How to connect a three-phase motor to a single-phase network with your own hands. Which capacitors to choose. Standard diagram for connecting a three-phase motor to a single-phase network

The most common drives of various electrical machines in the world are asynchronous motors. They were invented back in the 19th century and very quickly, due to the simplicity of their design, reliability and durability, are widely used both in industry and in everyday life.

However, not all consumers of electrical energy are provided with three-phase power supply, which makes it difficult to use reliable human assistants - three-phase electric motors. But there is still a way out, quite simply implemented in practice. You just need to connect the motor using a special circuit.

But first, it’s worth learning a little about the principles of operation and how to connect them.

How will an asynchronous motor operate when connected to a two-phase network?

On the stator asynchronous motor three windings are placed, which are designated by the letters C1, C2 - C6. The first winding belongs to the terminals C1 and C4, the second to C2 and C5, and the third to C3 and C6, with C1-C6 being the beginning of the windings, and C4-C6 being their end. IN modern engines a slightly different marking system has been adopted, designating the windings with the letters U, V, W, and their beginning and end are designated by the numbers 1 and 2. For example, the beginning of the first and winding C1 corresponds to U1, the end of the third winding C6 corresponds to W2, and so on.

All winding terminals are mounted in a special terminal box, which is found in any asynchronous motor. The plate that should be on each engine indicates its power, operating voltage (380/220 V or 220/127 V), as well as the possibility of connecting in two circuits: “star” or “delta”.

It is worth considering that the power of an asynchronous machine when connected to a single-phase network will always be 50-75% less than when connected to a three-phase network.

If you simply connect a three-phase motor to a 220 volt network by simply connecting the windings to the supply network, the rotor will not move for the simple reason that there is no rotating magnetic field. In order to create it, it is necessary to shift the phases on the windings using a special circuit.

From the course of electrical engineering it is known that the capacitor included in electrical circuit alternating current, will shift the voltage phase. This is due to the fact that during its charging there is a gradual increase in voltage, the time of which is determined by the capacitance of the capacitor and the amount of current flowing.

It turns out that the potential difference at the terminals of the capacitor will always be late in relation to the supply network. This effect is used to connect three-phase motors to a single-phase network.

The figure shows a connection diagram for a single-phase motor with in different ways. Obviously, the voltage between points A and C, as well as B and C, will increase with a delay, which will create the effect of a rotating magnetic field. The capacitor rating in delta connections is calculated by the formula: C=4800*I/U, where I is the operating current and U is the voltage. The capacitance in this formula is calculated in microfarads.

In connections using the “star” method, which is least preferably used in single-phase networks due to the lower power output, a different formula is used: C = 2800 * I/U. Obviously, capacitors require lower ratings, which is explained by lower starting and operating currents.

The diagram presented above is only suitable for those three-phase electric motors whose power does not exceed 1.5 kW. At more power it will be necessary to use another scheme, which, in addition to the performance characteristics, is guaranteed to ensure the engine starts and reaches operating mode. Such a diagram is presented in the following figure, where it is additionally possible to reverse the engine.

Capacitor Cp ensures engine operation normal mode, A Cp– needed when starting and accelerating the engine, which is done within a few seconds. Resistor R discharges the capacitor after starting and opening the pushbutton switch Kn, and the switch S.A. serves for reverse.

The capacitance of the starting capacitor is usually used twice as large as the capacitance of the running capacitor. In order to gain the required capacity, assembled batteries from capacitors are used. It is known that parallel connection of capacitors sums their capacitance, and series is inversely proportional.

When choosing capacitor ratings, they are guided by the fact that their operating voltage should be at least one step higher than the mains voltage, and this will ensure their reliable operation at start-up.

Modern element base allows the use of high-capacity capacitors with small dimensions, which greatly simplifies the connection of three-phase motors to a single-phase 220 volt network.

