In the hydrogen cooling of a synchronous generator, hydrogen gas is used for cooling because hydrogen gas has excellent cooling properties.
The power loss (I2R loss) in the form of heat loss occurs in a generator when the generator delivers power to electrical equipment. The life of the generator depends on how efficient the cooling system it has. The life of the insulating material deteriorates with an increase in temperature, and it is a must to cool the generator for getting good life of the generator. Natural air cooling and forced air cooling are adequate for the cooling of small-rating generators. However, for a large rating generator hydrogen cooling is effective and efficient.
A well-seated circulating system has to be put in place for the hydrogen cooling of the generators to take place. Between the shaft and the casing, special oil-seated glands are put in place. The oil glands are fit inside the generators to prevent the leaking of hydrogen outside the generator or air into the generator. Therefore, the oil glands must be purified frequently.
The hydrogen cooling system functions by circulating the hydrogen gas via fans and blowers across the stator and rotor. The hot hydrogen gas is then passed over the cooling coils inside the enclosed seating case. These cooling coils absorb heat from the hydrogen gas as they carry oil within them. The oil as mentioned earlier has the capability of extracting heat from hydrogen gas.
Hydrogen cooling system is widely used as a means for cooling alternators and generators due to their capability of increasing their capacity by around 25% as compared to the air-cooling ventilation system. Moreover, the full-load efficiency of the generator is incremented by about 1% on using hydrogen cooling systems.
Advantages of Hydrogen Cooling System in Synchronous Generators
The hydrogen cooling system overweighs the air-ventilated cooling system due to the following advantages.
- Firstly, the hydrogen cooling system has a higher cooling capacity in comparison to the air-cooling ventilation system. This is because of the greater thermal conductivity of the hydrogen gas, i.e., it has 1.5 times greater heat-transferring capability in comparison to air.
- Secondly, the losses due to windage and noise are highly minimized in the generators and alternators due to the fact that the rotating parts of the generator are present in the hydrogen gas environment that has a comparatively lower density than air.
- The low density of the hydrogen gas in comparison to air at the same temperature and pressure results in higher performance and efficiency of the generators. The density of Hydrogen is 25 % of that air. The lower density of hydrogen leads to 25 % less power requirement for pumping of hydrogen gas inside the generator.
- Air-cooling systems have a prevalent issue of corona discharge that is responsible for releasing toxic gases such as ozone, nitrogen oxide, nitric acid, etc., resulting in the electric breakdown of the insulation of the generator. While the hydrogen cooling systems minimize the issue of corona discharge of the generator’s insulation and thus increase the lifespan of the insulating material of the alternator.
- The hydrogen cooling system needs a smaller size of heat exchanger/cooler to cool the heated hydrogen
Precautionary Measures while using Hydrogen Cooling
The major issue with using hydrogen gas for cooling generators or alternators is that it is highly flammable and may result in a possible explosion if not used in the correct proportions. The explosion may occur when hydrogen gas and air are in the percentages ranging between 6% Hydrogen: 94% Air to 71% Hydrogen: 29% Air. Therefore, when the percentage of the hydrogen gas used is greater than 71 % in the given mixture of hydrogen and air, then it is safer as it is no longer combustible or flammable. Practically, in the case of bulky and large-sized generators, the ideal ratio of hydrogen and air used in order to prevent explosion or combustion is 9:1.
The pressure of hydrogen gas in the air-hydrogen gas mixture should be kept higher than the atmospheric pressure to prevent the possibility of explosion and the impure air from the outside from entering the generator.
Disadvantages of Hydrogen Cooling of Generators
Given below are the major drawbacks of using hydrogen cooling generators over air cooling ventilators.
- The frame used by the hydrogen-cooled generators is costlier in comparison to the air-cooled generators. This is due to the need of providing gas-tight shaft seals and construction that is explosion-proof.
- Installing cooling coils that carry oil or water within the casing, for the purpose of absorbing the heat from the hydrogen gas that is circulated in the ducts of the generators, requires extra labor and expense.
- Another main downside of using hydrogen gas for cooling is that it requires special ways or processes for passing the hydrogen gas through the alternator. The two ways to pass the hydrogen gas without any danger or threat of explosion are as follows.
- Hydrogen gas can be passed into the generator after vacuum pumping a unit of atmospheric pressure into the generator in order to avoid any possible explosion.
- The air around the generator or alternator can be firstly purified with CO2 before passing the hydrogen gas into the generator. This method reduces or lowers the risk of explosion or combustion.
This is all about the Hydrogen Cooling of a Synchronous Generator
