The principle of operation of an asynchronous motor with connection diagrams. Calculator: Calculation of the capacitance of the working and starting capacitors for asynchronous motors with a squirrel-cage rotor. Three-phase motor starting capacitor

One of the reasons for connection three phase motor To single-phase circuit is that the supply electrical energy for industrial facilities and for domestic needs is radically different.

For industrial production, electrical enterprises manufacture electric motors with a three-phase power system, and to start the motor you need to have 3 phases.

What to do if you purchased motors for industrial production, but need to connect to home socket? Some skilled specialists, using simple electrical circuits, adapt the electric motor to a single-phase network.

Winding connection diagram

To figure it out, a person who has encountered a similar problem for the first time needs to know how a three-phase motor works. If you open the connection cover, you can see the block and wires connected to the terminals, their number will be 6.

A three-phase electric motor has three windings and, accordingly, 6 terminals, they have a beginning and an end, and are connected in electrical configurations called “star and delta”.

This is interesting, but in most cases the standard switching is formed into a “star”, since the connection into a “delta” leads to a loss of power, but the engine speed increases. It happens that the wires are in an arbitrary position and are not connected to the connectors or there is no terminal at all. In this case, you need to use a tester or ohmmeter.

You need to ring each wire and find a pair, these will be the three windings of the motor. Next, we connect them into a “star” configuration as follows: beginning-end-beginning. We clamp three wires under one terminal. There should be three outputs left, and further switching will occur to them.

It is important to know: In the household network, a single-phase power supply system or “phase and zero” is organized. This configuration must be used to connect the motor. First, we connect one wire from the electric motor to any network wire, then, to the second end of the winding, we connect the network wire and one end of the capacitor block there.

The last wire from the motor and the unconnected contact of the set of capacitors remain free, we connect them and the circuit for starting a three-phase motor into a single-phase network is ready. They can be represented graphically as follows:

A, B, C - lines of a 3-phase circuit.
F and O – phase and zero.
C – capacitor.

In industrial production, a 3-phase voltage supply system is used. According to PUE standards, all network buses are marked with letter values and have the corresponding color:

A – yellow.

B – green.

C – red.

It is noteworthy that regardless of the location of the phases, in, bus “B”, with green, should always be in the middle. Attention! Phase-to-phase voltage is measured special device who have passed state inspection and workers who have the appropriate clearance group. Ideally, the phase-to-phase voltage is – 380 volts.

Electric motor device

Most often we come across electric motors with three-phase asynchronous circuit work. What is the engine? This is a shaft on which a squirrel-cage rotor is pressed, at the edges of which there are plain bearings.

The stator is made of transformer steel, with high magnetic permeability, cylindrical in shape with longitudinal grooves for laying wires and a surface insulating layer.

By special technology, the winding wires are laid in the stator channels and insulated from the housing. The symbiosis of stator and rotor is called an asynchronous electric motor.

How to calculate capacitor capacity

To start a 3-phase motor from a household network, it is necessary to perform some manipulations with capacitor units. To start an electric motor without a “load”, you need to select the capacitor capacity based on the formula 7-10 mF per 100 W of motor power.

If you look closely at the side of the electric motor, you will find its passport, where the power of the unit is indicated. For example: if the motor has a power of 0.5 kW, then the capacitance of the capacitor should be 35 - 50 mF.

It should be noted that only “permanent” capacitors are used, and in no case “electrolytic”. Pay attention to the inscriptions that are located on the side of the case; they indicate the capacitance of the capacitor, measured in microfarads, and the voltage for which they are designed.

The block of starting capacitors is assembled according to exactly this formula. Using the engine as a power unit: connecting it to a water pump or using it as a circular saw, requires an additional block of capacitors. This design is called working capacitor units.

They start the engine and, by connecting in series or parallel, select the capacitance of the capacitor so that the sound from the electric motor comes from the quietest, but there is a more accurate method for selecting the capacitance.