Results

• Asynchronous machines can also be connected to single-phase 220 volt networks using phase-shifting capacitors, the rating of which is calculated based on their operating voltage and current consumption.
• Motors with power over 1.5 kW require a connection and a starting capacitor.
• The triangle connection is the main one in single-phase networks.

Find out how everything is connected in practice from the video

Some craftsmen independently assemble wood or metal processing machines at home. For this purpose, any available motors of suitable power can be used. In some cases, you have to figure out how to connect a three-phase motor to single-phase network. This is the topic that this article is devoted to. It will also tell you how to choose the right capacitors.

Single-phase and three-phase

In order to correctly understand the subject of discussion, which explains the connection of a 380 to 220 volt motor, you need to understand what lies fundamental difference such units. All three-phase motors are asynchronous. This means that the phases in it are connected with some offset. Structurally, the engine consists of a housing in which a static part is placed that does not rotate, it is called a stator. There is also a rotating element called a rotor. The rotor is located inside the stator. Three-phase voltage is supplied to the stator, each phase is 220 volts. After this, formation occurs electromagnetic field. Due to the fact that the phases are in angular displacement, it appears electromotive force. It forces the rotor, which is located in the magnetic field of the stator, to rotate.

Note! Winding voltage three phase motor supplied through a type of connection that is made in the shape of a star or triangle.

Single-phase asynchronous units have a slightly different type of connection, since they are powered by a 220 volt network. It only has two wires. One is called phase, and the second is called zero. To start, the motor needs to have only one winding to which the phase is connected. But just one will not be enough for the starting impulse. Therefore, there is also a winding that is activated during start-up. For it to fulfill its role, it can be connected through a capacitor, which happens most often, or short-circuited.

Connecting a three-phase motor

The usual connection of a three-phase motor to a three-phase network can become not an easy task for those who have never encountered it. Some units only have three wires to connect to. They allow you to do this according to the “star” scheme. Other devices have six wires. In this case, there is a choice between a triangle and a star. You can see in the photo below real example star connections. The white winding fits the power cable and connects to only three terminals. Next, special jumpers are installed that provide proper nutrition windings

To make it clearer how to implement this yourself, below is a diagram of such a connection. The delta connection is somewhat simpler, since there are no three additional terminals. But this only means that the jumper mechanism is already implemented in the engine itself. In this case, there is no way to influence the way the windings are connected, which means it will be necessary to observe the nuances when connecting such a motor to a single-phase network.

Connection to a single-phase network

A three-phase unit can be successfully connected to a single-phase network. But it is worth considering that with a circuit called “star”, the power of the unit will not exceed half of its rated power. To increase this figure, it is necessary to provide a triangle connection. In this case, only a 30% drop in power can be achieved. There is no need to be afraid, because in a 220-volt network it is impossible for a critical voltage to arise that would damage the motor windings.

Connection diagrams

When a three-phase motor is connected to a 380 network, then each of its windings is powered by one phase. When connecting it to a 220-volt network, two windings receive a phase and neutral wire, and the third remains unused. To correct this nuance, you need to choose the right capacitor that will be able to supply voltage to it at the required moment. Ideally, there should be two capacitors in the circuit. One of them is the starting one, and the second is the working one. If the power of a three-phase unit does not exceed 1.5 kW, and the load is applied to it after it reaches the required speed, then only a working capacitor can be used.

Note! Without additional capacitors or other devices, it is not possible to directly connect a 380 to 220 motor.

In this case, it must be installed in the gap between the third contact of the triangle and the neutral wire. If you want to achieve the effect that the engine will rotate in reverse direction, then it is necessary to connect not the neutral, but the phase wire to one terminal of the capacitor. If the engine power exceeds that indicated above, then you will also need starting capacitor. It is mounted parallel to the worker. But it is worth considering that a non-latching switch must be installed in the wire that is connected between them. This button will allow you to use the capacitor only during startup. In this case, after turning on the engine, you will have to hold down this key for several seconds so that the unit reaches the required speed. After this, it must be released so as not to burn the windings.

