With water turbines with small and medium outputs, for the generation of electric current, it is known to provide a turbine rotor with a driving connection to the rotor of an electric-current generator. In these systems, it has been found to be advantageous, for economical reasons, to provide the water turbine and the electric-current generator above one another and to form the water turbine with a vertical shaft.
In one embodiment of such construction, the turbine has a rotor which is rotatable about a vertical axis along which the turbine shaft extends, the turbine shaft being journaled in a pair of spaced-apart bearings. A flywheel is mounted upon this shaft.
A controller for regulating the output of the unit is connected to the shaft by bevel gearing, i.e. a transmission providing a power takeoff from the main shaft in a direction transverse thereto. A series-connected generator can be coupled to the unit by a clutch. This construction has been found to be effective for capacities of up to 100 metric horsepower.
In another embodiment of a vertical-axis turbine, the turbine rotor is carried by an extended portion of the generator shaft. This arrangement has been found to be satisfactory only for direct-current machines and, indeed, only for machines with low outputs and manual control. Such units have been suitable for the generation of electric power of up to about 10 kw.
In yet another conventional embodiment, the turbine rotor, a flywheel and the rotor of the generator are provided upon a single vertical shaft. This latter configuration, as with the constructions discussed earlier, have even no power or turbine speed control possibilities, or where such possibilities are afforded, take up considerable space both as to the height of the unit and as to its horizontal dimensions. The capital cost of such machines is high, especially since a separate drive and transmission must be provided for a controller which draws power from the main shaft and diverts it away from the main shaft.
Systems which use gear-transmissions for operating one or another of the devices associated with a turbine generating unit also require special bearing arrangement for the additional shafts and have been found to be satisfactory only for small outputs and minimum control variations. In many cases control precision is difficult to achieve with such systems.
In practice it has been found that such systems cannot be scaled up to large/moderate outputs without creating additional problems. In such larger scale units the need for control and for precision in any control which is carried out is paramount. This is especially the case when the turbine-generator unit is to be used for supplying municipalities with electric power. Control precision is also a factor where the electric power to be supplied is to provide energy for television transmissions, switching systems and the like where fluctuations in the demand occur rapidly.
On the other hand, it is important that the turbine-generator unit be relatively compact and reliable, having a minimum number of parts and maximum facility for repair or service. The presence of transmissions, clutches and the like sharply increases the need for maintenance, the number of service calls and the requirements for monitoring the operation of the unit.