Asynchronous electric motor in generator mode. Generator from electric

Electric generators are an additional source of energy for the home. If the main power grids are far away, it may well replace them. Frequent power outages force the installation of alternating current generators.

They are not cheap, is there any point in spending more than 10,000 rubles? for the device, if you can make a generator from an electric motor yourself? Of course, some electrical engineering skills and tools will be useful for this. The main thing is that you don’t have to spend money.

You can assemble a simple generator with your own hands; it will be relevant if you need to cover a temporary shortage of electricity. It is not suitable for more serious cases, as it does not have sufficient functionality and reliability.

Naturally, there are many difficulties in the manual assembly process. Required parts and tools may not be available. Lack of experience and skills in such work can be intimidating. But a strong desire will be the main incentive and will help overcome all labor-intensive procedures.

Implementation of the generator and its operating principle

Thanks to electromagnetic induction, an electric current is generated in the generator. This happens because the winding moves in an artificially created magnetic field. This is the principle of operation of an electric generator.

The generator is driven by a low-power internal combustion engine. It can run on gasoline, gas or diesel fuel.

An electric generator has a rotor and a stator. The magnetic field is created using a rotor. Magnets are attached to it. The stator is the stationary part of the generator, and consists of special steel plates and a coil. There is a small gap between the rotor and stator.

There are two types of electric generator. The first has synchronous rotor rotation. It has a complex design and low efficiency. In the second type, the rotor rotates asynchronously. The principle of operation is simple.

Asynchronous motors lose a minimum of energy, while in synchronous generators the loss rate reaches 11%. Therefore, electric motors with asynchronous rotor rotation are very popular in household appliances and in various factories.

During operation, voltage surges may occur, which have a detrimental effect on household appliances. For this purpose, there is a rectifier at the output ends.

The asynchronous generator is easy to maintain. Its body is reliable and sealed. You don’t have to worry about household appliances that have an ohmic load and are sensitive to voltage surges. High efficiency and long service life make the device popular, and it can also be assembled independently.

What will you need to assemble the generator? First, you need to choose a suitable electric motor. You can take it from the washing machine. There is no point in making the stator yourself; it is better to use a ready-made solution that has windings.

You should immediately stock up on a sufficient number of copper wires and insulating materials. Since any generator will produce voltage surges, a rectifier will be needed.

According to the instructions for the generator, you need to do a power calculation yourself. In order for the future device to produce the required power, it needs to be given a speed slightly higher than the rated power.

Let's use a tachometer and turn on the engine, so you can find out the speed of rotation of the rotor. You need to add 10% to the resulting value, this will prevent the engine from overheating.

Capacitors will help maintain the required voltage level. They are selected depending on the generator. For example, for a power of 2 kW, a capacitor capacity of 60 μF will be required. You need 3 such parts with the same capacity. To make the device safe, it must be grounded.

Build process

Everything is simple here! Capacitors are connected to the electric motor in a delta configuration. During operation, you need to periodically check the temperature of the case. Its heating may occur due to incorrectly selected capacitor capacitors.

A homemade generator that does not have automation must be constantly monitored. Heating that occurs over time will reduce efficiency. Then the device needs to be given time to cool down. From time to time you should measure the voltage, speed, and current.

Incorrectly calculated characteristics are not able to provide the equipment with the necessary power. Therefore, before starting assembly, you should carry out drawing work and stock up on diagrams.

It is quite possible that a homemade device will experience frequent breakdowns. This should not be surprising, since it is practically impossible to achieve a hermetically sealed installation of all elements of an electric generator at home.

So, I hope it’s now clear how to make a generator from an electric motor. If you want to design a device whose power should be enough to simultaneously operate household appliances and lighting lamps, or construction tools, then you need to add up their power and select the desired engine. It is desirable that it has a small power reserve.

If you fail when manually assembling an electric generator, do not despair. There are many modern models on the market that do not require constant supervision. They can be of different power, and are quite economical. There are photos of generators on the Internet; they will help you estimate the dimensions of the device. The only negative is their high cost.

Photos of DIY generators

The energy of the electric current, entering the inside of an asynchronous motor, easily turns into motion energy at the exit from it. But what if a reverse transformation is required? In this case, you can build a homemade generator from an asynchronous motor. It will only function in a different mode: electricity will begin to be generated by performing mechanical work. The ideal solution is to transform it into a wind generator - a source of free energy.

