Methods of Ventilation

1) Natural of Ventilation : A fan is attached to either ends of the machine. The ventilation medium is nothing but an atmospheric air which is forced over the machine parts, carrying away the heat. This circulation is possible with or without ventilating ducts. The ventilating ducts if provided may be either axial or radial.
2) Closed Circuit Ventilation System : An atmospheric air may contain injurious elements like dust, moisture, acidic fumes etc. which are harmful for the insulation of the winding. Hence for large capacity machined closed circuit system is preferred for ventilation. The ventilating medium used is generally hydrogen. The hydrogen circulated over the machine parts is cooled with the help of water cooled heat exchangers. Hydrogen provides very effective cooling than air which increases the rating of the machine upto 30 to 40% for the same size. All modern alternators use closed circuit ventilation with the help of hydrogen as a ventilation medium.

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