If you need to turn on such a unit in reverse, then install a toggle switch with three outputs. The middle one must be permanently connected to the working capacitor. The extreme ones must be connected to the phase and neutral wires. Depending on which direction the rotation should be, you will need to set the toggle switch either to zero or to phase. Below is a schematic diagram of such a connection.

Selection of capacitor

There are no universal capacitors that would fit all units indiscriminately. Their characteristic is the capacity they are able to hold. Therefore, each one will have to be selected individually. The main requirement for it will be operation at a network voltage of 220 volts; more often they are designed for 300 volts. To determine which element is required, you need to use the formula. If the connection is made by a star, then it is necessary to divide the current by a voltage of 220 volts and multiply by 2800. The current indicator is taken to be the figure indicated in the engine characteristics. For a triangle connection, the formula remains the same, but the last coefficient changes to 4800.

For example, if it is written on the unit that the rated current that can flow through its windings is 6 amperes, then the capacity of the working capacitor will be 76 µF. This is when connected by a star, for a triangle connection the result will be 130 µF. But it was said above that if the unit experiences a load at start-up or has a power of more than 1.5 kW, then another capacitor will be needed - a starting capacitor. Its capacity is usually 2 or 3 times the working one. That is, for a star connection you will need a second capacitor with a capacity of 150-175 µF. It will have to be selected empirically. There may not be capacitors of the required capacity on sale, then you can assemble a unit to obtain the required figure. To do this, the available capacitors are connected in parallel so that their capacitance adds up.

Note! There is some limitation on the power of three-phase units that can be powered from a single-phase network. It is 3 kW. If this value is exceeded, the wiring may fail.

Why is it better to select starting capacitors empirically, starting with the smallest? The fact is that if its value is insufficient, current will be supplied greater value, which can damage the windings. If its value is greater than the required one, then the unit will not have enough impulse to start. You can more clearly imagine the connection using a video.

Conclusion

While working with electric shock follow safety precautions. Do not launch anything if you are not completely sure that the connection has been made correctly. Be sure to consult with an experienced electrician who will tell you whether the wiring can withstand the required load from the unit.

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. It can be done different ways, however, 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 big moment resistance during startup. In this case, it is necessary to provide a large starting torque. To this end, modifications were made to the previous circuit, and the capacitors required for the phase shift were replaced by two electronic keys. The first switch is connected in series with the phase winding, leading to an inductive shift of the current in it. Connection of the second key - parallel 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 normal connection You should know the operating principle of a three-phase motor. When connected to the network, along its windings in different moments time, the current begins to flow one by one. 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. Normal operation three-phase electric motor largely depends on the right choice 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 over 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 necessary, ensure rotation in different sides, 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 effective way It is considered to connect a three-phase motor to a single-phase network by connecting a third contact connected to a phase-shifting capacitor.

Greatest output power, which can be obtained at home, is up to 70% of the nominal value. 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 you will need additional connection starting capacitor. 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. Special attention should be given to capacitors, since the operation of the entire system depends on their action.

It happens that a three-phase electric motor falls into your hands. It is from these engines that homemade circular saws are made, sanding machines and various types of shredders. In general, a good owner knows what can be done with it. But the trouble is, a three-phase network in private homes is very rare, and it is not always possible to install it. But there are several ways to connect such a motor to a 220V network.

It should be understood that the engine power with such a connection, no matter how hard you try, will drop noticeably. Thus, a delta connection uses only 70% of the engine power, and a star connection uses even less - only 50%.

In this regard, it is desirable to have a more powerful engine.

Important! When connecting the motor, be extremely careful. Take your time. When changing the circuit, turn off the power supply and discharge the capacitor with an electric lamp. Work with at least two people.

