If the rotor of an asynchronous machine connected to a network with voltage U1 is rotated by means of a prime mover in the direction of the rotating stator field, but at a speed n2>
Why we use Asynchronous Electric Generator
An asynchronous generator is an asynchronous electric machine (electric motor) operating in generator mode. With the help of a drive motor (in our case, a turbine engine), the rotor of an asynchronous electric generator rotates in the same direction as the magnetic field. In this case, the rotor slip becomes negative, a braking torque appears on the shaft of the asynchronous machine, and the generator transmits energy to the network.
To excite the electromotive force in its output circuit, the residual magnetization of the rotor is used. Capacitors are used for this.
Asynchronous generators are not susceptible to short circuits.
An asynchronous generator is designed simpler than a synchronous generator (for example, a car generator): if the latter has inductance coils placed on its rotor, then the rotor of an asynchronous generator is similar to a regular flywheel. Such a generator is better protected from dirt and moisture, more resistant to short circuits and overloads, and the output voltage of an asynchronous electric generator has a lower degree of nonlinear distortion. This allows the use of asynchronous generators not only to power industrial devices that are not critical to the shape of the input voltage, but also to connect electronic equipment.
It is the asynchronous electric generator that is the ideal current source for devices with active (ohmic) loads: electric heaters, welding converters, incandescent lamps, electronic devices, computer and radio equipment.
Advantages of an asynchronous generator
Such advantages include a low clear factor (harmonic factor), which characterizes the quantitative presence of higher harmonics in the output voltage of the generator. Higher harmonics cause uneven rotation and unnecessary heating of electric motors. Synchronous generators can have a clearing factor of up to 15%, and the clearing factor of an asynchronous electric generator does not exceed 2%. Thus, an asynchronous electric generator produces almost only useful energy.
Another advantage of an asynchronous electric generator is that it completely lacks rotating windings and electronic parts, which are sensitive to external influences and are quite often susceptible to damage. Therefore, the asynchronous generator is subject to little wear and tear and can serve for a very long time.
The output of our generators is immediately 220/380V AC, which can be used directly to household appliances (for example, heaters), to charge batteries, to connect to a sawmill, and also for parallel operation with a traditional network. In this case, you will pay the difference between what is consumed from the network and what is generated by the windmill. Because the voltage goes directly to industrial parameters, then you will not need various converters (inverters) when connecting the wind generator directly to your load. For example, you can directly connect to a sawmill and, in the presence of wind, work as if you had simply connected to a 380V network.
If the rotor of an asynchronous machine connected to a network with voltage U1 is rotated by means of a prime mover in the direction of the rotating stator field, but with a speed n2>n1, then the movement of the rotor relative to the stator field will change (compared to the motor mode of this machine), since the rotor will overtake the stator field.
In this case, the slip will become negative, and the direction of the emf. E1 induced in the stator winding, and therefore the direction of current I1 will change to the opposite. As a result, the electromagnetic torque on the rotor will also change direction and from rotating (in motor mode) will turn into counteracting (in relation to the torque of the prime mover). Under these conditions, the asynchronous machine will switch from motor to generator mode, converting the mechanical energy of the primary engine into electrical energy. In the generator mode of an asynchronous machine, slip can vary in the range
in this case the emf frequency of the asynchronous generator remains unchanged, since it is determined by the speed of rotation of the stator field, i.e. remains the same as the frequency of the current in the network at which the asynchronous generator is switched on.
Due to the fact that in the generator mode of an asynchronous machine the conditions for creating a rotating stator field are the same as in the motor mode (in both modes the stator winding is connected to the network with voltage U1), and consumes magnetizing current I0 from the network, the asynchronous a machine in generator mode has special properties: it consumes reactive energy from the network, necessary to create a rotating stator field, but delivers active energy to the network, resulting from the conversion of the mechanical energy of the prime mover.
Unlike synchronous generators, asynchronous generators are not subject to the dangers of falling out of synchronism. However, asynchronous generators are not widely used, which is explained by a number of their disadvantages compared to synchronous generators.
An asynchronous generator can also operate in autonomous conditions, i.e. without being included in the general network. But in this case, to obtain the reactive power necessary to magnetize the generator, a bank of capacitors is used, connected in parallel with the load at the generator terminals.
An indispensable condition for such operation of asynchronous generators is the presence of residual magnetization of the rotor steel, which is necessary for the self-excitation process of the generator. Small e.m.f. Eost, induced in the stator winding, creates a small reactive current in the capacitor circuit, and therefore in the stator winding, which enhances the residual flux Fost. Subsequently, the process of self-excitation develops, as in a parallel-excitation direct current generator. By changing the capacitance of the capacitors, you can change the magnitude of the magnetizing current, and, consequently, the magnitude of the voltage of the generators. Due to the excessive bulkiness and high cost of capacitor banks, self-excited asynchronous generators have not become widespread. Asynchronous generators are used only in low-power auxiliary power plants, for example in wind power plants.
DIY generator
In my power plant, the current source is an asynchronous generator driven by a two-cylinder air-cooled gasoline engine UD-25 (8 hp, 3000 rpm). As an asynchronous generator, without any modifications, you can use a conventional asynchronous electric motor with a rotation speed of 750-1500 rpm and a power of up to 15 kW.
The rotation speed of an asynchronous generator in normal mode should exceed the rated (synchronous) speed value of the electric motor used by 10%. You can do this as follows. The electric motor is switched on and the idle speed is measured with a tachometer. The belt drive from the engine to the generator is designed in such a way as to provide a slightly increased number of revolutions of the generator. For example, an electric motor with a rated speed of 900 rpm produces 1230 rpm at idle. In this case, the belt drive is designed to ensure a generator rotation speed of 1353 rpm.
The windings of the asynchronous generator in my installation are connected in a star and produce a three-phase voltage of 380 V. To maintain the rated voltage of the asynchronous generator, it is necessary to correctly select the capacitance of the capacitors between each phase (all three capacitances are the same). To select the required container, I used the following table. Before acquiring the necessary skill in operation, you can check the heating of the generator by touch to avoid overheating. Heating indicates that too much capacitance is connected.
