Cooling of Alternators

Cooling is a vital aspect in the construction and operation of generators.  Cooling in generators can be broadly classified into two types
  • Open Circuit and
  • Closed Circuit
In Open Circuit cooling, air is drawn into the generator by means of fans and circulated inside.  The air is later released back into the atmosphere.  This is a simple method of cooling which does not require elaborate circulation equipment.  This kind of cooling is suitable for small alternators.

Closed Circuit cooling is used in large-sized alternators.  These alternators cannot be cooled by air as they generate a huge amount of heat.  

Here, hydrogen is usually used as the cooling medium.  The hydrogen is passed through the generators by means of pumps and then drawn back into a chamber.  Special circulation equipments such as radial and axial ducts, seals and pumps for this type of cooling.

Hydrogen can transfer heat better than air as it has a higher specific heat.  It has a low density which results in reduced windage losses for the alternator rotor.   The alternator frame can also be reduced.

Water can also be used as a cooling medium in closed circuit cooling systems.  Water has a better cooling capacity as compared to Hydrogen.  However, the circulation equipment for water are more expensive. Special systems for the purification of water are also required.

Some generators use both hydrogen and water cooling systems.