Single-phase
and special-purpose motors
618 221 Basic Electric Machines
Kittithuch Paponpen
Electronic and Computer System Engineering
Department of Electrical Engineering
Silpakorn University
Single-phase
and special-purpose motors
The universal motors
Single phase induction motor
Starting single phase induction motor
Split phase winding motor
Capacitor start motor
Permanent split capacitor motor
Capacitor start, capacitor run motor
Shaded pole motor
Other type of motor
Single-phase
and special-purpose motors
The universal motors
Introduction to universal motors
Application of universal motors
Speed control of universal motors
Introduction to universal motors
A motor that will operate on a single-phase ac power
source is to take a dc machine and run it from an ac
supply.
Equivalent circuit of a universal motor
Introduction to universal motors
Introduction to universal motors
Induced torque of a dc motor is given by τ ind = Kφ I A
Voltage applied to a shunt or dc motor is reverse
Direction of the filed flux reverse
Direction of the armature current reverse
Achieve a pulsating but unidirectional torque
Practical only for the series dc motor
Armature current and filed current in the machine
must reverse at the same time.
Introduction to universal motors
Introduction to universal motors
Field poles and stator frame must be laminated.
If the were not laminated, their core losses would be
enormous.
When the poles and stator are laminated, this motor is
called a universal motor.
Universal motor can run from either an ac or a dc source.
Introduction to universal motors
Universal motor with ac source
Commutation will be much poorer than it would be with a
dc source.
The extra sparking at the brushes
These spark shorten brush life can be source of radiofrequency interference in certain environments.
Introduction to universal motors
Torque-speed characteristic of a universal motor when
operating from ac and dc power supplies
Introduction to universal motors
The difference between supplying dc source and ac
source
1.
Have a large reactance at 50 or 60 Hz
Input voltage is dropped across these reactance
EA is small
IA and τ are small
Introduction to universal motors
The difference between supplying dc source and ac source
2.
Magnetic saturation could occur near the peak current in the
machine
Could lower the rms flux of the motor a given current level
τ decrease
Decrease in flux increase the speed, but this effect may
partially offset the speed decrease caused by the first effect.
Application of Universal Motors
It is not suitable for constant-speed applications
It is compact and gives more torque per ampere than
any other single-phase motor.
It is used where light weight and high torque are
important
Vacuum cleaners
Drills
Similar portable tools
Kitchen appliances
Single-phase induction motors
Introduction to single-phase induction motors
The double-revolving-Field Theory of single-phase
induction motors
The cross-filed theory of single-phase induction motors
Introduction to single-phase induction motors
Construction of a single-phase induction motor
Introduction to single-phase induction motors
There is not rotating stator magnetic field, it has no
starting torque
τ ind = kB R × BS
= kBR BS sin γ
= kBR BS sin180° = 0
How torque is produced in the rotor?
Introduction to single-phase induction motors
There are 2 basic theories which explain why a torque
is produced in the rotor.
The double-revolving-filed theory of single-phase
induction motor
The cross-field theory of single-phase induction
motor
Introduction to single-phase induction motors
The double-revolving-filed theory of single-phase
induction motor
The resolution of a single pulsating magnetic field
into two magnetic fields of equal magnitude by
rotation in opposite directions.
Introduction to single-phase induction motors
Introduction to single-phase induction motors
Torque-speed characteristic of 3φ
φ induction motor
Torque-speed characteristic curves of the two equal and oppositely rotating stator magnetic fields
Proportional to both the
strength of the rotor magnetic
field and the sine of the angle
between the fields.
When the rotor is turned
backward, IR and IS are very
high, but the angle between
the fields is very large, and
that angle limits the torque of
the motor.
Torque-speed characteristic of a 3φ
φ induction motor
Introduction to single-phase induction motors
Turn backward
Rotor of Single-phase induction motor
When the rotor of the motor
is forced to turn backward,
the angle γ between BR and
BS approaches 180o.
