1. Classification of single-
phase induction motor
(Starting methods of 1Ф
induction motor)
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2. Single-phase induction motors are classified and named
according to the method employed to make them self-starting.
(1) Split-phase induction motor : ( started by two phase motor
action through the use of an auxiliary or starting winding)
(i) Resistance-start split-phase induction motor
(2) Capacitor motors : ( started by two phase motor action
through the use of an auxiliary and a capacitor)
(i) Capacitor-start induction run motor
(ii) Capacitor run induction motor
(iii) Capacitor-start and Capacitor run induction motor
(3) Shaded-pole induction motor :(started by the motion of the
magnetic field produced by means of shading coil around
A portion of the pole structure)
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5. Centrifugal switch- operation
It is connected in series with the auxiliary
winding and mounted on the rotor shaft. When
the motor started and reaches 75% of
synchronous speed, CFS is mechanically
opened and in running condition auxiliary
winding remains cutout from the circuit.
Therefore, the motor runs only with main
winding.
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12. Characteristics
1.Starting torque – 1.5 times to 2 times the full load torque.
2. Starting current – 6 to 8 times the full load current.
3. Operating power factor – 0.55 to .65.
4. Efficiency – 60-65%
5.Power rating-(1/20 to 1/2kW)
6. Speed range- 2875 rpm to 700 rpm
Applications
It has low starting current and moderate
starting torque. It is used for easily started loads
and typical applications include fans, saws,
washing machines, grinders, blowers centrifugal
pumps, oil burners, domestic refrigerators etc.
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13. In the case of split-phase motors that are hermetically sealed in refrigeration
units, instead of internally-mounted CFS, an electromagnetic relay is used.
As shown in fig., the relay coil is connected in series with main winding and
the pair of contacts which are normally open, is included in the starting
winding. During starting period, Im is large relay contacts close, thereby
allowing Is to flow and the motor starts as usual. After motor reaches 75% of
full load speed, Im drops to a value that is low enough to cause the contacts to
open.
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14. Reversal of direction of rotation – may be
reversed by reversing the line connections of either the
main winding or the starting winding only when it is at
rest.
If reversal is attempted under running conditions,
nothing will happen because under normal operating
conditions the starting switch (CFS or RELAY) is in
open position and the motor is running as a pure 1Ф
induction motor and developing torque in the direction
of rotation.
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18. Characteristics
1.Starting torque- 3.5 to 4.5 times the
full load torque
2. α-varies from 30˚ to 80˚-Starting
torque can be improved
3. Power factor varies from 0.65 to 0.75
4. Efficiency– 65 to 70%
5. Power rating –1/10 to 3/4 kW
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19. Requirements of capacitor
Electrolytic capacitors are used
as starting capacitors ,value
around 50µF to a few hundred
micro-farads.
Capacitor designed for
extremely short time duty
service and is guaranteed for
not more than 20 periods of
operation/hr, each period not to
exceed 3 seconds.
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20. Reversal of direction of rotation
It may be reversed by reversing the
connections of one of the windings. The motor
is first brought to rest for this purpose.
Applications
This motor has high starting torque and
therefore is used for hard start loads such
as pumps, compressors, refrigeration
units, conveyors, certain machine tools
etc.
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21. Capacitor run induction motor
(permanent split-phase OR single value capacitor motor)
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24. Characteristics
1.Starting torque-0.5 to 0.8 times the full load
torque.
2.Higher power factor-0.8 t0 0.95
3. Efficiency -55 to 65%
4.Smaller full load current
5.Power rating – 1/20 to 3/4 HP
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25. Requirements of capacitor
Oil-filled or pyranol-insulated
foil-paper capacitors are used as
running capacitors. Low value
of capacitance(2 to 20µF) when
compared to the start capacitor.
This type is especially designed
for continuous –duty rating.
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26. Reversal of direction of rotation
It may be reversed by reversing the connections
of one of the winding. Reversing operation can
be done under running condition is possible.
Applications
It is used for both easy and hard to start loads.
Such motors are widely used in table and ceiling
fans, air circulators, hand blowers and other
portable tools etc. Because of the simplicity of
reversal, such motors are often used to operate
devices such as induction regulators, rheostats,
furnace valve control and arc welding control.
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27. Construction of ceiling fan
starting winding
Squirrel cage rotor
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Main winding
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33. Characteristics
1.Starting torque – 3 to 3.5 times the
full load torque.
2. Efficiency – 60% approx.
3. Power factor-0.9 approx.
4. Power rating- 1/8 to 3/4 HP
5. Pull out torque- up to 260% of
rated torque
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34. Reversal of direction of rotation
The direction of rotation of motor may be
reversed by interchanging the connections to
the supply of either the main winding or
auxiliary winding.
Applications
It combines the advantages of capacitor start
and permanent-capacitors and is used for hard
to start loads such as compressors, refrigerators,
pumps, conveyors etc. These motors are often
employed requiring a quite operating motor
such as in hospitals, studios etc.
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39. Theory of operation
Small motors requiring only small starting torque may
be made self-starting by using low resistance copper
bands called shading bands.
The emf induced in the shading band causes a current
to flow in the band. This current opposes the change of
flux to which it is due and thus there is a time lag
between the fluxes in the shaded and unshaded portion
of the pole.
The flux in the shaded portion of the pole lags the flux
in the other portion. The results is like a rotating field
moving in the direction from the unshaded to the
shaded portion of the pole and a starting torque is
produced.
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41. Characteristics
1.Low starting torque – 0.4 to 0.8 times
the full load torque.
2. Efficiency-35% approx.
3. Powerfactor-0.45 approx.
4. Pull out torque- 15% of full load
torque.
5.Power rating-1/300 to 1/20 HP (2.5W to
40W)
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42. Reversal of direction of rotation
The direction of rotation depends upon
the position of the shading coil on the
pole. i.e., unless the machine is
constructed so that the shading coil can be
shifted to the other side of pole, the
direction of rotation of such a machine
cannot be reversed.
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43. Applications
Because of their poor starting torque,
low power factor and poor efficiency
such motors are only suitable for low
power applications such as for toys,
portable fans , electric clocks, hair
dryers, slide projectors, humidifiers,
small business machines such as
photo copying machines, vending
machines, advertising displays etc.
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