The principle of operation of an asynchronous motor with connection diagrams. Connection diagrams for a three-phase electric motor

1. Connecting a three-phase electric motor - general diagram

When an electrician gets a job at any industrial enterprise, he must understand that he will have to deal with a large number of three-phase electric motors. And any self-respecting electrician (I’m not talking about those who do wiring in an apartment) should clearly know the wiring diagram for a three-phase motor.

I immediately apologize that in this article I often call a contactor a starter, although I have already explained in detail that. What can you do, I'm tired of this name.

The article will discuss connection diagrams for the most common asynchronous electric motor through a magnetic starter.

Various electric motor connection diagrams, their pros and cons. From simple to complex. Circuits that can be used in real life are designated: PRACTICAL DIAGRAM. So let's begin.

Connecting a three-phase motor

This means an asynchronous electric motor, winding connection - star or triangle, connection to a 380V network.

For the engine to operate, the working neutral conductor N (Neutral) is not needed, but the protective conductor (PE, Protect Earth) must be connected for safety reasons.

In the most general case, the diagram will look like this, as shown at the beginning of the article. Indeed, why not turn on the engine like a regular light bulb, only the switch will be a “three-key”?

2. Connecting the engine through a switch or circuit breaker

But no one even turns on a light bulb just like that; the lighting network and, in general, any load is always turned on only through circuit breakers.

Diagram of connecting a three-phase motor to the network via a circuit breaker

Therefore, in more detail, the general case will look like this:

3. Connecting the motor via a circuit breaker. PRACTICAL SCHEME

Diagram 3 shows a circuit breaker that protects the motor from overcurrent (“rectangular” bends in the supply lines) and from short circuits (“round” bends). By circuit breaker I mean a regular three-pole circuit breaker with a load thermal characteristic of C or D.

Let me remind you that in order to approximately select (estimate) the required thermal current of the thermal protection setting, you need to multiply the rated power of the three-phase motor (indicated on the nameplate) by 2.

Circuit breaker for turning on the electric motor. The current is 10A, through which you can turn on a 4 kW motor. No more and no less.

Scheme 3 has the right to life (due to poverty or ignorance of local electricians).

It works great, just like it has for many years. And one “fine” day the twist will burn out. Or the engine will burn out.

If you use such a circuit, you need to carefully select the current of the machine so that it is 10-20% greater than the operating current of the motor. And select the characteristic of the thermal release D so that the machine does not trip when starting.

For example, a 1.5 kW engine. We estimate the maximum operating current - 3A (real operating current may be less, we need to measure it). This means that the three-pole circuit breaker must be set to 3 or 4A.

The advantage of this motor connection diagram is the price and ease of execution and maintenance. For example, where there is one engine, and it is turned on manually for the entire shift. The disadvantages of such a scheme with switching on via an automatic machine are:

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Inability to regulate the thermal current of the machine. In order to reliably protect the engine, the shutdown current of the circuit breaker must be 10-20% greater than the rated operating current of the engine. The motor current must be periodically measured with clamps and, if necessary, the thermal protection current must be adjusted. But a regular machine does not have the ability to adjust (.
Inability to remotely and automatically turn on/off the engine.

These shortcomings can be eliminated; the diagrams below will show how.

A manual starter or automatic motor is a more advanced device. It has “Start” and “Stop” buttons, or an “On-Off” knob. Its advantage is that it is specially designed for starting and protecting the engine. The start is still manual, but the operating current can be adjusted within certain limits.

4. Connecting the motor via a manual starter. PRACTICAL SCHEME

Since motors usually have a high starting current, motor protective circuit breakers (automatic motors) usually have a thermal protection characteristic of type D. That is it can withstand short-term (starting) overloads of approximately 10 times the nominal value.

Here's what's on the side:

Motor circuit breaker - characteristics on the side wall

Setting current (thermal) – from 17 to 23 A, set manually. Cut-off current (trigger during short circuit) – 297 A.

In principle, a manual starter and an automatic motor are the same device. But the starter shown in the photo can switch the power supply to the engine. And the automatic motor constantly supplies power (three phases) to the contactor, which, in turn, switches the power to the motor. In short, the difference is in the connection diagram.

The advantage of the scheme is that you can adjust the thermal current setting. The downside is the same as in the previous scheme, there is no remote activation.

Motor connection diagram via magnetic starter

This wiring diagram for a three-phase motor should be given the closest attention. It is most common in all industrial equipment produced until about the 2000s. And in new Chinese simple machines it is still used to this day.

An electrician who does not know it is like a surgeon who cannot distinguish an artery from a vein; as a lawyer who does not know Article 1 of the Constitution of the Russian Federation; like a dancer who does not distinguish a waltz from a tectonic.

In this circuit, three phases go to the motor not through the machine, but through the starter. And the starter is turned on/off using the “ Start" And " Stop”, which can be brought to the control panel via 3 wires of any length.

5. Diagram of connecting the motor through a starter with start-stop buttons

Here, the control circuit power comes from phase L1 (wire 1 ) through a normally closed (NC) “Stop” button (wire 2 ).

If you now press the “Start” button, the power circuit of the coil of the KM electromagnetic starter will close (wire 3 ), its contacts will close, and three phases will go to the motor. But in such schemes, in addition to three “power” contacts, the starter has one more additional contact. It is called a “locking” or “self-latching contact”.

When the electromagnetic starter is turned on by pressing the SB1 “Start” button, the self-retaining contact also closes. And if it is closed, then even if the “Start” button is pressed, the power circuit of the starter coil will still remain closed. And the engine will continue to run until the “Stop” button is pressed.

