Hydrogen-cooled turbo generator

Hydrogen-cooled turbo generators are designed to provide a low-drag atmosphere and cooling for single-shaft and combined-cycle applications in combination with steam turbines.

[1] Because of the high thermal conductivity and other favorable properties of hydrogen gas, this is the most common type in its field today.

[2] The use of gaseous hydrogen as a coolant is based on its properties, namely low density, high specific heat, and the highest thermal conductivity (at 0.168 W/(m·K)) of all gases; it is 7 to 10 times better at cooling than air.

To control the centrifugal forces at high rotational speeds, the rotor diameter typically does not exceed 1.25 meters; the required large size of the coils is achieved by their length and so the generator is mounted horizontally.

The turbogenerator also contains a smaller generator producing direct current excitation power for the rotor coil.

Older generators used dynamos and slip rings for DC injection to the rotor, but the moving mechanical contacts were subject to wear.

The rotor usually contains caps or cage made of nonmagnetic material; its role is to provide a low impedance path for eddy currents which occur when the three phases of the generator are unevenly loaded.

A drop of only a few percent in hydrogen purity can increase windage losses by hundreds of kilowatts in a large generator.

[8] The absence of oxygen in the atmosphere within significantly reduces damage to the winding insulation from corona discharges; these can be problematic as the generators typically operate at high voltage, often 20 kV.

Degradation of bearings leads to higher oil leaks, which increases the amount of air transferred into the generator.

Carbon dioxide is favored as due to the very high density difference it easily displaces the hydrogen.

If it is done during slow-speed unloaded rotation, the generator fans will mix the gases, greatly increasing the time required to achieve purity.

Hydrogen is often produced on-site using a plant consisting of an array of electrolysis cells, compressors and storage vessels.