It has been experimentally proven that a magnetic field is created by an alternating electric field. This is the basis of the operating principle of an asynchronous motor, the design of which includes:

• The body is what we see from the outside;
• Stator is the stationary part of the electric motor;
• A rotor is an element that is driven.

The main element of the stator is the winding, to which an alternating voltage is applied (the principle of operation is not on permanent magnets, but on a magnetic field that is damaged by alternating electric). The rotor is a cylinder with slots in which the winding is placed. But the current entering it has the opposite direction. As a result, two alternating electric fields are formed. Each of them creates a magnetic field, which begins to interact with each other. But the design of the stator is such that it cannot move. Therefore, the result of the interaction of two magnetic fields is the rotation of the rotor.

Design and principle of operation of the electric generator

Experiments also confirm that a magnetic field creates an alternating electric field. Below is a diagram that clearly illustrates the principle of operation of the generator.

If a metal frame is placed and rotated in a magnetic field, the magnetic flux penetrating it will begin to change. This will lead to the formation of an induced current inside the frame. If you connect the ends to a current consumer, for example, an electric lamp, you can observe its glow. This suggests that the mechanical energy expended in rotating the frame within the magnetic field was converted into electrical energy, which helped light the lamp.

Structurally, an electric generator consists of the same parts as an electric motor: a housing, a stator and a rotor. The difference lies only in the principle of operation. The rotor is driven by the magnetic field created by the electric field in the stator winding. And an electric current appears in the stator winding due to a change in the magnetic flux penetrating it, due to the forced rotation of the rotor.

From electric motor to electric generator

Human life today is unthinkable without electricity. Therefore, power plants are being built everywhere, converting the energy of water, wind and atomic nuclei into electrical energy. It has become universal because it can be converted into the energy of movement, heat and light. This became the reason for the massive spread of electric motors. Electric generators are less popular because the state supplies electricity centrally. But still, sometimes it happens that there is no electricity and there is nowhere to get it from. In this case, a generator from an asynchronous motor will help you.

We have already said above that the electric generator and the engine are structurally similar to each other. This raises the question: is it possible to use this miracle of technology as a source of both mechanical and electrical energy? It turns out that it is possible. And we will tell you how to convert a motor into a current source with your own hands.

The meaning of the rework

If you need an electric generator, why make it from an engine if you can buy new equipment? However, high-quality electrical equipment is not a cheap pleasure. And if you have a motor that is not currently being used, why not put it to good use? With simple manipulations and at minimal cost, you will get an excellent current source that can power devices with active loads. These include computer, electronic and radio equipment, ordinary lamps, heaters and welding converters.

But savings are not the only advantage. Advantages of an electric current generator constructed from an asynchronous electric motor:

• The design is simpler than that of a synchronous analogue;
• Maximum protection of the insides from moisture and dust;
• High resistance to overloads and short circuits;
• Almost complete absence of nonlinear distortions;
• Clearance factor (a value expressing the uneven rotation of the rotor) no more than 2%;
• The windings are static during operation, so they do not wear out for a long time, increasing their service life;
• The generated electricity immediately has a voltage of 220V or 380V, depending on which engine you decide to convert: single-phase or three-phase. This means that current consumers can be directly connected to the generator, without inverters.

Even if the electric generator cannot fully meet your needs, it can be used in conjunction with a centralized power supply. In this case, we are again talking about saving: you will have to pay less. The benefit will be expressed as the difference obtained by subtracting the electricity generated from the amount of electricity consumed.

What is needed for remodeling?

To make a generator from an asynchronous motor with your own hands, you must first understand what is preventing the conversion of electrical energy from mechanical energy. Let us recall that for the formation of an induction current, the presence of a magnetic field that changes with time is necessary. When the equipment operates in motor mode, it is created in both the stator and the rotor due to power from the network. If you switch the equipment to generator mode, it turns out that there is no magnetic field at all. Where does he come from?

After the equipment operates in motor mode, the rotor retains residual magnetization. It is this force that causes an induced current in the stator due to forced rotation. And in order for the magnetic field to be maintained, it will be necessary to install capacitors that carry capacitive current. It is he who will maintain magnetization due to self-excitation.

We have sorted out the question of where the original magnetic field came from. But how to set the rotor in motion? Of course, if you spin it with your own hands, you can power a small light bulb. But the result is unlikely to satisfy you. The ideal solution is to turn the motor into a wind generator, or windmill.

