Motor Theory

Motor Theory
Application Manual for NEMA Motors
Section 2
Motor Theory
Part 1
Part 2
Part 3
Part 4
Page
Motor Basics
Basic Theory
1
Construction
10
Magnetism
15
Electromagnetism
17
Rotating Magnetic Field
23
Rotor Rotation
29
Motor Specifications
33
NEMA Motor Characteristics
37
De-rating Factors
44
AC Motors and AC Drives
46
AC Motors and Load
51
Enclosures
55
Mounting
59
Noise Theory
Introduction
65
Definitions and Terminology
65
Testing
76
Walsh-Healey Act
76
NEMA Noise Levels
77
Low Noise Machines
77
Customer Specification
78
Power Supply Variations
General Power Supply Variations
79
From Rated Value - Balanced Phase Voltages
84
Motor Terminology
ABCDEFGHIJLMNOPRSTUVW
87
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Motor Basics
Section
2
Part
1
Section Page 12of 115
Part
104/08
Page
1 / 64
Date
09/07
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
2
Part
1
Section Page 22of 115
Part
104/08
Page
2 / 64
Date
09/07
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
2
Part
1
Section Page 32of 115
Part
104/08
Page
3 / 64
Date
09/07
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
2
Part
1
Section Page 42of 115
Part
104/08
Page
4 / 64
Date
09/07
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
2
Part
1
Section Page 52of 115
Part
104/08
Page
5 / 64
Date
09/07
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
2
Part
1
Section Page 62of 115
Part
104/08
Page
6 / 64
Date
09/07
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
2
Part
1
Section Page 72of 115
Part
104/08
Page
7 / 64
Date
09/07
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
2
Part
1
Section Page 82of 115
Part
104/08
Page
8 / 64
Date
09/07
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
2
Part
1
Section Page 92of 115
Part
104/08
Page
9 / 64
Date
09/07
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
2
Part
1
SectionPage 102of 115
Part
104/08
Page
10 / 64
Date
09/07
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
2
Part
1
SectionPage 112of 115
Part
104/08
Page
11 / 64
Date
09/07
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
2
Part
1
SectionPage 122of 115
Part
104/08
Page
12 / 64
Date
09/07
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
2
Part
1
SectionPage 132of 115
Part
104/08
Page
13 / 64
Date
09/07
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
2
Part
1
SectionPage 142of 115
Part
104/08
Page
14 / 64
Date
09/07
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
2
Part
1
SectionPage 152of 115
Part
104/08
Page
15 / 64
Date
09/07
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
2
Part
1
SectionPage 162of 115
Part
104/08
Page
16 / 64
Date
09/07
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
2
Part
1
SectionPage 172of 115
Part
104/08
Page
17 / 64
Date
09/07
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
2
Part
1
SectionPage 182of 115
Part
104/08
Page
18 / 64
Date
09/07
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
2
Part
1
SectionPage 192of 115
Part
104/08
Page
19 / 64
Date
09/07
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
2
Part
1
SectionPage 202of 115
Part
104/08
Page
20 / 64
Date
09/07
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
2
Part
1
SectionPage 212of 115
Part
104/08
Page
21 / 64
Date
09/07
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
2
Part
1
SectionPage 222of 115
Part
104/08
Page
22 / 64
Date
09/07
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
2
Part
1
SectionPage 232of 115
Part
104/08
Page
23 / 64
Date
09/07
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
2
Part
1
SectionPage 242of 115
Part
104/08
Page
24 / 64
Date
09/07
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
2
Part
1
SectionPage 252of 115
Part
104/08
Page
25 / 64
Date
09/07
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
2
Part
1
SectionPage 262of 115
Part
104/08
Page
26 / 64
Date
09/07
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
2
Part
1
SectionPage 272of 115
Part
104/08
Page
27 / 64
Date
09/07
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
2
Part
1
SectionPage 282of 115
Part
104/08
Page
28 / 64
Date
09/07
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
2
Part
1
SectionPage 292of 115
Part
104/08
Page
29 / 64
Date
09/07
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
2
Part
1
SectionPage 302of 115
Part
104/08
Page
30 / 64
Date
09/07
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
2
Part
1
SectionPage 312of 115
Part
104/08
Page
31 / 64
Date
09/07
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
2
Part
1
SectionPage 322of 115
Part
104/08
Page
32 / 64
Date
09/07
Application Manual for NEMA Motors
Section
2
Part
1
SectionPage 332of 115
Part
104/08
Page
33 / 64
Date
09/07
Application Manual for NEMA Motors
Nameplate
The nameplate of a motor provides important information necessary
for selection and application. Below is the nameplate of a sample 15
horsepower AC motor. Specifications are given for the load and
operating conditions as well as motor protection and efficiency.
Voltage and Amps
AC motors are designed to operated at standard voltages and
Frequencies. This motor is designed for use on 230 VAC 60Hz and
200VAC 50Hz. Full load current for this motor is 38 amps (60Hz)
and 44 amps (50Hz).
Application Manual for NEMA Motors
Section
2
Part
1
SectionPage 342of 115
Part
104/08
Page
34 / 64
Date
09/07
Application Manual for NEMA Motors
RPM
Base speed is the nameplate speed, given in RPM, where the motor
develops rated horsepower at rated voltage and frequency. It is an
Indication of how fast the output shaft will turn the connected
equipment when fully loaded with proper voltage and frequency
applied.
The base speed of this motor is 1780 RPM (60Hz) and 1475 RPM
(50Hz). It is known that the synchronous speed of a 4-pole motor is
1800 RPM. When fully loaded there will be 1.1% slip. If the
connected equipment is operating at less than full load, the output
speed (RPM) will be slightly higher than nameplate.
% Slip = (1800-1780) x 100% / 1800
% Slip = 1.1
Service Factor
A motor designed to operate at its nameplate horsepower rating
has a service factor of 1.0. This means the motor can operate at
100% of its rated horsepower. Some applications may require a
motor to exceed the rated horsepower. In these cases a motor with
a service factor of 1.15 can be specified. The service factor is a
multiplier that may be applied to the rated power. A 1.15 service
factor motor can be operated 15% higher than the motor’s nameplate
horsepower. The 15 HP motor with a 1.15 service factor, for
example, can be operated at 22.5 HP. It should be noted that any
motor operating continuously at a service factor greater than 1 will
have a reduced life expectancy compared to operating it at its rated
horsepower. In addition, performance characteristics, such as full
load RPM and full load current, will be affected.
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
2
Part
1
SectionPage 352of 115
Part
104/08
Page
35 / 64
Date
09/07
Application Manual for NEMA Motors
Section
2
Part
1
SectionPage 362of 115
Part
104/08
Page
36 / 64
Date
09/07
Application Manual for NEMA Motors
Efficiency
AC motor efficiency is expressed as a percentage. It is an
indication of how much input electrical energy is converted to
output mechanical energy. The nominal efficiency of this motor is
93.0%. The higher the percentage the more efficiently the motor
converts the incoming electrical power to mechanical horsepower.
A 15 HP motor with 93.0% efficiency would consume less energy
than a 15 HP motor with an efficiency rating of 83%. This can
mean a significant savings in energy cost. Lower operating
temperature, longer life, and lower noise levels are typical benefits
of high efficiency motors.
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
2
Part
1
SectionPage 372of 115
Part
104/08
Page
37 / 64
Date
09/07
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
2
Part
1
SectionPage 382of 115
Part
104/08
Page
38 / 64
Date
09/07
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
2
Part
1
SectionPage 392of 115
Part
104/08
Page
39 / 64
Date
09/07
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
2
Part
1
SectionPage 402of 115
Part
104/08
Page
40 / 64
Date
09/07
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
2
Part
1
SectionPage 412of 115
Part
104/08
Page
41 / 64
Date
09/07
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
2
Part
1
SectionPage 422of 115
Part
104/08
Page
42 / 64
Date
09/07
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
2
Part
1
SectionPage 432of 115
Part
104/08
Page
43 / 64
Date
09/07
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
2
Part
1
SectionPage 442of 115
Part
104/08
Page
44 / 64
Date
09/07
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
2
Part
1
SectionPage 452of 115
Part
104/08
Page
45 / 64
Date
09/07
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
2
Part
1
SectionPage 462of 115
Part
104/08
Page
46 / 64
Date
09/07
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
2
Part
1
SectionPage 472of 115
Part
104/08
Page
47 / 64
Date
09/07
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
2
Part
1
SectionPage 482of 115
Part
104/08
Page
48 / 64
Date
09/07
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
2
Part
1
SectionPage 492of 115
Part
104/08
Page
49 / 64
Date
09/07
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
2
Part
1
SectionPage 502of 115
Part
104/08
Page
50 / 64
Date
09/07
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
2
Part
1
SectionPage 512of 115
Part
104/08
Page
51 / 64
Date
09/07
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
2
Part
1
SectionPage 522of 115
Part
104/08
Page
52 / 64
Date
09/07
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
2
Part
1
SectionPage 532of 115
Part
104/08
Page
53 / 64
Date
09/07
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
2
Part
1
SectionPage 542of 115
Part
104/08
Page
54 / 64
Date
09/07
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
2
Part
1
SectionPage 552of 115
Part
104/08
Page
55 / 64
Date
09/07
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
2
Part
1
SectionPage 562of 115
Part
104/08
Page
56 / 64
Date
09/07
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
2
Part
1
SectionPage 572of 115
Part
104/08
Page
57 / 64
Date
09/07
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
2
Part
1
SectionPage 582of 115
Part
104/08
Page
58 / 64
Date
09/07
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
2
Part
1
SectionPage 592of 115
Part
104/08
Page
59 / 64
Date
09/07
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
2
Part
1
SectionPage 602of 115
Part
104/08
Page
60 / 64
Date
09/07
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
2
Part
1
SectionPage 612of 115
Part
104/08
Page
61 / 64
Date
09/07
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
2
Part
1
SectionPage 622of 115
Part
104/08
Page
62 / 64
Date
09/07
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
2
Part
1
SectionPage 632of 115
Part
104/08
Page
63 / 64
Date
09/07
Application Manual for NEMA Motors
Section
2
Part
1
SectionPage 642of 115
Part
104/08
Page
64 / 64
Date
09/07
Application Manual for NEMA Motors
P-base
The bolts go thru the holes in the flange of a P-base motor and into
threaded mating holes of the equipment (usually a pump).
s
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
Section 2 2
Part
2
Part
2
Page 65 of 115
Page
1
04/08
Date
09/07
Noise Theory
Noise Theoryeral Power Supply VariationsNoise Theory
Introduction
This section is intended to describe the information, data and terms used when discussing
or measuring noise produced by rotating electrical machines. Among reasons for making a
noise analysis are: checking for compliance with a specification, code, ordinance or
acoustical criterion, as in user acceptance testing; or to obtain information on exposure of
personnel or equipment to noise, as in a sound survey. Noise analysis supplies data
necessary to rate the machine according to its acoustic power output, establish sound
control measures or predict sound pressure levels produced by the machine in a given
enclosure or environment.
Also included is an IEEE paper titled "Noise in Induction Motors - Causes and Treatment."
It is included to explain the possible causes of noise in an induction motor, and how they
can be predicted and reduced.
In addition, an IEEE paper titled "Specifying And Measuring The Noise Level Of Electric
Motors In Operation" is included to explain the new testing procedure using the sound
intensity method.
Definitions And Terminology
Noise (Sound)
Sound is a physical disturbance that results in a sensation in the ear of the listener. It is
usually the result of a mechanical vibration transferred to the air and then airborne to the
ear of the listener.
If it is pleasing and acceptable to the ear of the listener it is called "SOUND". If it is
unpleasant and unwanted by the listener it is called "NOISE". Sound emanating from a
recording can be "music" to a teenager while it is considered "noise" by his parents. Thus,
individual judgment and difference between hearing sensitivity in individuals play a large
part in the difference between sound and noise.
Cause of Sound
A particle moving back and forth in a specific pattern is said to be vibrating. The sequence
of repeated movement is called periodic motion. Each unique sequence of motions is a
cycle, and the time required to move through one cycle is called the period. The
FREQUENCY of the periodic motion is the number of cycles that occur per unit of time.
This is usually measured in cycles per second or hertz.
s
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
Section 2 2
Part
2
Part
2
Page 66 of 115
Page
2
04/08
Date
09/07
Noise Theory
This vibrating motion causes the air particles near it to undergo vibration. This produces a
variation in the normal atmospheric pressure. As the disturbance spreads, if it reaches the
eardrum of a listener it will initiate vibration motion of the eardrum and the listener will
experience the sensation of sound.
Sound travels in a waveform at a constant speed of 1127 ft./second in air. This speed is not
affected by the frequency. However, the particle velocity or the rate at which a given
particle of air moves about when a sound wave passes is proportional to the frequency.
