Classification of micro-hydro generator

Micro hydro generator  are generally classified according to the applicable head of the turbine: low head units (applicable head 1.2 to 20 meters), medium head units (applicable head 15 to 40 meters), and high head units (applicable head 25 meters or more).

Low-head units below 100KW
Low-head units below 100KW mostly adopt axial-flow turbines. Micro axial flow turbines are mostly vertical, which are divided into two types: axial flow turbines with worm shell (applicable head 4-20 meters) and open trough axial flow turbines (applicable head 1.2-6 meters). The structure of axial-flow hydraulic turbine with worm shell has a worm shell, while the open-slot axial-flow hydraulic turbine has no worm shell and is less expensive, but the worm shell needs to be poured with cement during installation as shown in Figure 1-3.


Medium-head turbine set below 100KW
The medium-head hydraulic turbine sets below 100KW mostly adopt two types of double-strike type and shaft-extension cross-flow type. The structure of the double-strike micro-hydro generator set is shown in Figure 1-4. The set is easy to install and the flow rate is adjustable. However, the speed is low, the generator needs to increase the speed of transmission, and the efficiency of the whole machine is low.

The structure of shaft-extension cross-flow micro-hydro generator set is shown in Figure 1-5, which has high efficiency and easy installation. But the cost is higher; mixed-flow unit, because of its high efficiency and long working life, is also often in the choice of example, but the unit cost is high.

High head unit below 100KW
Most of the high head units below 100KW use inclined strike turbines. There are vertical and horizontal inclined strike turbines, and small power units are mostly vertical, whose structure is shown in Figure 1-7; larger power units are horizontal, whose structure is shown in Figure 1-8. Inclined strike turbine has simple structure, low unit cost, adjustable flow rate and convenient installation.

Hydro Generator 
The transmission between the hydraulic turbine and the generator has two ways: direct and indirect. Direct transmission is used in the case where the turbine and generator rotational speed coincide, and a coupling is used to connect the turbine and generator. This form of transmission has high efficiency, simple structure and convenient maintenance; when the generator speed is different from the turbine speed, flat belt drive and v-belt are often used to connect the turbine and generator for indirect transmission. Micro whole hydro generator set is usually direct drive, good integrity and high efficiency.

The unit installed upright is called a vertical unit. It has an upright main shaft and is usually direct driven. The axial flow micro hydro generator set is a typical vertical unit. The unit whose main shaft is horizontally installed is called horizontal unit, and it generally adopts indirect drive, and there are also direct drive ones (such as cross-flow unit). The selected vertical unit has a small footprint and low civil construction investment.

Water turbine
Hydraulic turbine is the key equipment that converts water energy into mechanical energy and drives the generator to generate electricity, and its efficiency, life, operability, maintainability and maintenance cycle are important indicators. It is very important to choose the right model according to the head, flow rate and power consumption. Usually the price of low head, high flow rate turbine is higher than the price of high head, low flow rate turbine. If a high-head turbine is used instead of a low-head turbine, the power generation efficiency of the system will be significantly reduced.
For micro-hydro power generation with a single unit capacity of less than 100 KW, it is recommended to use the whole unit to ensure the quality of the unit and save investment.
At present, in the Chinese market, the price of micro-hydro generator sets, including the complete set, varies greatly, and the price of similar sets with the same nominal power varies more than 20 times; at the same time, the quality of micro-hydro generator sets also varies greatly, and the difference in efficiency is more than 2 times, the difference in life is more than 15 times, and the difference in maintenance cycle is more than 20 times, etc. When purchasing, the quality of the units should be identified from the following aspects: design and manufacturing standards; product completeness; manufacturing quality; service commitment, etc.

The structure of generators varies mainly due to the different excitation methods. At present, there are three kinds of micro-hydro generators commonly used in China: permanent magnet synchronous generator; capacitor-excited asynchronous generator; synchronous generator.
The permanent magnet synchronous generator has the simplest structure, but the performance of different products varies greatly, and its unit capacity is small. Capacitor-excited asynchronous generators are converted from asynchronous motors with excitation capacitors. With the advantage of mass production of asynchronous motors, the price is low, but the reliability of excitation capacitors is poor, the efficiency is low, and the phenomenon of demagnetization is easy. Synchronous generators for micro-hydro power generation have high efficiency, good voltage regulation and high reliability. brushless synchronous generators are recommended for micro-hydro power generation systems above 10KW.

Micro-hydro power generation has small power and small capacity for load change when running off-grid. Due to the suddenness of load change, micro-hydro power generation without automatic voltage and frequency stabilization controller cannot be used as a power source for general household appliances. The controller has the following roles in micro-hydro power generation.
First, to ensure the quality of the output power. Make the steady-state voltage adjustment rate, transient voltage adjustment rate and frequency change range conform to the provisions of relevant standards; second, protect the safety of the micro-hydro generator set itself to avoid accidents such as flyaway, over-voltage and over-current; third, improve the adaptability of micro-hydro power generation to different micro-hydro resources.
Load balancing type voltage and frequency stabilization electronic regulator is a widely used voltage and frequency automatic control device for small power micro hydro power generation (below 50KW). The controller is connected in parallel to the generator inlet line, when the power consumption is less than the generator output power, causing the output voltage to be higher than 220V or the frequency to increase, the controller automatically connects the excess power to the dummy load (usually a randomly equipped resistive load, such as electric heaters, electric furnaces), so that the voltage is stabilized at about 220V to protect the generator and appliances, and let the appliances work at the rated voltage; when the voltage decreases When the voltage decreases, the controller automatically disconnects the dummy load to bring the voltage back up. When the voltage drops, the controller automatically disconnects the dummy load to bring the voltage back up. Users can switch on and off the electrical equipment at will as they do with grid electricity. According to the different requirements of voltage adjustment rate, waveform distortion rate and three-phase load balancing rate of micro hydro power generation, load balancing type voltage and frequency stabilization electronic regulator has various control and loading methods, and the complexity and cost of the circuit varies greatly.
Micro hydroelectric power generation systems above 100KW usually use electric or hydraulic servo voltage and frequency regulation control mechanism similar to small hydroelectric power generation systems.
Pressure water pipes and valves
Valves and piping are used to direct water from the front pool to the turbine under a certain pressure. They are probably the most expensive item in the project budget, often accounting for 40% of the investment in high drop systems. The size and form of the valve’s passage diameter, the roughness of the pressure water pipe wall, and the length, diameter, strength, and corrosion resistance of the pipe are all closely related to the efficiency, longevity, and reliability of micro-hydro power generation. The use of ball valves in micro-hydro can result in less head loss than the use of other types of valves. In systems with heads less than 40m, PVC pipe is recommended in preference. Translated with (free version)

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