This is the name of a device that converts the kinetic energy of the wind into mechanical, and then into electrical. Wind generators are equipped with blades that move when they meet the wind. They can rotate in both vertical and horizontal planes.

From theory to practice

Let's build a wind generator from a motor with our own hands. For easy understanding, diagrams and videos are included with the instructions. You will need:

• Device for transmitting wind energy to the rotor;
• Capacitors for each stator winding.

It is difficult to formulate a rule according to which you could choose a wind catching device the first time. Here you need to be guided by the fact that when the equipment is operating in generator mode, the rotor speed should be 10% higher than when operating as an engine. You need to take into account not the nominal frequency, but the idle speed. Example: the rated frequency is 1000 rpm, and in idle mode it is 1400. Then to generate current you will need a frequency of approximately 1540 rpm.

The selection of capacitors by capacity is made according to the formula:

C is the required capacity. Q – rotor rotation speed in revolutions per minute. P is the number “pi” equal to 3.14. f – phase frequency (constant value for Russia, equal to 50 Hertz). U – network voltage (220 if one phase, and 380 if three).

Calculation example : Three-phase rotor rotates at 2500 rpm. ThenC = 2500/(2*3.14*50*380*380)=56 µF.

Attention! Do not select a container larger than the calculated value. Otherwise, the active resistance will be high, which will lead to overheating of the generator. This can also happen when the device is started without load. In this case, it will be useful to reduce the capacitance of the capacitor. To make it easy to do it yourself, place the container not as a whole, but as a prefabricated one. For example, 60 μF can be made up of 6 pieces of 10 μF connected in parallel to each other.

How to connect?

Let's look at how to make a generator from an asynchronous motor, using the example of a three-phase motor:

1. Connect the shaft to a device that rotates the rotor using wind energy;
2. Connect the capacitors in a triangle pattern, the vertices of which are connected to the ends of the star or the vertices of the stator triangle (depending on the type of winding connection);
3. If a voltage of 220 Volts is required at the output, connect the stator windings in a triangle (the end of the first winding with the beginning of the second, the end of the second with the beginning of the third, the end of the third with the beginning of the first);
4. If you need to power devices from 380 Volts, then a star circuit is suitable for connecting the stator windings. To do this, connect the beginning of all windings together, and connect the ends to the appropriate containers.

Step-by-step instructions on how to make a low-power single-phase wind generator with your own hands:

1. Remove the electric motor from the old washing machine;
2. Determine the working winding and connect a capacitor in parallel with it;
3. Ensure that the rotor rotates using wind energy.

You will get a windmill, like in the video, and it will produce 220 Volts.

For electrical appliances powered by DC, an additional rectifier will be required. And if you are interested in monitoring the power supply parameters, install an ammeter and a voltmeter at the output.

Advice! Due to the lack of constant wind, wind generators may sometimes stop working or not work at full capacity. Therefore, it is convenient to organize your own power plant. To do this, the windmill is connected to the battery during windy weather. The accumulated electricity can be used during calm periods.

An electric motor is a device that acts as an energy converter and operates in the mode of obtaining mechanical energy from electrical energy. Through simple transformations without the use of a permanent magnet, but thanks to residual magnetization, the motor begins to work as a power source. These are two mutually inverse phenomena that help you save: you don’t need to buy a wind generator if an electric motor is lying around idle. Watch the video and learn.

An asynchronous (induction) generator is an electrical product that operates on alternating current and has the ability to reproduce electrical energy. A distinctive feature is the high rotor speed.

This parameter is significantly higher than that of the synchronous analogue. The operation of an asynchronous machine is based on its ability to convert mechanical energy into electricity. Allowable voltage is 220V or 380V.

Applications

Today, the scope of application of asynchronous devices is quite wide. They are used:

• in the transport industry (braking system);
• in agricultural work (units that do not require power compensation);
• in everyday life (motors of autonomous water or wind power plants);
• for welding work;
• to ensure uninterrupted power supply to critical equipment such as medical refrigerators.

In theory, it is quite possible to convert an asynchronous motor into an asynchronous generator. To do this, you need:

• have a clear understanding of electric current;
• carefully study the physics of generating electricity from mechanical energy;
• provide the required conditions for the occurrence of current on the stator winding.

