Patent Application
20090284017
1. Field of the Invention
The present invention relates to hydro-generators submerged in water converting the hydraulic energy of currents, waves and other the movements into other energy, such as electricity, hydrogen gas, or other energy-bearer. Typically, these units have an energy converter transforming the hydraulic energy into mechanical energy, for example through rotating turbine runner, displacement bodies, foils, buoys, and pneumatic or other devices. The mechanical energy is transmitted through the so-called drive train to the hydro-generator's generator. Typically the drive train and the generator is contained in a bulb housing separating the surrounding water from the gas or air filled internal space housing the drive train, the generator and the auxiliary equipment. The drive train consists of a combination of bearings, shafts, couplings, transmissions, sealing, hydraulic and mechanical components. The generator part of the hydro-generator unit converts the mechanical energy supplied through the drive train into other form of energy, such as electricity, hydrogen or other energy-bearer. The additional auxiliary equipment may provide for removal of leakage water, measurement, control and protective actions.
2. Description of the Prior Art
The problem with this type of equipment is the prevention of water intrusion from the surrounding into the gas or air filled bulb housing in order to protect the drive train, generator and auxiliary equipment from the effect of water and the replacement of gas or air leaking out from the bulb housing. The prior solutions were based on balancing the pressure of the internal gas or air atmosphere in relation to the surrounding water pressure. This could be achieved by having an automatic control system that pumps the leakage water out from the bulb housing and another system for replacement of the lost gas. Typically, the energy needed for the pump action could be generated by the hydro-generator. However, the replacement of the lost gas may be a demanding task. There are three major options: A compressed gas container may be used as a reservoir, a pipeline may carry in the gas from the shore or the gas may be produced inside the unit for example through electrolysis. All these options have some disadvantage. The compressed gas reservoir must be refilled from time to time causing indispensable and costly maintenance operations. The compressed gas line from the shore to the bulb housing might be damaged and in stead of supplying gas the gas may escape from the bulb housing through the leaking pipe line. The third option, with gas generation inside the bulb housing would surely introduce many additional components and costs or this solution would be primarily reserved for hydro-generator units which has hydrogen and not electricity as main energy product.
The invention relates to hydro-generating unit, contained in a water tight bulb housing and submerged in water, comprised of a combination of a converter transforming the hydraulic energy of the water into mechanical energy, a drive train transmitting the mechanical energy to the generator and auxiliary equipment. The internal space of the bulb housing is filled with incompressible fluid except an uppermost limited space inside the bulb housing and expansion chamber capable to accept the excess fluid volumes created by heat expansions.
In accordance with this invention the space inside the bulb housing of hydro-generator submerged in water including the internal volumes contained by the enclosures of the generator, components of the drive train and auxiliary equipment is completely filled with incompressible fluid except expansion chamber that may contain compressible gas. The terms compressible and incompressible are not absolute but relative terms expressing the relatively higher compressibility of gaseous substances in relation to fluids. The following description is an example showing a hydro-generator based on rotating turbine runner and mainly rotating components. However, this invention is not limited on this design but covers also hydro-generators with non-rotating reciprocating, pneumatic or hydraulic components.
FIG. 1—shows the longitudinal cross section of turbine type hydro-generator unit in accordance with the invention. The hydro-generator unit is positioned below the water surface 22 and above the bottom 23 of water body that may flow in changing direction 37.
The hydro-generator's turbine runner consisting of hub 1 and blades 2, is arranged at the end of the bulb housing 3. The bulb housing is a large diameter steel tube. The turbine shaft 4 enters into the housing through a shaft seal 6 that can be a minimum leak and minimum wear mechanical seal. The shaft seal is installed in a plate 13 perpendicular to the shaft 4 which plate 13 at the outer periphery is connected to the housing 3 by flexible sealing 15. A thin cover plate 14 is mounted on the housing covering the gap between the rotating turbine hub 1 and the stationary housing 3. The purpose of the plate 14 is to prevent that larger object to enter into the gap between the plate 13 and the turbine hub 1.
The turbine shaft 4 is supported in two bearings 5 and 7. Bearing 7 is designed both for radial and axial shaft forces. A shaft coupling 8 connects the turbine shaft 4 and the low-speed shaft of the speed-increasing gear 9. The outgoing high-speed shaft of the speed increaser and the shaft of the generator 11 are connected by a shaft coupling 10.
The generator 11 with the complete drive train consisting of the speed increasing transmission 9, bearings 5 and 7 supporting the shaft 4 are assembled on a common frame 20 removable from the brackets 21 integral with the bulb housing 3.
The generator 11 in this case assumed to be a synchronous generator. In order to make the generator maintenance-free a so-called brushless design is chosen. A brushless design means that the rotor contains permanent magnets or the rotor is equipped with field windings which get a direct current supply from the rotor of an excitation machine which is installed on common shaft with the generator rotor. In this case the current from the excitation machine can go directly to the synchronous generator's rotor coils without passing through a brush —collector-ring system. This latter arrangement usually contains diodes installed in the rotating system converting the excitation machine's alternating current into direct current. The direct current is fed into the synchronous generator's rotor coils. The generator stator 12 supplies alternating current (AC), in this case a three-phase current through the main leads 18. This current may have a changing voltage level and frequency dependent on the rotational speed of the generator and turbine shaft. An automatic that controls the excitation machine's stator current supply may stabilize the voltage. Of course this is not the case at a permanent magnet excited generator rotor. The type of generator does not limit the application area of this invention.
In accordance with the invention, the free space inside of the bulb housing 24 is filled with incompressible fluid covering at least the shaft seal 6 and all sensitive location where leakage between the outside water and the inside of the bulb housing may occur. The uppermost narrow space in the bulb housing above the level 39 may be filled with gas. Also the free volumes inside the generator and components of the drive train are filled with incompressible fluid. The incompressible fluid in the bulb housing 24 and inside the different parts of the generator and drive train may be identical or different satisfying different requirements with respect to electric insulation capacity, viscosity, heat transfer capacity, etc. However, it is an advantage if a common fluid is used everywhere suitable for all application area. For example there are electrical machines where the rotor is running in water while the stator 12 is filled with a different kind of fluid with better electrical insulation properties. There are bearings used in the industry for operation with a wide variety of lubricating mediums, gas, water, oil, grease, etc. The type of the bearings used, for example hydrodynamic, spiral groove, roller bearing, etc. does not limit the validity of this invention. Finding a common fluid filling all needs is not a major obstacle.
The major advantage of this invention is that sealing system, for example the shaft seal 6 separating the internal incompressible fluid from the surrounding water is less of a technical challenge than separation of a gas from the surrounding water especially if the very different thermal expansion of a gas and a fluid is considered.
Another feature of the invention is the pressure-balancing device between the surrounding water and the incompressible fluid inside the bulb housing 3.
In accordance with the invention the incompressible fluid acting as a cooling medium transferring heat from the generator and drive train to the bulb housing 3 will benefit from a circulation pump 38 promoting the motion and heat transfer capacity of the incompressible fluid. The flow's 36 direction in and out of the circulation pump and the distribution by ducts and guides shall be adapted to the local conditions and the design of the circulation pump 38, the pump control, duct and guide system shall not limit the validity of this invention.