So, in any connection scheme, capacitors are used. In essence, they act as the third phase. Thanks to it, the phase to which one terminal of the capacitor is connected shifts exactly as much as necessary to simulate the third phase. Moreover, to operate the engine, one tank is used (working), and for starting, another (starting) is used in parallel with the working one. Although this is not always necessary.

For example, for a lawn mower with a blade in the form of a sharpened blade, a 1 kW unit and only working capacitors will be sufficient, without the need for containers for starting. This is due to the fact that the engine is idling when starting and it has enough energy to spin the shaft.

If you take a circular saw, a hood or other device that puts an initial load on the shaft, then without extra cans Starting capacitors are not needed. Someone may say: “why not connect the maximum capacity so that there is not enough?” But it's not that simple. With such a connection, the motor will overheat and may fail. Don't risk your equipment.

Important! Whatever the capacitance of the capacitors, their operating voltage must be at least 400V, otherwise they will not work for a long time and may explode.

Let's first consider how a three-phase motor is connected to a 380V network.

Three-phase motors come with either three terminals - for connection to a star only - or with six connections, with the ability to select a circuit - star or delta. The classic scheme can be seen in the figure. Here in the picture on the left there is a star connection. The photo on the right shows how it looks on a real engine frame.

It can be seen that for this it is necessary to install special jumpers on the required pins. These jumpers come with the motor. In the case where there are only 3 terminals, the star connection is already made inside the motor housing. In this case, it is simply impossible to change the winding connection diagram.

Some say that they did this to prevent workers from stealing units from home for their own needs. Be that as it may, such engine options can be successfully used for garage purposes, but their power will be noticeably lower than those connected by a triangle.

Connection diagram for a 3-phase motor in a 220V network connected by a star.

As you can see, the 220V voltage is distributed over two series-connected windings, where each is designed for such a voltage. Therefore, the power is lost almost twice, but such an engine can be used in many low-power devices.

The maximum power of a 380V motor in a 220V network can only be achieved using a delta connection. In addition to minimal power losses, the engine speed also remains unchanged. Here, each winding is used for its own operating voltage, hence the power. The connection diagram for such an electric motor is shown in Figure 1.

Fig. 2 shows a terminal with a 6-pin terminal for delta connection. The three resulting outputs are supplied with: phase, zero and one terminal of the capacitor. The direction of rotation of the electric motor depends on where the second terminal of the capacitor is connected - phase or zero.

In the photo: an electric motor only with working capacitors without starting capacitors.

If there is an initial load on the shaft, it is necessary to use capacitors for starting. They are connected in parallel with the workers using a button or switch at the time of switching on. As soon as the engine reaches maximum speed, the starting tanks should be disconnected from the workers. If it is a button, we simply release it, and if it is a switch, then we turn it off. Then the engine uses only working capacitors. Such a connection is shown in the photo.

How to select capacitors for a three-phase motor using it in a 220V network.

The first thing you need to know is that the capacitors must be non-polar, that is, not electrolytic. It is best to use containers of the brand ― MBGO. They were successfully used in the USSR and in our time. They perfectly withstand voltage, current surges and the damaging effects of the environment.

They also have mounting eyes that help you easily place them at any point on the device’s body. Unfortunately, getting them now is problematic, but there are many other modern capacitors that are no worse than the first ones. The main thing is that, as mentioned above, their operating voltage is not less than 400V.

Calculation of capacitors. Capacity of the working capacitor.

In order not to resort to long formulas and torture your brain, there is a simple way to calculate a capacitor for a 380V motor. For every 100 W (0.1 kW) 7 µF is taken. For example, if the motor is 1 kW, then we calculate it like this: 7 * 10 = 70 µF. It is extremely difficult to find such a capacity in one jar, and it is also expensive. Therefore, most often the containers are connected in parallel, gaining the required capacity.

Starting capacitor capacity.

This value is taken at the rate of 2-3 times greater than the capacity of the working capacitor. It should be taken into account that this capacity is taken in total with the working one, that is, for a 1 kW motor, the working one is equal to 70 μF, multiply it by 2 or 3, and get the required value. This is 70-140 µF of additional capacitance - starting. At the moment of switching on, it is connected to the working one and the total is 140-210 µF.