Since the topic of magnetic starters is very extensive, it is included in a separate article. The article has been significantly expanded and supplemented. Everything is covered there - connecting various loads, protection (thermal and short-circuit), reversing circuits, control from different points, etc. The numbering of the schemes has been preserved. I recommend.

Connecting a three-phase motor via electronic devices

All methods of starting the engine described above are called Starting by direct voltage supply. Often, in powerful drives, such a start-up is a difficult test for the equipment - belts burn, bearings and fasteners break, etc.

Therefore, the article would be incomplete if I did not mention current trends. Nowadays, electronic power devices are increasingly used to connect a three-phase motor instead of electromagnetic starters. By this I mean:

Solid state relays - their power elements are thyristors (triacs), which are controlled by an input signal from a button or from a controller. There are both single-phase and three-phase. .
Soft (soft) starters (soft starters, soft starters) are advanced solid state machines. You can set the protection current, acceleration/deceleration time, turn on reverse, etc. And on this topic. Practical application of soft starters - .Connection of two-speed asynchronous motors. Key words – Rarity, Retro, USSR.
I’ll end here, thank you for your attention, I couldn’t cover everything, write questions in the comments!

There are situations in life when you need to connect some industrial equipment to a regular home power supply network. A problem immediately arises with the number of wires. Machines intended for use in enterprises usually have three, but sometimes four, terminals. What to do with them, where to connect them? Those who tried to try various options were convinced that the motors simply did not want to spin. Is it even possible to connect a single-phase three-phase motor? Yes, you can achieve rotation. Unfortunately, in this case, the power drop is inevitable by almost half, but in some situations this is the only way out.
Voltages and their ratio
In order to understand how to connect a three-phase motor to a regular outlet, you need to understand how the voltages in the industrial network relate. Well-known voltage values are 220 and 380 Volts. Previously, there was still 127 V, but in the fifties this parameter was abandoned in favor of a higher one. Where did these “magic numbers” come from? Why not 100, or 200, or 300? It seems that round numbers are easier to count.
Most industrial electrical equipment is designed to be connected to a three-phase network. The voltage of each phase in relation to the neutral wire is 220 Volts, just like in a home socket. Where does 380 V come from? It is very simple, just consider an isosceles triangle with angles of 60, 30 and 30 degrees, which is a vector stress diagram. The length of the longest side will be equal to the length of the thigh multiplied by cos 30°. After some simple calculations, you can make sure that 220 x cos 30° = 380.
Three-phase motor device
Not all types of industrial motors can operate from a single phase. The most common of them are the “workhorses” that make up the majority of electrical machines in any enterprise - asynchronous machines with a power of 1 - 1.5 kVA. How does such a three-phase motor work in the three-phase network for which it is intended?
The inventor of this revolutionary device was the Russian scientist Mikhail Osipovich Dolivo-Dobrovolsky. This outstanding electrical engineer was a proponent of the theory of a three-phase power supply network, which has become dominant in our time. three-phase operates on the principle of induction of currents from the stator windings to closed rotor conductors. As a result of their flow through the short-circuited windings, a magnetic field arises in each of them, interacting with the stator power lines. This produces a torque that leads to circular motion of the motor axis.
The windings are angled 120° so that the rotating field generated by each phase pushes each magnetized side of the rotor in succession.
Triangle or star?
A three-phase motor in a three-phase network can be switched on in two ways - with or without a neutral wire. The first method is called “star”, in this case each of the windings is under (between phase and zero), equal in our conditions to 220 V. The connection diagram of a three-phase motor with a “triangle” involves connecting three windings in series and applying linear (380 V) voltage to switching nodes. In the second case, the engine will produce about one and a half times more power.
How to turn the motor in reverse?
Control of a three-phase motor may require changing the direction of rotation to the opposite, that is, reverse. To achieve this, you just need to swap two of the three wires.
To make it easier to change the circuit, jumpers are provided in the motor terminal box, usually made of copper. For star switching, gently connect the three output wires of the windings together. The “triangle” turns out to be a little more complicated, but any average qualified electrician can handle it.
Phase shifting tanks
So, sometimes the question arises about how to connect a three-phase motor to a regular home outlet. If you just try to connect two wires to the plug, it will not rotate. In order for things to work, you need to simulate the phase by shifting the supplied voltage by some angle (preferably 120°). This effect can be achieved by using a phase-shifting element. Theoretically, this could be inductance or even resistance, but most often a three-phase motor in a single-phase network is switched on using electrical circuits designated by the Latin letter C on the diagrams.
As for the use of chokes, it is difficult due to the difficulty of determining their value (if it is not indicated on the device body). To measure the value of L, a special device or a circuit assembled for this purpose is required. In addition, the choice of available chokes is usually limited. However, any phase-shifting element can be selected experimentally, but this is a troublesome task.
What happens when you turn on the engine? Zero is applied to one of the connection points, phase is applied to the other, and a certain voltage is applied to the third, shifted by a certain angle relative to the phase. It is clear to a non-specialist that the operation of the engine will not be complete in terms of mechanical power on the shaft, but in some cases the very fact of rotation is sufficient. However, already at startup, some problems may arise, for example, the lack of an initial torque capable of moving the rotor from its place. What to do in this case?
Start capacitor
At the moment of starting, the shaft requires additional efforts to overcome the forces of inertia and static friction. To increase the torque, you should install an additional capacitor, connected to the circuit only at the moment of start, and then turned off. For these purposes, the best option is to use a locking button without fixing the position. The connection diagram for a three-phase motor with a starting capacitor is shown below, it is simple and understandable. At the moment the voltage is applied, press the “Start” button, and it will create an additional phase shift. After the engine spins up to the required speed, the button can (and even should) be released, and only the working capacity will remain in the circuit.
Calculation of container sizes