Specifics of the device and principle of operation

The main elements of asynchronous generators are the rotor and stator. The rotor is a short-circuited part, the rotation of which produces an electromotive force. Aluminum is used to make conductive surfaces. The stator is equipped with a three-phase or single-phase winding arranged in a star shape.

As shown in the photo of an asynchronous type generator, other components are:

• cable input (electric current is output through it);
• temperature sensor (needed to monitor the heating of the winding);
• flanges (purpose – a tighter connection of elements);
• slip rings (not connected to each other);
• regulating brushes (they trigger a rheostat, which allows you to regulate the rotor resistance);
• short-circuit device (used if it is necessary to forcefully stop the rheostat).

The operating principle of asynchronous generators is based on the conversion of mechanical energy into electrical energy. The movement of the rotor blades leads to the generation of electric current on its surface.

As a result, a magnetic field is formed that induces single- and three-phase voltage on the stator. The generated energy can be regulated by changing the load on the stator windings.

Features of the scheme

The generator circuit of an asynchronous motor is quite simple. It does not require special skills. When you start the development without connecting to the power supply, rotation will begin. Having reached the appropriate frequency, the stator winding will begin to generate current.

If you install a separate battery of several capacitors, the result of such manipulation will be a leading capacitive current.

The parameters of the generated energy are influenced by the technical characteristics of the generator and the capacitance of the capacitors used.

Types of asynchronous motors

It is customary to distinguish the following types of asynchronous generators:

With squirrel-cage rotor. A device of this type consists of a stationary stator and a rotating rotor. The cores are steel. An insulated wire is placed in the grooves of the stator core. A rod winding is installed in the grooves of the rotor core. The rotor winding is closed by special jumper rings.

With wound rotor. This product is quite expensive. Requires specialized maintenance. The design is similar to that of a generator with a squirrel-cage rotor. The difference lies in the use of insulated wire as windings.

The ends of the winding are attached to special rings placed on the shaft. Brushes pass through them, connecting the wire with the rheostat. An asynchronous type generator with a wound rotor is less reliable.

Converting the engine into a generator

As stated earlier, it is acceptable to use an induction motor as a generator. Let's take a look at a small master class.

You will need a motor from a regular washing machine.

• Let's reduce the thickness of the core and make several blind holes.
• Let's cut a strip from sheet steel, the size of which is equal to the size of the rotor.
• We will install neodymium magnets (at least 8 pieces). Let's secure them with glue.
• Cover the rotor with a sheet of thick paper and secure the edges with adhesive tape.
• We coat the rotor end with a mastic composition for sealing purposes.
• Fill the free space between the magnets with resin.
• After the epoxy hardens, remove the paper layer.
• Sand the rotor using sandpaper.
• Using two wires, we connect the device to the working winding and remove unnecessary wires.
• If desired, we replace the bearings.

We install the current rectifier and mount the charging controller. Our DIY asynchronous motor generator is ready!

More detailed instructions on how to make an asynchronous type generator can be found on the Internet.

• Provide the generator with protection from mechanical damage and precipitation.
• Make a special protective case for the assembled machine.
• Remember to regularly monitor generator parameters.
• Don't forget to ground the unit.
• Avoid overheating.

Photos of asynchronous generators

Existing electricity supply organizations have repeatedly proven their incompetence in serving consumers, and more and more people are facing problems with electricity supply. Most often with power outages or even lack of electricity owners of mansions and dachas outside the city face. In this regard, people stock up on kerosene lamps, candles and gasoline generators.

But it is not always possible to buy a good generator, and residents are forced to face the question of how to make a generator with their own hands, spending much less on it than on a factory unit.

Generator operating principle

In great demand, the generator can be based on a gasoline or diesel engine. In most cases, the main device for generating electricity is an asynchronous motor, which produces energy for the working electrical network. Gasoline generator with asynchronous engine is working with high efficiency, and the rotor speed of an asynchronous motor is higher than that of the motor itself.

Installations using an asynchronous motor are used not only in domestic conditions, but also in many other power plants, such as:

• Wind power plants.
• For operation of the welding machine.
• To support electricity in conjunction with a small hydroelectric power plant.

In most cases, starting occurs due to the connection of current, however, for mini-stations this is not entirely rational, since the generator must generate electricity and not consume it. Due to this disadvantage, manufacturers are increasingly offering self-exciting devices, for which only a series connection of a capacitor is required to start.