The capacitors are suitable type KBG-MN or others with an operating voltage of at least 400 V. When the generator is turned off, an electric charge remains on the capacitors, so it is necessary to take precautions against electric shock. Capacitors should be securely enclosed.
When working with hand-held power tools at 220 V, I use a step-down transformer TSZI from 380 V to 220 V. When connecting a three-phase motor to a power station, it may happen that the generator does not “master” starting it the first time. Then you should give a series of short-term engine starts until it picks up speed, or spin it manually.
Stationary asynchronous generators of this kind, used for electrical heating of a residential building, can be driven by a wind engine or turbine installed on a small river or stream, if there are any near the house. At one time, in Chuvashia, the Energozapchast plant produced a generator (micro-hydroelectric power station) with a capacity of 1.5 kW based on an asynchronous electric motor. V.P. Beltyukov from Nolinsk made a wind turbine and also used an asynchronous motor as a generator. Such a generator can be driven using a walk-behind tractor, mini tractor, scooter engine, car engine, etc.
I installed my power station on a small, lightweight single-axle trailer - a frame. For off-farm work, I load the necessary power tools into the car and attach my installation to it. I cut hay with a rotary mower, use an electric tractor to plow the land, harrow, plant, and hill up. For such work, complete with the station I carry a reel with a four-core KRPT cable. There is one thing to consider when winding the cable. If you wind it in the usual way, a solenoid is formed, which will have additional losses. To avoid them, the cable must be folded in half and wound onto a reel, starting from the bend.
In late autumn, we have to prepare firewood for the winter from dead wood. Again, I use power tools. At my summer cottage, I use a circular saw and a planer to process the material for carpentry work.
As a result of a long-term test of the operation of our Sailing Wind Generator with a traditional induction motor (IM) excitation circuit based on the use of a magnetic starter as a switch, a number of shortcomings were revealed, which led to the creation of the Control Cabinet. Which has become a universal device for turning any Asynchronous motor into a Generator! Now it’s enough to connect the wires from the motor’s IM to our control device and the generator is ready.
How to turn any Induction Motor into a generator - House without foundation
How to turn any Asynchronous Motor into a generator - A house without a foundation Why we use an Asynchronous Electric Generator An asynchronous generator is one that operates in generator mode
For the needs of constructing a private residential building or cottage, a home craftsman may need an autonomous source of electrical energy, which can be bought in a store or assembled with your own hands from available parts.
A homemade generator can operate on the energy of gasoline, gas or diesel fuel. To do this, it must be connected to the engine through a shock-absorbing coupling, which ensures smooth rotation of the rotor.
If local natural conditions allow, for example, frequent winds blow or a source of running water is located nearby, then you can create a wind or hydraulic turbine and connect it to an asynchronous three-phase motor to generate electricity.
Thanks to such a device, you will have a constantly working alternative source of electricity. It will reduce energy consumption from public networks and allow you to save on its payment.
In some cases, it is permissible to use single-phase voltage to rotate an electric motor and transmit torque to a homemade generator to create your own three-phase symmetrical network.
How to choose an asynchronous motor for a generator based on design and characteristics
Technological features
The basis of a homemade generator is an asynchronous three-phase electric motor with:
Stator device
The magnetic cores of the stator and rotor are made of insulated electrical steel plates, in which grooves are created to accommodate the winding wires.
Three separate stator windings can be connected at the factory according to the following diagram:
Their terminals are connected inside the terminal box and connected with jumpers. The power cable is also installed here.
In some cases, wires and cables may be connected in other ways.
Symmetrical voltages are supplied to each phase of the asynchronous motor, shifted along the angle by a third of the circle. They generate currents in the windings.
It is convenient to express these quantities in vector form.
Rotor design features
Wound rotor motors
They are equipped with a winding made like a stator winding, and the leads from each are connected to slip rings, which provide electrical contact with the starting and adjustment circuit through pressure brushes.
This design is quite difficult to manufacture and expensive. It requires periodic monitoring of operation and qualified maintenance. For these reasons, it makes no sense to use it in this design for a homemade generator.
However, if there is a similar motor and there is no other use for it, then the leads of each winding (those ends that are connected to the rings) can be short-circuited among themselves. In this way, the wound rotor will turn into a short-circuited one. It can be connected according to any scheme discussed below.
Squirrel-cage motors
Aluminum is poured inside the grooves of the rotor magnetic circuit. The winding is made in the form of a rotating squirrel cage (for which it received such an additional name) with jumper rings short-circuited at the ends.
This is the simplest motor circuit, which has no moving contacts. Due to this, it operates for a long time without the intervention of electricians and is characterized by increased reliability. It is recommended to use it to create a homemade generator.
Markings on the motor housing
In order for a homemade generator to work reliably, you need to pay attention to:
- IP class, characterizing the quality of protection of the housing from environmental influences;
- power consumption;
- speed;
- winding connection diagram;
- permissible load currents;
- Efficiency and cosine φ.
The winding connection diagram, especially for old engines that have been in operation, should be called and checked using electrical methods. This technology is described in detail in the article on connecting a three-phase motor to a single-phase network.
The principle of operation of an asynchronous motor as a generator
Its implementation is based on the method of reversibility of an electric machine. If the motor, disconnected from the mains voltage, begins to forcibly rotate the rotor at the design speed, then an EMF will be induced in the stator winding due to the presence of residual magnetic field energy.
All that remains is to connect a capacitor bank of the appropriate rating to the windings and a capacitive leading current will flow through them, which has a magnetizing character.
In order for the self-excitation of the generator to occur, and a symmetrical system of three-phase voltages to form on the windings, it is necessary to select a capacitance of capacitors greater than a certain critical value. In addition to its value, the output power is naturally influenced by the design of the engine.
For normal generation of three-phase energy with a frequency of 50 Hz, it is necessary to maintain a rotor speed that exceeds the asynchronous component by the slip value S, which lies within the range S=2÷10%. It must be maintained at the synchronous frequency level.
A sinusoid's deviation from the standard frequency value will negatively affect the operation of equipment with electric motors: saws, planes, various machines and transformers. This has virtually no effect on resistive loads with heating elements and incandescent lamps.