So, we found out that in order to turn on a three-phase motor in a single-phase network, an additional connection circuit is required, which, in addition to the start button, includes two capacitors. You need to know their value, otherwise the system will not work. First, let's determine the amount of electrical capacitance required to make the rotor move. When connected in parallel, it is the sum:
C = C st + Wed, where:
C st - starting additional capacity that can be switched off after takeoff;
C p is a working capacitor that provides rotation.
We also need the value of the rated current I n (it is indicated on the plate attached to the engine at the manufacturer). This parameter can also be determined using a simple formula:
I n = P / (3 x U), where:
U - voltage, when connected as a “star” - 220 V, and if connected as a “triangle”, then 380 V;
P is the power of a three-phase motor; sometimes, if the plate is lost, it is determined by eye.
So, the dependencies of the required operating power are calculated using the formulas:
С р = Ср = 2800 I n / U - for “star”;
C p = 4800 I n / U - for a “triangle”;
The starting capacitor should be 2-3 times larger than the working capacitor. The unit of measurement is microfarads.
There is also a very simple way to calculate capacity: C = P /10, but this formula gives the order of the number rather than its value. However, in any case you will have to tinker.
Why adjustment is needed
The calculation method given above is approximate. Firstly, the nominal value indicated on the body of the electrical capacitance may differ significantly from the actual one. Secondly, paper capacitors (generally speaking, an expensive thing) are often second-hand, and they, like any other items, are subject to aging, which leads to an even greater deviation from the specified parameter. Thirdly, the current that will be consumed by the motor depends on the magnitude of the mechanical load on the shaft, and therefore it can only be assessed experimentally. How to do it?
This requires a little patience. The result can be a fairly large set of capacitors connected in parallel and in series. The main thing is to secure everything well after finishing the work so that the soldered ends do not fall off due to vibrations emanating from the motor. And then it would be a good idea to analyze the result again and, perhaps, simplify the design.
Composing a battery of containers
If the master does not have at his disposal special electrolytic clamps that allow you to measure the current without opening the circuits, then you should connect an ammeter in series to each wire that enters the three-phase motor. In a single-phase network, the total value will flow, and by selecting capacitors one should strive for the most uniform loading of the windings. It should be remembered that when connected in series, the total capacitance decreases according to the law:
It is also necessary not to forget about such an important parameter as the voltage for which the capacitor is designed. It must be no less than the nominal value of the network, or better yet, with a margin.
Discharge resistor
The circuit of a three-phase motor connected between one phase and a neutral wire is sometimes supplemented with resistance. It serves to prevent the charge remaining on the starting capacitor from accumulating after the machine has already been turned off. This energy can cause an electric shock, which is not dangerous, but extremely unpleasant. In order to protect yourself, you should connect a resistor in parallel with the starting capacitance (electricians call this “bypassing”). The value of its resistance is large - from half a megohm to a megohm, and it is small in size, so half a watt of power is enough. However, if the user is not afraid of being “pinched,” then this detail can be completely dispensed with.
Using Electrolytes
As already noted, film or paper electrical containers are expensive, and purchasing them is not as easy as we would like. It is possible to make a single-phase connection to a three-phase motor using inexpensive and readily available electrolytic capacitors. At the same time, they won’t be very cheap either, since they must withstand 300 Volts of DC. For safety, they should be bypassed with semiconductor diodes (D 245 or D 248, for example), but it would be useful to remember that when these devices break through, alternating voltage will reach the electrolyte, and it will first heat up very much, and then explode, loudly and effectively. Therefore, unless absolutely necessary, it is still better to use paper-type capacitors that operate under either constant or alternating voltage. Some craftsmen completely allow the use of electrolytes in starting circuits. Due to short-term exposure to alternating voltage, they may not have time to explode. It's better not to experiment.
If there are no capacitors
Where do ordinary citizens who do not have access to in-demand electrical and electronic parts purchase them? At flea markets and flea markets. There they lie, carefully soldered by someone’s (usually elderly) hands from old washing machines, televisions and other household and industrial equipment that are out of use and out of use. They ask a lot for these Soviet-made products: sellers know that if a part is needed, they will buy it, and if not, they will not take it for nothing. It happens that just the most necessary thing (in this case, a capacitor) is just not there. So what should we do? No problem! Resistors will also do, you just need powerful ones, preferably ceramic and vitrified ones. Of course, ideal resistance (active) does not shift the phase, but nothing is ideal in this world, and in our case this is good. Every physical body has its own inductance, electrical power and resistivity, whether it is a tiny speck of dust or a huge mountain. Connecting a three-phase motor to a power outlet becomes possible if in the above diagrams you replace the capacitor with a resistance, the value of which is calculated by the formula:
R = (0.86 x U) / kI, where:
kI - current value for three-phase connection, A;
U - our trusty 220 Volts.
What engines are suitable?
Before purchasing a motor for a lot of money, which a zealous owner intends to use as a drive for a grinding wheel, circular saw, drilling machine or any other useful household device, it would not hurt to think about its applicability for these purposes. Not every three-phase motor in a single-phase network will be able to operate at all. For example, the MA series (it has a squirrel-cage rotor with a double cage) should be excluded so that you do not have to carry considerable and useless weight home. In general, it is best to experiment first or invite an experienced person, an electrician, for example, and consult with him before purchasing. A three-phase asynchronous motor of the UAD, APN, AO2, AO and, of course, A series is quite suitable. These indices are indicated on the nameplates.
Content:
Many owners, especially owners of private houses or cottages, use equipment with 380 V motors operating from a three-phase network. If an appropriate power supply circuit is connected to the site, then no difficulties arise with their connection. However, quite often a situation arises when a section is powered by only one phase, that is, only two wires are connected - phase and neutral. In such cases, you have to decide how to connect a three-phase motor to a 220 volt network. This can be done in various ways, but it should be remembered that such intervention and attempts to change parameters will lead to a drop in power and a decrease in the overall efficiency of the electric motor.