To accurately select a capacitor, you need to have a device called a capacitor store. By experimenting with different connection combinations, we achieve same value voltage between all three windings. Then they read the capacitance and select the desired capacitor.

Necessary materials

In the process of connecting a 3-phase motor to a single-phase network, you will need some materials and devices:

A set of capacitors with different ratings or a “store of capacitors”.
Electrical wires, type PV-2.5.
Voltmeter or tester.
3 position switch.

Basic tools should be at hand: voltage indicator, dielectric pliers, insulating tape, fasteners.

Parallel and series connection of capacitors

The capacitor belongs to electronic parts and when different combinations switching, its nominal values may vary.

Parallel connection:

Serial connection:

It should be noted that when parallel connection The capacitances of the capacitors will add up, but the voltage will decrease, and vice versa, the series version gives an increase in voltage and a decrease in capacitance.

In conclusion, we can say that there are no hopeless situations, you just need to put in a little effort and the result will not be long in coming. Electrical engineering is an educational and useful science.

How to connect a three-phase motor to a single-phase network, see instructions in the following video:

The theoretical material presented in the first part of the topic, devoted to the single-phase connection of a three-phase electric motor, is intended so that the home master can consciously transfer industrial devices of a 380-volt network to household electrical wiring of 220.

Thanks to it, you will not just mechanically repeat our recommendations, but will implement them consciously.

Optimal diagrams for connecting a three-phase motor to a single-phase household network

Among the many ways to connect an electric motor in practice, only two are widely used, called briefly:

star;
triangle.

The name is given by the method of connecting windings in an electrical circuit inside the stator. Both methods differ in that they apply a different voltage to each phase of the motor.

In a star circuit, linear voltage is applied directly to two windings connected in series. Their electrical resistance folds up, provides greater resistance to passing current.

In a triangle, linear voltage is applied to each winding individually and therefore has less resistance. Currents are created higher in amplitude.

Let us pay attention to these two differences and draw practical conclusions for their use:

the star circuit has reduced currents in the windings, allows you to operate the electric motor for a long time with minimal loads, and provide small torques on the shaft;
more high currents created by the triangle design provide better output power, allow the engine to be used under extreme loads, so it requires reliable cooling for long-term work.

These two differences are explained in detail in the picture. Look at her carefully. For clarity, red arrows specifically mark the incoming voltages from the line (linear) and those applied to the windings (phase). For a triangle circuit they are the same, but for a star they are reduced by connecting two windings through the neutral.

These methods should be analyzed in relation to the operating conditions of your future mechanism at the design stage, before the start of its creation. Otherwise, the motor of the star circuit may not be able to cope with the connected loads and will stop, while the motor of the delta circuit may overheat and eventually burn out. The motor current load can be determined by selecting the connection diagram.

How to find out the connection diagram for the stator windings of an asynchronous motor

At every plant, it is customary to place information plates on the housing of electrical equipment. An example of its implementation for a three-phase electric motor is shown in the photograph.

The home handyman should not pay attention to all the information, but only to:

power consumption: its value is used to judge the performance of the connected drive;
winding connection diagram - the question has just been sorted out;
the number of revolutions that may require connecting a gearbox;
currents in phases - windings are created for them;
impact protection class external environment- determines operating conditions, including protection from atmospheric moisture.

Factory information can usually be trusted, but it was created for a new engine being sold. This scheme may undergo reconstruction several times during its entire operation, losing its original appearance. An old engine may become inoperable if stored improperly.

Electrical measurements of its circuit should be performed and the insulation condition should be checked.

How to determine stator winding connection diagrams

To carry out electrical measurements, it is necessary to have access to each end of all three windings. Typically, six of their pins are connected to their own bolts inside the terminal box.