Electrical connection diagrams
In practice, all common methods of connecting the stator windings of an asynchronous motor are used. By choosing one of them, they create different conditions for the operation of the equipment and generate voltage of certain values.
Star circuits
Popular option for connecting capacitors
The connection diagram for an asynchronous motor with star-connected windings for operation as a three-phase network generator has a standard form.
Scheme of an asynchronous generator with capacitors connected to two windings
This option is quite popular. It allows you to power three groups of consumers from two windings:
The working and starting capacitors are connected to the circuit using separate switches.
Based on the same circuit, you can create a homemade generator by connecting capacitors to one winding of an asynchronous motor.
Triangle diagram
When assembling the stator windings in a star configuration, the generator will produce a three-phase voltage of 380 volts. If you switch them to a triangle, then - 220.
The three schemes shown in the pictures above are basic, but not the only ones. Based on them, other connection methods can be created.
How to calculate generator characteristics based on engine power and capacitor capacity
To create normal operating conditions for an electric machine, it is necessary to maintain equality between its rated voltage and power in generator and electric motor modes.
For this purpose, the capacitance of the capacitors is selected taking into account the reactive power Q they generate at various loads. Its value is calculated by the expression:
From this formula, knowing the engine power, to ensure full load, you can calculate the capacity of the capacitor bank:
However, the operating mode of the generator should be taken into account. At idle, the capacitors will unnecessarily load the windings and heat them up. This leads to large energy losses and overheating of the structure.
To eliminate this phenomenon, capacitors are connected in stages, determining their number depending on the applied load. To simplify the selection of capacitors for starting an asynchronous motor in generator mode, a special table has been created.
Starting capacitors of the K78-17 series and similar ones with an operating voltage of 400 volts or more are well suited for use as part of a capacitive battery. It is entirely acceptable to replace them with metal-paper counterparts with the appropriate denominations. They will have to be assembled in parallel.
It is not worth using models of electrolytic capacitors to operate in the circuits of an asynchronous homemade generator. They are designed for direct current circuits, and when passing through a sinusoid changing in direction, they quickly fail.
There is a special scheme for connecting them for such purposes, when each half-wave is directed by diodes to its own assembly. But it's quite complicated.
Design
The autonomous device of the power plant must fully meet the requirements for the safe operation of operating equipment and be implemented as a single module, including a hinged electrical panel with devices:
- measurements - with a voltmeter up to 500 volts and a frequency meter;
- load switching - three switches (one common one supplies voltage from the generator to the consumer circuit, and the other two connect capacitors);
- protection - an automatic switch that eliminates the consequences of short circuits or overloads and an RCD (residual current device) that saves workers from insulation breakdown and phase potential entering the housing.
Main power supply redundancy
When creating a homemade generator, it is necessary to ensure its compatibility with the grounding circuit of the working equipment, and when operating autonomously, it must be reliably connected to the ground circuit.
If a power plant is created for backup power supply of devices operating from the state network, then it should be used when the voltage from the line is disconnected, and when restored, it should be stopped. For this purpose, it is enough to install a switch that controls all phases simultaneously or connect a complex automatic system for turning on backup power.
Voltage selection
The 380 volt circuit has an increased risk of injury to humans. It is used in extreme cases, when it is not possible to get by with a phase value of 220.
Generator overload
Such modes create excessive heating of the windings with subsequent destruction of the insulation. They occur when the currents passing through the windings are exceeded due to:
- incorrect selection of capacitor capacity;
- connecting high power consumers.
In the first case, it is necessary to carefully monitor the thermal conditions during idle. If excessive heating occurs, the capacitance of the capacitors must be adjusted.
Features of connecting consumers
The total power of a three-phase generator consists of three parts generated in each phase, which is 1/3 of the total. The current passing through one winding should not exceed the rated value. This must be taken into account when connecting consumers, distributing them evenly across phases.
When a homemade generator is designed to operate on two phases, it cannot safely generate electricity more than 2/3 of the total value, and if only one phase is involved, then only 1/3.
Frequency control
A frequency meter allows you to monitor this indicator. When it is not installed in the design of a homemade generator, you can use the indirect method: at idle, the output voltage exceeds the nominal 380/220 by 4–6% at a frequency of 50 Hz.
How to make a homemade generator from an asynchronous motor, DIY apartment design and renovation
Tips for the home craftsman on how to make a homemade generator from an asynchronous three-phase electric motor with circuit diagrams. pictures and videos
How to make a homemade generator from an asynchronous motor
Hi all! Today we’ll look at how to make a homemade generator from an asynchronous motor with your own hands. I’ve been interested in this question for a long time, but somehow I didn’t have time to tackle its implementation. Now let's do a little theory.
If you take and spin up an asynchronous electric motor from some prime mover, then following the principle of reversibility of electric machines you can make it generate electric current. To do this, you need to rotate the shaft of an asynchronous motor with a frequency equal to or slightly higher than its asynchronous rotation frequency. As a result of residual magnetism in the magnetic circuit of the electric motor, some EMF will be induced at the terminals of the stator winding.
Now let’s take and connect non-polar capacitors C to the terminals of the stator winding, as shown in the figure below.
In this case, a leading capacitive current will begin to flow through the stator winding. It will be called magnetizing. Those. The asynchronous generator will self-excite and the EMF will increase. The value of the EMF will depend on the characteristics of both the electrical machine itself and the capacitance of the capacitors. Thus, we have turned an ordinary asynchronous electric motor into a generator.
Now let's talk about how to choose the right capacitors for a homemade generator from an asynchronous motor. The capacity must be selected so that the generated voltage and output power of the asynchronous generator corresponds to the power and voltage when it operates as an electric motor. See the table below for data. They are relevant for exciting asynchronous generators with a voltage of 380 volts and a rotation speed of 750 to 1500 rpm.
As the load on the asynchronous generator increases, the voltage at its terminals will tend to fall (the inductive load on the generator will increase). To maintain the voltage at a given level, it is necessary to connect additional capacitors. To do this, you can use a special voltage regulator, which, when the voltage at the generator stator terminals decreases, will connect additional capacitor banks using contacts.
