1. Field of the Invention
The present invention relates to a hydraulic machine such as a water turbine or a pump turbine. In particular, the invention is concerned with a hydraulic machine applicable also to water containing earth and sand.
2. Description of the Related Art
In hydraulic power generation, water energy created by utilizing the difference between upper and lower water levels is converted into rotational energy by means of a water turbine, and the rotational energy is then converted into electric energy by means of a generator. Recent proportions of atomic power generation and thermal power generation are not less than 80%. However, these power generation methods are inferior from the standpoint of a quick response characteristic. It is hydraulic power generation that is best used to achieve a quick response characteristic.
In pumping-up power generation, which is a hydraulic power generation, water at a lower point or elevation is pumped up into an upper pond through a pump by means of an electric motor utilizing night dump power to store energy, and the water thus pumped up during the night is utilized during the daytime to provide a required amount of electric power. Such a type of a hydraulic machine will hereinafter be referred to as a "pump turbine". Since natural water is utilized, the problem of earth and sand mixed in water energy, or pressurized water, is incidental to hydraulic power generation. Earth and sand mixed in pressurized water strike strongly against the water flowing portion of a water turbine and cause wear of components of the water turbine, which wear may result in damage and eventually inoperativeness of the water turbine. Therefore, a keen desire exists for the development of water turbine components which can resist wear even in collision with earth and sand and also for the attainment of promptness in the replacement of components.
The material of guide vanes so far adopted generally in water turbines and pump turbines corresponds to JIS (Japanese Industrial Standard) SC450 Carbon Steel Castings or JIS-SCS1 Stainless Steel Castings. This material is subject to wear when it collides with earth and sand. As a result of the wear or damage caused by earth and sand, it is periodically required to disassemble the whole of a generator and replace the guide vanes with new ones or repair the old ones, by welding, portions which have been damaged by earth and sand.
However, in repair by welding, the guide vane shafts are bent by the heat of welding and hence it is necessary to transport the guide vanes from the power plant to a machine shop and subject them to machining again. Thus, also in the replacement of guide vanes with new ones or in the repair by welding, a large amount of cost and a long period of time have so far been needed.
Moreover, it has heretofore been necessary for a guide vane operating mechanism in a water turbine or a pump turbine to use a thrust bearing ring for bearing the weight of each guide vane and also for bearing an upward water pressure acting on the guide vane. More particularly, each guide vane is disposed movably between stationary upper and lower covers and it is necessary to provide clearances between the guide vane and those covers. For ensuring those clearances there has been used a strong thrust bearing ring. When passing through the said guide vane clearances, pressurized water increases its flow velocity and strikes violently against upper and lower end faces of the vane portion of the guide vane and also against upper and lower facing plates attached respectively to the upper and lower covers, causing wear which is attributable to earth and sand contained in the pressurized water.
Further, the pressure water leaks from the guide vane clearances and causes deterioration in operation efficiency of the water turbine. In the pump turbine, guide vanes are fully closed during operation of the pump and the water level in a runner chamber is depressed by compressed air. But pressure water from the casing side leaks through the guide vane clearances and strikes against the runner which is rotating in air, thus resulting in that the electric motor for rotating the runner is required to be provided with a large input.
Additionally, the upper and lower casings are apt to cause wear and damage in the guide vane clearances due to collision with earth and sand and when they are to be replaced with new ones, it is necessary to disassemble the whole of both the generator and the water turbine. Accordingly, a very long period is needed for such entire disassembly, replacement of the upper and lower facing plates and the subsequent entire assembly.
Thus, according to the prior art, the components which come into contact with pressurized water containing earth and sand are difficult to be resistant to the pressurized water, and the whole of the generator must be disassembled for the repair of guide vanes and for the replacement of facing plates. During this disassembly, the supply of electric power is interrupted and thus there has been a problem in power transmission system and electric power management.