output from the motor shaft. Efficiency is stamped on the nameplate of most
domestically-produced electric motors.
FRAME SIZE
Motors, like suits of clothes, shoes and hats, come in various sizes to match the
requirements of the application. In general, the frame size gets larger with increasing
horsepowers or with decreasing speeds. In order to promote standardization in the
motor industry, NEMA (National Electrical Manufacturers Association) prescribes
standard frame sizes for certain dimensions of standard motors. For example, a motor
with a frame size of 56, will always have a shaft height above the base of 3-1/2
inches. (See The Mystery of Motor Frame Size for more details.) 2
FREQUENCY
This is the frequency for which the motor is designed. The most commonly occurring
frequency in this country is 60 cycles but, on an international basis, other frequencies
such as 40, and 50 cycles can be found.
FULL LOAD
An indication of the approximate speed that the motor will run when it is putting out
SPEED
full rated output torque or horsepower is called full load speed.
HIGH INERTIA
These are loads that have a relatively high flywheel effect. Large fans, blowers, punch
LOAD
presses, centrifuges, commercial washing machines, and other types of similar loads
can be classified as high inertia loads.
INSULATION
The insulation class is a measure of the resistance of the insulating components of a
CLASS
motor to degradation from heat. Four major classifications of insulation are used in
motors. they are, in order of increasing thermal capabilities, A, B, F, and H. (See
Motor Temperature Rating for more details.)
LOAD TYPES
Constant Horsepower
The term constant horsepower is used in certain types of loads where the torque
requirement is reduced as the speed is increased and vice-versa. The constant
horsepower load is usually associated with metal removal applications such as drill
presses, lathes, milling machines, and other similar types of applications.
Constant Torque
Constant torque is a term used to define a load characteristic where the amount of
torque required to drive the machine is constant regardless of the speed at wh