The generator rotation speed in normal mode should exceed synchronous speed by 5-10 percent. That is, if the rotation speed is 1000 rpm, then you need to spin it at a frequency of 1050-1100 rpm.
One big advantage of an asynchronous generator is that it can be used as an ordinary asynchronous electric motor without modifications. But it is not recommended to get too carried away and make generators from electric motors with a power of more than 15-20 kV*A. A homemade generator from an asynchronous motor is an excellent solution for those who do not have the opportunity to use a classic kronotex laminate generator. Good luck with everything and bye!
How to make a homemade generator from an asynchronous motor, DIY repairs
How to make a homemade generator from an asynchronous motor Hello everyone! Today we’ll look at how to make a homemade generator from an asynchronous motor with your own hands. This question has been asking me for a long time
The invention relates to the field of electrical engineering and power engineering, in particular to methods and equipment for generating electrical energy, and can be used in autonomous power supply systems, in automation and household appliances, in aviation, marine and road transport.
Due to the non-standard generation method and the original design of the motor-generator, the generator and electric motor modes are combined in one process and are inextricably linked. As a result, when a load is connected, the interaction of the magnetic fields of the stator and rotor forms a torque, which coincides in direction with the torque created by the external drive.
In other words, as the power consumed by the generator load increases, the rotor of the motor-generator begins to accelerate, and the power consumed by the external drive decreases accordingly.
Rumors have been circulating on the Internet for a long time that a generator with a Gram ring armature was capable of generating more electrical energy than was expended in mechanical energy, and this was due to the fact that there was no braking torque under load.
The results of experiments that led to the invention of the motor generator.
There have long been rumors on the Internet that a generator with a Gram ring armature was capable of generating more electrical energy than was expended in mechanical energy and this was due to the fact that there was no braking torque under load. This information prompted us to conduct a series of experiments with ring winding, the results of which we will show on this page. For experiments, 24 pieces of independent windings with the same number of turns were wound on a toroidal core.
1) Initially, the winding weights were connected in series, the load terminals were located diametrically. A permanent magnet with the ability to rotate was located in the center of the winding.
After the magnet was set in motion using the drive, the load was connected and the drive revolutions were measured with a laser tachometer. As one would expect, the speed of the drive motor began to fall. The more power the load consumed, the more the speed dropped.
2) For a better understanding of the processes occurring in the winding, a DC milliammeter was connected instead of the load.
When the magnet rotates slowly, you can observe the polarity and magnitude of the output signal in a given position of the magnet.
From the figures it can be seen that when the magnet poles are opposite the winding terminals (Fig. 4;8), the current in the winding is 0. When the magnet is positioned when the poles are in the center of the winding, we have a maximum current value (Fig. 2;6).
3) At the next stage of experiments, only one half of the winding was used. The magnet also rotated slowly, and the readings of the device were recorded.
The instrument readings completely coincided with the previous experiment (Figure 1-8).
4) After that, an external drive was connected to the magnet and it began to rotate at maximum speed.
When the load was connected, the drive began to gain momentum!
In other words, during the interaction of the poles of the magnet and the poles formed in the winding with the magnetic core, when current passes through the winding, a torque appears, directed along the direction of the torque created by the drive motor.
Figure 1, the drive is strongly braking when the load is connected. Figure 2, when a load is connected, the drive begins to accelerate.
5) To understand what is happening, we decided to create a map of the magnetic poles that appear in the windings when current passes through them. To achieve this, a series of experiments were carried out. The windings were connected in different ways, and direct current pulses were applied to the ends of the windings. In this case, a permanent magnet was attached to the spring and was located in turn next to each of the 24 windings.
Based on the reaction of the magnet (whether it was repelled or attracted), a map of the manifesting poles was compiled.
From the pictures you can see how the magnetic poles appeared in the windings when turned on differently (the yellow rectangles in the pictures are the neutral zone of the magnetic field).
When changing the polarity of the pulse, the poles, as expected, changed to the opposite, so different options for turning on the windings are drawn with the same power polarity.
6) At first glance, the results in Figures 1 and 5 are identical.
Upon closer analysis, it became clear that the distribution of the poles around the circle and the “size” of the neutral zone are quite different. The force with which the magnet was attracted or repelled from the windings and magnetic circuit is shown by gradient shading of the poles.
7) When comparing the experimental data described in paragraphs 1 and 4, in addition to the fundamental difference in the response of the drive to connecting the load, and a significant difference in the “parameters” of the magnetic poles, other differences were identified. During both experiments, a voltmeter was turned on in parallel with the load, and an ammeter was turned on in series with the load. If the instrument readings from the first experiment (point 1) are taken as 1, then in the second experiment (point 4), the voltmeter reading was also equal to 1. The ammeter reading was 0.005 from the results of the first experiment.
8) Based on what was stated in the previous paragraph, it is logical to assume that if a non-magnetic (air) gap is made in the unused part of the magnetic circuit, then the current strength in the winding should increase.
After the air gap was made, the magnet was again connected to the drive motor and spun to maximum speed. The current strength actually increased several times, and began to be approximately 0.5 of the results of the experiment under point 1,
but at the same time a braking torque appeared on the drive.
9) Using the method described in paragraph 5, a map of the poles of this structure was compiled.
10) Let’s compare two options
It is not difficult to assume that if the air gap in the magnetic core is increased, the geometric arrangement of the magnetic poles according to Figure 2 should approach the same arrangement as in Figure 1. And this, in turn, should lead to the effect of accelerating the drive, which is described in paragraph 4 (when connecting load, instead of braking, an additional torque is created to the drive torque).
11) After the gap in the magnetic circuit was increased to the maximum (to the edges of the winding), when a load was connected instead of braking, the drive began to pick up speed again.
In this case, the map of the poles of the winding with the magnetic core looks like this:
Based on the proposed principle of generating electricity, it is possible to design alternating current generators that, when increasing the electrical power in the load, do not require an increase in the mechanical power of the drive.
Operating principle of the Motor Generator.
According to the phenomenon of electromagnetic induction, when the magnetic flux passing through a closed circuit changes, an emf appears in the circuit.