Due to the fact that the rotor speed of an asynchronous generator is higher than the motor itself, it can produce electricity. In the most common models of generators, to generate electricity there must be at least 1500 revolutions per minute.

The superiority of the rotor speed at startup over the synchronous speed is called slip and is calculated as a percentage of the synchronous speed, but since the stator rotates with high speed than the rotor, a flow of charged electrons with alternating polarity is formed.

At start-up, the connected device controls the synchronous speed and subsequently the slip. When leaving the stator, the electrons move around the rotor, but the active energy is already in the stator coils.

The principle of operation of the engine is to convert mechanical energy into electrical energy, and strong power is required to start and generate current. torque. The most suitable option, according to electricians, is to maintain optimal speed throughout the entire operating time of the generator.

Advantages of an asynchronous generator

Synchronous and asynchronous generators have different designs. The design of synchronous is more complex, sensitivity to voltage drops is greater, and therefore productivity is lower than asynchronous. Magnetic coils are placed on the rotor of a synchronous motor; they complicate rotor rotation, and the rotor of an asynchronous generator is similar to a conventional flywheel.

The loss of efficiency of a synchronous generator due to a design feature is about 11%, while for an asynchronous generator the loss is up to 5%. Therefore, asynchronous devices are more in demand both in everyday life and in industry. The increase in demand is due not only to high efficiency, but also to other advantages:

• A simple housing design that can protect against moisture and dust, which reduces the need for daily maintenance.
• Resistance to voltage surges and the presence of a rectifier, which serves as protection for connected electrical appliances.
• Capable of powering highly sensitive devices, such as welding devices, computers and incandescent lamps.
• High efficiency and minimal energy consumption for heating the unit itself.
• Long service life due to the reliability of parts and their resistance to wear during use.

Thanks to such positive nuances, the generator can be used for 15 years, and its design allows you to make an asynchronous generator with your own hands.

Walk-behind tractor for electric generator

For residents of villages and towns outside the city, the use of a walk-behind tractor to assemble a generator is not an innovation, since the unit is very common, and many carry out land work with its help, although a walk-behind tractor, like other equipment, is often subject to breakdowns.

If the unit is seriously damaged, the owners buy a new one, but not everyone wants to part with the old one, so old copies can be used to independently construct a 220 V alternating current generator. Engine operation can be ensured optimal performance asynchronous motor within the voltage range from 220 to 380. The motor power must be selected at least 15 kW, and the shaft speed must be from 800 to 1500 rpm. Such characteristics are necessary to fully ensure the electrical network of the home. After all, with a low-power engine it will not be possible to obtain enough energy, and it is irrational to create a generator for several lighting devices.

There are craftsmen who make a wind generator from an asynchronous motor with their own hands, but in any case, before assembly, you must first calculate the power consumption of the building. After all, in small country houses there may be one TV or drill, for which there will be enough power an electric generator converted from an ordinary chainsaw.

Material preparation and assembly

Buying an asynchronous motor risks a big financial loss, and self-assembly may require minimal electrical skills, parts and tools. But if you decide to make a 220 V alternating current generator with your own hands, then you need to prepare for this:

1. For normal operation of the generator, the rotor rotation speed must be greater than the engine speed. Therefore, you need to disconnect the engine from the mains and calculate the rotor rotation speed; for this you can use a tachometer.
2. Calculate the operating speed of the future generator. For example: engine speed is 1200 rpm, and the operating speed of the generator will be 1320 rpm. This value can be calculated by adding 10% of the tachometer reading to the engine speed;
3. For the operation of an asynchronous motor, capacitors of the same capacity are required for connection between phases.
4. The capacitor capacity should not be too high, otherwise severe overheating of the generator is inevitable.
5. The capacitors must be insulated and provide the calculated rotation speed of the generator rotor.

Such a simple device can already be used as a source of electricity, but since the device produces high voltage, it is better to use it with a step-down transformer.

Gasoline unit

To assemble a gasoline device, it is necessary to install a walk-behind tractor and an electric motor on the same frame, taking into account the parallel arrangement of the shafts. Through two pulleys, torque will be transmitted from the walk-behind tractor to the engine. One pulley must be installed on the shaft of the gasoline unit, and the second on the electric motor. Due to the correct ratio of the pulley size will be determined speed motor rotor.

After installing all the parts and connecting the belt drive, you can proceed to the electrical part:

1. The electric motor winding must be connected in a star configuration.
2. The capacitors connected to the phases should form a triangle.
3. Between the end of the winding, the midpoint produces 220 V, and 380 V between the windings.