But, among the methods of factory installation, there is one when special asynchronous models are made according to a star circuit so that the neutral point is assembled by the ends of the windings inside the housing, and one core of its assembly is connected to the input box. This option, which is unsuccessful for us, will require unscrewing the studs securing the covers on the body to remove them. Then you need to get to the junction of the windings and disconnect their ends.

Electrical inspection of stator winding ends

After finding both ends for one winding, they must be marked with their own markings for subsequent checks and connections.

Polarity measurements of stator windings

Since the windings are wound strictly in a certain way, then we need to accurately find their beginnings and endings. There are two simple electrical methods for this:

short-term supply direct current in one winding to create a pulse;
use of a source of variable EMF.

In both cases, the principle of electromagnetic induction works. After all, the windings are assembled inside a magnetic circuit, which ensures good transformation of electricity.

Battery pulse test

The work is performed on two windings at once. The picture shows this process for three - so it's less to draw.

The process consists of two stages. First, unipolar windings are determined, and then a control check is carried out to eliminate possible error of the measurements taken.

To search for unipolar terminals, a DC voltmeter switched to the limit of the sensitive scale is connected to any free winding. We will use it to implement , which appears due to the transformation of the impulse.

The negative terminal of the battery is rigidly connected to an arbitrary end of the second winding, and the positive terminal is briefly touched to its second end. This moment is shown in the picture by the contact of the button.

Observe the behavior of the voltmeter needle, which reacts to the supply of an impulse in its circuit. It can move towards plus or minus. The coincidence of the polarities of both windings will be shown by a positive deviation, and the difference - negative.

When the pulse is removed, the arrow will go to reverse side. They also pay attention to this. Then the ends are marked.

After this, the measurement is performed on the third winding, and control check carried out by switching the battery to another circuit.

Testing with a step-down transformer

EMF source alternating current at 24 volts it is recommended to use in order to ensure electrical safety. It is not recommended to neglect this requirement.

First, take two arbitrary windings, for example, No. 2 and No. 3. Connect their terminals together in pairs and connect a voltmeter, but with alternating current, to these places. The remaining winding No. 1 is supplied with voltage from the step-down transformer and the readings from it appear on the voltmeter.

If the vectors are directed equally, then they will not influence each other and the voltmeter will show their total value - 24 volts. When the polarity is reversed, the opposing vectors on the voltmeter will add up and add up to the number 0, which will be displayed on the scale as an arrow. Immediately after measuring, the ends should also be marked.

Then you need to check the polarity for the remaining pair and perform a test measurement.

With such simple electrical experiments, one can reliably determine the belonging of the ends to the windings and their polarity. This will help to assemble them correctly for the capacitor starting circuit.

Checking the insulation resistance of the stator windings

If the engine was stored in an unheated room, it came into contact with moist air and became damp. Its insulation is broken and can create leakage currents. Therefore, its quality must be assessed by electrical measurements.

A tester in ohmmeter mode is not always able to detect such a violation. It will only show an obvious defect: the power of its current source is too low and does not provide an accurate measurement result. To check the condition of the insulation, you must use a megohmmeter - a special device with powerful source power supply providing application to the measuring circuit high voltage 500 or 1000 volts.

An assessment of the insulation condition must be carried out before applying operating voltage to the windings. If leakage currents are detected, you can try to dry the engine in a warm, well-ventilated environment. Often this technique allows you to restore functionality electrical diagram, assembled inside the stator core.

Starting an asynchronous motor according to a star circuit

For this method, the ends of all windings K1, K2, K3 are connected at the neutral point and are isolated, and line voltage is applied to their beginnings.

The working zero of the network is rigidly connected to one beginning, and the phase potential to the other two in the following way:

the first winding is rigidly connected;
the second cuts through the capacitor assembly.

For fixed connection for an asynchronous motor, it is necessary to first determine the phase and working zero of the supply network.

How to choose capacitors

The electric motor starting circuit uses two chains to connect the winding through capacitor assemblies:

working - connected in all modes;
starting - used only for intensive rotation of the rotor.

