Electrical equipment of micro hydroelectric power stations. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Alternative energy sources

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Hydrogenerators

A hydro generator is an electric current generator driven by a hydro turbine. Typically, a hydro generator is a synchronous generator (Fig. 31), the rotor of which is connected to a hydro turbine (directly or through transmission mechanisms).

Fig.31. Synchronous generator

It is also permissible to use an ordinary asynchronous electric motor in generator mode, that is, the rotation of this electric motor from a hydraulic turbine will also produce electric current, but in asynchronous mode (Fig. 32). However, their use is limited by the fact that they are active power generators and reactive power consumers. Therefore, asynchronous generators can only work in a system where there is a source of reactive power. Reactive power comes from capacitors connected in parallel with the load, or in order to improve the operational properties of the asynchronous generator, capacitors connected in series with the load are additionally installed. But the efficiency of this option is lower than using a synchronous generator.

Fig.32. asynchronous motor

The design of a hydrogenerator is mainly determined by the position of the axis of its rotor, the rotational speed, as well as the type and power of the turbine. Powerful low-speed hydro generators are usually manufactured with a vertical axis of rotation, high-speed generators with a bucket hydro turbine - with a horizontal axis of rotation.

The frequency of rotation of hydrogenerators for micro hydroelectric power plants varies from 600 to 1500 rpm. The choice of generator for speed characteristics depends on the type of turbine used. In addition, there are design and operational features of hydrogenerators. Slow-speed generators are more durable and reliable, but at the same time they are large and expensive.

The principle of operation of the generator

The principle of operation of any generator is based on the phenomenon of electromagnetic induction. The conversion of the mechanical energy of the motor (rotational) into electric current energy is explained by the following figure:

If a frame rotates uniformly in a uniform magnetic field, then a variable electromotive force arises in it, the frequency of which is equal to the frequency of rotation of the frame. Whether we rotate the frame in a magnetic field, or a magnetic field around the frame, or a magnetic field inside the frame, the result will be the same - an electromotive force that changes according to a harmonic law.

Distinctive features of synchronous and asynchronous generators

A synchronous generator is a synchronous electric machine operating in the generator mode, in which the stator magnetic field rotation frequency is equal to the rotor rotation frequency. The rotor consists of a winding. When voltage is applied to a winding with magnetic poles, a magnetic field appears, which creates a rotating magnetic field. This magnetic field, crossing the stator winding, creates an electromotive force in it.

Depending on the type of winding, the rotor can be short-circuited or phase. The rotating magnetic field created by the auxiliary stator winding induces a magnetic field on the rotor, which, rotating together with the rotor, creates an electromotive force in the working stator winding.

The rotor, when starting the power plant, creates a weak magnetic field, but with an increase in speed, the electromotive force in the excitation winding also increases. The voltage from this winding, through the automatic adjustment unit (AVR), is supplied to the rotor, controlling the output voltage by changing the magnetic field. For example, a connected inductive load demagnetizes the generator and lowers the voltage, and when a capacitive load is connected, the generator is biased and the voltage rises. This is called "anchor reaction". To ensure the stability of the output voltage, it is necessary to change the magnetic field of the rotor by regulating the current in its winding (for synchronous generators), which is provided by the AVR unit (voltage stabilizer). Thanks to this method of regulation, regardless of the change in the load current and the speed of the HPP turbine, the high stability of the generator output voltage is maintained.

The advantage of synchronous generators is the high stability of the output voltage, and the disadvantage is the possibility of overcurrent, since with an excessive load, the regulator can excessively increase the current in the rotor winding. Another disadvantage of synchronous generators is the presence of a brush assembly, which sooner or later will have to be serviced, however, at present this disadvantage has been practically eliminated. Since modern synchronous generators are mostly brushless, their rotor does not have a collector-brush assembly, and the current in the excitation winding (in the rotor) is induced by an alternating magnetic field created by the main and / or additional stator winding.

Asynchronous generator - an asynchronous electric machine operating in braking mode, the rotor of which rotates ahead of schedule, but in the same direction as the stator magnetic field.

In an asynchronous generator, the rotor is made in the form of a permanent magnet or an electromagnet. The number of rotor poles can be two, four, etc., but always a multiple of two. In this case, the lower the rotation speed of the generator, the more poles the generator should have.

The rotating magnetic field always remains unchanged and is not adjustable, as a result of which the voltage and frequency at the generator output depend on the rotor speed and, consequently, on the stability of the turbine rotation.

Despite the ease of maintenance, low sensitivity to a short circuit and low cost, asynchronous generators are used quite rarely, as they have a number of disadvantages: unreliability of operation under extreme loads; dependence of the output voltage and current frequency on the stable operation of the hydro turbine, etc.

Authors: Kartanbaev B.A., Zhumadilov K.A., Zazulsky A.A.

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