The capacity of the installed capacitors is selected depending on the power of the electric motor. The device generates electricity, which means it needs to be grounded, otherwise the device can quickly wear out or cause electric shock to a person.

As a device with low power, you can use a single-phase motor from a washing machine, drainage pump or other household appliance. Just like a three-phase motor, it must be connected in parallel to the winding. You can also use a phase shift capacitor during design, but the power will have to be increased to the required limit.

Such simple devices with a single-phase motor can be used to illuminate the house or connect low-power electrical appliances. In this case, alteration of the circuit may allow connecting the device to a heater or electric furnace. Similar devices can be manufactured in the same way using neodymium or other permanent magnets.

Advantages of a homemade design

The main and important advantage is savings. The homemade version will require much less investment than factory-made counterparts.

If you assemble it yourself correctly, electrical equipment can be quite reliable and productive in operation.

The only drawback of such a device is that it can be difficult for a beginner to understand all the intricacies of the assembly and manufacture of the device. If connected and assembled incorrectly, irreversible damage may occur, after which the time and money spent will be wasted.

Hydro and wind power stations

In addition to gasoline devices, there are other designs. The electric motor shaft can be driven using a windmill or water flow. The designs are not the simplest, but thanks to them, you can do without the use of gasoline or diesel fuel.

You can assemble a device such as a hydrogenerator yourself. If there is a flowing river near the house, water can be used as a force to rotate the shaft. In this case, a hydraulic wheel with blades is installed in the river bed. This creates a flow that rotates the turbine and the electric motor shaft, and depending on the number of installed turbines and blades, the water flow and generator voltage will increase or decrease.

The design of a wind turbine is a little more complicated, since the wind load is not a constant value. The speed of the windmill, which is transmitted to the motor shaft, must be adjusted depending on the required speed of the electric motor. The regulator in this mechanism is the gearbox. The complexity of the design lies in the fact that when the wind increases, a reduction gearbox is needed, and when the wind decreases, a step-up gearbox is needed.

All asynchronous devices that generate electricity have an increased level of danger, and therefore they need insulation. Such equipment must be handled very carefully and kept hidden from external weather conditions:

• Autonomous devices are equipped with measuring sensors to record operating data. It is recommended to install a tachometer and voltmeter.
• Installation of a switch or separate on and off buttons.
• The unit must be grounded.
• The efficiency of an asynchronous device can decrease by 30–50%, which is an inevitable phenomenon when converting electrical energy from mechanical energy.
• It is necessary to monitor the installation temperature and operating mode, as the device may overheat while idling.

Follow these simple rules of operation, and the device will serve for a long time and will not cause inconvenience.

Although the homemade device is easy to assemble, it does require some effort, concentration when working with the structure and the correct electrical connection. It is financially advisable to assemble a device of this type if you have a working unused engine. Otherwise, the main element of the device will cost half the price of a market installation. It is better to assemble a wind or other generator from proven and functional parts to increase the service life of the generator.

A pensioner makes windmills and saves on electricity

Pensioner from Amur region decided toalone to fightincrease in tariffs forelectricity. The desire to do the almost impossible arose afterthe next bills arrived forpublic utilities.

Then the former power engineer drew up his own plan for electrification of the entire site. Now the blades are spinning at the top and the lights at the bottom are lighting up. ABOUT how the wind brought change

Asynchronous electric motor as a generator

Operation of an asynchronous electric motor in generator mode

The article describes how to build a three-phase (single-phase) 220/380 V generator based on an AC asynchronous electric motor.

A three-phase asynchronous electric motor, invented at the end of the 19th century by the Russian electrical engineer M.O. Dolivo-Dobrovolsky, has now become predominantly widespread in industry, agriculture, and also in everyday life. Asynchronous electric motors are the simplest and most reliable to operate. Therefore, in all cases where this is permissible under the conditions of the electric drive and there is no need for reactive power compensation, asynchronous AC motors should be used.