At the moment of startup, both of these circuits operate in parallel, and when brought into operating mode, the starting circuit is turned off.

The capacity of the working capacitors must correspond to the power consumption electric motor. To calculate it, use the empirical formula:

C slave=2800∙I/U.

The values of the rated current I and voltage U included in it precisely introduce an adjustment according to electrical power engine.

The capacity of starting capacitors is usually 2–3 times higher than the working one.

The correct selection of capacitors affects the formation of currents in the windings. They must be checked after starting the engine under load. To do this, measure the currents in each winding and compare them in magnitude and angle. Good operation carried out with the minimum possible distortion. Otherwise, the engine will run unstably, and one or two windings will begin to overheat.

The starting circuit shows the switch SA, which puts into operation the a short time starting starting capacitor. There are many button designs that allow you to perform this operation.

However, I would like to draw attention to special device, produced in Soviet times by industry for washing machines with an activator - a centrifuge.

Its closed case contains a mechanism consisting of:

two contacts that close when the top “Start” button is pressed;
one contact that opens the entire circuit from the “Stop” button.

When you press the Start button, the circuit phase is supplied to the engine through working capacitors in one chain and starting capacitors in another. When the button is released, one contact is broken. It is connected to the starting capacitors.

Starting an asynchronous motor using a triangle pattern

There are practically no big differences between this method and the previous one. The starting and working chains operate according to the same algorithms.

In this scheme it is necessary to take into account increased currents flows in the windings and other methods of selecting capacitors for them.

Their calculation is carried out using a formula similar to the previous one, but different:

C slave=4800∙I/U.

The relationship between the starting and running capacitors does not change. Do not forget to evaluate their selection by control measurements of currents under rated load.

Final conclusions

Existing technical methods allow you to connect three-phase asynchronous motors to a single-phase 220 volt network. Numerous researchers offer a wide range of experimental schemes for this purpose.
However, this method does not ensure efficient use of electrical power resources due to large energy losses associated with poor-quality voltage conversion for connection to the stator phases. Therefore, the engine operates with low efficiency and increased costs.
Long-term operation of machines with such engines is not economically justified.
The method can only be recommended for connecting non-critical mechanisms for a short period of time.
With the aim of effective use asynchronous electric motor it is necessary to use a full three-phase connection or a modern, expensive inverter converter of appropriate power.
A single-phase electric motor with the same power in a household network is better able to cope with all tasks, and its operation will be cheaper.

Thus, the designs asynchronous motors, previously widely connected to home wiring, are now not popular, and the method of connecting them is outdated and rarely used.

Option similar mechanism shown by a photograph of an emery board with the protective shield and stop stop removed for clarity. Even with this design, it is difficult to work on it due to power losses.

Practical advice from Alexander Shenrok, presented in his video, clearly complements the material in the article and allows you to better understand this topic. I recommend viewing it, but be critical of measuring the insulation resistance with a tester.

Ask questions in the comments, share the article with friends via social network buttons.

Asynchronous electric motors, widely used in production, are connected with a “delta” or “star”. The first type is mainly used for motors with prolonged starting and operation. The joint connection is used to start high-power electric motors. The “star” connection is used at the beginning of the start-up, then switching to the “delta” connection. A connection diagram for a 220-volt three-phase electric motor is also used.

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There are many varieties of motors, but for everyone, main characteristic is the voltage supplied to the mechanisms and the power of the engines themselves.

When connected to 220V, the motor is subject to high starting currents, which reduce its service life. In industry, delta connections are rarely used. Powerful electric motors are connected in a star.

To switch from a 380 to 220 motor connection diagram, there are several options, each of which has advantages and disadvantages.

It is very important to understand how to connect three phase electric motor to the 220v network. To connect a three-phase motor to 220V, note that it has six terminals, which corresponds to three windings. Using a tester, the wires are pinged to find the coils. We connect their ends in twos - we get a “triangle” connection (and three ends).