Therefore, the frequency of the sound must be investigated when determining the effect of
sound on the human ear.
Sound Pressure
When a sound wave is initiated it produces a fluctuation in the atmospheric pressure. This
fluctuation in air pressure around the normal atmospheric pressure is called SOUND
PRESSURE.
Normal atmospheric pressure is approximately 1 million dynes per cm2. By definition 1
dyne per cm2 is equal to 1 microbar or to .10 Pascals. Therefore, atmospheric pressure is
approximately 1 million microbars or 105 Pascals. This is equal to 14.7 pounds per square
inch, which is the more common term we are used to seeing.
Microphones used in noise measurement are sensitive to sound pressure; hence sound
pressure has enjoyed more popularity in the acoustical field.
Level
In acoustics, a level is the logarithm of the ratio of a quantity to a reference quantity of the
same kind. The base of the logarithm, reference quantity and kind of level must be
specified.
s
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
Section 2 2
Part
2
Part
2
Page 67 of 115
Page
3
04/08
Date
09/07
Noise Theory
Decibel and Sound Pressure Level
Sound pressure produced by different sources can vary over a wide range. Sound sources
can cause pressure fluctuations as low as .0002 or as high as 200 microbars. This
represents a range of 200/.0002 or a million to one. Because of this extensive range it is
more convenient to use logarithmic rather than linear scales in the acoustic field. Thus,
values are expressed in SOUND PRESSURE LEVEL (Lp) rather than in sound pressure.
The unit used to express this Lp is called DECIBEL (dB). It is a dimensionless unit that
expresses logarithmically the ratio of the quantity under consideration (in this case sound
pressure) to a reference value of the same dimensions as the quantity. 0.0002 microbars
was chosen as the reference level because it is the minimum sound pressure discernible
by a sensitive human ear at 1000 Hertz.
By definition;
Lp = 20 log10
P
dB P
Where;
P = sound pressure in microbars produced by sound source
Po = reference pressure in microbars taken as .002 microbars
which is equal to .002 dynes/cm2 or 20x10-6 Pascals
Sound Power
Microphones used in recording sound are sensitive to sound pressure. The values
recorded express the sound level of the area surrounding the equipment. However, they do
not adequately express the energy produced by the generating source. The recorded
sound levels are affected by the direction of the sound, the distance between the sound
and the microphone and the acoustical properties of the room in which the measurement is
taken. They will vary from a maximum in a reverberant room to a minimum in an
atmosphere where sound waves are free to travel continuously away from the noise source
in all directions (FREE FIELD).
Because of the inability to duplicate these variables everywhere, the sound pressure level
recorded cannot be used for scientific analysis until it has been modified to compensate for
these variables.
The modified data is called SOUND POWER, which is defined as the total sound energy
radiated, by a source per unit of time.
s
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
Section 2 2
Part
2
Part
2
Page 68 of 115
Page
4
04/08
Date
09/07
Noise Theory
Again, this is expressed as SOUND POWER LEVEL (Lw) in decibels. Mathematically it is
expressed as follows:
Lw provides data that the acoustic designer can use in determining the actual overall noise
level at a given spot due to all noise generating sources.
W
Lw 10 log 10 W
(dB)
0
Where; W = sound power in watts produced by sound source
Wo = Reference power taken as 10-12watts or 1 Pico watt
(see ANSI S1.8-1964).
"A" and "C" Scales
The human ear is not equally sensitive to all frequencies. Instead the human ear is more
sensitive to higher frequencies and less responsive to lower frequencies. A 1000 HZ sound
will appear much louder to the ear than a 100 HZ sound even though they both have the
same level. Therefore, in order to determine the effect of various frequencies it is
necessary to determine the actual sound levels of these frequencies that appear to be
equally "loud" to the human ear. This has been done through testing a large cross section
of the population.
By plotting these results as a family of curves and smoothing out the irregularities, it has
been determined that "weighting networks" can be designed to approximate these values.
The sound meter can record sound picked up by the microphone and passed through these
weighing networks. This is similar to the levels that the ear thinks it hears. The two most
commonly used are the "C" network and the "A" network.
The "C" network (or C Scale) represents a higher "loudness level" and has a relatively flat
curve. It weighs each frequency equally and therefore gives true values of sound levels
emanating from the source.
The "A" network (or A Scale) represents a lower "loudness level". It discriminates primarily
against the lower frequencies. Therefore, it comes closest to the discrimination of the ear
both for loudness of low level noises and to hearing damage risk from loud noises. The
Walsh-Healey Act selected this “A” Scale as the basis for reporting overall sound pressure
levels.
s
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
Section 2 2
Part
2
Part
2
Page 69 of 115
Page
5
04/08
Date
09/07
Noise Theory
Conversions Between "A" and "C" Scales
The various frequencies are weighted differently for the "A" and "C" scales. Therefore, in
order to convert from one scale to another each band of frequencies must be adjusted
individually.
The following are the correction factors to convert from "C" Scale to "A" Scale;
Octave Band
63
125
250
500
1000
2000
4000
8000
Correction (dB)
-26
-16
-9
-3
0
+1
+1
-1
The correction factors can only be used when converting between scales when both scales
are on the same basis, either Sound Power or Sound Pressure. They cannot be used for
converting between Scales when one Scale is on Sound Power basis and the other Scale
is on Sound Pressure basis.
Band Level
Band level is the total level of all noise in a specified frequency band.
Narrow Band
A narrow band is generally defined as a band of frequencies whose width is not less than
one percent or more than eight percent of the band center frequency.
Application Manual for Above NEMA Motors Noise Theory
s
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
Section 2 2
Part
2
Part
2
Page 70 of 115
Page
6
04/08
Date
09/07
Noise Theory
Band Center Frequency
Band center frequency is the geometric mean between the extreme frequencies of the
band.
fc =
fh f l
fc = the band center frequency
Where; fh = high frequency limit of the band
f I = low frequency limit of the band
Free Field Over a Reflective Plane
Free field conditions exist when sound from the source can travel freely and continuously
away from the source and in which the effects of the boundaries are negligible over the
region of interest. In this environment the sound pressure level decreases 6 dB each time
the distance from the source is doubled.
Broad Band, Octave Band, and Third Octave
The average human ear can hear over a wide range of frequencies varying from 20Hz to
16,000Hz. In order to simplify calculations this range is broken into ten parts called
"OCTAVE BANDS". Each band covers a 2 to 1 range of frequencies. The higher frequency
is twice the lower. In order to further simplify matters, each band is generally referred to by
its center (geometrically mean) frequency. In most cases the lowest and the highest band
contribute very little valuable data and therefore are omitted. The bands normally
considered are with center frequencies as follows: 63Hz, 125Hz, 250Hz, 500Hz, 1000Hz,
2000Hz, 4000Hz, and 8000Hz.
Laboratory equipment selects only the sound in the frequency band under consideration
and records it exclusive of all other frequencies. Thus, the sound content from a source is
available in distinct bands for engineering analysis.
s
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
Section 2 2
Part
2
Part
2
Page 71 of 115
Page
7
04/08
Date
09/07
Noise Theory
When engineering analysis requires more detailed frequency data, equipment is available
to further subdivide each octave into three parts. These are called "ONE-THIRD
OCTAVES" which divide the full octave geometrically rather than arithmetically. A one-third
octave is a bandwidth in which the ratio of extreme frequencies is equal to the cube root of
2 or 1.260.
Sometimes it is of interest to study discrete frequencies of sound. Equipment is also
available to measure the sound level of any such pure tones that might emanate from a
sound source.
Anechoic Room
An anechoic room is one constructed so that all the sound striking the boundaries of the
room is absorbed. This is also called a Free Field room.
Reverberant Room
A reverberant room is an enclosure in which all the surfaces have been made as sound
reflective as possible. In a reverberant room the measured sound pressure level is
independent of the distance from the source and is essentially constant when measured
beyond the near field region.
Airborne Noise
Airborne noise is undesired sound in the air. This is the noise that is received by the ear of
the observer.
Structure borne Noise
Structure borne noise is undesired vibration in or of solid bodies such as machinery,
foundations or structures.
Frequencies for Acoustical Measurements
Until 1960 the variety of frequencies used for acoustical measurements made comparison
of results inconvenient. The 1960 issue of the American Standard of Preferred Frequencies
S1.6-1960 establishes an octave center frequency series based on multiples of 1000 cycles
per second. This simplification affords a maximum number of center frequencies common
to both the octave band series and the one-third octave band series.
s
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
Section 2 2
Part
2
Part
2
Page 72 of 115
Page
8
04/08
Date
09/07
Noise Theory
Preferred Frequencies For Acoustical Measurements
Octave Band
Edge Frequencies
Octave Band
Center Frequency
45/90
90/180
180/355
355/710
710/1400
1400/2800
2800/5600
5600/11200
63
125
250
500
1000
2000
4000
8000
Sound Pressure vs. Sound Power
The definitions of sound pressure level, sound power level and vibration acceleration level
are of academic interest only. Sound level instruments are calibrated to read or record
sound pressure levels directly in dB. Sound power is obtained only by calculation from
measured values of sound pressure levels. Sound pressure levels are useful in determining
the noise level of an area surrounding a piece of equipment. They do not, however,
adequately express the noise produced by the equipment itself. Sound pressure levels are
influenced by the room environment, by the presence of other sound sources and by the
distance and location of the microphone. For the same source, they will be highest in a
reverberant room and lowest under anechoic or free field conditions. It is evident then, that
sound pressure levels can never be repeated or duplicated except under identical test
conditions.
Sound power of a source is the total sound energy radiated by the source per unit of time. It
is then essentially independent of the environment in which the source is located or
distance from the source. Sound power is the only basic measure of the acoustic properties
of a machine, and every effort should be made to encourage expression of noise test
results and noise limit specifications in terms of sound power levels.
In a free field over a reflecting plane, sound pressure can be converted to sound power by
the following formula:
Lw
L p 10Log10
2S r 2
1.0
r = radius from the center of the motor at which the pressure was measured in
meters.
s
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
Section 2 2
Part
2
Part
2
Page 73 of 115
Page
9
04/08
Date
09/07
Noise Theory
Combining Sound Levels
Of major importance to the plant operators is the sound pressure level at a specific spot in
the plant, usually at the operator’s station. This can be determined if the sound levels are
known from each generating source.
Keep in mind that sound levels are energy values and therefore they must be combined on
an energy basis not arithmetically. Knowing the sound level of each source, one can
calculate the sum total, using the following chart, or the following formula.
Lp(1)
Lp(2)
Lp(n) º
ª
LP 10 log10 «antilog10
antilog10
antilog10
10
10
10 »¼
¬
Lp
= total sound pressure level or total sound level.
Lp(1) = level in decibels of the first measurement.
Lp(n) = level in decibels in the nth measurement.
dB Adjustments for Combining Sound Sources
Difference Between Two Levels
to be Combined in dB
Value to be Added to the Higher
of the Two Levels to be Combined in dB
0  3.0
1  2.5
2  2.0
3
4  1.5
5
6  1.0
7  0.8
8  0.6
9  0.5
10  0.4
11 
12  0.3
13  0.2
14 
15  0.1
s
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
Section 2 2
Part
2
Part
2
Page 74 of 115
Page
10
04/08
Date
09/07
Noise Theory
For example, assume a motor at 80 dBA and a compressor at 82 dBA is installed together.
The difference is 2 dBA; therefore, the overall noise will be 84.1 dBA (82 + 2.1 increase).
Assume a duplicate unit is now installed right next to the first unit. Combine that new unit
(84.1 dBA) with the existing unit (84.1 dBA). The difference is zero; therefore, the result of
the two units will be 87.1 dBA. If a third unit is now added, you combine 87.1 with an 84.1.
The difference is 3 dBA, which results in a 1.75 dBA increase, for a total of 88.85. A fourth
unit would result in an increase of about 1.25 dBA overall, or a total of just over 90 dBA,
which is a 6 dBA increase over the original single unit.
Each 3 dBA increase represents a doubling of the sound level at the operator's station; that
is, 83 dBA is approximately twice as loud as 80 dBA.
Note that when the difference between two pieces of equipment is greater than 10 dBA,
there is virtually no change in the overall level caused by adding the quieter machine.
The chart shown previously can also be used to determine the overall sound level of a
motor when the individual octave bands are known. The bands are combined two at a time,
using the result of the previous combination with the next band level. For example, assume
a motor has a following spectrum:
Octave Band:
125 250 500 1000 2000 4000 8000
A Scale Sound Level: 80 86 84
88
85
80
70
Following similar calculations gives an overall level of 92.6 dBA.
The following chart shows adjustments to estimate the sound coming from a source in a
plant location.
For example, if the sound level in the plant with the motor operating is 90 dBA, and with the
motor shut down is 86 dBA, then the sound level of the motor above would be 87.8 dBA (90
- 2.2).
