Characteristics of Hydro Turbine Generator Compared with Steam Turbine Generator

Compared with steam turbine generator, hydro generator has the following characteristics:
(1) The speed is low. Limited by the water head, the rotating speed is generally less than 750r / min, and some are only dozens of revolutions per minute.
(2) The number of magnetic poles is large. Because the speed is low, in order to generate 50Hz electric energy, it is necessary to increase the number of magnetic poles, so that the magnetic field of cutting stator winding can still change 50 times per second.
(3) The structure is large in size and weight. On the one hand, the speed is low; On the other hand, in case of load rejection of the unit, in order to avoid the rupture of steel pipe caused by strong water hammer, the emergency closing time of guide vane is required to be long, but this will cause the speed rise of the unit to be too high. Therefore, the rotor is required to have large weight and inertia.
(4) Vertical axis is generally adopted. In order to reduce land occupation and plant cost, large and medium-sized hydro generators generally adopt vertical shaft.

Hydro generators can be divided into vertical and horizontal types according to the different arrangement of their rotating shafts: vertical hydro generators can be divided into suspended and umbrella types according to the different positions of their thrust bearings.
(1) Suspended Hydrogenerator. The thrust bearing is installed in the center or upper part of the upper frame of the rotor, which has stable operation and convenient maintenance, but the height is large and the plant investment is large.
(2) Umbrella hydro generator. The thrust bearing is installed in the center body or its upper part of the lower frame of the rotor. Generally, large hydro generators with medium and low speed should adopt umbrella type due to their large structural size, so as to reduce the unit height, save steel and reduce plant investment. In recent years, the structure of installing the thrust bearing on the top cover of the water turbine has been developed, and the height of the unit can be reduced.


2. Main components
Hydro generator is mainly composed of stator, rotor, thrust bearing, upper and lower guide bearings, upper and lower frames, ventilation and cooling device, braking device and excitation device.
(1) Stator. It is a component for generating electric energy, which is composed of winding, iron core and shell. Because the stator diameter of large and medium-sized hydro generators is very large, it is generally composed of segments for transportation.
(2) Rotor. It is a rotating part generating magnetic field, which is composed of support, wheel ring and magnetic pole. The wheel ring is a ring-shaped component composed of fan-shaped iron plate. The magnetic poles are distributed outside the wheel ring, and the wheel ring is used as the path of the magnetic field. One strand of large and medium-sized rotor is assembled on site, and then heated and sleeved on the main shaft of the generator. In recent years, the rotor shaftless structure has been developed, that is, the rotor support is directly fixed on the upper end of the main shaft of the turbine. The biggest advantage of this structure is that it can solve the quality problems of large castings and forgings caused by the large unit; In addition, it can also reduce the rotor lifting weight and lifting height, so as to reduce the plant height and bring certain economy to the power plant construction.
(3) Thrust bearing. It is a component that bears the total weight of the rotating part of the unit and the axial hydraulic thrust of the turbine.
(4) Cooling system. Hydrogenerator usually uses air as cooling medium to cool the stator, rotor winding and stator core. Small capacity hydro generators often adopt open or pipe ventilation, while large and medium-sized hydro generators often adopt closed self circulation ventilation. In order to improve the cooling intensity, some high-capacity hydro generator windings adopt the internal cooling mode of hollow conductor directly passing through the cooling medium, and the cooling medium adopts water or new medium. The stator and rotor windings are internally cooled by water, and the cooling medium is water or new medium. The stator and rotor windings that adopt water internal cooling are called double water internal cooling. The stator and rotor windings and stator core that adopt water cooling are called full water internal cooling, but the stator and rotor windings that adopt water internal cooling are called semi water internal cooling.
Another cooling method of hydro generator is evaporative cooling, which connects liquid medium into the conductor of hydro generator for evaporative cooling. Evaporative cooling has the advantages that the thermal conductivity of the cooling medium is much greater than that of air and water, and can reduce the weight and size of the unit.
(5) The excitation device and its development are basically the same as those of thermal power units.

Post time: Sep-01-2021

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