According to Lenz's rule: An induced current arising in a closed conducting circuit has such a direction that the magnetic field it creates counteracts the change in magnetic flux that caused the current. In this case, it does not matter exactly how the magnetic flux moves in relation to the circuit (Fig. 1-3).
The method of exciting EMF in our motor-generator is similar to Figure 3. It allows us to use Lenz’s rule to increase the torque on the rotor (inductor).
1) Stator winding
2) Stator magnetic circuit
3) Inductor (rotor)
4) Load
5) Rotor rotation direction
6) Central line of the magnetic field of the inductor poles
When the external drive is turned on, the rotor (inductor) begins to rotate. When the beginning of the winding is crossed by the magnetic flux of one of the poles of the inductor, an emf is induced in the winding.
When a load is connected, current begins to flow in the winding and the poles of the magnetic field that arises in the windings, according to E. H. Lenz’s rule, are directed towards meeting the magnetic flux that excited them.
Since the winding with the core is located along a circular arc, the magnetic field of the rotor moves along the turns (circular arc) of the winding.
In this case, at the beginning of the winding, according to Lenz’s rule, a pole appears identical to the pole of the inductor, and at the other end it is opposite. Since like poles repel and opposite poles attract, the inductor tends to take a position that corresponds to the action of these forces, which creates an additional moment directed along the direction of rotation of the rotor. The maximum magnetic induction in the winding is achieved at the moment when the center line of the inductor pole is opposite the middle of the winding. With further movement of the inductor, the magnetic induction of the winding decreases, and at the moment the central line of the inductor pole leaves the winding, it is equal to zero. At the same moment, the beginning of the winding begins to cross the magnetic field of the second pole of the inductor, and according to the rules described above, the edge of the winding from which the first pole begins to move away begins to push it away with increasing force.
Drawings:
1) Zero point, the poles of the inductor (rotor) are symmetrically directed to different edges of the winding in the winding EMF = 0.
2) The central line of the north pole of the magnet (rotor) crossed the beginning of the winding, an EMF appeared in the winding, and accordingly a magnetic pole identical to the pole of the exciter (rotor) appeared.
3) The rotor pole is at the center of the winding and the EMF is at its maximum value in the winding.
4) The pole approaches the end of the winding and the emf decreases to a minimum.
5) Next zero point.
6) The center line of the south pole enters the winding and the cycle repeats (7;8;1).
In an effort to obtain autonomous sources of electricity, specialists have found a way to convert a three-phase asynchronous AC electric motor into a generator with their own hands. This method has a number of advantages and some disadvantages.
Appearance of an asynchronous electric motor
The section shows the main elements:
- cast iron body with radiator fins for efficient cooling;
- a squirrel-cage rotor housing with magnetic field shift lines relative to its axis;
- switching contact group in a box (borno), for switching stator windings in star or delta circuits and connecting power supply wires;
- dense bundles of copper wires of the stator winding;
- steel rotor shaft with a groove for fixing the pulley with a wedge key.
A detailed disassembly of the asynchronous electric motor, indicating all the parts, is shown in the figure below.
Detailed disassembly of an asynchronous motor
Advantages of generators converted from asynchronous motors:
- ease of circuit assembly, no need to disassemble the electric motor, no rewinding of the windings;
- the ability to rotate the electric current generator with a wind or hydraulic turbine;
- The generator from an asynchronous motor is widely used in motor-generator systems to convert a single-phase 220V AC network into a three-phase network with a voltage of 380V.
- the possibility of using a generator in the field, spinning it from internal combustion engines.
As a disadvantage, one can note the difficulty of calculating the capacitance of capacitors connected to the windings; in fact, this is done experimentally.
Therefore, it is difficult to achieve the maximum power of such a generator; there are difficulties with power supply to electrical installations that have a large starting current, such as circular saws with three-phase AC motors, concrete mixers and other electrical installations.
Generator operating principle
The operation of such a generator is based on the principle of reversibility: “any electrical installation that converts electrical energy into mechanical energy can perform the reverse process.” The principle of operation of generators is used; rotation of the rotor causes an EMF and the appearance of an electric current in the stator windings.
Based on this theory, it is obvious that an asynchronous electric motor can be converted into an electric generator. In order to consciously carry out reconstruction, it is necessary to understand how the generation process occurs and what is required for this. All motors driven by alternating current are considered asynchronous. The stator field moves slightly ahead of the rotor magnetic field, pulling it along with it in the direction of rotation.
To obtain the reverse process, generation, the rotor field must advance the movement of the stator magnetic field, ideally rotating in the opposite direction. This is achieved by connecting a large capacitor to the power supply network; to increase the capacity, groups of capacitors are used. The capacitor unit is charged by accumulating magnetic energy (an element of the reactive component of alternating current). The charge of the capacitor is in phase opposite to the current source of the electric motor, so the rotation of the rotor begins to slow down, the stator winding generates current.
Conversion
How to practically convert an asynchronous electric motor into a generator with your own hands?
To connect the capacitors, you need to unscrew the top cover of the boron (box), where the contact group is located, switching the contacts of the stator windings and the power wires of the asynchronous motor are connected.
Open boron with contact group
The stator windings can be connected in a “Star” or “Triangle” configuration.
Connection circuits "Star" and "Triangle"
The nameplate or product data sheet shows possible connection diagrams and motor parameters for various connections. Indicated:
- maximum currents;
- supply voltage;
- power consumption;
- number of revolutions per minute;
- Efficiency and other parameters.
Engine parameters indicated on the nameplate
In a three-phase generator from an asynchronous electric motor, which is made by hand, the capacitors are connected in a similar “Triangle” or “Star” circuit.
The connection option with a “Star” ensures the starting process of generating current at lower speeds than when connecting the circuit in a “Triangle”. In this case, the voltage at the generator output will be slightly lower. Delta connection provides a slight increase in output voltage, but requires higher rpm when starting the generator. In a single-phase asynchronous electric motor, one phase-shifting capacitor is connected.
Connection diagram of capacitors on a generator in a “Triangle”
Capacitors of the KBG-MN model or other brands of at least 400 V non-polar are used; bipolar electrolytic models are not suitable in this case.