Introduction to single-phase induction motors
The torque-speed characteristic of a single-phase induction motor
Introduction to single-phase induction motors
The cross-filed theory of single-phase induction motor
This concerned with the voltages and currents that
the stationary stator magnetic fields can induce in
the bars of the rotor when the rotor is moving.
Introduction to single-phase induction motors
If the rotor is turning, the rotor current will peak at an angle different
from that of the rotor voltage.
Introduction to single-phase induction motors
This delayed rotor current produces a rotor magnetic field at an angle
different from the angle of the stator magnetic field.
Introduction to single-phase induction motors
The magnitudes of the magnetic fields as a function of time
Starting single-phase induction motors
Split-phase winding
Capacitor-type winding
Shaded stator poles
Comparison of single-phase induction motors
Split-phase winding
Split-phase winding
Split-phase winding
Split-phase winding
Applications
Split-phase induction motor have a moderate
starting torque with a fairly low starting current.
They are available for sizes in the fractionalhorsepower range and are quite inexpensive.
For applications which do not require very high
starting torques
Fans
Blowers
Centrifugal pumps
Capacitor-start motors
Capacitor-start motors
Capacitor-start motors
Capacitor-start motors
Applications
Capacitor-start motors are more expensive than
split-phase motors.
Used in applications where a high starting torque is
required
Compressors
Pumps
Air conditions
Other pieces of equipment that must start under a load.
Permanent Split-Capacitor motors
Simpler than capacitor-run
motors
Starting switch is not need
Disadvantages
Lower starting torque
Capacitor-start, capacitor-run motors
Advantages
Largest starting
torque
Shaded-pole motors
Salient pole and short-circuit coil,
shaded coil
Time vary flux is induced in the pole
by the main winding.
When the pole flux varies, it induces a
voltage and a current in the shading
coil which oppose the original change
in flux.
This opposition retards the flux
changes under the shaded portions of
the coils and therefore produces a
slight imbalance between the two
oppositely rotating stator magnetic
filed.
Shaded-pole motors
Less starting torque
Less efficient
Much higher slip
Used only in very small motor (0.5 hp or less) with very low
starting torque
Cheapest design available
Comparison of single-phase induction motors
From best to worse
Capacitor-start, capacitor-run motor
Capacitor-start motor
Permanent split-capacitor motor
Split-phase motor
Shaded-pole motor
Other types of motors
Reluctance motors
Hysteresis motors
Stepper motors
Brushless DC motors
Reluctance motors
Reluctance torque, this torque
occur because the external field
induces an internal magnetic field
in the iron object.
Since rotor will be locked into the
stator magnetic filed, it is a
synchronous motor
No stating torque
Two-pole reluctance motor
Reluctance motors
Rotor design of a synchronous induction or self-starting reluctance motor.
Reluctance motors
Hysteresis motors
Employs the phenomenon of hysteresis to produce a
mechanical torque.
Rotor is a smooth cylinder of magnetic material with no teeth
or winding.
When magnetic filed of the stator sweeps around the surface of
the rotor, the rotor flux cannot follow it, because the metal of
the rotor has a large hysteresis loss.
The greater hysteresis loss of the rotor material, the greater the
angle by which the rotor magnetic field lags the stator
magnetic field.
It is a synchronous motor
Hysteresis motors
Hysteresis motors
A small hysteresis motor with a shaded-pole stator, suitable for running an
electrical clock.
Stepper motors
It is a synchronous motor
Rotate a specific number of degrees for every electric
pulse received by its control unit, 7.5o -15o / pulse
Used in many control systems, since the position of a
shaft or other piece of machinery can be controlled
precisely with them.
Stepper motors
Stepper motors
Operation of step motor
Brushless DC motors
Combining a small motor like a permanent magnetic stepper
motor with rotor position sensor and a solid-state electronic
switching circuit.
Run from a dc power source but do not have commutators and
brushes.
Brushless DC motors
Brushless DC motors
Advantages
Relative high efficiency
Long life and high reliability
Little or no maintenance
Very little noise compared to a dc motor with brushes
Very high speeds are possible (greater than 50,000 r/min)
Disadvantages
More expensive than a compare brush dc motor