Difference Between
Total Sound and Ambient in dB
Value to be Subtracted
From Total Sound in dB
3  3.0
4  2.0
5  1.5
6
7  1.0
8  0.75
9  0.5
10  0.4
11 
12  0.3
13  0.2
14 
15 
s
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
Section 2 2
Part
2
Part
2
Page 75 of 115
Page
11
04/08
Date
09/07
Noise Theory
Effect of Distance
In a free field where sound from a point source can spread out equally in all directions, the
sound pressure decreases with distance. Tests have proven that the product of pressure
times the distance is a constant. Noise levels at other distances can be calculated from the
following:
L p2
L p1 20 Log10
r1
r2
Where: Lp1 = sound pressure at distance r1
Lp2 = sound pressure at distance r2
r1 and r2 are radius from the center of the motor
On a motor four feet wide, three feet from the surface would have an r =
4
+ 3 = 5. Five
2
feet from the surface would have an r = 7. The values for r1 and r2 can be in either meters
or feet.
s
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
Section 2 2
Part
2
Part
2
Page 76 of 115
Page
12
04/08
Date
09/07
Noise Theory
Testing
All testing and calculations are made in strict accordance with the latest issues of
"American Standard Method for the Physical Measurement of Sound" and with IEEE No. 85
"Test Procedure for Airborne Noise Measurements on Rotating Electric Equipment."
Complete Octave, Third Octave and Narrow Band results are not required on every study.
Sufficient information only is developed to satisfy the requirements of the problem or
situation.
Sound Intensity Method of Noise Testing
We have developed the procedure and acquired the equipment to conduct sound intensity
testing of motors under load. This enables accurate determination of the sound power level
produced by loaded motors. This method is available upon request. Industry standards
have not yet been fully established for this method, but we are working closely with ANSI,
IEEE and IEC to establish these standards. To understand this approach, see the IEEE
article "Specifying And Measuring The Noise Level Of Electric Motors In Operation".
Walsh-Healey Act
The Federal Government saw the need for keeping noise "pollution" within reasonable
limits and also the need for limiting noise levels to "safe" values by current medical and
acoustical standards. Therefore, the Walsh-Healey Act was passed and amended in 1969
setting these limits.
The limits are based on the hours per day human beings are exposed to the noise level.
The acceptable levels range from a maximum of 115 dBA for 15 minutes to 90 dBA for 8
hours or more.
These levels are overall levels as measured on the "A" Scale of a standard sound level
meter at slow response.
s
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
Section 2 2
Part
2
Part
2
Page 77 of 115
Page
13
04/08
Date
09/07
Noise Theory
NEMA Noise Levels
NEMA has published overall sound power levels that should not be exceeded by polyphase
squirrel-cage motors. It should be recognized that the distribution of noise as a function of
frequency affects the acceptance of sound and that machines with the same overall sound
level can have different noise qualities.
Low Noise Machines
Modifications are usually necessary if a machine is to be classified as having low noise.
Most of the work done to lower noise levels is aimed at sound absorption or a reduction in
vibration of mechanical components in frequencies most sensitive to the ear. Under usual
conditions in the area near a machine a 1.0-decibel change in noise level is about the
minimum that can be detected by the average individual. On this basis, a 1.0 dB reduction
would hardly be important. A reduction of 3 dB is usually significant and 6 dB is certainly
worthwhile.
Airborne noise produced by a motor can be attenuated by treatment with sound absorbing
materials. Directional fans and careful attention to airflow and velocity can be expected to
result in considerable noise reduction at the fundamental and harmonics of the blade
passing frequency.
Different types of machines require different methods of noise reduction depending upon
their construction. Noise can be caused by anyone, or all, of several sources. Magnetic
forces varying periodically, turbulent airflow and fan configuration, mechanical unbalance
and bearings, fits and friction forces and the mounting arrangement on a base or structure
can all be potential sources. Each must be considered individually to make sure that its
contribution to the total noise level of the motor is as small as possible.
s
Application Manual for NEMA Motors
Application Manual for NEMA Motors
Section
Section 2 2
Part
2
Part
2
Page 78 of 115
Page
14
04/08
Date
09/07
Noise Theory
Customer Specification
Our customers usually express their noise limit specifications to us in terms of overall
sound pressure level or sound power level at no load.
Since the speech interference level is defined as the arithmetic average of the sound
pressure level of the noise in each of the octave bands 710 to 1400 Hz, 1400 to 2800 Hz,
and 2800 to 5600 Hz, specifications will be in terms of full octave band sound pressure
levels when this is the prime consideration.
When the user is concerned with the noise radiated by a machine in relation to other
sources of noise in the same areas, he might well specify octave band sound power or
pressure levels.
Sound power levels are always related to sound pressure levels that would exist under free
field conditions. Using sound power, it is possible for the user to predict the sound pressure
levels that will exist in the space environment in which the machine will ultimately be used.
Overall sound pressure or sound power level can also be computed. As far as testing
procedure is concerned, however, the type of specification is immaterial since the results
can easily be converted.
Application Manual for NEMA Motors
Section
2
PartSection 3 2
PagePart
79 of 115 3
Page 04/08 1
Date
09/07
Application Manual for NEMA Motors
General Power Supply Variation
General
Induction motors will operate successfully under the following conditions of voltage and frequency
variation, but not necessarily in accordance with the standards established for operating under rated
conditions:
1. Where the variation in voltage does not exceed 10% above or below normal, with all phases balanced.
2. Where the variation in frequency does not exceed 5% above or below normal.
3. Where the sum of the voltage and frequency variations does not exceed 10% above or below
normal (provided the frequency variation does not exceed 5%)
The approximate variations in motor performance, caused by these deviations from nameplate values,
are discussed on the following pages.
The effect of electrical supply variations on motor performance should be considered when selecting
and applying AC Induction motors. Variation in motor supply voltage and frequency may cause:
1. An increase in motor torque and/or speed which may be damaging to the driven machine.
2. A decrease in motor torque and/or speed which may cause a reduction in output of the driven machine.
3. Damage to the motor.
Although the AC Induction motor is designed to successfully operate when subjected to slight
variations in power supply voltage and frequency, the performance (torque, speed, operating
temperature, efficiency, power factor) is optimum when the power supply voltage and frequency
are in accordance with the nameplate values.
Power supply variations may be classified into three categories:
1. Frequency variation from rated.
2. Unbalanced voltage between phases
3. Balanced phase voltage with voltage variation from rated value.
Application Manual for NEMA Motors
Section
2
PartSection 3 2
PagePart
80 of 115 3
Page 04/08 2
Date
09/07
Application Manual for NEMA Motors
General Power Supply Variation
For ease of understanding, we shall consider the singular effect each of the preceding categories has
on motor performance. In actual practice, it is common to simultaneously encounter a combination of
two or more of the power supply variations listed in the preceding three categories, hence the
combined effect will be the resultant of each singular effect; in other words, the effect of a particular
variation will be superimposed upon the effect of another variation.
Unbalance Voltage Between Phases
General
The multiple phase AC induction motor is designed for use on a balanced voltage system, that is, the
voltage in each phase is equal. When the voltage of each phase is unequal, a small rotating magnetic
field is created. This magnetic field rotates in the opposite direction of the main magnetic field,
therefore, it in effect is a “bucking” field causing induced voltages and resultant high currents. To
determine the effect of unbalanced phase voltages on motor performance, it is necessary to express
the voltage unbalance in percent as shown in the following formula:
% Volts Unbalance =
Max. volts deviation
x 100
from avg. volts
avg. volts
Example:
Actual phase voltages at motor terminal of 3 phase motor are 236,229 and 225 volts.
Average Voltage =
236 + 229 + 225
3
= 230 volts
Determine Maximum Voltage Deviation From Average Voltage
236 Volts
230 Volts
6
230 Volts
229 Volts
1
230 Volts
225 Volts
5
Maximum Voltage Deviation From Average Voltage = 6 Volts
% voltage unbalance =
6
x 100 = 2.61%
230
Section
2
PartSection 3 2
PagePart
81 of 115 3
Page 04/08 3
Application Manual for NEMA Motors
Date
09/07
Application Manual for NEMA Motors
General Power Supply Variation
Current
In general, a small voltage unbalance on any type of induction motor results in a considerably greater
current unbalance. For a given voltage deviation, the current deviation is greatest at no load and
decreases with loading with the least effect being exhibited under locked conditions. This
phenomenon is conveniently shown in the following graph.
Percent Current Unbalance
20
ad
No
15
Lo
ad
Lo
ll
Fu
ull
ce F
10
d
Loa
Twi
5
Locked
0
1
2
3
Percent Voltage Unbalance
Full Load Speed
Unbalance phase voltage does not appreciably affect full load motor speed. There is a slight tendency
for the full load speed to be reduced as the percentage of phase voltage unbalance increases.
Torque
Unbalanced phase voltages have little practical effect on AC induction motor torques.
Torque with
unbalanced
phase voltage
expressed as
a percent of
full load torque
=
Torque with
balanced
phase voltage
expressed as
a percent of
full load torque
% voltage
unbalance
x K x 1100
2
Where K = 1 for locked rotor torque (LRT) and 2 for breakdown torque (BDT).
Section
2
PartSection 3 2
PagePart
82 of 115 3
Page 04/08 4
Application Manual for NEMA Motors
Date
09/07
Application Manual for NEMA Motors
General Power Supply Variation
Example:
Let locked rotor torque (balanced) = 150% of full load torque and voltage
unbalance = 2.61%.
Torque with
unbalanced
phase voltage
expressed as
a percent of
full load torque
= 150 x 1 x 1-
2.61
100
2
= 149.9%
Motor Temperature
A small unbalanced phase voltage will cause a significant increase in motor temperature. Although
there is no exact formula to determine the effect of voltage phase unbalance on temperature rise,
laboratory tests indicate the percentage increase in motor temperature is approximately equal to
twice the square of the percentage voltage unbalance. This can be expressed by the following
formula:
Temp. rise on
unbalanced
system
=
Temp. rise on
balanced
system
x
(% voltage unbalance)2
1+2
100
Example:
Let the voltage unbalance = 2.61% and the full load motor temperature rise at balanced voltage be
equal to 80°C.
1 + 2 (2.61%) 2
100
Temp. rise on
unbalanced
system
= 80°C x
Temp. rise on
unbalanced
system
= 80°C x 1.136 = 90.9°C
Application Manual for NEMA Motors
Section
2
PartSection 3 2
PagePart
83 of 115 3
Page 04/08 5
Date
09/07
Application Manual for NEMA Motors
General Power Supply Variation
Efficiency
A marked reduction of motor efficiency results when unbalanced phase voltages exist. The increased
currents caused by the reverse rotating “bucking magnetic field” cause a reduction in full load
efficiency.
Power Factor
Full load power factor decreases as the degree of voltage unbalance increases.
Application Manual for NEMA Motors
Section
2
PartSection 3 2
PagePart
84 of 115 3
Page 04/08 6
Date
09/07
Application Manual for NEMA Motors
Voltage Variation From Rated Value With Balanced Phase Voltages
Current
Three motor currents are often used when dealing with induction motors. They are: locked-rotor or
starting, no-load and full-load current.
Locked rotor current varies nearly directly with the applied voltage; a 10% voltage increase results in
approximately a 10% current increase.
No-load current consists primarily of magnetization current; this current establishes the magnetic field
in the electrical steel within the motor. Increased applied voltages results in higher no-load currents;
conversely, a reduction of no-load current results when the applied voltage is decreased. The degree
of no-load or magnetization current change is a function of the motor design or geometry of electrical
motor parts, type of materials used and degree of magnetic loading.
Full-load current is actually a summation of two currents; these are the no-load (magnetization)
component and the load component of the full-load current.
As mentioned above, the no-load (magnetization) current increases with a voltage increase; the
amount of increase is a function of the motor design.
The load component of the full-load current varies approximately inversely to the voltage variation. A
voltage increase tends to result in a corresponding decrease in the load component of the full-load
current. This phenomenon can be explained by considering the fact that electrical power is basically
the product of voltage and current. Therefore, if the mechanical load of the motor remains constant,
the electrical input power to the motor also remains nearly constant; hence the load component of the
current is reduced when voltage is increased.
Since full-load current is the summation of both the no-load and load component currents, the
manner in which the full load current varies with voltage depends on the way the two currents vary
with voltage.
In general, the magnetizing (no-load) current of small motors is a large percent of the full load
current. The motor magnetizing current increases when voltage is increased; hence an increase in
impressed motor voltage on small AC induction motors causes an increase in full load current.
Application Manual for NEMA Motors
Section
2
PartSection 3 2
PagePart
85 of 115 3
Page 04/08 7
Date
09/07
Application Manual for NEMA Motors
Voltage Variation From Rated Value With Balanced Phase Voltages
As the motor HP increases, the magnetizing current becomes a lesser percent of the total full load
current; therefore, the full load current tends to decrease with increased voltage.