To begin with, two ends network wire(220 V) connect to any two ends of our “triangle”. The remaining end (the remaining pair of twisted coil wires) is connected to the end of the capacitor, and the remaining capacitor wire is also connected to one of the ends of the power wire and coils.

Whether we choose one or the other will depend on which direction the engine starts to rotate. Having completed all the above steps, we start the engine by applying 220 V to it.

The electric motor should work. If this does not happen, or it does not reach the required power, you need to return to the first stage to swap the wires, i.e. reconnect the windings.

If, when turned on, the motor hums but does not spin, you need to additionally install (via a button) a capacitor. At the moment of starting, it will give the engine a push, forcing it to spin.

Video: How to connect an electric motor from 380 to 220

Calling, i.e. resistance measurement is carried out by a tester. If you don't have one, you can use a battery and regular lamp for a flashlight: the identified wires are connected to the circuit in series with the lamp. If the ends of one winding are found, the lamp lights up.

It is much more difficult to determine the beginning and ends of the windings. You can't do without a voltmeter with an arrow.

You will need to connect a battery to the winding, and a voltmeter to the other.

By breaking the contact of the wire with the battery, observe whether the arrow deviates and in which direction. The same actions are carried out with the remaining windings, changing the polarity if necessary. Make sure that the arrow deviates in the same direction as during the first measurement.

Star-delta circuit

In domestic engines, the “star” is often already assembled, but the triangle needs to be implemented, i.e. connect three phases, and assemble a star from the remaining six ends of the winding. Below is a drawing to make it easier to understand.

The main advantage of connecting a three-phase circuit with a star is that the motor produces the most power.

Nevertheless, such a connection is loved by amateurs, but is not often used in production, since the connection diagram is complex.

For it to work you need three starters:

The stator winding is connected to the first of them, K1, on one side, and the current on the other. The remaining ends of the stator are connected to starters K2 and K3, and then to obtain a “triangle”, the winding with K2 is also connected to the phases.

Having connected to phase K3, slightly shorten the remaining ends to obtain a “star” circuit.

Important: It is unacceptable to turn on K3 and K2 at the same time, so that a short circuit does not occur, which can lead to the shutdown of the electric motor circuit breaker. To avoid this, electrical interlocking is used. It works like this: when one of the starters is turned on, the other is turned off, i.e. its contacts open.

How the scheme works

When K1 is turned on using a time relay, K3 is turned on. The three-phase motor, connected according to the "star" circuit, operates with more power, than usual. After some time, the contacts of relay K3 open, but K2 starts. Now the motor operation pattern is “triangle”, and its power becomes less.

When a power cut is required, K1 is started. The pattern is repeated in subsequent cycles.

A very complex connection requires skill and is not recommended for beginners.

Other motor connections

There are several schemes:

More often than the option described, a circuit with a capacitor is used, which will help to significantly reduce power. One of the contacts of the working capacitor is connected to zero, the second - to the third output of the electric motor. As a result, we have a low-power unit (1.5 W). At high power engine, a starting capacitor will need to be added to the circuit. At single-phase connection it simply compensates for the third output.
It is easy to connect an asynchronous motor with a star or triangle when moving from 380V to 220V. Such motors have three windings. To change the voltage, it is necessary to swap the outputs going to the tops of the connections.
When connecting electric motors, it is important to carefully study the passports, certificates and instructions, because in imported models there is often a “triangle” adapted for our 220V. Such motors, if you ignore this and turn on the star, simply burn out. If the power is more than 3 kW, the motor cannot be connected to the household network. This is fraught short circuit and even failure of the RCD machine.

Connecting a three-phase motor to a single-phase network

The rotor connected to the three-phase circuit of a three-phase motor rotates due to the magnetic field created by the current flowing into different time on different windings. But, when such a motor is connected to a single-phase circuit, no torque arises that could rotate the rotor. Most in a simple way connecting three-phase motors to a single-phase circuit is to connect its third contact through a phase-shifting capacitor.