Connecting a 3-phase 220 motor without capacitors

As a rule, circuits without capacitors are used to start low-power three-phase motors in a single-phase network - from 0.5 to 2.2 kilowatts. Start-up time is spent approximately the same as when operating in three-phase mode.

These circuits are used under the control of pulses with different polarities. There are also symmetrical dinistors that supply control signals to the flow of all half-cycles present in the supply voltage.

There are two options for connecting and starting. The first option is used for electric motors with a speed of less than 1500 per minute. The windings are connected in a triangle. A special chain is used as a phase-shifting device. By changing the resistance, a voltage is generated across the capacitor, shifted by a certain angle relative to the main voltage. When the voltage level required for switching is reached in the capacitor, the dinistor and triac are triggered, causing activation of the power bidirectional switch.

The second option is used when starting engines whose rotation speed is 3000 rpm. This category also includes devices installed on mechanisms that require a large moment of resistance during startup. In this case, it is necessary to provide a large starting torque. To this end, changes were made to the previous circuit, and the capacitors required for the phase shift were replaced by two electronic switches. The first switch is connected in series with the phase winding, leading to an inductive shift of the current in it. The connection of the second switch is parallel to the phase winding, which contributes to the formation of a leading capacitive current shift in it.

This connection diagram takes into account the motor windings, which are displaced in space by 120 0 C. When setting, the optimal angle of current shift in the phase windings is determined, ensuring reliable starting of the device. When performing this action, it is quite possible to do without any special equipment.

Connecting a 380V to 220V electric motor via a capacitor

For a normal connection, you should know the principle of operation of a three-phase motor. When connected to the network, current begins to flow alternately through its windings at different times. That is, in a certain period of time, the current passes through the poles of each phase, also creating a rotational magnetic field in turn. It exerts an influence on the rotor winding, causing rotation by pushing in different planes at certain times.

When such a motor is connected to a single-phase network, only one winding will participate in the creation of rotating torque and the impact on the rotor in this case occurs only in one plane. This force is completely insufficient to shift and rotate the rotor. Therefore, in order to shift the phase of the pole current, it is necessary to use phase-shifting capacitors. The normal operation of a three-phase electric motor largely depends on the correct choice of capacitor.

Calculation of a capacitor for a three-phase motor in a single-phase network:
- With an electric motor power of no more than 1.5 kW, one operating capacitor will be sufficient in the circuit.
- If the engine power is more than 1.5 kW or it experiences heavy loads during startup, in this case two capacitors are installed at once - a working one and a starting one. They are connected in parallel, and the starting capacitor is needed only for starting, after which it is automatically turned off.
- The operation of the circuit is controlled by the START button and the power off toggle switch. To start the engine, press the start button and hold it until it is fully turned on.
If it is necessary to ensure rotation in different directions, an additional toggle switch is installed that switches the direction of rotation of the rotor. The first main output of the toggle switch is connected to the capacitor, the second to the neutral, and the third to the phase wire. If such a circuit contributes to a weak increase in speed, in this case it may be necessary to install an additional starting capacitor.

Connecting a 3-phase motor at 220 without loss of power

The simplest and most effective way is to connect a three-phase motor to a single-phase network by connecting a third contact connected to a phase-shifting capacitor.

The highest output power that can be obtained in domestic conditions is up to 70% of the rated one. Such results are obtained when using the “triangle” scheme. Two contacts in the distribution box are directly connected to the wires of the single-phase network. The connection of the third contact is made through a working capacitor with any of the first two contacts or wires of the network.

In the absence of loads, a three-phase motor can be started using only a run capacitor. However, if there is even a small load, the speed will increase very slowly, or the engine will not start at all. In this case, an additional connection of a starting capacitor will be required. It turns on for literally 2-3 seconds so that the engine speed can reach 70% of the nominal speed. After this, the capacitor is immediately turned off and discharged.

Thus, when deciding how to connect a three-phase motor to a 220 volt network, all factors must be taken into account. Particular attention should be paid to capacitors, since the operation of the entire system depends on their action.

In various amateur electromechanical machines and devices, in most cases three-phase asynchronous motors with a squirrel cage rotor are used. Alas, a three-phase network in everyday life is a very rare phenomenon, therefore, to power them from an ordinary electrical network, amateurs use a phase-shifting capacitor, which does not allow the full power and starting properties of the motor to be realized.
Asynchronous three-phase electric motors, namely them, due to their widespread use, often have to be used, consist of a stationary stator and a moving rotor. Winding conductors are laid in the stator slots with an angular distance of 120 electrical degrees, the beginnings and ends of which (C1, C2, C3, C4, C5 and C6) are brought out into the junction box.

Delta connection (for 220 volts)

Star connection (for 380 volts)

Three-phase motor junction box with jumper positions for star connection

When a three-phase motor is turned on to a three-phase network, a current begins to flow through its windings at different times in turn, creating a rotating magnetic field that interacts with the rotor, forcing it to spin. When the motor is connected to a single-phase network, no torque capable of moving the rotor is created.

If you can connect the engine on the side to a three-phase network, then determining the power is not difficult. We place an ammeter at the break in one of the phases. Let's launch. We multiply the ammeter readings by the phase voltage.