What does a poleless capacitor of the KBG-MN brand look like?
Calculation of capacitor capacity for the motor used
| Generator rated output power, kW | Estimated capacity in, µF |
|---|---|
| 2 | 60 |
| 3,5 | 100 |
| 5 | 138 |
| 7 | 182 |
| 10 | 245 |
| 15 | 342 |
In synchronous generators, the generation process is excited on the armature windings from the current source. 90% of asynchronous motors have squirrel-cage rotors, without winding; excitation is created by a residual static charge in the rotor. It is enough to create an EMF at the initial stage of rotation, which induces current and recharges the capacitors through the stator windings. Further recharging already comes from the generated current; the generation process will be continuous as long as the rotor rotates.
It is recommended to install the automatic load connection to the generator, sockets and capacitors in a separate closed panel. Lay the connecting wires from the boron generator to the switchboard in a separate insulated cable.
Even when the generator is not working, you must avoid touching the capacitor terminals of the socket contacts. The charge accumulated by the capacitor remains for a long time and can cause electric shock. Ground the housings of all units, motor, generator, control panel.
Installation of a motor-generator system
When installing a generator with a motor with your own hands, you must take into account that the specified number of rated revolutions of the asynchronous electric motor used at idle is greater.
Scheme of a motor-generator on a belt drive
On an engine of 900 rpm at idle speed there will be 1230 rpm, in order to obtain sufficient power at the output of a generator converted from this engine, you must have a number of revolutions 10% higher than idle speed:
1230 + 10% = 1353 rpm.
Belt drive is calculated using the formula:
Vg = Vm x Dm\Dg
Vg – required generator rotation speed 1353 rpm;
Vm – motor rotation speed 1200 rpm;
Dm – pulley diameter on the motor is 15 cm;
Dg – diameter of the pulley on the generator.
Having a 1200 rpm motor where the pulley is Ø 15 cm, all that remains is to calculate Dg - the diameter of the pulley on the generator.
Dg = Vm x Dm/ Vg = 1200 rpm x 15cm/1353 rpm = 13.3 cm.
Generator with neodymium magnets
How to make a generator from an asynchronous electric motor?
This homemade generator eliminates the use of capacitor units. The source of the magnetic field, which induces EMF and creates current in the stator winding, is built on permanent neodymium magnets. In order to do this yourself, you must sequentially perform the following steps:
- Remove the front and rear covers of the asynchronous motor.
- Remove the rotor from the stator.
What does the rotor of an asynchronous motor look like?
- The rotor is ground, the top layer 2 mm larger than the thickness of the magnets is removed. In everyday conditions, it is not always possible to bore a rotor with your own hands, in the absence of turning equipment and skills. You need to contact specialists in turning workshops.
- A template is prepared on a sheet of plain paper for placing round magnets, Ø 10-20 mm, up to 10 mm thick, with an attractive force of 5-9 kg per sq/cm, the size depends on the size of the rotor. The template is glued to the surface of the rotor, the magnets are placed in strips at an angle of 15 - 20 degrees relative to the rotor axis, 8 pieces per strip. The figure below shows that on some rotors there are dark-light stripes of displacement of the magnetic field lines relative to its axis.
Installing magnets on the rotor
- The rotor on magnets is calculated so that there are four groups of strips, in a group of 5 strips, the distance between the groups is 2Ø of the magnet. The gaps in the group are 0.5-1Ø of the magnet, this arrangement reduces the force of sticking of the rotor to the stator; it must be rotated with the efforts of two fingers;
- The magnetic rotor, made according to a calculated template, is filled with epoxy resin. After it dries a little, the cylindrical part of the rotor is covered with a layer of fiberglass and again impregnated with epoxy resin. This will prevent the magnets from flying out when the rotor rotates. The top layer on the magnets should not exceed the original diameter of the rotor, which was before the groove. Otherwise, the rotor will not fall into place or will rub against the stator winding when rotating.
- After drying, the rotor can be put back in place and the lids closed;
- To test an electric generator, it is necessary to turn the rotor with an electric drill, measuring the voltage at the output. The number of revolutions when the desired voltage is reached is measured by a tachometer.
- Knowing the required number of generator revolutions, the belt drive is calculated according to the method described above.
An interesting application option is when an electric generator based on an asynchronous electric motor is used in a self-feeding electric motor-generator circuit. When part of the power generated by the generator goes to the electric motor, which spins it. The rest of the energy is spent on the payload. By implementing the principle of self-feeding, it is practically possible to provide the house with autonomous power supply for a long time.
Video. G generator from an asynchronous motor.
For a wide range of electricity consumers, buying powerful diesel power plants like TEKSAN TJ 303 DW5C with an output power of 303 kVA or 242 kW does not make sense. Low-power gasoline generators are expensive; the best option is to make your own wind generators or a self-powered motor-generator device.
Using this information, you can assemble a generator with your own hands, using permanent magnets or capacitors. Such equipment is very useful in country houses, in the field, as an emergency power source when there is no voltage in industrial networks. They cannot handle a full-fledged house with air conditioners, electric stoves and heating boilers, or a powerful circular saw motor. You can temporarily provide electricity to essential household appliances, lighting, refrigerators, TVs and others that do not require large amounts of power.
In order for an asynchronous motor to become an alternating current generator, a magnetic field must be formed inside it; this can be done by placing permanent magnets on the motor rotor. The whole alteration is both simple and complex at the same time.
First you need to select a suitable engine that is most suitable for working as a low-speed generator. These are multi-pole asynchronous motors; 6- and 8-pole, low-speed motors are well suited, with a maximum speed in motor mode of no more than 1350 rpm. Such motors have the largest number of poles and teeth on the stator.
Next, you need to disassemble the engine and remove the armature-rotor, which must be ground on a machine to a certain size for gluing magnets. Neodymium magnets, usually small round magnets are glued. Now I will try to tell you how and how many magnets to glue.
First you need to find out how many poles your motor has, but it is quite difficult to understand this from the winding without the appropriate experience, so it is better to read the number of poles on the motor marking, if of course it is available, although in most cases it is. Below is an example of engine markings and a description of the markings.
