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.