In a good network it is 380. We get the power P=I*U. We subtract 10-12% for efficiency. You get the actually correct result.

There are mechanical instruments for measuring revolutions. Although it is also possible to determine by ear.

Among the various methods of connecting three-phase electric motors to a single-phase network, the most common is connecting the third contact through a phase-shifting capacitor.

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

The rotational speed of a three-phase motor operating from a single-phase network remains almost the same as when it is connected to a three-phase network. Alas, this cannot be stated about power, the losses of which reach significant values. Clear values of power loss depend on the switching circuit, operating conditions of the motor, and the capacitance value of the phase-shifting capacitor. Approximately, a three-phase motor in a single-phase network loses within 30-50% of its own power.

Not many three-phase electric motors are ready to perform well in single-phase networks, but most of them cope with this task completely satisfactorily - except for power loss. Mainly, for operation in single-phase networks, asynchronous motors with a squirrel-cage rotor (A, AO2, AOL, APN, etc.) are used.

Asynchronous three-phase motors are designed for 2 rated network voltages - 220/127, 380/220, and so on. Electric motors with an operating voltage of windings of 380/220V (380V for star, 220 for delta) are more common. The highest voltage is for the "star", the lowest - for the "triangle". In the passport and on the motor plate, in addition to other characteristics, the operating voltage of the windings, their connection diagram and the likelihood of its change are indicated.

Three-phase motor labels

The designation on plate A states that the motor windings can be connected both as a “triangle” (at 220V) and a “star” (at 380V). When connecting a three-phase motor to a single-phase network, it is better to use a delta circuit, since in this case the motor will lose less power than when switched on as a star.

Plate B informs you that the motor windings are connected in a star configuration, and the junction box does not take into account the possibility of switching them to delta (there are no more than 3 terminals). In this case, all that remains is to either come to terms with a large loss of power by connecting the motor in a star configuration, or, having penetrated the electric motor winding, try to bring out the missing ends in order to connect the windings in a delta configuration.

If the operating voltage of the motor is 220/127V, then the motor can only be connected to a single-phase 220V network using a star circuit. When you turn on 220V in a delta circuit, the engine will burn out.

Beginnings and ends of windings (various options)

Probably the main difficulty in connecting a three-phase motor to a single-phase network is to understand the electrical wires going into the junction box or, in the absence of one, simply leading out of the motor.

The most common option is when the windings in an existing 380/220V motor are already connected in a delta circuit. In this case, you simply need to connect the current-carrying electrical wires and the working and starting capacitors to the motor terminals according to the connection diagram.

If the windings in the motor are connected by a “star”, and there is a possibility of changing it to a “triangle”, then such a case also cannot be classified as labor-intensive. You just need to change the connection circuit of the windings to a “triangle” one, using jumpers for this.

Determination of the beginnings and ends of the windings. The situation is more difficult if 6 wires are brought out into the junction box without indicating their belonging to a specific winding and marking the beginnings and ends. In this case, it comes down to solving two problems (Although before doing this, you should try to search the Internet for some documentation for the electric motor. It may describe what electrical wires of different colors refer to.):

identifying pairs of wires related to one winding;

finding the beginning and end of the windings.

The first problem is solved by “ringing” all the wires with a tester (measuring resistance). When there is no device, it is possible to solve it using a light bulb from a flashlight and batteries, connecting the existing electrical wires into the circuit alternately with the light bulb. If the latter lights up, it means that the two ends being tested belong to the same winding. This method identifies 3 pairs of wires (A, B and C in the figure below) related to 3 windings.

Determination of pairs of wires belonging to one winding

The second task is to determine the beginnings and ends of the windings; here it will be somewhat more complicated and you will need a battery and a pointer voltmeter. Digital is not suitable for this task due to inertia. The procedure for determining the ends and beginnings of the windings is shown in diagrams 1 and 2.

Finding the beginning and end of the windings

A battery is connected to the ends of one winding (for example, A), and a pointer voltmeter is connected to the ends of the other (for example, B). Now, when you break the contact of wires A with the battery, the voltmeter needle will swing in some direction. Then you need to connect a voltmeter to winding C and do the same operation with breaking the battery contacts. If necessary, changing the polarity of winding C (switching ends C1 and C2) it is necessary to ensure that the voltmeter needle swings in the same direction as in the case of winding B. Winding A is checked in the same way - with a battery connected to the winding C or B.

Ultimately, all manipulations should result in the following: when the battery contacts break with any of the windings, an electric potential of the same polarity should appear on the other two (the device arrow swings in one direction). Now all that remains is to mark the conclusions of the 1st bundle as the beginning (A1, B1, C1), and the conclusions of the other as the ends (A2, B2, C2) and connect them according to the desired pattern - “triangle” or “star” (when the motor voltage is 220 /127V).

Extracting missing ends. Probably the most difficult option is when the engine has a fusion of windings in a star configuration, and there is no ability to switch it to a delta (no more than 3 electrical wires are brought into the distribution box - the beginning of the windings C1, C2, C3).

In this case, to turn on the motor according to the “triangle” circuit, you need to bring the missing ends of the windings C4, C5, C6 into the box.

Schemes for connecting a three-phase motor to a single-phase network

Triangle connection. In the case of a home network, based on the belief of obtaining greater output power, single-phase connection of three-phase motors in a delta circuit is considered more suitable. With all this, their power can reach 70% of the nominal. 2 contacts in the junction box are connected directly to the electrical wires of a single-phase network (220V), and the 3rd - through the working capacitor Cp to any of the first 2 contacts or the electrical wires of the network.