When connected to a single-phase network, such a motor has the same rotation speed as when operating from a three-phase network. But the same cannot be said about power: its losses are significant and they depend on the capacity of the phase-shifting capacitor, the operating conditions of the motor, and the selected connection diagram. Losses approximately reach 30-50%.

The circuits can be two-, three-, or six-phase, but the most commonly used are three-phase. A three-phase circuit is understood as a set of electrical circuits with the same frequency of sinusoidal EMF, which differ in phase, but are created by a common energy source.

If the load in the phases is the same, the circuit is symmetrical. For three-phase asymmetrical circuits it is different. The total power is made up of active power three-phase circuit and reactive.

Although most motors cope with operation from a single-phase network, not all can work well. Better than others in this sense are asynchronous motors, which are designed for a voltage of 380/220 V (the first is for star, the second is for delta).

This operating voltage is always indicated in the passport and on the plate attached to the engine. It also shows the connection diagram and options for changing it.

If "A" is present, this indicates that either a delta or star circuit can be used. “B” indicates that the windings are connected in a “star” and cannot be connected in any other way.

The result should be: when the contacts of the winding with the battery are broken, an electric potential of the same polarity (i.e., the arrow deflects in the same direction) should appear on the two remaining windings. The start (A1, B1, C1) and end (A2, B2, C2) terminals are marked and connected according to the diagram.

Using a magnetic starter

The good thing about using a 380 electric motor connection diagram is that it can be started remotely. The advantage of a starter over a switch (or other device) is that the starter can be placed in a cabinet, and the controls can be placed in the work area; the voltage and currents are minimal, therefore, the wires are suitable for a smaller cross-section.

In addition, connection using a starter ensures safety in the event that the voltage “disappears,” since this opens the power contacts, and when the voltage appears again, the starter will not supply it to the equipment without pressing the start button.

Connection diagram for a 380V electric asynchronous motor starter:

At contacts 1,2,3 and start button 1 (open), voltage is present at the initial moment. It is then fed through closed contacts this button (when you press “Start”) to the contacts of the coil starter K2, closing it. The coil creates a magnetic field, the core is attracted, the contacts of the starter close, driving the motor.

At the same time, the NO contact closes, from which the phase is supplied to the coil through the “Stop” button. It turns out that when the “Start” button is released, the coil circuit remains closed, as do the power contacts.

By pressing “Stop”, the circuit is broken, returning the power contacts to open. The voltage disappears from the conductors and NO supplying the engine.

Video: Connecting an asynchronous motor. Determination of engine type.

For a variety of work electrical devices Asynchronous motors are used, which are simple and reliable in operation and installation - you can easily install them yourself. The connection of a three-phase motor to a single-phase and three-phase network is carried out by star and delta.

general information

An asynchronous three-phase motor consists of the following main parts: windings, a moving rotor and a stationary stator. The windings can be connected to each other, and to them open contacts the main power supply of the network is connected either in series, i.e. the end of one winding is connected to the beginning of the next.

Photo - star diagram clearly

The connection can be made to a single-phase, two-phase and three-phase network, while the motors are mainly designed for two voltages - 220/380 V. Switching the type of winding connection allows you to change the rated voltage. Despite the fact that, in principle, it is possible to connect the motor to a single-phase network, it is rarely used, since the capacitor reduces the efficiency of the device. And from rated power the consumer receives approximately 60%. But if there is no other option, then you need to connect it using a delta circuit, then the motor overload will be less than with a star.

Before connecting the windings in a single-phase network, it is necessary to check the capacitance of the capacitor that will be used. For this you need a formula:

C µF = P W /10

If the initial parameters of the capacitor are unknown, then it is recommended to use a starting model that can “adapt” to the operation of the engine and control its speed. Also often, to operate a device with a squirrel-cage rotor, a current relay or a standard magnetic switch. This detail of the circuit allows you to provide full automation workflow. Moreover, for household models (with a power from 500 V to 1 kW), you can use a starter from a washing machine or refrigerator, further increasing the capacitor capacity or changing the relay winding.