It should be noted that the magnetization (no-load) and load component currents are added
vectorially.
Torque
Locked, pull-up (minimum) and breakdown torque vary approximately as the square of the applied
voltage.
Motor Temperature
Motor temperature is predominately influenced by motor current; heating due to motor current is
directly proportional to the square of the motor current.
A 10% increase or decrease in voltage form the nameplate voltage may increase motor heating,
however, such an increase in heating will not exceed safe limits provided motor is operated at values
of nameplate HP and ambient temperature or less.
Efficiency (Full-Load)
Efficiency is a measure of the amount of electrical power lost in the form of heat compared to the
mechanical power delivered to the load. Higher motor currents cause higher motor temperatures
which in turn result in a lower motor efficiency.
Power Factor (Full-Load)
Power factor is directly related to magnetization or no-load current. Higher voltages cause higher
magnetization currents which in turn result in a lower power factor.
Speed (Full-Load)
Full-load speed increases slightly with a voltage increase.
Application Manual for NEMA Motors
Section
2
PartSection 3 2
PagePart
86 of 115 3
Page 04/08 8
Date
09/07
Application Manual for NEMA Motors
Frequency Variation From Rated Value With Rated Balance Voltage Applied
Current
No-load, locked rotor and full-load current vary inversely with a change in applied frequency. The
change in no-load and locked rotor current magnitude resulting from a change in frequency within
±5% of rated frequency is approximately 5% or less, whereas the change in full-load current is
negligible.
Torque
Locked rotor, minimum pull up, and breakdown torques vary approximately inversely as the
square of the frequency change.
Motor Temperature
Motor temperature is predominately influenced by motor current; heating due to the motor current is
directly proportional to the square of the motor current. A 5% increase or decrease in frequency from
the nameplate frequency may increase motor heating, however such an increase in heating will not
exceed safe limits provided motor is operated at values of nameplate HP and ambient temperature or
less.
Efficiency
Since a variance in frequency within ±5% of rated frequency has a negligible effect on full-load motor
current, the effect of frequency change on full-load motor efficiency is also negligible.
Power Factor
An increase in applied frequency causes a reduction in the magnitude of the magnetizing current
component of the full-load current which causes a slight increase in power factor.
Speed (Full-Load)
Since the full-load speed is directly proportional to frequency, a 5% frequency increase will result in a
correspondent 5% increase in speed.
Application Manual for NEMA Motors
Section
2
Part
4
SectionPage 872of 115
Part
404/08
Page
1 / 29
Date
09/07
Application Manual for NEMA Motors
Motor Terminology
AC (ALTERNATING CURRENT) - The commonly available electric power supplied by
an AC generator and is distributed in single- or three-phase forms. AC current changes its
direction of flow (cycles).
AC MOTOR - A motor (see Motor definition) operating on AC current that flows in either
direction (AC current). There are two general types: induction and synchronous.
ACTIVE IRON - The amount of steel (iron) in the stator and rotor of a motor. Usually the
amount of active iron is increased or decreased by lengthening or shortening the rotor and
stator (they are generally the same length).
AIR GAP - The space between the rotating (rotor) and stationary (stator) members in an
electric motor.
AIR PRESSURE SWITCH - Used on motors with blowers to measure the difference in
pressure across the filter to detect a clogged filter.
AIR TEMPERATURE SWITCH - A device used with an air hood motor to detect the
temperature of the exhausted air. When used in this manner an air temperature switch will
detect blockage in the cooling air system or long-term motor overload.
ALTITUDE - The atmospheric altitude (height above sea level) at which the motor will be
operating; NEMA standards call for an altitude not exceeding 3,300 feet (1,000 meters). As
the altitude increases above 3,300 feet and the air density decreases, the air’s ability to cool
the motor decreases. For higher altitudes, higher grades of insulation or motor derating are
required. DC motors require special brushes for operation at high altitudes.
AMBIENT TEMPERATURE - The temperature of the surrounding cooling medium, such
as gas or liquid, which comes into contact with the heated parts of the motor. The cooling
medium is usually the air surrounding the motor. The standard NEMA rating for ambient
temperature is not to exceed 40oC.
ANTI-FRICTION BEARING - An anti-friction bearing is a bearing utilizing rolling
elements between the stationary and rotating assemblies.
ARMATURE - The portion of the magnetic structure of a DC or universal motor which
rotates.
ARMATURE CURRENT, AMPS - Rated full load armature circuit current.
Application Manual for NEMA Motors
Section
2
Part
4
SectionPage 882of 115
Part
404/08
Page
2 / 29
Date
09/07
Application Manual for NEMA Motors
ARMATURE INDUCTANCE, mH - Armature inductance in milli-henries (saturated).
ARMATURE REACTION - The current that flows in the armature winding of a DC motor
tends to produce magnetic flux in addition to that produced by the field current. This effect,
which reduces the torque capacity, is called armature reaction and can effect the
commutation and the magnitude of the motor’s generated voltage.
ARMATURE RESISTANCE, OHMS - Armature resistance is measured in ohms at 25o
C (cold).
AXIAL THRUST - The force or loads that are applied to the motor shaft in a direction
parallel to the axis of the shaft (Such as from a fan or pump.).
BACK END OF A MOTOR - The back end of a normal motor is the end that carries the
coupling or driving pulley (NEMA). This is sometimes called the drive end (D.E.), pulley end
(P.E.) etc.
BASE SPEED, RPM - The speed in revolutions per minute (RPM) which a DC motor
develops at rated armature and field voltage with rated load applied.
BEARINGS - Bearings reduce friction and wear while supporting rotating elements. When
used in a motor, they must provide a relatively rigid support for the output shaft. (See pages x
and y). Bearings act as the connection point between the rotating and stationary elements of
a motor. There are various types such as roller, ball, sleeve (journal) and needle. Ball
bearings are used in virtually all types and sizes of electric motors. They exhibit low friction
loss, are suited for high speed operation and are compatible with a wide range of
temperatures. There are various types of ball bearings such as open, single shielded and
sealed.
BEARING LIFE - Rating life, L10 (B10), is the life in hours or revolutions in which 90% of the
bearings selected will obtain or exceed. Median life (average life), L50 (B50), is the life in hours
or revolutions in which 50% of the bearings selected will obtain or exceed.
BRAKES - An external device or accessory that brings a running motor to a standstill
and/or holds a load. Can be added to a motor or incorporated as part of it.
BRAKING TORQUE - The torque required to bring a motor down to a standstill. The
term is also used to describe the torque developed by a motor during dynamic braking
conditions.
BREAK AWAY TORQUE - (See Locked Rotor Torque.)
Application Manual for NEMA Motors
Section
2
Part
4
SectionPage 892of 115
Part
404/08
Page
3 / 29
Date
09/07
Application Manual for NEMA Motors
BREAKDOWN TORQUE - The maximum torque a motor will develop at rated
voltage without a relatively abrupt drop or loss in speed.
BRUSH - A piece of current conducting material (usually carbon or graphite) which rides
directly on the commutator of a commutated motor and conducts current from the power
supply to the armature windings.
CE - This designation shows that a product such as a motor or control meets European
Standards for safety and environmental protection. A CE mark is required for products used in
most European countries, and is designated as:
CIV (CORONA INCEPTION VOLTAGE) - The minimum voltage amount that begins
the process of ionization (corona) of motor windings.
CSA - Canadian Standards Association like U.L., sets specific standards for products used
in Canada. The CSA mark is:
“C” FLANGE OR C-FACE - A type of flange used with close-coupled pumps, speed
reducers and similar equipment where the mounting holes in the flange are threaded to
receive bolts. Normally the “C” flange is used where a pump or similar item is to be connected
on the motor. The “C” type flange is a NEMA standard design and available with or without
feet.
CANOPY (DRIP COVER) - A protective cover placed on the top of a motor being
mounted vertically to protect it from liquids or solids that might drop onto the motor (functions
as an umbrella for the motor).
CAPACITOR - A device which, when connected in an alternating-current circuit, causes
the current to lead the voltage in time phase. The peak of the current wave is reached ahead
of the peak of the voltage wave. This is the result of the successive storage and discharge of
electric energy used in single phase motors to start, or in three-phase motors for power
factor correction.
CAPACITOR MOTOR - A single-phase induction motor with a main winding arranged for
direct connection to the power source, and an auxiliary winding connected in series with a
capacitor. There are three types of capacitor motors:
x capacitor start, in which the capacitor phase is in the circuit only during starting
x permanent-split capacitor, which has the same capacitor and capacitor phase
in the circuit for both starting and running
Application Manual for NEMA Motors
Section
2
Part
4
SectionPage 902of 115
Part
404/08
Page
4 / 29
Date
09/07
Application Manual for NEMA Motors
x
two-value capacitor motor, in which there are different values of capacitance
for starting and running.
CAPACITOR START - The capacitor start single-phase motor is basically the same as
the split phase start, except that it has a capacitor in series with the starting winding. The
addition of the capacitor provides better phase relation and results in greater starting torque
with much less power input. As in the case of the split phase motor, this type can be reversed
at rest, but not while running unless special starting and reversing switches are used. When
properly equipped for reversing while running, the motor is much more suitable for this service
than the split phase start since it provides greater reversing ability at less watts input.
CENTRIFUGAL CUTOUT SWITCH - A centrifugally operated automatic mechanism
used in conjunction with split phase and other types of single-phase induction motors.
Centrifugal cutout switches will open or disconnect the starting winding when the rotor has
reached a predetermined speed and reconnect it when the motor speed falls below it.
Without such a device, the starting winding would be susceptible to rapid overheating and
subsequent burnout.
CLUTCH - A mechanical device for engaging and disengaging a motor. It is often used
when many starts and stops are required.
COGGING - A term used to describe non-uniform angular velocity. It refers to rotation
occurring in jerks or increments rather than smooth motion. When an armature coil enters the
magnetic field produced by the field coils, it tends to speed up and slow down when leaving it.
This effect becomes apparent at low speeds. The fewer the number of coils, the more
noticeable it can be.
COIL (STATOR OR ARMATURE) - The electrical conductors wound into the core slot,
electrically insulated from the iron core. These coils are connected into circuits or windings,
which carry independent current. It is these coils that carry and produce the magnetic field
when the current passes through them.
There are two major types:
x “Mush” or “random” wound, round wire found in smaller and medium motors
where coils are randomly laid in slot of stator core
x Formed coils of square wire individually laid in, one on top of the other, to give
an evenly stacked layered appearance.
COMMUTATOR - A cylindrical device mounted on the armature shaft and consisting of a
number of wedge-shaped copper segments arranged around the shaft (insulated from it and
each other). The motor brushes ride on the periphery of the commutator and electrically
connect and switch the armature coils to the power source.
Application Manual for NEMA Motors
Section
2
Part
4
SectionPage 912of 115
Part
404/08
Page
5 / 29
Date
09/07
Application Manual for NEMA Motors
COMPOUND WOUND DC MOTORS - Designed with both a series and shunt field winding,
the compound motor is used where the primary load requirement is heavy starting torque and
variable speed is not required (See Paralleling). Also used for parallel operation. The load
must tolerate a speed variation from full load to no-load. Industrial machine applications
include large planers, boring mills, punch presses, elevators and small hoists.
CONDUCTOR - A material such as copper or aluminum which offers low resistance or
opposition to the flow of electric current.
CONDUIT BOX - The metal container usually on the side of the motor where the stator
(winding) leads are attached to leads going to the power supply.
CONSTANT HP (HORSEPOWER) - A designation for variable speed motors used for
loads requiring the same amount of horsepower regardless of their motor speed during a
normal operation.
CONSTANT TORQUE - Refers to loads with horsepower requirements that change
linearly at different speeds. Horsepower varies with the speed, i.e., 2/1 HP at 1800/900
RPM (seen on some two-speed motors). Applications include conveyors, some crushers and
constant-displacement pumps.
CONSTANT SPEED - A DC motor which changes speed only slightly from a no-load
to a full-load condition. For AC motors, these are synchronous motors.
CORE - The iron portion of the stator and rotor made up of cylindrical laminated electric
steel. The stator and rotor cores are concentric and separated by an air gap, with the rotor
core being the smaller of the two and inside to the stator core.
CORONA - This is the electrical discharge breakdown of a winding through the application
of excessive voltage.
COUNTER ELECTROMOTIVE FORCE (CEMF) - The induced voltage in a motor
armature caused by conductors moving through or “cutting” field magnetic flux. This induced
voltage opposes the armature current and tends to reduce it.
COUPLING - The mechanical connector joining the motor shaft to the equipment to be
driven.
CURRENT - This time rate of flow of electrical charge and is measured in amps (amperes).