There are two main types of asynchronous motors:with squirrel-cage rotor and with phase rotor . An asynchronous squirrel-cage electric motor consists of a stationary part - the stator and a moving part - the rotor, rotating in bearings mounted in two motor shields. The stator and rotor cores are made of separate electrical steel sheets insulated from one another. A winding made of insulated wire is placed in the grooves of the stator core. A rod winding is placed in the grooves of the rotor core or molten aluminum is poured. Jumper rings short-circuit the rotor winding at the ends (hence the name short-circuited). Unlike a squirrel-cage rotor, a winding made like a stator winding is placed in the slots of a phase-wound rotor. The ends of the winding are brought to slip rings mounted on the shaft. Brushes slide along the rings, connecting the winding to a starting or control rheostat. Asynchronous electric motors with a wound rotor are more expensive devices, require qualified maintenance, are less reliable, and therefore are used only in those industries where they cannot be done without them. For this reason, they are not very common, and we will not consider them further.

A current flows through the stator winding connected to a three-phase circuit, creating a rotating magnetic field. The magnetic field lines of the rotating stator field cross the rotor winding bars and induce an electromotive force (EMF) in them. Under the influence of this EMF, current flows in the short-circuited rotor rods. Magnetic fluxes arise around the rods, creating a general magnetic field of the rotor, which, interacting with the rotating magnetic field of the stator, creates a force that forces the rotor to rotate in the direction of rotation of the stator magnetic field. The rotor rotation frequency is slightly less than the rotation frequency of the magnetic field created by the stator winding. This indicator is characterized by slip S and is for most engines in the range from 2 to 10%.

Most commonly used in industrial installationsthree-phase asynchronous electric motors, which are produced in the form of unified series. These include the single 4A series with a rated power range from 0.06 to 400 kW, the machines of which are highly reliable, have good performance and meet world standards.

Autonomous asynchronous generators are three-phase machines that convert the mechanical energy of the primary engine into alternating current electrical energy. Their undoubted advantage over other types of generators is the absence of a commutator-brush mechanism and, as a consequence, greater durability and reliability. If an asynchronous motor disconnected from the network is set into rotation from any primary motor, then, in accordance with the principle of reversibility of electrical machines, when a synchronous rotation speed is reached, a certain EMF is formed at the terminals of the stator winding under the influence of a residual magnetic field. If you now connect a battery of capacitors C to the terminals of the stator winding, then a leading capacitive current will flow in the stator windings, which in this case is magnetizing. The battery capacity C must exceed a certain critical value C0, depending on the parameters of the autonomous asynchronous generator: only in this case does the generator self-excite and a three-phase symmetrical voltage system is installed on the stator windings. The voltage value ultimately depends on the characteristics of the machine and the capacitance of the capacitors. Thus, an asynchronous squirrel-cage electric motor can be converted into an asynchronous generator.

Standard circuit for connecting an asynchronous electric motor as a generator.

You can select the capacitance so that the rated voltage and power of the asynchronous generator are equal to the voltage and power, respectively, when it operates as an electric motor.

Table 1 shows the capacitances of the capacitors for excitation of asynchronous generators (U=380 V, 750...1500 rpm). Here reactive power Q is determined by the formula:

Q = 0.314 U2 C 10-6,

where C is the capacitance of the capacitors, μF.

As can be seen from the above data, the inductive load on the asynchronous generator, which reduces the power factor, causes a sharp increase in the required capacity. To maintain a constant voltage with increasing load, it is necessary to increase the capacitor capacity, that is, connect additional capacitors. This circumstance must be considered as a disadvantage of the asynchronous generator.

The rotation frequency of an asynchronous generator in normal mode must exceed the asynchronous one by a slip value S = 2...10%, and correspond to the synchronous frequency. Failure to comply with this condition will lead to the fact that the frequency of the generated voltage may differ from the industrial frequency of 50 Hz, which will lead to unstable operation of frequency-dependent consumers of electricity: electric pumps, washing machines, devices with a transformer input. A decrease in the generated frequency is especially dangerous, since in this case the inductive resistance of the windings of electric motors and transformers decreases, which can cause their increased heating and premature failure. An ordinary asynchronous squirrel-cage electric motor of appropriate power can be used as an asynchronous generator without any modifications. The power of the electric motor-generator is determined by the power of the connected devices. The most energy-intensive of them are:

· household welding transformers;

· electric saws, electric jointers, grain crushers (power 0.3...3 kW);

· electric furnaces of the "Rossiyanka" and "Dream" types with a power of up to 2 kW;

· electric irons (power 850…1000 W).