Video: how to connect a three-phase 220V motor

Connection methods

With a single-phase network, it is necessary to shift the phase using special parts, most often a capacitor. But in some conditions it will be replaced by a thyristor. If you install a thyristor switch in the motor housing, then when closed position it not only shifts the phases, but also significantly increases the starting torque. This helps to increase efficiency up to 70%, which is an excellent indicator for such a connection. Using only this part, you can avoid using a fan and the main types of capacitors - starting and running.

But this connection is not ideal either. When operating an electric motor with a thyristor, 30% more electric current is consumed than with capacitors. Therefore, this option is used only in production or in the absence of a choice.

Let's consider how a three-phase asynchronous motor is connected to a three-phase network if a triangle circuit is used.

Photo - simple triangle

The drawing shows two capacitors - starting and working, a start button, a diode signaling the start of work and a resistor system for braking and stopping completely. also in in this case A switch is used that has three positions: “hold”, “start”, “stop”. When the handle is installed in the first position, the contacts begin to receive electricity. It is important here to switch to the “start” mode immediately after the engine starts, otherwise the windings may catch fire due to overload. At the end of the working process, the handle is fixed at the “stop” point.

Photo - connection using electrolyte capacitors

Sometimes, when connected in phase, it is more convenient to stop a three-phase motor using the energy stored in the capacitor. Sometimes electrolytes are used instead, but this is more difficult option device installation. In this case, the parameters of the capacitor are very important, in particular, its capacitance - braking and the time to completely stop the moving parts depend on it. This circuit also uses rectifying diodes and resistors. They will help, if necessary, stop the engine faster. But their specifications should look like this:

The resistor's resistance should not exceed 7 kOhm;
The capacitor must withstand voltages of 350 volts and above (depending on the mains voltage).

Having at hand a circuit that stops the motor, you can use a capacitor to connect it in reverse. The main difference from the previous drawing is the modernization of the three-phase two-speed motor with a double switch and a magnetic start relay. The switch, as in previous versions, has several main positions, but is fixed only to “start” and “stop” - this is very important.

Photo - reverse using a starter

Reversing motor connection is also possible via a magnetic starter. In this case, it is necessary to change the order of the stator phases, then it will be possible to ensure a change in the direction of rotation. To do this, immediately after pressing the “Forward” starter button, press the “Back” button. After this, the blocking contact will turn off the forward coil and transfer the power to reverse - the direction of rotation will change. But you need to be careful when connecting the starter - if the contacts are swapped, then during the transition there will not be a reversal, but a short circuit.

One more in an unusual way How you can connect a three-phase motor is the option of using a four-pole RCD. Its feature is the ability to use the network without zero.

In most cases, the ED only requires 3 phases and 1 ground wire, zero is not necessary, since the load is symmetrical;
The connection principle is as follows: we assign the power phases to circuit breaker, and connect the zero directly to the RCD terminal - N, after that we do not connect it to anything;
The cables from the machine are also connected to the RCD in the same way. We ground the engine and that's it.

Three-phase electric motors have become widespread both in industrial use and for personal purposes due to the fact that they are much more efficient than motors for a conventional two-phase network.

A three-phase induction motor is a device consisting of two parts: a stator and a rotor, which are separated by an air gap and have no mechanical connection with each other.

The stator has three windings wound on a special magnetic core, which is made from plates of special electrical steel. The windings are wound in the stator slots and are located at an angle of 120 degrees to each other.

The rotor is a bearing-supported structure with an impeller for ventilation. For electric drive purposes, the rotor may be in direct connection with the mechanism or through gearboxes or other mechanical energy transmission systems. Rotors in asynchronous machines can be of two types:

A squirrel-cage rotor, which is a system of conductors connected to the ends by rings. A spatial structure is formed that resembles a squirrel wheel. Currents are induced in the rotor, creating its own field that interacts with the magnetic field of the stator. This sets the rotor in motion.

