this presentation is about types of ventilation given to the electrical machines,an analysis for the best type,future improvements,and their importance in electrical machines
2. What is cooling ?
Process by which heat resulting from losses
occurring in a machine is given upto a primary
coolant by increasing its temperature
Heated primary coolant may be replaced by a
new coolant at lower temperature or may be
cooled by a secondary coolant in some form
of heat exchanger
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3. Cooling and Ventilation
In most cases cooling of electrical machines is
done by air streams and this cooling is called as
Ventilation .
Depending upon the origin of the cooling,
cooling can be classified into
Cooling system
Natural cooling
Separate cooling
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4. COOLING SYSTEM
CLASSIFICATION
Based on manner of cooling:
Open circuit ventilation
Surface ventilation
Closed circuit ventilation
Liquid cooling
Inner cooling of windings
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6. Induced and forced
ventilation
Both self ventilation and separate ventilation
can be subdivided into two categories
1) Induced ventilation (with internal fan /
external fan)
2) Forced ventilation (with internal fan / external
fan)
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7. INDUCED VENTILATION WITH
INTERNAL & EXTERNAL FAN
Internal fan’s rotation
creates an decreased
pressure inside the
machines causing the
air to be sucked inside
the machine as air
flows from high
pressure to low
pressure
Then the air is pushed
out by the fan into
atmosphere
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9. Radial and Axial Ventilation
The ventilating systems can be classified
into three types depending upon how the air
passes over the heated machine parts are
Radial
Axial
Combined radial and axial
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10. Radial ventilating system
This system is most commonly
employed because the movement of
rotor induces a natural centrifugal
movement of air which may be
augmented by provisions of fans if
required
This method is suitable for machines
about 20kW
For, larger machines , the core is
normally divided to provide radial
ventilating ducts
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11. Working
Air flowing up the radial ducts only a layer
3mm wide in contact with the core walls is
effective in cooling
The middle 4mm wide band contributes
very little to cooling of the core
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12. Advantages
Minimum energy
losses for ventilation
Sufficiently uniform
temperature rise of
machines in the axial
direction
Disadvantages
It makes the
machine lengths
larger as space for
ventilating ducts has
to be provided along
the core length
It may become
unstable in respect
to quantity of cooling
air flowing
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13. Axial ventilating system
It is suitable for induction machines of
medium output and high speed machines.
Axial ducts are provided and two types of
axial system
1. Simple axial system
2. Double axial system
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14. WHY WE USED IN HIGH
SPEED MACHINES ?
By use of a solid rotor and reduced core
length and in order to avoid centrifugal stresses,
axial ventilation is preferred.
To increase the cooling surface holes are
punched where heat dissipation is more
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15. Advantages & Disadvantages
It improves cooling but requires a large core
diameter for the increased core depth.
Non uniform heat transfer.
Increased Iron loss.
In large number of cases this loss is more
than compensated by improved cooling.
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16. Combined Axial and Radial
ventilating system
This method is usually employed for large motors
and small turbo alternators.
Since the area of ducts to carry cooling air
becomes large.
So to minimise losses this type is preferred
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17. The air is drawn into the machines from one
end is encouraged to pass through the ducts
by and finally the rotor mounted fans forces
out the air
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18. Cooling of totally enclosed
machines
They are used in applications where the use
of open and protected machines is
inadmissible
In a totally enclosed machine, there is no air
connection with outside and all heat
developed inside should be dissipated into the
surroundings from the external surface of the
frame
It is quite uneconomical
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20. 1.Ventilated Frame machines
A fan is mounted on
the shaft outside the
working parts of the
machine and it blows
the air over the
carcass through the
space between main
housing and thin cover
plate
Suitable for power
outputs upto 25kw
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21. For larger rating , it is
necessary to provide in
addition , circulation of air
inside the machine to
improve heat dissipation.
This is done by providing a
fan inside the machine which
may circulate air in the inner
portion
Air inside the machine acts
as primary coolant
Air outside the machine
acts as Secondary
coolant
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22. 2.Ventilated radiator machines
In such machines , internal
fan circulates air inside the
machine.
At higher ratings the
outside air may be cooled
by water if there is a
convenient source of water
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