Application Manual for NEMA Motors
Section
2
Part
4
SectionPage 922of 115
Part
404/08
Page
6 / 29
Date
09/07
Application Manual for NEMA Motors
CYCLES PER SECOND (HERTZ) - One complete reverse of flow of alternating current per
rate of time. (A measure of frequency.) 60 Hz (cycles per second) AC power is common
throughout the US and 50 Hz is common in many foreign countries.
“D” FLANGE - A special end shield with untapped holes for through bolts in the flange. It
is primarily used for mounting the motor to gear boxes or bulkheads. They are available in
frame sizes 143T through 445T.
DC (DIRECT CURRENT) - A current that flows only in one direction in an electric circuit.
It may be continuous or discontinuous and it may be constant or varying.
DC MOTOR - A motor using either generated or rectified DC power (see Motor). A DC
motor is often used when adjustable-speed operation is required.
DEFINITE PURPOSE MOTOR - A definite purpose motor is any motor design listed and
offered in standard ratings with standard operating characteristics but with special mechanical
features for use under service conditions other than usual or for use on a particular type of
application (NEMA).
DUAL VOLTAGE - Some motors can operate on two different voltages, depending
upon how it is built and connected. The voltages are either multiples of two or the ¥3 of one
another.
DUTY CYCLE - The relationship between the operating and rest times or repeatable
operation at different loads. A motor which can continue to operate within the temperature
limits of its insulation system after it has reached normal operating (equilibrium) temperature
is considered to have a continuous duty (CONT.) rating. A motor which never reaches
equilibrium temperature but is permitted to cool down between operations, is operating under
intermittent (INT) duty. Conditions such as a crane and hoist motor are often rated 15 or 30
minute intermittent duty.
DYNAMOMETER - A device which places a load on the motor to accurately measure its
output torque and speed by providing a calibrated dynamic load. Helpful in testing motors for
nameplate information and an effective device in measuring efficiency.
DESIGN A, B, C, D – FOR AC MOTORS - NEMA has standard motor designs with
various torque characteristics to meet specific requirements posed by different application
loads. The design “B” is the most common design.
DIMENSIONS - NEMA has standard frame sizes and dimensions designating the height of
the shaft, the distance between mounting bolt holes and various other measurements.
Integral AC motor NEMA sizes run from 143T-445T, and the center of the shaft height in
inches can be figured by taking the first two digits of the frame number and dividing it by 4.
Application Manual for NEMA Motors
Section
2
Part
4
SectionPage 932of 115
Part
404/08
Page
7 / 29
Date
09/07
Application Manual for NEMA Motors
Fractional horsepower motors, for which NEMA spells out dimensions, utilize 42, 48 and 56
frames. The shaft height in inches can be established by dividing the frame number by 16.
DRIP-PROOF GUARDED - A drip-proof machine with ventilating openings guarded (with
screens) as in a guarded motor.
DRIP-PROOF MOTOR - An open motor in which the ventilating openings are so
constructed that drops of liquid or solid particles falling on it, at any angle not greater than 15
degrees from the vertical, cannot enter either directly or by striking and running along a
horizontal or inwardly inclined surface.
DUAL TORQUE - A dual speed motor with torque values that vary with speed (as
the speed changes the horsepower remains constant).
EDDY CURRENT - Localized currents induced in an iron core by alternating magnetic flux.
These currents translate into losses (heat) and their minimization is an important factor in
lamination design.
EFFICIENCY - The efficiency of a motor is the ratio of electrical input to mechanical output.
It represents the effectiveness with which the motor converts electrical energy into
mechanical energy. NEMA has set up codes, which correlate to specific nominal efficiencies.
A decrease in losses (the elements keeping the motor from being 100% efficient) of 10%
constitutes an upward improvement of the motor of one code on the NEMA table. Each
nominal efficiency has a corresponding minimum efficiency number.
ELECTRICAL DEGREE - A unit of measurement of time as applied to alternating
current. One complete cycle equals 360 electrical degrees. One cycle in a rotating electrical
machine is accomplished when the rotating field moves from one pole to the next pole of the
same polarity. There are 360 electrical degrees in this time period. Therefore, in a two pole
machine there are 360 degrees in one revolution, and the electrical and mechanical degrees
are equal. In a machine with more than two poles, the number of electrical degrees per
revolution is obtained by multiplying the number of pairs of poles by 360.
ELECTRICAL TIME CONSTANT (FOR DC MOTORS) - The ratio of electrical
inductance to armature resistance. Electrical time constant in seconds defined as Electrical
TC = (La x Ia) / Hot IR voltage drop
Where La is the armature circuit inductance in henries and Ia is the rated full load armature
current.
ELECTRICAL UNBALANCE - In a three-phase supply, where the voltages of the three
different phases are not exactly the same. Measured as a percent of unbalance.
Application Manual for NEMA Motors
Section
2
Part
4
SectionPage 942of 115
Part
404/08
Page
8 / 29
Date
09/07
Application Manual for NEMA Motors
ELECTROMOTIVE FORCE (EMF) - A synonym for voltage, usually restricted to
generated voltage.
ENCAPSULATED WINDING - A motor which has its winding structure completely
coated with an insulating resin (such as epoxy). This construction type is designed for
exposure to more severe atmospheric conditions than the normal varnished winding.
ENCLOSURE - The housing or frame of the motor:
ODG ................Open Drip-Prof, Guarded
ODG-FV...........Open Drip-Proof, Force Ventilated
ODG-SV...........Open Drip-Proof, Separately Ventilated
ODP.................Open Drip-Proof
HP...................Vertical P-Base, Normal Thrust
LP ...................Vertical P-Base, Medium Thrust, Extended Thrust
Prot.................Protected
TEAO...............Totally-Enclosed, Air-Over
TEBC...............Totally-Enclosed, Blower-Cooled
TECACA...........Totally-Enclosed, Closed Circult, Air to Air
TEDC-A/A .......Totally-Enclosed, Dual Cooled, Air to Air
TEDC-Q/W ......Totally-Enclosed, Dual Cooled, Air to Water
TEFC ...............Totally-Enclosed, Fan-Cooled
TENV...............Totally-Enclosed, Non-Ventilated
TETC ...............Totally-Enclosed, Tube Cooled
TEWAC............Totally-Enclosed, Water/Air Cooled
TEXP ...............Totally-Enclosed, Explosion-Proof
IP-22...............Open Drip-Proof (IEC Standard)
IP-44...............Totally-Enclosed (IEC Standard)
IP-54...............Splash Proof (IEC Standard)
IP-55...............Washdown (IEC Standard)
WPI .................Weather Protected, Type I
WPII ................Weather Protected, Type II
XP ...................Explosion-Proof
ENDSHIELD - The part of the motor housing which supports the bearing and acts as a
protective guard to the electrical and rotating parts inside the motor. This part is frequently
called the “end bracket” or “end bell.”
EXPLOSION-PROOF ENCLOSURE - A totally enclosed enclosure, which is
constructed to withstand an explosion of a specified gas, vapor or dust which, may occur
within it. Should such an explosion occur, the enclosure would prevent the ignition or
explosion of the gas or vapor which may surround the motor enclosure. These motors are
listed with Underwriter’s Laboratories.
Application Manual for NEMA Motors
Section
2
Part
4
SectionPage 952of 115
Part
404/08
Page
9 / 29
Date
09/07
Application Manual for NEMA Motors
EXPLOSION-PROOF-HAZARDOUS LOCATIONS
x
x
DIVISION I – Locations in which ignitable concentrations of flammable or
combustible material exist and come in contact with the motor.
DIVISION II – Locations in which ignitable concentrations of flammable or
combustible material exist but are contained within closed systems or containers
and normally would not come in contact with the motor.
EXPLOSION-PROOF-U.L. CLASSIFICATIONS
x
CLASS I – Those in which flammable gasses or vapors are or may be present
in the air in quantities sufficient to product explosive or ignitable mixtures.
Group C – Atmospheres containing ethyl or ether vapors.
Group D – Atmospheres containing gasoline, hexane, benzine, butane,
propane, alcohol, acetone, benzol, lacquer solvent vapors, natural gas, etc.
x
CLASS II – Those which are hazardous because of the presence of
combustible dust.
Group E – Atmospheres containing metal dust, including aluminum,
magnesium, or their commercial alloys.
Group F – Atmospheres containing carbon black, charcoal, coal or coke dust.
Group G – Atmospheres containing flour, starch, grain or combustible plastics
or chemical dusts.
EXTERNALLY VENTILATED - A motor using an external cooling system. This is
required in applications where the motor’s own fan will not provide sufficient cooling. These
cooling systems are used in certain duty cycle applications, with slow speed motors, or in
environments with extreme dirt. Often a duct with an external blower is used to bring clean air
into the motor’s air-intake.
FIELD - A term commonly used to describe the stationary (stator) member of a DC motor.
The field provides the magnetic field with which the mechanically rotating (armature or rotor)
member interacts.
FIELD WEAKENING - The introduction of resistance in series with the shunt wound
field of DC motor to reduce the voltage and current which weakens the strength of the
magnetic field and thereby increases the motor speed.
Application Manual for NEMA Motors
Section
2
Part
4
SectionPage 962of 115
Part
404/08
Page
10 / 29
Date
09/07
Application Manual for NEMA Motors
FLANGE - Mounting endshield with special rabbets and bolt holes for mounting such
equipment as pumps and gear boxes to the motor or for overhanging the motor on the driven
machine. (see “C” flange and “D” flange).
FLUX - The magnetic field which is established around an energized conductor or
permanent magnet. The field is represented by flux lines creating a flux pattern between
opposite poles. The density of the flux lines is a measure of the strength of the magnetic
field.
FORM FACTOR - A figure of merit which indicates how much rectified current departs
from pure (non-pulsating) DC. A large departure from unity form factor (pure DC) increases
the heating effect of the motor and reduces brush life. Mathematically, form factor is the ratio
of the root-mean square (rms) value of the current to the average (av) current or Irms /lav.
FORM WOUND - A type of coil in which each winding is individually formed and placed
into the stator slot. A cross sectional view of the winding would be rectangular. Usually form
winding is used on high voltage (2300 volts and above) and large motors (449T and above).
Form winding allows for better insulation on high voltage than does random (mush) winding.
FRACTIONAL-HORSEPOWER MOTOR (FHP) - A motor usually built in a frame
smaller than that having a continuous rating of one horsepower, open construction, at
1700 - 1800 rpm. Within NEMA frame sizes, FHP encompasses the 42, 48 and 56 frames.
(In some cases the motor rating does exceed one horsepower, but the frame size
categorizes the motor as a fractional). The height in inches from the center of the shaft to the
bottom of the base can be calculated by dividing the frame size by 16.
FRAME - The supporting structure for the stator parts of an AC motor. In a DC motor, the
frame usually forms a part of the magnetic coil. The frame also determines mounting
dimensions (see Frame Size).
FRAME SIZE - Refers to a set of physical dimensions of motors as established by NEMA.
These dimensions include critical mounting dimensions. NEMA 48 and 56 frame motors are
considered fractional horsepower sizes even though they can exceed one horsepower.
NEMA 143T to 449T is considered integral horsepower AC motors and 5000 series and
above are called large motors. (For definition of letters following frame number,
see Suffixes).
FREQUENCY - The rate at which alternating current makes a complete cycle of reversals.
It is expressed in cycles per second. In the U.S., 60 cycles (Hz) is the standard while in other
countries 50 Hz (cycles) is common. The frequency of the AC current will affect the speed of
a motor (See Speed.)
Application Manual for NEMA Motors
Section
2
Part
4
SectionPage 972of 115
Part
404/08
Page
11 / 29
Date
09/07
Application Manual for NEMA Motors
FRONT END OF A MOTOR - The front end of a normal motor is the end opposite the
coupling or driving end (NEMA). This is sometimes called the opposite drive end (ODE.) or
commutator end (C.E).
FULL-LOAD CURRENT - The current flowing through the line when the motor is
operating at full-load torque and full-load speed with rated frequency and voltage applied to
the motor terminals.
FULL-LOAD TORQUE - That torque of a motor necessary to produce its rated
horsepower at full-load speed, sometimes referred to as running torque.
GEARHEAD - The portion of a gearmotor, which contains the actual gearing which,
converts the basic motor speed to the rated output speed.
GEARMOTOR - A gearhead and motor combination to reduce the speed of the
motor to obtain the desired speed or torque.
GENERAL PURPOSE MOTOR - A general-purpose motor is any motor having a NEMA
“B” design, listed and offered in standard ratings, with standard operating characteristics and
mechanical construction for use under usual service conditions without restriction to a
particular application or type of application (NEMA).
GROUNDED MOTOR - A motor with an electrical connection between the motor frame
and ground.
GUARDED MOTOR - An open motor in which all openings giving direct access to
live or rotating parts (except smooth shafts) are limited in size by the design of the structural
parts or by screens, grills, expanded metal, etc., to prevent accidental contact with such
parts. Such openings shall not permit the passage of a cylindrical rod 1/2-inch in diameter.
