Hydrogen is a cooling medium used in high capacity generators which generate large quantities of heat.
Hydrogen has a higher capacity to transfer heat, its specific heat is about 14 times that of air of similar weight.
The density of hydrogen is lesser than that of air. This reduces the windage losses. Thus the efficiency is improved.
Hydrogen also improves the life of the insulation as the hydrogen circulated is pure without dirt, moisture, etc. This reduces the maintenance required.
Alternators which are to be hydrogen cooled have special circulating ducts in the windings to circulate hydrogen along with seals to prevent leakage and pumps. The hydrogen used for cooling is locally produced using electrolyzers. These equipments produce hydrogen by the electrolysis of water. The hydrogen is used in a closed circuit at a pressure of around 6 bar(kg/cm2)
The major risk of using hydrogen is its flammability. Hydrogen burns readily in the presence of oxygen(air). To prevent this, the hydrogen is maintained at a purity of more than 70%. This ensures that there is very little oxygen available so as to prevent combustion. The high pressure in the hydrogen cooling circuit ensures that no air can enter the circuit. A small quantity of hydrogen may leak into the atmosphere. This is compensated by adding hydrogen.
Hydrogen is a odorless gas. Hence, special gas detection equipment are required to detect its leakage.