By engine brand. For 3-phase: Motor type Power, kW Voltage, V Rotation speed, (sync.), rpm Efficiency, % Weight, kg
For example: DAF3 400-6-10 UHL1 400 6000 600 93.7 4580 Engine designation: D - engine; A - asynchronous; F - with wound rotor; 3 - closed version; 400 - power, kW; b - voltage, kV; 10 - number of poles; UHL - climatic version; 1 - accommodation category.
It happens that engines are not of our production, as in the photo above, and the markings are unclear, or the markings are simply not readable. Then there is only one method left, this is to count how many teeth you have on the stator and how many teeth one coil occupies. If, for example, the coil takes up 4 teeth, and there are only 24 of them, then your motor is six-pole.
The number of stator poles needs to be known in order to determine the number of poles when gluing magnets to the rotor. This quantity is usually equal, that is, if there are 6 stator poles, then the magnets must be glued with alternating poles in the amount of 6, SNSNSN.
Now that the number of poles is known, we need to calculate the number of magnets for the rotor. To do this, you need to calculate the circumference of the rotor using the simple formula 2nR where n=3.14. That is, we multiply 3.14 by 2 and by the radius of the rotor, we get the circumference. Next, we measure our rotor along the length of the iron, which is in an aluminum mandrel. Afterwards, you can draw the resulting strip with its length and width, you can do it on a computer and then print it out.
You need to decide on the thickness of the magnets, it is approximately equal to 10-15% of the rotor diameter, for example, if the rotor is 60mm, then magnets need to be 5-7mm thick. For this purpose, magnets are usually bought round. If the rotor is approximately 6 cm in diameter, then the magnets can be 6-10 mm high. Having decided which magnets to use, on the template the length of which is equal to the length of the circle
An example of calculating magnets for a rotor, for example, the diameter of the rotor is 60 cm, we calculate the circumference = 188 cm. We divide the length by the number of poles, in this case by 6, and we get 6 sections, in each section the magnets are glued with the same pole. But that is not all. Now you need to calculate how many magnets will fit into one pole in order to evenly distribute them along the pole. For example, the width of a round magnet is 1 cm, the distance between the magnets is about 2-3 mm, which means 10 mm + 3 = 13 mm.
We divide the length of the circle into 6 parts = 31mm, this is the width of one pole along the length of the rotor circumference, and the width of the pole along the iron, let’s say 60mm. This means the pole area is 60 by 31 mm. This turns out to be 8 in 2 rows of magnets per pole with a distance of 5mm between them. In this case, it is necessary to recalculate the number of magnets so that they fit as tightly as possible on the pole.
Here is an example with magnets 10mm wide, so the distance between them is 5mm. If you reduce the diameter of the magnets, for example, by 2 times, that is, 5 mm, then they will fill the pole more densely, as a result of which the magnetic field will increase due to the greater amount of the total mass of the magnet. There are already 5 rows of such magnets (5mm) and 10 in length, that is, 50 magnets per pole, and the total number per rotor is 300 pcs.
In order to reduce sticking, the template must be marked so that the displacement of the magnets when sticking is the width of one magnet; if the width of the magnet is 5mm, then the displacement is 5mm.
Now that you have decided on the magnets, you need to grind the rotor so that the magnets fit. If the height of the magnets is 6mm, then the diameter is ground down to 12+1mm, 1mm is a margin for hand bending. Magnets can be placed on the rotor in two ways.
The first method is to first make a mandrel in which holes for the magnets are drilled according to a template, after which the mandrel is put on the rotor, and the magnets are glued into the drilled holes. On the rotor, after grooving, you need to additionally grind down the separating aluminum strips between the iron to a depth equal to the height of the magnets. And fill the resulting grooves with annealed sawdust mixed with epoxy glue. This will significantly increase efficiency; the sawdust will serve as an additional magnetic circuit between the rotor iron. The sampling can be done with a cutting machine or on a machine.
The mandrel for gluing magnets is done like this: the machined shaft is wrapped in polyintel, then a bandage soaked in epoxy glue is wound layer by layer, then ground to size on a machine and removed from the rotor, a template is glued and holes are drilled for the magnets. Then the mandrel is put back on the rotor and glued magnets are usually glued with epoxy glue. Below in the photo there are two examples of sticking magnets, the first example in 2 photos is sticking magnets using a mandrel, and the second on the next page directly through the template. In the first two photos you can clearly see and I think it’s clear how the magnets are glued.
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Continued on the next page.
An asynchronous or induction type generator is a special type of device that uses alternating current and has the ability to generate electricity. The main feature is the relatively fast turns that the rotor makes; in terms of the rotation speed of this element, it is significantly superior to the synchronous variety.
One of the main advantages is the ability to use this device without significant circuit modifications or lengthy setup.
A single-phase type of induction generator can be connected by applying the required voltage to it, this will require connecting it to a power source. However, a number of models produce self-excitation; this ability allows them to function in a mode independent of any external sources.
This is accomplished by sequentially bringing the capacitors into working condition.
Generator circuit from an asynchronous motor
generator circuit based on an asynchronous motor In virtually any electric-type machine, designed as a generator, there are 2 different active windings, without which the operation of the device is impossible:
- Field winding, which is located on a special anchor.
- Stator winding, which is responsible for the formation of electric current, this process occurs inside it.
In order to visualize and more accurately understand all the processes occurring during the operation of the generator, the best option would be to take a closer look at its operation diagram:
- Voltage, which is supplied from a battery or any other source, creates a magnetic field in the armature winding.
- Rotating device elements together with a magnetic field can be implemented in different ways, including manually.
- A magnetic field, rotating at a certain speed, generates electromagnetic induction, due to which an electric current appears in the winding.
- The vast majority of schemes used today does not have the ability to provide voltage to the armature winding, this is due to the presence of a squirrel-cage rotor in the design. Therefore, regardless of the speed and time of rotation of the shaft, the power supply devices will still be de-energized.
When converting an engine into a generator, the independent creation of a moving magnetic field is one of the main and mandatory conditions.