Ensuring launch. It is possible to start a three-phase motor without a load using a working capacitor (more details below), but if the electric motor has some kind of load, it either will not start or will pick up speed extremely slowly. Then, for a quick start, you need an auxiliary starting capacitor Sp (the calculation of the capacitance of the capacitors is described below). The starting capacitors are turned on only for the duration of the engine startup (2-3 seconds, until the speed reaches approximately 70% of the nominal), then the starting capacitor must be disconnected and discharged.

It is convenient to start a three-phase motor using a special switch, one pair of contacts of which closes when the button is pressed. When it is released, some contacts open, while others remain on - until the "stop" button is pressed.

Switch for starting electric motors

Reverse. The direction of rotation of the motor depends on which contact ("phase") the third phase winding is connected to.

The direction of rotation can be controlled by connecting the latter, through a capacitor, to a two-position switch connected by its two contacts to the first and 2nd windings. Depending on the position of the switch, the engine will rotate in one direction or the other.

The figure below shows a circuit with a starting and running capacitor and a reverse button, which allows for comfortable control of a three-phase motor.

Connection diagram for a three-phase motor to a single-phase network, with reverse and a button for connecting a starting capacitor

Star connection. A similar scheme for connecting a three-phase motor to a network with a voltage of 220V is used for electric motors whose windings are designed for a voltage of 220/127V.

Capacitors. The required capacity of working capacitors for operating a three-phase motor in a single-phase network depends on the connection circuit of the motor windings and other characteristics. For a star connection, the capacitance is calculated using the formula:
Cp = 2800 I/U
For a triangle connection:
Cp = 4800 I/U
Where Cp is the capacitance of the working capacitor in microfarads, I is the current in A, U is the network voltage in V. The current is calculated by the formula:
I = P/(1.73 U n cosph)
Where P is the electric motor power kW; n - engine efficiency; cosф - power factor, 1.73 - coefficient that determines the correspondence between linear and phase currents. The efficiency and power factor are indicated in the passport and on the motor plate. Traditionally, their value is located in the spectrum of 0.8-0.9.
In practice, the capacitance value of the working capacitor when connected in a triangle can be calculated using the simplified formula C = 70 Pn, where Pn is the rated power of the electric motor in kW. According to this formula, for every 100 W of electric motor power, you need about 7 μF of working capacitor capacity.
The correct selection of capacitor capacity is checked by the results of engine operation. If its value is greater than required under these operating conditions, the engine will overheat. If the capacity is less than required, the power output of the motor will become very low. It makes sense to look for a capacitor for a three-phase motor, starting with a small capacitance and gradually increasing its value to a rational one. If possible, it is much better to choose a capacitance by measuring the current in the electrical wires connected to the network and to the working capacitor, for example, with a current clamp. The current value should be closer. Measurements should be made in the mode in which the engine will operate.
When determining the starting capacity, we first proceed from the requirements for creating the required starting torque. Do not confuse the starting capacitance with the capacitance of the starting capacitor. In the above diagrams, the starting capacitance is equal to the sum of the capacitances of the working (Cp) and starting (Sp) capacitors.
If, due to operating conditions, the electric motor starts without load, then the starting capacitance is traditionally assumed to be the same as the working capacitance, in other words, a starting capacitor is not needed. In this case, the connection diagram is simplified and cheaper. To simplify this and generally reduce the cost of the circuit, it is possible to organize the possibility of disconnecting the load, for example, by making it possible to quickly and comfortably change the position of the motor to drop the belt drive, or by making the belt drive a pressing roller, for example, like the belt clutch of walk-behind tractors.

Starting under load requires the presence of an additional tank (Sp) that is connected temporarily to start the engine. An increase in the switchable capacitance leads to an increase in the starting torque, and at a certain specific value, the torque reaches its maximum value. A further increase in capacitance leads to the opposite effect: the starting torque begins to decrease.

Based on the condition of starting the engine under a load closest to the rated load, the starting capacitance must be 2-3 times greater than the working capacitance, that is, if the capacity of the working capacitor is 80 µF, then the capacitance of the starting capacitor must be 80-160 µF, which will provide the starting capacitance (sum of the capacitance of the working and starting capacitors) 160-240 µF. Although, if the engine has a small load when starting, the capacitance of the starting capacitor may be less or may not exist at all.

Starting capacitors operate for a short time (only a few seconds during the entire connection period). This makes it possible to use cheaper starting electrolytic capacitors, specially designed for this purpose, when starting the engine.

Note that for a motor connected to a single-phase network through a capacitor, operating in the absence of a load, the winding fed through the capacitor carries a current 20-30% higher than the rated one. Therefore, if the engine is used in an underloaded mode, the capacity of the working capacitor should be minimized. But then, if the engine was started without a starting capacitor, the latter may be required.

It is much better to use not 1 large capacitor, but several much smaller ones, partly due to the ability to select a good capacitance, connecting additional ones or disconnecting unnecessary ones, the latter are used as starting ones. The required number of microfarads is obtained by connecting several capacitors in parallel, based on the fact that the total capacitance in a parallel connection is calculated using the formula:

Determination of the beginning and end of the phase windings of an asynchronous electric motor