Features of the selection of capacitors.

Capacitors, both working and starting, can be selected using the method from smallest to largest. Having thus selected the average capacity, you can gradually add and monitor the operating mode of the engine so that it does not overheat and has enough power on the shaft. Also, the starting capacitor is selected by adding until it starts smoothly without delays.

The operation of three-phase electric motors is considered much more efficient and productive than single-phase motors, designed for 220 V. Therefore, if there are three phases, it is recommended to connect the appropriate three-phase equipment. As a result, connecting a three-phase motor to a three-phase network provides not only economical, but also stable work devices. The connection diagram does not require the addition of any starting devices, since immediately after starting the engine, a magnetic field is formed in its stator windings. The main condition for the normal operation of such devices is the correct connection and compliance with all recommendations.

Connection diagrams

The magnetic field created by the three windings ensures the rotation of the electric motor rotor. Thus, Electric Energy transforms into mechanical.

The connection can be made in two main ways - star or triangle. Each of them has its own advantages and disadvantages. The star circuit provides a smoother start of the unit, however, the engine power drops by approximately 30% of the rated value. In this case, the delta connection has certain advantages, since there is no loss of power. However, this also has its own peculiarity associated with the current load, which increases sharply during startup. This condition has a negative impact on the insulation of wires. The insulation may be punctured and the engine may fail completely.

Particular attention should be paid to European equipment equipped with electric motors designed for voltages of 400/690 V. They are recommended for connection to our 380 volt networks only using the delta method. If connected with a star, such motors immediately burn out under load. This method Applicable only to domestic three-phase electric motors.

Modern units have a connection box into which the ends of the windings are led out. Their number can be three or six. In the first case, the connection diagram is initially assumed to be a star method. In the second case, the electric motor can be connected to a three-phase network in both ways. That is, with a star circuit, the three ends located at the beginning of the windings are connected into a common twist. The opposite ends are connected to the phases of the 380 V network from which power is supplied. With the triangle option, all ends of the windings are connected in series to each other. The phases are connected to three points at which the ends of the windings are connected to each other.

Using a star-delta circuit

Relatively rarely used combined scheme connection, known as star-delta. It allows for a smooth start with a star circuit, and during the main operation a triangle is turned on, providing maximum power to the unit.

This connection diagram is quite complex, requiring the use of three windings installed in the connections at once. The first MP is connected to the network and with the ends of the windings. MP-2 and MP-3 are connected to opposite ends of the windings. The delta connection is made to the second starter, and the star connection is made to the third. Strictly prohibited simultaneous activation second and third starters. This will lead to short circuit between the phases connected to them. To prevent similar situations An interlock is established between these starters. When one MP turns on, the contacts of the other open.

The entire system operates according to to the following principle: simultaneously with turning on MP-1, MP-3, connected by a star, turns on. After a smooth start of the engine, after a certain period of time set by the relay, the transition to normal operating mode occurs. Next, MP-3 is turned off and MP-2 is turned on according to a triangle diagram.

Three-phase motor with magnetic starter

Connecting a three-phase motor using a magnetic starter is carried out in the same way as through circuit breaker. This circuit is simply supplemented with an on/off block with corresponding START and STOP buttons.

One normally closed phase connected to the motor is connected to the START button. When pressed, the contacts close, after which current flows to the motor. However, it should be noted that if the START button is released, the contacts will be open and no power will be supplied. To prevent this, magnetic switch is equipped with one more additional contact connector, the so-called self-retaining contact. It functions as a locking element and prevents the circuit from breaking when the START button is turned off. The circuit can only be completely disconnected using the STOP button.

Thus, connecting a three-phase motor to a three-phase network can be done in various ways. Each of them is selected in accordance with the unit model and specific operating conditions.