Generator device
Before taking any action to remodelinto the generator, you need to understand the structure of this machine, which looks like this:
- Stator, which is equipped with a 3-phase network winding located on its working surface.
- Winding organized in such a way that it resembles a star in shape: 3 initial elements are connected to each other, and 3 opposite sides are connected to slip rings that do not have any points of contact with each other.
- Slip rings have reliable fastening to the rotor shaft.
- In design There are special brushes that do not make any independent movements, but help turn on the rheostat with three phases. This allows you to change the resistance parameters of the winding located on the rotor.
- Often, in the internal device there is such an element as an automatic short circuiter, which is necessary to short-circuit the winding and stop the rheostat, which is in working condition.
- Another additional element of the generator device may be a special device that moves the brushes and slip rings apart at the moment when they go through the closing stage. This measure helps to significantly reduce friction losses.
Making a generator from an engine
In fact, any asynchronous electric motor can be converted with your own hands into a device that functions like a generator, which can then be used in everyday life. Even an engine taken from an old-style washing machine or any other household equipment may be suitable for this purpose.
In order for this process to be successfully implemented, it is recommended to adhere to the following algorithm of actions:
- Remove the engine core layer, due to which a depression will be formed in its structure. This can be done on a lathe; it is recommended to remove 2 mm. throughout the core and make additional holes with a depth of about 5 mm.
- Take dimensions from the resulting rotor, after which a template in the form of a strip is made from tin material, which will correspond to the dimensions of the device.
- Install in the resulting free space there are neodymium magnets, which must be purchased in advance. Each pole will require at least 8 magnetic elements.
- Fixation of magnets can be done using universal superglue, but it must be taken into account that when approaching the surface of the rotor they will change their position, so they must be held firmly with your hands until each element is glued. Additionally, it is recommended to use safety glasses during this process to avoid any glue splashing into your eyes.
- Wrap the rotor plain paper and tape that will be needed to secure it.
- The end part of the rotor cover with plasticine, which will ensure sealing of the device.
- After completed actions it is necessary to process the free cavities between the magnetic elements. To do this, the remaining free space between the magnets must be filled with epoxy resin. The most convenient way would be to cut a special hole in the shell, transform it into a neck and seal the borders with plasticine. You can pour resin inside.
- Wait until it hardens completely filled with resin, after which the protective paper shell can be removed.
- The rotor must be fixed using a machine or a vice so that it can be processed, which consists of grinding the surface. For these purposes, you can use sandpaper with a medium grit setting.
- Determine state and the purpose of the wires coming out of the engine. Two should lead to the working winding, the rest can be cut off so as not to get confused in the future.
- Sometimes the rotation process is quite poor, most often the cause is old worn out and tight bearings, in which case they can be replaced with new ones.
- Rectifier for generator can be assembled from special silicon, which are designed specifically for these purposes. You also don’t need a controller for charging; virtually all modern models are suitable.
After all the above steps have been completed, the process can be considered complete; the asynchronous motor has been converted into a generator of the same type.
Assessing the level of efficiency - is it profitable?
The generation of electric current by an electric motor is quite real and feasible in practice, the main question is how profitable is it?
The comparison is made primarily with a synchronous version of a similar device, in which there is no electrical excitation circuit, but despite this fact, its structure and design are not simpler.
This is due to the presence of a capacitor bank, which is an extremely technically complex element that is absent in an asynchronous generator.
The main advantage of an asynchronous device is that the available capacitors do not require any maintenance, since all the energy is transferred from the magnetic field of the rotor and the current that is generated during the operation of the generator.
The electric current created during operation virtually does not have higher harmonics, which is another significant advantage.
Asynchronous devices do not have any other advantages besides those mentioned, but they do have a number of significant disadvantages:
- During their operation there is no possibility of ensuring the nominal industrial parameters of the electric current generated by the generator.
- High degree of sensitivity even to the slightest changes in workload parameters.
- If the permissible load parameters on the generator are exceeded, a lack of electricity will be detected, after which recharging will become impossible and the generation process will be stopped. To eliminate this drawback, batteries with significant capacity are often used, which have the ability to change their volume depending on the magnitude of the loads applied.
The electric current produced by an asynchronous generator is subject to frequent changes, the nature of which is unknown, it is random and cannot be explained in any way by scientific arguments.
The impossibility of taking into account and appropriate compensation for such changes explains the fact that such devices have not gained popularity and have not become particularly widespread in the most serious industries or household affairs.
Functioning of an asynchronous motor as a generator
In accordance with the principles on which all such machines operate, the operation of an induction motor after conversion into a generator occurs as follows:
- After connecting the capacitors to the terminals, a number of processes occur on the stator windings. In particular, a leading current begins to move in the winding, which creates a magnetization effect.
- Only if the capacitors match parameters of the required capacity, the device self-excites. This promotes a symmetrical 3-phase voltage system on the stator winding.
- Final voltage value will depend on the technical capabilities of the machine used, as well as on the capabilities of the capacitors used.
Thanks to the described actions, the process of converting a squirrel-cage asynchronous motor into a generator with similar characteristics occurs.
Application
In everyday life and in production, such generators are widely used in various fields and areas, but they are most in demand to perform the following functions:
- Use as engines for , this is one of the most popular features. Many people make their own asynchronous generators to use them for these purposes.
- Work as a hydroelectric power station with little output.
- Providing food and electricity from a city apartment, private country house or individual household equipment.
- Perform basic functions welding generator.
- Uninterrupted equipment alternating current of individual consumers.
It is necessary to have certain skills and knowledge not only in the manufacture, but also in the operation of such machines; the following tips can help with this:
- Any type of asynchronous generators Regardless of the area in which they are used, it is a dangerous device, for this reason it is recommended to isolate it.
- During the manufacturing process of the device it is necessary to consider the installation of measuring instruments, since it will be necessary to obtain data on its functioning and operating parameters.
- Availability of special buttons, with which you can control the device, greatly facilitates the operation process.
- Grounding is a mandatory requirement that must be implemented before operating the generator.
- During work, The efficiency of an asynchronous device can periodically decrease by 30-50%; it is not possible to overcome the occurrence of this problem, since this process is an integral part of energy conversion.