HEAT EXCHANGER - A device which will transfer the heat from inside the motor to
another medium, through a radiator type heat exchanger.
HERTZ (Hz) - One cycle per second (as in 60 Hz which is 60 cycles per second).
HORSEPOWER (HP) - The measure of rate of work. One horsepower is equivalent to
lifting 33,000 pounds to a height of one foot in one minute. The horsepower of a motor is
expressed as a function of torque and speed. For motors the following approximate formula
may be used:
HP = (T x RPM) / 5252
Application Manual for NEMA Motors
Section
2
Part
4
SectionPage 982of 115
Part
404/08
Page
12 / 29
Date
09/07
Application Manual for NEMA Motors
where HP = horsepower, T = torque (in. lb- ft.), and
RPM = revolutions per minute.
HYSTERESIS LOSS - The resistance offered by materials to becoming magnetized
(magnetic orientation of molecular structure). This results in energy being expended and
corresponding loss. Hysteresis loss in a magnetic circuit is the energy expended to
magnetize and demagnetize the core.
IDENTIFICATION - In most instances, the following information will help identify a motor:
1. Frame designation (actual frame size in which the motor is built).
2. Horsepower, speed, design and enclosure.
3. Voltage, frequency and number of phases of power supply.
4. Class of insulation and time rating.
5. Application
INDUCTANCE - The characteristic of an electric circuit by which varying current in it
produces a varying magnetic field which causes voltages in the same circuit or in a nearby
circuit.
INDUCTION MOTOR - An induction motor is an alternating current motor in which the
primary winding on one member (usually the stator) is connected to the power source and a
secondary winding or a squirrel-cage secondary winding on the other member (usually
the rotor) carries the induced current. There is no physical electrical connection to the
secondary winding, its current is induced.
INERTIAL LOAD - A load (flywheel, fan, etc.) which tends to cause the motor shaft to
continue to rotate after the power has been removed (stored kinetic energy). If this continued
rotation cannot be tolerated, some mechanical or electrical braking means must be applied.
This application may require a special motor due to the energy required to accelerate the
inertia. Inertia is measured in either lb-ft2 or oz-in2.
Inertia reflected to the shaft of the motor= (Load RPM)2 / Motor RPM
INSULATOR - A material which tends to resist the flow of electric current (paper, glass,
etc.). In a motor the insulation serves two basic functions:
1. Separates the various electrical components from one another
2. It protects itself and the electrical components from attack of contaminants and other
destructive forces.
INSULATION SYSTEM - Five specialized elements are used, which together constitute
the motor”s INSULATION SYSTEM. The following are typical in an AC motor:
Application Manual for NEMA Motors
Section
2
Part
4
SectionPage 992of 115
Part
404/08
Page
13 / 29
Date
09/07
Application Manual for NEMA Motors
1. TURN-TO-TURN INSULATION between separate wires in each coil. Usually
enamel to random wound coils of smaller motors – tape on “form wound” coils of
larger motors.
2. PHASE-TO-PHASE INSULATION between adjacent coils in different phase groups.
A separate sheet material on smaller motors – not required on form wound coils
because the tape also performs this function.
3. PHASE-TO-GROUND INSULATION between windings as a whole and the “ground”
or metal part of the motor. A sheet material, such as the liner used in stator slots,
provides both di-electric and mechanical protection.
4. SLOT WEDGE to hold conductors firmly in the slot.
5. IMPREGNATION to bind all the other components together and fill in the air space.
A total impregnation, applied in a fluid form and hardened, provides protection
against contaminants.
INSULATION CLASS - Since there are various ambient temperature conditions a motor
might encounter and different temperature ranges within which motors run and insulation is
sensitive to temperature; motor insulation is classified by the temperature ranges at which it
can operate for a sustained period of time. There are four common classes:.
*(Including Ambient and 110° Hot Spot)
When a motor insulation class is labeled on the nameplate, the total insulation system is
capable of sustained operation at the
above temperature.
INTERMITTENT DUTY - A requirement of service that demands operation for alternate
intervals of (1) load and no load; or (2) load and rest; (3) load, no load and rest; such
alternative intervals being definitely specified.
INTERPOLES - An auxiliary set of field poles carrying armature current to reduce the field
flux caused by armature reaction in a DC motor.
INVERTER - An electronic device that converts fixed frequency and fixed voltages to
variable frequency and voltage. Enables the user to electrically adjust the speed of an AC
motor.
I2R - Losses due to current flowing in a conductor caused by resistance (equals the current
squared times the resistance).
Application Manual for NEMA Motors
Section
2
Part
4
Section
Page 1002of 115
Part
404/08
Page
14 / 29
Date
09/07
Application Manual for NEMA Motors
J SECONDS (DC MOTORS) - J is the per unit moment of inertia. It is defined as the
time in seconds to accelerate the motor armature to rated base speed using rated full load
torque.
J =(WR2 x Base RPM (seconds)) / (308 x Rated Torque)
JACKSCREW - A device used for leveling the positioning of a motor. These devices are
adjustable screws that fit on the base or motor frame. Also a device for removing endshields
from a motor assembly.
KILOWATT (kW) - Since the watt is a relatively small unit power, the kilowatt –
(kW) 1,000 watts – is used where larger units of power measurement are desirable.
LAMINATIONS - The steel portion of the rotor and stator cores make up a series of thin
laminations (sheets) which are stacked and fastened together by cleats, rivets or welds.
Laminations are used instead of a solid piece in order to reduce eddy-current losses.
LARGE MOTORS - Usually refers to AC motors with 5000 series frames and above
or DC motors with 500 series frames and larger.
LOAD - The burden imposed on a motor by the driven machine. It is often stated as the
torque required to overcome the resistance of the machine it drives. Sometimes “load” is
synonymous with “required power.”
LOCKED ROTOR CURRENT - Steady state current taken from the line with the rotor at
standstill (at rated voltage and frequency). This is the current seen when starting the motor
and load.
LOCKED ROTOR TORQUE - The minimum torque that a motor will develop at rest for
all angular positions of the rotor (with rated voltage applied at rated frequency).
LOSSES - A motor converts electrical energy into a mechanical energy and in so doing,
encounters losses. These losses are all the energy that is put into a motor and not
transformed to usable power but are converted into heat causing the temperature of
the windings and other motor parts to rise.
LUBRICATION - In order to reduce wear and avoid overheating certain motor components
lubrication is required (application of an oil or grease). The bearings are the major motor
component requiring lubrication (as per manufacturer’s instructions). Excess lubrication can
however damage the windings and internal switches, etc.
MAGNETIC POLARITY - It is a fundamental principle of a winding that adjacent poles
Application Manual for NEMA Motors
Section
2
Part
4
Section
Page 1012of 115
Part
404/08
Page
15 / 29
Date
09/07
Application Manual for NEMA Motors
must be wound to give opposite magnetic polarity. This does not mean that the coils actually
have to be wound in this direction before being placed into the stator. It does mean that
the winding must be connected so that, if the current proceeds through one pole in a
clockwise direction, it must proceed through the next pole in a counterclockwise direction.
This principle is used to determine the correctness of connection diagrams.
MEDIUM MOTORS - Motors in NEMA 143T to 449T frames.
MEGGER TEST - A measure of an insulation system’s resistance. This is usually
measured in megohms and tested by passing a high voltage at low current through the motor
windings and measuring the resistance of the various insulation systems.
MOTOR - A device that takes electrical energy and converts it into mechanical energy to
turn a shaft.
MULTI-SPEED MOTORS - A motor wound in such a way that varying connections at the
starter can change the speed to a predetermined speed. The most common multispeed
motor is a two-speed although three and four-speeds are sometimes available. Multispeed
motors can be wound with two sets of windings or one winding. They are also available with
constant torque, variable torque or constant horsepower.
NAMEPLATE - The plate on the outside of the motor describing the motor horsepower,
voltage, speed efficiency, design, enclosure, etc.
NAVY SERVICE “A” - Motors designed to meet requirements of MIL M-17059 or
MIL M-17060 for high shock and service and are essential to the combat effectiveness of a
ship. These motors are usually made of nodular iron.
N.E.C. TEMPERATURE CODE (“T” CODE) - A National Electrical Code index for
describing maximum allowable “skin” (surface) temperature of a motor under any normal or
abnormal operating conditions. The “T” codes are applicable to U.L. listed explosion-proof
motors. The skin temperature shall not exceed the minimum ignition temperature of the
substances to be found in the hazardous location. The “T” code designations apply to motors
and other types of electrical equipment subject to hazardous location classification.
NEMA - The National Electrical Manufacturers Association is a nonprofit organization
organized and supported by manufacturers of electric equipment and supplies. NEMA has set
standards for:
• Horsepower ratings
• Speeds
• Frame sizes and dimensions
• Standard voltages and frequencies with allowable variations
• Service factors
Application Manual for NEMA Motors
Section
2
Part
4
Section
Page 1022of 115
Part
404/08
Page
16 / 29
Date
09/07
Application Manual for NEMA Motors
• Torque
• Starting current & KVA
• Enclosures
NEMA I - (See Weather Protected Machine, Type I.)
NEMA II - (See Weather Protected Machine, Type II.)
NODULAR IRON (DUCTILE IRON) - Special cast iron with a crystalline formation,
which makes it capable of handling high shock.
OIL MIST LUBRICATION-DRY SUMP - A method for lubricating anti-friction bearings,
which utilizes oil, dispersed on an air stream. The mist is exhausted from the bearing housing
so as not to permit oil to accumulate.
OIL MIST LUBRICATION-WET SUMP - Similar to Oil Mist Lubrication – Dry Sump,
except that a pool of oil is developed in the bearing chamber. This oil pool will continue to
supply oil to the bearing in the event that the oil mist is interrupted and is fed from a source
outside the bearing housing such as a constant level oiler.
OPEN BEARING - A ball bearing that does not have a shield, seal or guard on
either of the two sides of the bearing casing.
OPEN EXTERNALLY-VENTILATED MACHINE - A machine which is ventilated with
external air by means of a separate motor-driven blower mounted on machine enclosure.
OPEN PIPE-VENTILATED MACHINE - An open machine except that openings for
admission of ventilating air are so arranged that inlet ducts or pipes can be connected to
them. Air may be circulated by means integral with machine or by means external to and not
a part of the machine. In the latter case, this machine is sometimes known as a separatelyor force-ventilated machine.
OPEN (PROTECTED) MOTOR - A motor having ventilating openings which permit
passage of external cooling air over and around the windings. The term “open machine,”
when applied to large apparatus without qualification, designates a machine having no
restriction to ventilation other than that necessitated by mechanical construction.
“P” BASE - A special mounting similar to “D” flange except with a machined fit tenon
recessed instead of protruding. Usually found on pumps.
PARALLELING - When two or more DC motors are required to operate in parallel – that
is, to drive a common load while sharing the load equally among all motors – they should
have speed-torque characteristics which are identical. The greater the speed droop with load,
Application Manual for NEMA Motors
Section
2
Part
4
Section
Page 1032of 115
Part
404/08
Page
17 / 29
Date
09/07
Application Manual for NEMA Motors
the easier it becomes to parallel motors successfully. It follows that series motors will operate
in parallel easier than any other type. Compound motors, which also have drooping speed
characteristics (high regulation), will generally parallel without special circuits or equalization.
It may be difficult to operate shunt or stabilized-shunt motors in parallel because of their
nearly constant speed characteristics. Modifications to the motor control must sometimes be
made before these motors will parallel within satisfactory limits.
PART WINDING START MOTOR - Is arranged for starting by first energizing part of
the primary winding and subsequently energizing the remainder of this winding in one or more
steps. The purpose is to reduce the initial value of the starting current drawn or the starting
torque developed by the motor. A standard part winding start induction motor is arranged so
that one-half of its primary winding can be energized initially and subsequently the remaining
half can be energized, both halves then carry the same current.
PERMANENT MAGNET SYNCHRONOUS
(HYSTERESIS SYNCHRONOUS) - A motor with magnets embedded into the rotor
assembly, which enable the rotor to align itself with the rotating magnetic field of the stator.
These motors have zero slip (constant speed with load) and provide higher torque, efficiency
and draw less current than comparable reluctance synchronous motors.
PHASE - Indicates the space relationships of windings and changing values of the recurring
cycles of AC voltages and currents. Due to the positioning (or the phase relationship) of the
windings, the various voltages and currents will not be similar in all aspects at any given
instant. Each winding will lead or lag another in position. Each voltage will lead or lag
another voltage in time. Each current will lead or lag another current in time. The most
common power supplies are either single- or three-phase (with 120 electrical degrees
between the three phases).
PLUG REVERSAL - Reconnecting a motor’s winding in reverse to apply a reverse
braking torque to its normal direction of rotation while running. Although it is an effective
dynamic braking means in many applications, plugging produces more heat than other
methods and should be used with caution.