I would especially like to dwell on the operation of household welding transformers. Their connection to an autonomous source of electricity is most desirable, because when operating from an industrial network, they create a number of inconveniences for other electricity consumers. If a household welding transformer is designed to work with electrodes with a diameter of 2...3 mm, then its total power is approximately 4...6 kW, the power of the asynchronous generator to power it should be within 5...7 kW. If a household welding transformer allows working with electrodes with a diameter of 4 mm, then in the heaviest mode - “cutting” metal, the total power consumed by it can reach 10...12 kW, respectively, the power of an asynchronous generator should be within 11...13 kW.

As a three-phase bank of capacitors, it is good to use so-called reactive power compensators, designed to improve cosφin industrial lighting networks. Their typical designation: KM1-0.22-4.5-3U3 or KM2-0.22-9-3U3, which is deciphered as follows. KM - cosine capacitors impregnated with mineral oil, the first number is the size (1 or 2), then the voltage (0.22 kV), power (4.5 or 9 kvar), then the number 3 or 2 means three-phase or single-phase version, U3 (temperate climate of the third category).

In the case of self-manufacturing of the battery, you should use capacitors such as MBGO, MBGP, MBGT, K-42-4, etc. for an operating voltage of at least 600 V. Electrolytic capacitors cannot be used.

The option discussed above for connecting a three-phase electric motor as a generator can be considered classic, but not the only one. There are other methods that have proven themselves just as well in practice. For example, when a bank of capacitors is connected to one or two windings of an electric motor generator.

Two-phase mode of an asynchronous generator.

Fig.2 Two-phase mode of an asynchronous generator.

This circuit should be used when there is no need to obtain three-phase voltage. This switching option reduces the working capacity of the capacitors, reduces the load on the primary mechanical engine in idle mode, etc. saves "precious" fuel.

As low-power generators that produce an alternating single-phase voltage of 220 V, you can use single-phase asynchronous squirrel-cage electric motors for household use: from washing machines such as "Oka", "Volga", watering pumps "Agidel", "BTsN", etc. Their capacitor battery can connect in parallel with the working winding, or use an existing phase-shifting capacitor connected to the starting winding. The capacity of this capacitor may need to be increased slightly. Its value will be determined by the nature of the load connected to the generator: active loads (electric furnaces, light bulbs, electric soldering irons) require a small capacity, inductive loads (electric motors, televisions, refrigerators) require more.

Fig. 3 Low-power generator from a single-phase asynchronous motor.

Now a few words about the primary mechanical engine, which will drive the generator. As you know, any transformation of energy is associated with its inevitable losses. Their value is determined by the efficiency of the device. Therefore, the power of a mechanical motor must exceed the power of an asynchronous generator by 50...100%. For example, with an asynchronous generator power of 5 kW, the power of a mechanical motor should be 7.5...10 kW. Using a transmission mechanism, the speed of the mechanical engine and the generator are matched so that the operating mode of the generator is set at the average speed of the mechanical engine. If necessary, you can briefly increase the generator power by increasing the speed of the mechanical engine.

Each autonomous power plant must contain the required minimum of attachments: an AC voltmeter (with a scale of up to 500 V), a frequency meter (preferably) and three switches. One switch connects the load to the generator, the other two switch the excitation circuit. The presence of switches in the excitation circuit makes it easier to start a mechanical engine, and also allows you to quickly reduce the temperature of the generator windings; after completion of work, the rotor of the unexcited generator is rotated for some time by the mechanical engine. This procedure extends the active life of the generator windings.

If using a generator it is intended to power equipment that is normally connected to an alternating current network (for example, lighting in a residential building, household electrical appliances), then it is necessary to provide a two-phase switch that will disconnect this equipment from the industrial network while the generator is operating. Both wires must be disconnected: “phase” and “zero”.

In conclusion, some general advice.

1. The alternator is a hazardous device. Use 380 V only when absolutely necessary; in all other cases, use 220 V.

2. According to safety requirements, the electric generator must be equipped with grounding.

3. Pay attention to the thermal mode of the generator. He "does not like" idling. The thermal load can be reduced by more carefully selecting the capacitance of the exciting capacitors.

4. Make no mistake about the amount of electrical current produced by the generator. If one phase is used when operating a three-phase generator, then its power will be 1/3 of the total power of the generator, if two phases will be 2/3 of the total power of the generator.

5. The frequency of the alternating current produced by the generator can be indirectly controlled by the output voltage, which in the “no-load” mode should be 4...6% higher than the industrial value of 220/380 V.