Hydrogen is used for the cooling of Rotor winding i.e. field winding and Rotor Core in Turbo Generator. As shown in figure below, there are small windows on the Rotor structure which allows the passage of Hydrogen. This hydrogen cools the Rotor structure and filed winding. This hydrogen after cooling becomes hot which in turn is cooled by a Heat Exchanger having water in tube tube side.
The use of Hydrogen for cooling of Generator Rotor has many advantages as listed below.
- Hydrogen is used as the cooling medium in Turbo Generators due to its high thermal conductivity.
- Hydrogen reduces the amount of wind resistance and friction on the spinning generator shaft, thus increasing the generator’s efficiency. A reduction in hydrogen purity from 98 to 95% on a large generator can increase losses from friction and windage by 32%; this is equivalent to 685 KW (0.7MW) for a 900 MW Generator.
- Hydrogen’s density at 98% purity is of the order of 1/10 that of air at a comparable pressure. This reduces the fan and windage loss to such a low value that it is feasible to raise hydrogen pressure to as much as 75 psi relative to atmospheric pressure without adversely affecting efficiency. This higher pressure greatly increases the heat removal capability of the hydrogen.
- Hydrogen’s properties are such that its heat transfer coefficient is 50% more effective than that of air at the same pressure. Therefore, hydrogen is much more effective in removing heat from a surface.