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Yaskawa Electric
America
Motor Basics
07/08/2002
PP.AFD.02.MotorBasics
1 of 55
Three Phase Motor Construction
Windings - Electromagnets
Rotor bars
Rotor
Stator
Three Phase Motor Construction
Stator
Windings
Enclosure
Air Gap
Stator
Rotor
Shaft
End View
Three Phase Motor Construction
T1
T2’
T3’
T3
End View
T2
T1’
Motor Operation
Motor Operation
Motor Operation
Motor Operation
Three Phase Motor Construction
T1
denotes current
+is moving away
from you
+
T2’
T3’
+
+
T3
End View
T2
T1’
denotes current
is moving
towards you
Rotation of the motor
One Cycle*
T1
T3
T2
+
+
S
N
* - current waveform
+
Rotation of the motor
One Cycle*
T1
T3
T2
+
+
S
+
N
+
+
+
* - current waveform
Rotation of the motor
One Cycle*
T1
T3
T2
+
+
S
+
+
+
N
+
+
+
+
* - current waveform
Rotation of the motor
One Cycle*
T1
T3
T2
+
+
S
+
+
+
N
+
+
N
+
+
+
S
+
* - current waveform
+
Rotation of the motor
One Cycle*
T1
T3
T2
+
+
S
+
+
+
N
+
+
N
+
+
+
N
+
+
+
S
+
* - current waveform
+
Rotation of the motor
One Cycle*
T1
T3
T2
+
+
S
+
+
+
N
+
+
N
+
+
+
N
+
+
+
N
+
+
S
+
* - current waveform
+
+
Rotation of the motor
One Cycle*
T1
T3
T2
+
+
S
+
+
+
+
+
S
N
+
+
N
N
+
+
+
N
+
+
+
N
+
+
S
+
* - current waveform
+
+
+
Calculating Synchronous
Speed of the Motor
120 f
No 
P
Poles & Synchronous RPM @ 60Hz
Magnetic Poles
2
4
6
8
7200
P
=
Synchronous RPM
3600
1800
1200
900
Synchronous RPM
7200
Synchronous RPM
=
P
Three Phase Motor Construction
T1
T2’
T3’
T3
End View
T2
T1’
Three Phase Motor Construction
T1
T2’
T3’
T3
End View
T2
T1’
Three Phase Motor Construction
T3b
T2b’
T1b’
T1a
T3b’
T2b
T3b’
T2a
T1a’
T1b
End View
T2a’
T3b
Magnetic
Poles
What is Slip ?
To produce torque in an induction motor, current
must flow in the rotor.

To induce current flow in the rotor, the rotor
speed must be slightly slower than the
synchronous speed.

The difference between the synchronous speed
and the rotor speed (rated speed) is called the slip.

Flux
Stator
Slip
Rotor
Calculating Motor Rated Speed
Formula to find actual motor RPM
N
=
120 f
P
( 1-s )
Where:
N
- RPM of the motor
f
- Frequency in Hz
P
- Number of poles of the motor
s
- (No - N) / No
Speed - Torque Curve
(300%)
(600%)
Slip
TORQUE
CURRENT
(300%)
(200%)
Locked Rotor
Torque (150%)
Breakdown
Torque
(200-250%)
Pull Up Torque
(125%)
Full Load
Torque (100%)
No Load
Current
(30%)
SPEED
Rated Speed Synch Speed
Speed - Torque Curve
TORQUE
SPEED
Typical NEMA Design Characteristics
NEMA Design A
High breakdown torque

Normal starting torque

High starting current

Low full load slip
TORQUE

300%
Used in applications
that require:


Occasional overloads

Better efficiency
200%
100%
0
SPEED
100%
Typical NEMA Design Characteristics
NEMA Design B
300%
Normal breakdown torque

Normal starting torque

Low starting current

Normal full load slip


less than 5%
TORQUE

Design A
200%
100%
Design B
General Purpose Motor
0
SPEED
100%
Typical NEMA Design Characteristics
NEMA Design C
Low breakdown torque

High starting torque

Low starting current

Normal full load slip

less than 5%
TORQUE

300%
Design C
Design A
200%
100%
Design B
Used in applications
that require:


high breakaway torque
0
SPEED
100%
Typical NEMA Design Characteristics
NEMA Design D
300%
Design D
High breakdown torque

High starting torque

Normal starting current

High full load slip

5 - 13%
Design C
TORQUE

Design A
200%
100%
Design B
Used in applications
that require:


high breakaway torque
0
SPEED
100%
Motor Nameplate Data
Understanding the Nameplate
HP- Horsepower
The horsepower
figure stamped on
the nameplate is the
horsepower the
motor is rated to
develop when
connected to a circuit
of the voltage,
frequency and
number of phases
specified on the
motor nameplate.

Rotational Horsepower Formula

HP =
The horsepower formula in simplified form
Torque x RPM
OR
Torque =
5250
HP x 5250
RPM
Where:
Torque - Amount of torque in lb.ft.
RPM - RPM of the motor
5250 - constant obtained by dividing 33,000
by 6.28
Understanding the Nameplate
RPM - Revolutions per Minute
The RPM value represents
the approximate speed at which
the motor will run when properly
connected and delivering its
rated output

Understanding the Nameplate
Poles
2
4
6
8
Synchronous RPM
3600
1800
1200
900
Typical Nameplate RPM
3450
1725
1140
850
Understanding the Nameplate
Voltage
The rated voltage
figure on the motor
nameplate refers to
the voltage of the
supply circuit to
which the motor
should be connected,
to produce rated
horsepower and RPM.