A massive rotor is a solid structure made of a ferromagnetic alloy, in which currents are simultaneously induced and is a magnetic circuit. Due to the emergence of eddy currents in the massive rotor, magnetic fields interact, which is the driving force of the rotor.

The main driving force in a three-phase asynchronous motor is the rotating magnetic field, which arises, firstly, due to the three-phase voltage, and, secondly, relative position stator windings. Under its influence, currents arise in the rotor, creating a field that interacts with the stator field.

An asynchronous motor is called because the rotor speed lags behind the rotation speed magnetic field, the rotor is constantly trying to “catch up” with the field, but its frequency is always lower.

Simplicity of design, which is achieved due to the absence of collector groups that wear out quickly and create additional friction.

To power an asynchronous motor, no additional transformations are required; it can be powered directly from an industrial three-phase network.

Due to comparatively small amount parts, asynchronous motors are very reliable, have long term operation, easy to use maintenance and repairs.

Of course, three-phase machines are not without their drawbacks.

Asynchronous electric motors have an extremely low starting torque, which limits their scope of application.

When started, these engines consume high currents at start-up, which may exceed those allowed in a particular power supply system.

Asynchronous motors consume considerable reactive power, which does not lead to an increase in the mechanical power of the engine.

Various schemes for connecting asynchronous motors to a 380 volt network

In order to make the engine work, there are several various schemes connections, the most used among them are star and delta.

How to correctly connect a three-phase star motor

This connection method is mainly used in three-phase networks with line voltage 380 volts. The ends of all windings: C4, C5, C6 (U2, V2, W2) are connected at one point. To the beginnings of the windings: C1, C2, C3 (U1, V1, W1), - phase conductors A, B, C (L1, L2, L3) are connected through the switching equipment. In this case, the voltage between the beginnings of the windings will be 380 volts, and between the point of connection of the phase conductor and the point of connection of the windings will be 220 volts.

The electric motor plate indicates the possibility of connection using the “star” method in the form of a Y symbol, and it may also indicate whether it can be connected using another scheme. A connection according to this scheme can be with a neutral, which is connected to the connection point of all windings.

This approach allows you to effectively protect the electric motor from overloads using a four-pole circuit breaker.

A star connection does not allow an electric motor adapted for 380 volt networks to develop full power due to the fact that each individual winding will have a voltage of 220 volts. However, such a connection prevents overcurrent and the motor starts smoothly.

The terminal box will immediately show when the motor is connected in a star configuration. If there is a jumper between the three terminals of the windings, then this clearly indicates that this particular circuit is used. In any other cases, a different scheme applies.

We make the connection according to the “triangle” scheme

In order for a three-phase motor to develop its maximum rated power, a connection called “triangle” is used. In this case, the end of each winding is connected to the beginning of the next one, which in reality forms a schematic diagram triangle.

The winding terminals are connected as follows: C4 is connected to C2, C5 to C3, and C6 to C1. With the new marking it looks like this: U2 connects to V1, V2 to W1, and W2 to U1.

In three-phase networks, there will be a linear voltage of 380 volts between the terminals of the windings, and a connection to the neutral (working zero) is not required. This scheme also has the peculiarity that large inrush currents arise, which the wiring may not withstand.

In practice it is sometimes used combined connection, when a star connection is used at the start-up and acceleration stage, and in operating mode special contactors switch the windings to a delta circuit.

In the terminal box, a delta connection is determined by the presence of three jumpers between the winding terminals. On the engine nameplate, the possibility of delta connection is indicated by the symbol Δ, and the power developed in star and delta configurations can also be indicated.

Three-phase asynchronous motors occupy a significant part among electricity consumers due to their obvious advantages.