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DSC_7636-mb-hydrogen-store (Photo credit: swh)Generator is designed to be able to survive in conditions of normal working temperatures of up to working temperature is abnormal, for example: during a short circuit current.For the same dimensions, the ability to withstand heat will determine the output power rating to withstand the heat that is owned generator.Kemampuan determined two factors: a. Isolation level
b. Cooling rate (ability to dissipate heat)
Heat that caused the generator caused by loss - loss of power (power losses) consisting of:
- Loss - loss of copper / loss - loss of power
- Loss - loss of iron / loss - loss of magnet
- Loss - loss of mechanical
Generator with output power ratings above 300 MVA-Ugi has lost about 1%. Loss - the loss in the form of heat. To keep the heat does not damage the insulating mechanical generator systems listrikdan the pans should be channeled out / absorbed from the generator. Functions performed by the heat absorption refrigeration system.
Steam turbine generator PLTGU Freshwater Estuary using a generator with output power rating of 200 MVA (288 MVA) so that the media selection hydrogen gas (H2) as a coolant is appropriate. Media selection hydrogen gas (H2) as a refrigerant is based on:
A. The density of Hydrogen is only 1/14 times the density of air at the same pressure and temperature. The use of hydrogen gas will reduce the losses - losses due to friction wind generator and sound (noise).
2. Heat transfer capability of hydrogen gas in the system of forced convection (forced convection) 1.5 times the amount of air the heat transfer capability.
3. For the same mass, the heat absorbing capacity of 14.5 times the amount of hydrogen gas of air, because at the same temperature and pressure of the mass of hydrogen is only 1/14 times the mass of air. Then the magnitude of the heat capacity of hydrogen: 14.5 / 14 = 1.035 times the heat-absorbing ability of the air at the same temperature and pressure. So better cooling hydrogen gas from the air.
4. Hydrogen gas does not occur on oxidation reactions and impurities so the generator insulation life will be longer.
5. The thermal conductivity of hydrogen gas air 7 times.
6. In the high-speed machines such as generators, loss - loss of wind is calculated as part of the loss - a total loss, because the density of hydrogen of about 7% more dense than air. Loss - loss of air-cooled hydrogen generator is reduced to 10% of air-cooled generator, so that the generator efficiency is increased by 1%.
The use of hydrogen gas media will reduce the heat to be removed and at the same time will increase the ability to dissipate heat from the generator.
The selection of media as a medium for cooling the hydrogen gas should be noted that - as follows:
a. Hydrogen gas is a gas that is very dangerous (explosive) that require special handling. Concentration of 4-76% hydrogen gas in the air is an explosive mixture (mixture explosivi). Hydrogen gas purity must be guarded / secured at a high level.
b. Require special handling in the process of charging and discharging hydrogen gas from the generator.
c. Requires two systems Auxillary namely:
- Seal oil system: to maintain the hydrogen gas remains in the generator.
- Gas system / Hydrogen plant: to maintain the pressure and purity of hydrogen gas.
Generator cooling circulation system can be viewed as shown below:
Generators and water cooled heat exchanger must be insulated hydrogen gas terahadap meeting. The main problem that occurs in isolation bearings which can be space / narrow gap between the rotor and the generator body is not moving. Spaces / narrow gap that allows its happening kebocorangas the hydrogen to the outside air pressure is smaller. This is very dangerous because it can cause an explosion and fire. To overcome the space / narrow gap is closed with a coating of oil / oil seal oil system is required.
To prevent the mixture that is explosive in the combustion chamber pressure is maintained so that hydrogen gas is greater than the outside air pressure so that when the hydrogen gas leak will point out.
Minimum pressure of hydrogen gas to the outside air is 3440 N/m2 (0.0344 barg). At this pressure the maximum output power rating of the generator can be increased by about 30% above the rating of air-cooled generator. While the peak efficiency (full load efficiency) rose about 0.5%. Tend to use hydrogen gas pressure is higher (between 1.03 barg s / d 4.13 barg) to mass of hydrogen gas generator in a larger space so that the heat absorbing capacity increases. Raising the hydrogen gas pressure of 0.0344 to 1.03 barg barg will increase the output (for the same rise in temperature) of about 15%. Hydrogen gas pressure increases from 0.0344 to 2.07 barg barg would raise output (for the same temperature increase) by 25%. Methods to improve the ability to absorb heat from the generator is to develop a conductor cooling / cooling liner.
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