This presentation describes Single phase Induction Motor operation and types

2. Starting Methods of 1-phase Induction Motors:
 As single phase Induction Motors do not possess inherent self starting
torque, one has to employ some external means to make it self starting.
 Commercial single phase induction motors are classified in accordance
with the methods of starting employed.
 The types and methods usually employed in industry are as follows:
1. Split phase method
2. Shaded pole method

3. Split phase method:
 When a motor is provided with two windings, even though these are excited from the
same voltage, the currents in the two windings can be made out-of-phase by adjustment of
the impedance of the auxiliary winding in relation to the main winding.
 As a result main m.m.f. Fm and auxiliary winding m.m.f. Fa constitute an unbalanced
field set with 90° electrical space phase relationship.
 The two symmetrical components, now being unequal Ff ≠ Fb (Ff > Fb is desired); results
in the net production of starting torque.
This is how a single phase motor is made self starting.

4. Phase Splitting Methods:
• Two of important methods of phase splitting are:
a) Resistance Split phase method.
b) Capacitor Split phase methods.

5. Resistance Phase Splitting:
 Schematic diagram is as shown in Figure.
 The motor employs an auxiliary winding with a
higher R/X ratio as compared to the main
winding.
This difference in the R/X ratio causes the
auxiliary winding current Ia to lead the main
winding current Im by angle α, as shown in
Phasor diagram.
The fields created by the two currents also have a
phase difference of α, thereby constituting an
unbalanced system.
 The result is the production of the starting
torque.
V
Iaa
Im
α

6.  When motor attains 75 or 80% of synchronous
speed the auxiliary or starting winding is taken out of
circuit.
 Otherwise it will result in overheating and burning
out of auxiliary winding owing to its low current
carrying capacity & noisy performance.
 The starting torque is 150 to 200% of full-load
running torque
 The starting current is 6 to 8 times full-load current.
 Because of low starting torque, this motor is rarely
used in sizes larger than 1/4 kW.
 Standard sizes are from 1/8 kW to 1/4 kW with a
speed of 1440 rpm.
Applications:
 fans
 blowers
 centrifugal pumps
 refrigerators,
 duplicating machines,
 wood working tools,
 grinders,
 oil burners
 other low starting torque
applications.

7. Capacitor Split phase Motor:
 By using a capacitor in series with the auxiliary winding high starting torques can
be obtained.
 The auxiliary winding along with the capacitor may be disconnected after
starting.
 However, generally the capacitor and auxiliary windings are allowed to remain
connected.
 It helps in improving the overall motor performance and in particular the power
factor.
 Thus, two types of capacitor split-phase motors (also known as capacitor motor)
exist.
 Capacitor Start Motor
 Capacitor Start and Run Motor.

8. Capacitor start motor:
 The motor uses the capacitor only for the purpose of starting.
 The capacitor value is usually chosen as to give α = 90° elect
The range of capacitance is 250µF or above.

9.  As the motor picks up the speed, the starting winding is to be
disconnected, because:
The capacitance that gives the largest starting torque is four times
too big for the best running conditions
if the capacitor is used only for starting, it can be electrolytic type
of capacitor which is much larger than smaller and cheaper paper
capacitors required for continuous operation.
 This type of motor has become popular because of development of
cheap and reliable electrolytic condensers.
 The usual size range is from 1/10 to 1/2 kW but larger sizes are also
available.

10.  A typical torque-speed characteristic
is shown in Figure.
 Applications:
 Refrigerators
 Compressors
 Other applications involving a
hard starting torque such as in
small portable hoists.
 The direction of rotation of motor
may be reversed by interchanging the
connections to the supply of either
main or auxiliary winding.

11. Capacitor Start Capacitor Run Motor:
 Its also called Two-value capacitor
motor.
 The schematic diagram is shown in
Figure.
 As the name suggests, the motor uses
a capacitor not only for starting but
also continuous (run) operation.
 The capacitor used permanently is
called the “run capacitor”.

12.  The run capacitor CR
small value oil impregnated paper continuous rating capacitor.
 Start capacitor CS
much larger value electrolytic short duty capacitor.
 When the motor attains 70% of synchronous speed the starting capacitor CS is
taken out of the circuit by the operation of centrifugal switch.
 Capacitor CR remains permanently in series with the starting or auxiliary winding.
 These motors besides their ability to start heavy loads,
they are extremely quiet in operation,
have better efficiency and power factor when loaded
and develop up to 25% greater overloaded capacities.
 The disadvantage of these machines is only high cost.

13.  The Speed- Torque characteristic is as shown in figure.
 These motors are often employed requiring a quiet operating motor.
 This type of motors are becoming increasingly popular and are now manufactured
in the larger sized single phase motors.
 The direction of rotation may be reversed by interchanging the connections to the
supply of either main or auxiliary windings.