POLARIZATION TEST - A ratio of one-minute megger test (see Megger Test) to ten
minute megger test. Used to detect contaminants in winding insulation done typically on high
voltage V.P.I. motors, which are tested by water immersion.
POLES - In an AC motor, refers to the number of magnetic poles in the stator winding. The
number of poles determines the motor’s speed. (See Synchronous Speed). In a DC motor,
refers to the number of magnetic poles in the motor. They create the magnetic field in which
the armature operates (speed is not determined by the number of poles).
POLYPHASE MOTOR - Two- or three-phase induction motors have their windings, one
for each phase, evenly divided by the same number of electrical degrees. Reversal of the
Application Manual for NEMA Motors
Section
2
Part
4
Section
Page 1042of 115
Part
404/08
Page
18 / 29
Date
09/07
Application Manual for NEMA Motors
two-phase motor is accomplished by reversing the current through either winding. Reversal
of a three-phase motor is accomplished by interchanging any two of its connections to the
line. Polyphase motors are used where a polyphase (three-phase) power supply is available
and is limited primarily to industrial applications.
Starting and reversing torque characteristics of polyphase motors are exceptionally good.
This is due to the fact that the different windings are identical and, unlike the capacitor
motor, the currents are balanced. They have an ideal phase relation, which results in a true
rotating field over the full range of operation from locked rotor to full speed.
POWER CODE - Identifies the type of power supply providing power to a DC motor.
Frequency, voltage, and type of rectifier configuration.
POWER FACTOR - A measurement of the time phase difference between the voltage and
current in an AC circuit. It is represented by the cosine of the angle of this phase difference.
For an angle of 0 degrees, the power factor is 100% and the volt/amperes of the circuit are
equal to the watts (this is the ideal and an unrealistic situation). Power factor is the ration of
Real Power-kW to total kVA or the ratio of actual power (watts) to apparent power (volt
amperes).
PRIMARY WINDING - The winding of a motor, transformer or other electrical device
which is connected to the power source.
PROTECTIVE RELAY - The principal function of a relay is to protect service from
interruption, or to prevent or limit damage to apparatus.
PULL-IN TORQUE - The maximum constant torque, which a synchronous motor
will accelerate into synchronism at, rated voltage and frequency.
PULL-UP TORQUE - The minimum torque developed by an AC motor during the
period of acceleration from zero to the speed at which breakdown occurs. For motors, which
do not have a definite breakdown torque, the pull-up torque is the minimum torque
developed during the process of achieving rated speed.
R – R - (r bar) is the per unit armature circuit resistance using counter
emf as a base:
R = Hot IR voltage drop, where Terminal volts-(Hot IR voltage drop)
and
Hot IR voltage drop = (Rated 1a x Hot Arm. Cir. Resistance) +2.0 (Brush drop) volts.
Application Manual for NEMA Motors
Section
2
Part
4
Section
Page 1052of 115
Part
404/08
Page
19 / 29
Date
09/07
Application Manual for NEMA Motors
RPM (REVOLUTIONS PER MINUTE) - The number of times per minute the shaft of
the motor (machine) rotates. This is a function of design and the power supply.
RANDOM WOUND - The standard type of stator winding used in motors under 1,000
volts. The coils are random wound with round wire as opposed to flat form wound coils.
RTD (RESISTANCE THERMAL DETECTORS)
WINDING RTD A resistance device used to measure temperature change in the motor
windings to detect a possible over heating condition. These detectors are embedded
into the winding slot and their resistance varies with temperature.
BEARING RTD A probe used to measure bearing temperature to detect an
overheating condition. The RTD’s resistance varies with the temperature of the
bearings.
REACTANCE (INDUCTIVE) - The characteristic of a coil when connected to alternating
current, which causes the current to lag the voltage in time phase. The current wave reaches
its peak later than the voltage wave reaches its peak.
REFLECTIVE WAVE - Reflective waves can occur in variable-speed motor applications
when the drive and motor are placed a considerable distance apart. The combination of long
lead (cable) lengths and the fast switching semiconductors in the drive can cause voltage
spikes at the motor’s terminals. These spikes can cause the motor’s insulation to deteriorate.
RELAY - A device that is operative by a variation in the conditions of one electric circuit to
effect the operation of other devices in the same or another electric circuit.
RELUCTANCE - The characteristic of a magnetic material which resists the flow
of magnetic lines of force through it.
RELUCTANCE SYNCHRONOUS MOTOR - A synchronous motor with a special rotor
design which directly lines the rotor up with the rotating magnetic field of the stator, allowing
for no slip under load. Reluctance motors have lower efficiencies, power factors and torques
than their permanent magnet counterparts.
RESISTANCE - The degree of obstacle presented by a material to the flow of electric
current is known as resistance and is measured in ohms (ȍ).
RESILIENT MOUNTING - A suspension system or cushioned mounting designed to
reduce the transmission of normal motor noise and vibration to the mounting surface. This
type of mounting is typically used in fractional horsepower motors for fans and blowers.
Application Manual for NEMA Motors
Section
2
Part
4
Section
Page 1062of 115
Part
404/08
Page
20 / 29
Date
09/07
Application Manual for NEMA Motors
REVERSING - Unless otherwise specified, a general-purpose DC motor is reversible. A
DC motor can be reversed by changing the polarity of the field or the armature, but not both.
When rapid reversing is necessary, the armature circuit is reversed. In some cases, it is
advantageous to reverse the field connections of shunt motors, since the controls have to
handle much less current, especially on large motors, than do armature-circuit contactors. An
AC motor is reversed by reversing the connections of one leg on three-phase power or by
reversing the leads on single phase.
ROLLER BEARING - A special bearing system with cylindrical rollers capable of handling
belted applications too large for standard ball bearings.
ROTATING MAGNETIC FIELD - The force created by the stator once power is applied
to it that causes the rotor to turn.
ROTOR - The rotating member of an induction motor made up of stacked laminations. A
shaft running through the center and a squirrel cage made in most cases of aluminum, which
holds the laminations together, and act as a conductor for the induced magnetic field. The
squirrel cage is made by casting molten aluminum into the slots cut into each lamination.
SCREENS - Are protection which can be placed over openings in the fan cover on a fancooled motor or ventilation openings of a protected motor to help keep out large particles
and/or animals, but not block ventilation.
SECONDARY WINDING - Winding which is not connected to the power source, but
which carries current induced in it through its magnetic linkage with the primary winding.
SERIES DC MOTORS - Where high starting torques are required for a DC motor, the
series motor is used. The load must be solidly connected to the motor and never decrease to
zero to prevent excessive motor speeds. The load must tolerate wide speed variations from
full load to light load. Typical areas of application are industrial trucks, hoists, cranes and
traction duty.
SERVICE FACTOR (SF) –
1.When used on a motor nameplate, a number which indicates how much above the
nameplate rating a motor can be loaded without causing serious degradation (i.e., a 1.15 SF
can produce 15% greater torque than the 1.0 SF rating of the same motor).
2.When used in applying motors or gearmotors, a figure of merit, which is used to “adjust”,
measured loads in an attempt to compensate for conditions which are difficult to measure or
define. Typically, measured loads are multiplied by service factors (experience factors) and
the result in an “equivalent required torque” rating of a motor or gearmotor.
Application Manual for NEMA Motors
Section
2
Part
4
Section
Page 1072of 115
Part
404/08
Page
21 / 29
Date
09/07
Application Manual for NEMA Motors
SHORT-CIRCUIT - A defect in a winding which causes part of the normal electrical circuit
to be bypassed. This frequently results in reducing the resistance or impedance to such an
extent as to cause overheating of the winding and subsequent burnout.
SHAFT - The rotating member of the motor which protrudes past the bearings for
attachment to the driven apparatus.
SHUNT WOUND DC MOTORS - Integral-horsepower shunt motors are used where the
primary load requirements are for minimum speed variation from full load to no-load and/or
constant horsepower over an adjustable speed range at constant potential. Shunt motors are
suitable for average starting torque loads. Typical applications include individual drives for
machine tools such as drills and lathes, and centrifugal fans and blowers which are regulated
by means of the discharge opening.
SKEW - Arrangement of laminations on a rotor or armature to provide a slight angular
pattern of their slots with respect to the shaft axis. This pattern helps to eliminate low speed
cogging effects in an armature and minimize induced vibration in a rotor as well as reduce
associated noise. It can also help to increase starting torque.
SLEEVE BEARINGS - A type of bearing with no rolling elements, where the motor
shaft rides on a film of oil.
SLIP - The difference between the speed of the rotating magnetic field (which is always
synchronous) and the rotor in a non-synchronous induction motor is known as slip. It is
expressed as a percentage of synchronous speed. Slip generally increases with an increase
in torque.
SPACE HEATER - Small resistance heater units mounted in a motor that are energized
during motor shutdown to prevent condensation of moisture in the motor windings.
SPECIAL PURPOSE MOTOR - Motor with special operating characteristics or special
mechanical construction, or both, designed for a particular application and not falling within
the definition of a general purpose or definite purpose motor.
SPLASH-PROOF MOTOR - An open motor in which the ventilating openings are so
constructed that drops of liquid or solid particles falling on it, or coming toward it in a straight
line at any angle not greater than 100 degrees from the vertical, cannot enter either directly
or by striking and running along a surface of the motor.
SPLIT PHASE START - Motors, which employ a main winding and an auxiliary winding,
called the starting winding. The windings are unlike and thereby “split” the single phase of the
power supply by causing a phase displacement between the currents of the two windings thus
Application Manual for NEMA Motors
Section
2
Part
4
Section
Page 1082of 115
Part
404/08
Page
22 / 29
Date
09/07
Application Manual for NEMA Motors
producing a rotating field. After the motor has attained approximately 75% of rated speed, the
starting winding is automatically disconnected by means of a centrifugal switch or by a relay.
The motor then continues to run on a single oscillating field, which in conjunction with the
rotation of the rotor, results in a rotating field effect. Since there is no rotating field, after the
starting winding is de-energized, the rotation cannot be changed until the motor has come to
rest or at least slowed down to the speed at which the automatic switch closes. Special
starting switches are available as well as special reversing switches which have a means for
shunting the open contracts of the automatic switch while the motor is running and thus
permits the split phase motor to be reversed while rotating. This type of starting is found
typically on single phase fractional motors.
SPEED - The speed of the motor refers to the RPM’s (revolutions per minute) of the shaft.
For a three-phase AC motor the synchronous speed =
120 x frequency / # of poles
Where the frequency is measured in Hertz (or cycles per second). The number of poles are a
function of design.
STABILIZED SHUNT-WOUND MOTOR - A stabilized shunt-wound motor is a directcurrent motor in which the shunt field circuit is connected either in parallel with the armature
circuit or to a separate source of excitation voltage and which also has a light series winding
added to prevent a rise in speed or to obtain a slight reduction in speed with increase in load.
STANDARDS ORGANIZATIONS
ABS - American Bureau of Shipping
ANSI -American National Standards Institute
API - American Petroleum Institute
BASEEFA - British Approval Service for Electrical
Equipment in Flammable Atmospheres
BISSC - Baking Industry Standards Committee
CE - Compliance to European Standards
CSA - Canadian Standards Association
EPACT1997 - U.S. Energy Policy Act
IEC - International Electrotechnical Commission
IEEE - Institute of Electrical and Electronics Engineers
ISO - International Standards Organization
MIL - Military Specifications
MSHA - U.S. Mining, Safety, Health Administration
NAFTA - North American Free Trade Agreement
NEC - National Electric Code
NEMA - National Electrical Manufacturers Association
UL - Underwriter’s Laboratories
UR - Underwriter’s Laboratories Recognized
Application Manual for NEMA Motors
Section
2
Part
4
Section
Page 1092of 115
Part
404/08
Page
23 / 29
Date
09/07
Application Manual for NEMA Motors
USDA - U.S. Department of Agriculture
USCG - U.S. Coast Guard
STARTING CURRENT - Amount of current drawn at the instant a motor is energized--in
most cases much higher than the required for running. Same as locked rotor current.
STARTING TORQUE - The torque or twisting force delivered by a motor at the instant
it is energized. Starting torque is often higher than rated running or full load torque.
STATOR - That part of an AC induction motor’s magnetic structure which does not rotate. It
usually contains the primary winding. The stator is made up of laminations with a large hole
in the center in which the rotor can turn; there are slots in the stator in which the windings for
the coils are inserted.
STRESS CONES - A physical protection placed over the external connections point on
medium and high voltage motor leads. Stress cones are used to avoid dielectric breakdown
of motor leads in the vicinity of the external connection. Stress cones generally require an
oversized conduit box on large motors.