Three-phase asynchronous motors, which are often used due to their widespread use, consist of a stationary stator and a moving rotor. Winding conductors are laid in the stator slots with an angular distance of 120 electrical degrees, the beginnings and ends of which (C1, C2, C3, C4, C5 and C6) are brought out into the junction box. The windings can be connected according to a “star” (the ends of the windings are connected to each other, the supply voltage is supplied to their beginnings) or a “triangle” (the ends of one winding are connected to the beginning of another).
In the distribution box, the contacts are usually shifted - opposite C1 is not C4, but C6, opposite C2 - C4.
When a three-phase motor is connected to a three-phase network, a current begins to flow through its windings at different times in turn, creating a rotating magnetic field that interacts with the rotor, causing it to rotate. When the motor is turned on in a single-phase network, no torque is created that can move the rotor.
Among the different ways to connect three-phase electric motors to a single-phase network, the simplest is to connect the third contact through a phase-shifting capacitor.
The rotation speed of a three-phase motor operating from a single-phase network remains almost the same as when it is connected to a three-phase network. Unfortunately, this cannot be said about power, the losses of which reach significant values. The exact values of power loss depend on the connection diagram, engine operating conditions, and the capacitance value of the phase-shifting capacitor. Approximately, a three-phase motor in a single-phase network loses about 30-50% of its power.
Not all three-phase electric motors are capable of working well in single-phase networks, but most of them cope with this task quite satisfactorily - except for the loss of power. Basically, for operation in single-phase networks, asynchronous motors with a squirrel-cage rotor (A, AO2, AOL, APN, etc.) are used.
Asynchronous three-phase motors are designed for two rated mains voltages - 220/127, 380/220, etc. The most common electric motors with an operating voltage of the windings are 380/220V (380V for star, 220 for delta). Higher voltage for star, lower for delta. In the passport and on the motor plate, among other parameters, the operating voltage is indicated winding voltage, their connection diagram and the possibility of changing it.
Designation on the plate A indicates that the motor windings can be connected either as a “triangle” (at 220V) or a “star” (at 380V). When connecting a three-phase motor to a single-phase network, it is advisable to use a delta circuit, since in this case the motor will lose less power than when connected to a star.
Tablet B informs that the motor windings are connected in a star configuration, and the distribution box does not provide the ability to switch them to delta (there are only three terminals). In this case, you can either accept a large loss of power by connecting the motor in a star configuration, or, by penetrating the electric motor winding, try to bring out the missing ends in order to connect the windings in a delta configuration.
If the operating voltage of the engine is 220/127V, then the engine can only be connected to a single-phase 220V network using a star circuit. If you connect 220V in a delta circuit, the engine will burn out.
Beginnings and ends of windings (various options)
Perhaps the main difficulty in connecting a three-phase motor to a single-phase network is to understand the wires going into the junction box or, in the absence of one, simply leading out of the motor.
The simplest case is when the windings in an existing 380/220V motor are already connected in a delta circuit. In this case, you just need to connect the current supply wires and the working and starting capacitors to the motor terminals according to the connection diagram.
If the windings in the motor are connected by a “star”, and it is possible to change it to a “triangle”, then this case also cannot be classified as complex. You just need to change the connection diagram of the windings to a “triangle”, using jumpers for this.
Determination of the beginnings and ends of windings. The situation is more complicated if 6 wires are brought out into the junction box without indicating their belonging to a specific winding and marking the beginnings and ends. In this case, it comes down to solving two problems (But before doing this, you need to try to find some documentation for the electric motor on the Internet. It may describe what wires of different colors belong to.):
- identifying pairs of wires belonging to one winding;
- finding the beginning and end of the windings.
The first task is solved by “ringing” all the wires with a tester (measuring resistance). If you don’t have a device, you can solve the problem using a flashlight light bulb and batteries, connecting the existing wires in a circuit in series with the light bulb. If the latter lights up, it means that the two ends being tested belong to the same winding. In this way, three pairs of wires (A, B and C in the figure below) belonging to three windings are determined.
The second task (determining the beginning and end of the windings) is somewhat more complicated and requires a battery and a pointer voltmeter. Digital is not suitable due to inertia. The procedure for determining the ends and beginnings of the windings is shown in diagrams 1 and 2.
To the ends of one winding (for example, A) a battery is connected to the ends of the other (for example, B) - pointer voltmeter. Now, if you break the contact of the wires A with a battery, the voltmeter needle will swing in one direction or another. Then you need to connect a voltmeter to the winding WITH and do the same operation with breaking the battery contacts. If necessary, change the polarity of the winding WITH(switching ends C1 and C2) you need to ensure that the voltmeter needle swings in the same direction, as in the case of the winding IN. The winding is checked in the same way. A- with a battery connected to the winding C or B.
As a result of all manipulations, the following should happen: when the battery contacts break from any of the windings, an electric potential of the same polarity should appear on the other 2 (the device needle swings in one direction). Now all that remains is to mark the terminals of one bundle as the beginning (A1, B1, C1), and the terminals of the other as the ends (A2, B2, C2) and connect them according to the required circuit - “triangle” or “star” (if the motor voltage is 220/127V ).
Retrieving missing ends. Perhaps the most difficult case is when the engine has a star connection of the windings, and there is no way to switch it to a delta (only three wires are brought into the distribution box - the beginning of the windings C1, C2, C3) (see figure below) . In this case, to connect the motor according to the "triangle" diagram, it is necessary to bring the missing ends of the windings C4, C5, C6 into the box.
To do this, gain access to the motor winding by removing the cover and possibly removing the rotor. The place of adhesion is found and released from insulation. The ends are separated and flexible stranded insulated wires are soldered to them. All connections are reliably insulated, the wires are secured with a strong thread to the winding and the ends are brought out to the terminal board of the electric motor. They determine whether the ends belong to the beginnings of the windings and connect them according to the “triangle” pattern, connecting the beginnings of some windings to the ends of others (C1 to C6, C2 to C4, C3 to C5). The job of bringing out missing ends requires some skill. The motor windings may contain not one, but several solders, which are not so easy to understand. Therefore, if you do not have the proper qualifications, you may have no choice but to connect a three-phase motor in a star configuration, accepting a significant loss of power.
Schemes for connecting a three-phase motor to a single-phase network
Delta connection. In the case of a household network, from the point of view of obtaining greater output power, the most appropriate is a single-phase connection of three-phase motors in a delta circuit. Moreover, their power can reach 70% of the nominal. Two contacts in the distribution box are connected directly to the wires of a single-phase network (220V), and the third is connected through a working capacitor Cp to any of the first two contacts or network wires.
Start-up support. A three-phase motor without a load can also be started from a working capacitor (more details below), but if the electric motor has some kind of load, it either will not start or will pick up speed very slowly. Then, for a quick start, an additional starting capacitor Sp is required (calculation of the capacitor capacity is described below). The starting capacitors are turned on only while the engine is starting (2-3 seconds, until the speed reaches approximately 70% of the nominal), then the starting capacitor must be disconnected and discharged.