Key piece of information
when selecting an inverter.
Effects of Voltage Variation
on the Motor at 60Hz
High Voltage
Low Voltage

Higher than normal current
Higher than normal motor
temperature


Higher than normal current
Lower than normal power
factor

Understanding the Nameplate
Phase
The phase figure on
the motor nameplate
describes the
alternating current
system that the motor
has been designed for.

Key piece of information
when selecting an inverter.
Understanding the Nameplate
Hz-Frequency
The frequency figure
on the motor
nameplate describes
the alternating
current system
frequency that must
be applied to the
motor to achieve
rated speed and
horsepower.

Understanding the Nameplate
Amps
The amp figure on
the motor nameplate
represents the
approximate current
draw by the motor
when developing
rated horsepower on
a circuit of the
voltage and
frequency specified
on the nameplate.

Key piece of information
when selecting an inverter.
Understanding the Nameplate
NEMA Design
The NEMA Design
rating specifies the
speed torque curve
that will be produced
by the motor.

Understanding the Nameplate
Insulation Class
The insulation class
letter designates the
amount of allowable
temperature rise
based on the
insulation system
and the motor
service factor.

Insulation Class Information

Most common insulation classes are class B and F
Insulation Class
A
B
F
H
Ambient Temp.
40oC
40oC
40oC
40oC
Temp. Rise
65oC
90oC
115oC
140oC
Total Temp.
105oC
130oC
155oC
180oC
Understanding the Nameplate
S.F. - Service Factor
The number by which
the horsepower rating is
multiplied to determine
the maximum safe load
that a motor may be
expected to carry
continuously


Example - a 10HP motor with a
service factor of 1.15 will
deliver 11.5 horsepower
continuously without exceeding
the allowable temperature rise
of its insulation class
Understanding the Nameplate
Frame
The frame designation
refers to the physical
size of the motor as
well as certain
construction features
such as the shaft and
mounting dimensions.

Types of Motor Enclosures
Open Drip-proof (ODP)
 Totally enclosed non-ventilated (TENV)
 Totally enclosed fan cooled (TEFC)
 Totally enclosed blower cooled (TEBC)

Types of Motor Enclosures
ODP


Open drip-proof
Ventilating openings
permit passage of
external cooling air over
and around the
windings of the motor.
Small degree of
protection against liquid
or solid particles
entering the enclosure.
Types of Motor Enclosures


TENV
Totally enclosed
non-ventilated
Totally enclosed
enclosure with no
means of external
cooling.
Types of Motor Enclosures


TEFC
Totally enclosed
fan-cooled
Totally enclosed
enclosure with
external cooling
means, such as a
shaft connected fan
Types of Motor Enclosures


TEBC
Totally enclosed
blower-cooled
Totally enclosed
enclosure with
external cooling
means such as a
separately
controlled
motor/blower
TEFC Speed Ranges

Constant Torque
4:1
(15-60 Hz)

Constant Torque
10:1 (6-60 Hz)

Variable Torque
1-60 Hz
2:1 (30-60 Hz) CT
TENV/TEBC Speed Ranges

Constant Torque
0 to Base Speed
100:1
(0.6-60 Hz)
1000:1
(0.06-60 Hz)
Motor Retrofit Summary






RPM
Volts
Phase
Amps
NEMA Design
Frame + any prefix
or suffix letter codes





Location
Mounting Orientation
Application
Enclosure Style
Motor Control Method
 Inverter-Duty?
Motor Basics Exercise

Answer the following questions using your knowledge and/or the documents from this class.
1.) Write down the formula to calculate synchronous motor speed
(please use the simplified form).
2.) To calculate the actual motor speed what has to be included in the
above formula ?
3.) The majority of electric motors used in general purpose applications in
industry today are what NEMA design ?
4.) A NEMA design D motor is characterized by very high breakdown torque,
and a large percentage of slip ? (True or False)
5.) Name the two pieces of information needed off the motor nameplate
when selecting an inverter.
Motor Basics Exercise

Answer the following questions using your knowledge and/or the documents from this class.
1.) Write down the formula to calculate synchronous motor speed
(please use the simplified form).
120 x f / P
2.) To calculate the actual motor speed what has to be included in the
above formula?
slip
(120 x f / P) - slip
3.) The majority of electric motors used in general purpose applications in
industry today are what NEMA design?
NEMA design B
4.) A NEMA design D motor is characterized by very high breakdown torque,
and a large percentage of slip ? (True or False)
True
5.) Name two key pieces of information needed off the motor nameplate
when selecting an inverter.
Voltage and Full Load Amps (FLA)

Yaskawa Electric America
Technical Training
Services
 09/06/2001
07/08/2002
PP.AFD.02.MotorBasics
55 of 55
 Yaskawa Electric America Technical Training Services

For training information, please:

Call us at 1-800-YASKAWA and select option #6

Check out our website at www.yaskawa.com

E-mail us at [email protected]
07/08/2002
PP.AFD.02.MotorBasics
56 of 55