SUFFIXES TO NEMA FRAMES - Letter suffixes sometimes follow the NEMA frame
size designations. Some of these suffixes, according to NEMA standards, have the following
meanings:
FRACTIONAL HORSEPOWER MOTORS
C - Face mounting
G - Gasoline pump motor
H - Indicates a frame having a larger “F” dimension
J - Jet pump motor
Y - Special mounting dimensions (see manufacturer)
Z - All mounting dimensions are standard except the shaft extension
INTEGRAL HORSEPOWER MOTORS
A - DC motor or generator
C – C-Face mounting on drive end
D – D-Flange mounting on drive end
P - Vertical hollow and solid shaft motors with P-Base flange
HP - Vertical solid shaft motors with P-Base flange (normal thrust)
JM - Close-coupled pump motor with C-Face mounting and special shaft extensions
JP - Close-coupled pump motor with C-Face mounting and special long shaft extension
LP - Vertical solid shaft motors with P-Base flange (medium thrust)
S - Standard short shaft for direct connection
T - Standardized shaft --“T” frame
V - Vertical mounting
Y - Special mounting dimensions
Z - All mounting dimensions standard except shaft Extension
Application Manual for NEMA Motors
Section
2
Part
4
Section
Page 1102of 115
Part
404/08
Page
24 / 29
Date
09/07
Application Manual for NEMA Motors
SURGE PROTECTION - A capacitor device usually mounted in the conduit box to
flatten the voltage surges that may occur as a result of lighting or a power supply surge
(short-period peak). These surges can result in more than twice the rated voltage going to
the windings and in turn cause winding damage.
SYNCHRONOUS MOTOR - A motor which operates at a constant speed up to full load.
The rotor speed is equal to the speed of the rotating magnetic field of the stator – there is no
slip. There are two major synchronous motor types: reluctance and permanent magnet.
A synchronous motor is often used where the exact speed of a motor must be maintained.
SYNCHRONOUS SPEED - The speed of the rotating magnetic field set up by the stator
winding of an induction motor. In a synchronous motor, the rotor locks into step with the
rotating magnetic field and the motor is said to run at synchronous speed. Approximately the
speed of the motor in revolutions per minute(RPM) with no load on it is equal to:
120 x Frequency / # of poles
“T” FRAME - Current NEMA designation identifying AC induction motor frames. (NEMA
has dimension tables which offer standard frame measurements.) Replaced the previous
standard “U” frame in 1965.
TACHOMETER - A small generator normally used as a rotational speed sensing device.
Tachometers are typically attached to the output shaft of DC or AC adjustable-speed motors
requiring close speed regulation. The tachometer feeds its signal to a control which adjusts
its output to the DC or AC motor accordingly (called “closed loop feedback” control).
TEMPERATURE - Has direct effect on motor life when considering life expectancy. The
following application considerations that affect a motor’s operating temperature should be
taken into account:
1) Bearings
2) Lubricants
3) Duty Cycle
4) Radial Loading
5) Axial Loading
6) Mounting
7) Enclosure
8) Ambient Temperature
9) Ventilation
As a general rule, each 10oC increase in total temperature over the maximum permissible to
the motor’s insulation system, reduces its life by half. Bearing or gear lubricant life is reduced
Application Manual for NEMA Motors
Section
2
Part
4
Section
Page 1112of 115
Part
404/08
Page
25 / 29
Date
09/07
Application Manual for NEMA Motors
by half for every 25oF (approximately 14oC ) increase in temperature. Heat eventually causes
deterioration of most lubricants and seals leading to leakage and increased friction.
“T” (TEMPERATURE CODES)
(See N.E.C. Temperature Codes.)
TEMPERATURE RISE - Some of the electrical energy losses inherent in motors are
converted to heat causing some of the motor parts to heat up when the motor is running. The
heated parts are at a higher temperature than the air surrounding them which causes a rise
above room (ambient) temperature. It is important to match the proper motor and insulation
system (NEMA temp. codes) to the expected ambient temperature. If a motor has been built
with greater than 1.0 service factor, then it can operate at a temperature somewhat higher
than the motor’s rated operating temperature. In all cases, the actual insulation thermal
capability usually is higher than the motor’s operating temperature to allow for any excessive
heat areas. This is called hot spot allowance. (see Insulation Systems for NEMA
standard temperature codes). Each temperature code has an associated temperature rise
which when added to the ambient and hot spot should not exceed the temperature handling
of the insulation system.
TEMPERATURE TESTS - Tests conducted to determine the temperature rise of certain
parts of a motor above the ambient temperature, when operating under specific conditions.
TESTS
ROUTINE
A routine test is a basic test done in the factory to the requirements of NEMA MG1, paragraph
12.51 and IEEE-112-1978. It includes the following measurements: no load current/watts;
winding resistance; and high potential test.
COMPLETE
A complete test is a test which meets the requirements of IEEE-112-1978. It includes the
tests conducted in a Routine Test as well as a full-load heat run; no-load current and watts
determination of torques; efficiencies at 125, 100, 75, 50 and 25 percent of full load; power
factor at 125, 100, 75, 50 and 25 percent of full load.
WITNESS
A witness test is a test performed with a customer representative present.
NOISE
A test performed to verify the motor sound level, conducted in accordance with IEEE-85. The
tests are performed under no-load conditions in sound room.
THERMAL PROTECTOR (INHERENT) - An inherent overheating protective device
which is responsive to motor temperature and when properly applied to a motor, protects the
Application Manual for NEMA Motors
Section
2
Part
4
Section
Page 1122of 115
Part
404/08
Page
26 / 29
Date
09/07
Application Manual for NEMA Motors
motor against dangerous overheating due to overload or failure to start. This protection is
available with either manual or automatic reset.
THERMISTOR – THERMALLY SENSITIVE RESISTOR - A semiconductor used to
measure temperature that can be attached to an alarm or meter to detect motor overheating.
THERMOCOUPLE – THERMAL DETECTION DEVICE - A temperature detecting
device made of two dissimilar metals which generates a voltage as a function of temperature.
Thermocouples can be attached to a meter or alarm to detect overheating of motor windings
or bearings.
THERMOSTAT - Units applied directly to the motor’s windings which senses winding
temperature and may automatically break the circuit in an overheating situation.
TORQUE - Turning force delivered by a motor or gearmotor shaft, usually expressed in
lb-ft = (HP x 5252) / RPM = full load torque
TOTALLY-ENCLOSED ENCLOSURE - A motor enclosure, which prevents free
exchange of air between the inside and the outside of the enclosure but is not airtight.
Different methods of cooling can be used with this enclosure.
TOTALLY-ENCLOSED AIR-TO-AIR COOLED MACHINE - A totally enclosed
machine cooled by circulating internal air through a heat exchanger which in turn, is cooled by
circulating external air. Provided with an air-to-air heat exchanger for cooling ventilating air
and fan or fans integral with rotor shaft or separate, for circulating external air.
TOTALLY-ENCLOSED FAN-COOLED ENCLOSURE - Provides for exterior cooling
by means of a fan(s) integral with the machine, but external to the enclosed parts.
TOTALLY-ENCLOSED NON-VENTILATED ENCLOSURE - Has no provisions for
external cooling of the enclosed parts. The motor is cooled by heat radiation from the exterior
surfaces to the surrounding atmosphere.
TOTALLY-ENCLOSED PIPE VENTILATED MACHINE - A totally-enclosed
machine except for openings arranged so inlet and outlet ducts or pipes may be connected to
them for the admission and discharge of ventilating air. Air may be circulated by means
integral with the machine or by means external to and not a part of the machine. In latter
case, these machines shall be known as separately-forced-ventilated machines.
TOTALLY-ENCLOSED WATER AIR-COOLED MACHINE - A totally-enclosed
machine cooled by circulating air which in turn, is cooled by circulating water. Provided with
water-cooled heat exchanger for cooling ventilating air and fan or fans, integral with rotor
shaft or separate, for circulating ventilating air.
Application Manual for NEMA Motors
Section
2
Part
4
Section
Page 1132of 115
Part
404/08
Page
27 / 29
Date
09/07
Application Manual for NEMA Motors
TRANSFORMER - A device which converts electrical power (alternating current) to
electrical power of a different voltage. In this device, both primary and secondary windings are
usually stationary and are wound on a common magnetic core.
THRUST BEARINGS - Special bearings used to handle higher than normal axial forces
exerted on the shaft of the motors as is the case with some fan or pump blade mountings.
TUBE COOLED - A motor in which heat is dissipated by air-to-air heat exchange
“U” FRAME - A previously used NEMA designation indicating frame size and dimension
(prior to 1965 the standard frame sizes per horsepower rating).
U.L. (UNDERWRITER’S LABORATORY) - An independent testing organization,
which examines and tests - devices, systems and materials with particular reference to life,
fire and casualty hazards. It develops standards for motors and controls used in hazardous
locations through cooperation with manufacturers. U.L. has standards and tests for
explosion-proof and dust ignition-proof motors, which must be met and passed before
application of the U.L. label. UL also has a recognized component mark for Canada and the
US:
VACUUM DEGASSED BEARINGS - Vacuum degassing is a process used in the
purifying of steel for ball bearings ensuring a very dense and consistent bearing surface. This
results in a longer lasting superior bearing.
VARIABLE TORQUE - A multi-speed motor used on loads with torque requirements,
which vary with speed as with some centrifugal pumps and blowers. The horsepower varies
as the square of the speed.
VERTICAL MOTOR - A motor being mounted vertically (shaft up or down) as in
many pump applications.
VERTICAL “P” BASE MOTOR - A vertical motor with a special mounting face
conforming to NEMA design “P” and with a ring groove on the shaft.
VOLTAGE - The force that causes a current to flow in an electrical circuit. Analogous to
pressure in hydraulics, voltage is often referred to as electrical pressure. The voltage of a
motor is usually determined by the supply to which it is attached. NEMA requires that motor
be able to carry its rated horsepower at nameplate voltage plus or minus 10% although not
necessarily at the rated temperature rise.
Application Manual for NEMA Motors
Section
2
Part
4
Section
Page 1142of 115
Part
404/08
Page
28 / 29
Date
09/07
Application Manual for NEMA Motors
VOLTAGE DROP - Loss encountered across a circuit impedance from power source to
applicable point (motor) caused by the resistance in conductor. Voltage drop across a
resistor takes the form of heat released into the air at the point of resistance.
WK2 (MOMENT OF INERTIA) - The moment of inertia is expressed as Wk2 in terms of
pound-feet
squared. It is the product, the weight of the object in pounds and the square of the radius of
gyration in feet. If the application is such that the motor is driving through a pulley or gear so
that the driven equipment is operating at a higher or lower speed than the rotor, it is
necessary to calculate the inertia reflected to the motor shaft. This is an equivalent Wk2
(reflected to motor shaft) = Wk2 based on the speed (rpm) of the motor.
Wk2 (reflected to motor shaft) =
Wk2 (driven equipment) x (driven equipment rpm/motor rpm)2
WATT - The amount of power required to maintain a current of one ampere at a pressure of
one volt. Most motors are rated in Kwatt equal to 1,000 watts. One horsepower is equal to
746 watts.
WEATHER-PROTECTED MACHINE
TYPE I (WPI) weather-protected machine is an open machine with its ventilating passages so
constructed as to minimize the entrance of rain, snow and airborne particles to the electric
parts. Its ventilating openings are constructed to prevent the passage of a cylindrical rod 3/4
inch in diameter.
WEATHER-PROTECTED MACHINE
TYPE II (WPII) have, in addition to the enclosure defined for a Type I weather-protected
machine, its ventilating passages at both intake and discharge so arranged that high velocity
air and airborne particles blown into the machine by storms or high winds can be discharged
without entering the internal ventilating passages leading directly to the electric parts of the
machine itself. The normal path of the ventilating air which enters the electric parts of the
machines are arranged by baffling or through a separate housing to provide at least three
abrupt changes in direction, none of which shall be less than 90o. In addition, an area of low
velocity not exceeding 600 feet per minute shall be provided in the intake air path to minimize
the possibility of moisture or dirt being carried into the electric parts of the machine.
WOUND ROTOR INDUCTION MOTOR - A wound rotor induction motor is an
induction motor in which the secondary circuit consists of polyphase winding or coils with
terminals that are either short circuited or closed through suitable circuits. A wound rotor
motor is sometimes used when high breakdown torque and soft start or variable-speed
operation are required.
Application Manual for NEMA Motors
Section
2
Part
4
Section
Page 1152of 115
Part
404/08
Page
29 / 29
Date
09/07
Application Manual for NEMA Motors
WYE-DELTA STARTING - A method for starting a motor at rated voltage but drawing
locked rotor current and producing reduced locked rotor torque to provide lower starting
torque than a straight delta connection. Once the load and motor have been started, the
wiring will switch from the wye connection to a delta connection in which mode it must run and
deliver full torque.
Was this manual useful for you? yes no
Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Download PDF

advertisement