Connecting a three-phase electric motor to a single-phase network using a delta circuit with a starting capacitor Sp
It is convenient to start a three-phase motor using a special switch, one pair of contacts of which closes when the button is pressed. When it is released, some contacts open, while others remain on - until the "stop" button is pressed.
Reverse. The direction of rotation of the motor depends on which contact ("phase") the third phase winding is connected to.
The direction of rotation can be controlled by connecting the latter, through a capacitor, to a two-position toggle switch connected by its two contacts to the first and second windings. Depending on the position of the toggle switch, the engine will rotate in one direction or the other.
The figure below shows a circuit with a starting and running capacitor and a reverse button, which allows for convenient control of a three-phase motor.
Star connection. A similar scheme for connecting a three-phase motor to a network with a voltage of 220V is used for electric motors whose windings are designed for a voltage of 220/127V.
The required capacity of working capacitors for operating a three-phase motor in a single-phase network depends on the connection diagram of the motor windings and other parameters. For a star connection, the capacitance is calculated using the formula:
For a triangle connection:
Where Cp is the capacitance of the working capacitor in microfarads, I is the current in A, U is the network voltage in V. The current is calculated by the formula:
I = P/(1.73 U n cosph)
Where P is the electric motor power kW; n - engine efficiency; cosф - power factor, 1.73 - coefficient characterizing the relationship between linear and phase currents. The efficiency and power factor are indicated in the data sheet and on the engine plate. Typically their value is in the range of 0.8-0.9.
In practice, the capacitance value of the working capacitor when connected in a triangle can be calculated using the simplified formula C = 70 Pn, where Pn is the rated power of the electric motor in kW. According to this formula, for every 100 W of electric motor power, about 7 μF of working capacitor capacity is required.
The correct selection of capacitor capacity is checked by the results of engine operation. If its value is greater than required under given operating conditions, the engine will overheat. If the capacitance is less than required, the motor output will be too low. It makes sense to select a capacitor for a three-phase motor, starting with a small capacitance and gradually increasing its value to the optimal one. If possible, it is better to select the capacitance by measuring the current in the wires connected to the network and to the working capacitor, for example, with a current clamp. The current value should be as close as possible. Measurements should be made in the mode in which the engine will operate.
When determining the starting capacity, we proceed, first of all, from the requirements for creating the necessary starting torque. Do not confuse the starting capacitance with the capacitance of the starting capacitor. In the above diagrams, the starting capacitance is equal to the sum of the capacitances of the working (Cp) and starting (Sp) capacitors.
If, due to operating conditions, the electric motor starts without load, then the starting capacitance is usually taken to be equal to the working capacitance, that is, a starting capacitor is not needed. In this case, the switching circuit is simplified and cheaper. To simplify this and, most importantly, reduce the cost of the circuit, it is possible to organize the possibility of disconnecting the load, for example, by making it possible to quickly and conveniently change the position of the engine to loosen the belt drive, or by making a pressure roller for the belt drive, for example, like the belt clutch of walk-behind tractors.
Starting under load requires the presence of additional capacity (Cn) connected while the engine is starting. An increase in the switchable capacitance leads to an increase in the starting torque, and at a certain value, the torque reaches its maximum value. A further increase in capacitance leads to the opposite result: the starting torque begins to decrease.
Based on the condition of starting the engine under a load close to the rated load, the starting capacitance should be 2-3 times greater than the working capacitance, that is, if the capacity of the working capacitor is 80 µF, then the capacitance of the starting capacitor should be 80-160 µF, which will give the starting capacitance (the sum capacity of the working and starting capacitors) 160-240 µF. But if the engine has a small load when starting, the capacity of the starting capacitor may be less or, as stated above, it may not exist at all.
Starting capacitors operate for a short time (only a few seconds during the entire switching period). This allows you to use when starting the engine the cheapest launchers electrolytic capacitors specially designed for this purpose (http://www.platan.ru/cgi-bin/qweryv.pl/0w10609.html).
Note that for a motor connected to a single-phase network through a capacitor, operating without load, the winding fed through the capacitor carries a current 20-30% higher than the rated one. Therefore, if the engine is used in an underloaded mode, the capacity of the working capacitor should be reduced. But then, if the engine was started without a starting capacitor, the latter may be required.
It is better to use not one large capacitor, but several smaller ones, partly due to the possibility of selecting the optimal capacitance by connecting additional ones or disconnecting unnecessary ones; the latter can be used as starting ones. The required number of microfarads is obtained by connecting several capacitors in parallel, based on the fact that the total capacitance in a parallel connection is calculated by the formula: C total = C 1 + C 1 + ... + C n.
Metallized paper or film capacitors are usually used as workers (MBGO, MBG4, K75-12, K78-17 MBGP, KGB, MBGCh, BGT, SVV-60). The permissible voltage must be at least 1.5 times the mains voltage.
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