But the operating voltage of our household network is 220 V. And in order to connect an industrial three-phase motor to a regular consumer network, phase-shifting elements are used:

• starting capacitor;
• working capacitor.

Connection diagrams for an operating voltage of 380 V

Industrially produced asynchronous three-phase motors can be connected in two main ways:

• star connection";
• delta connection".

Electric motors are structurally made of a movable rotor and a housing into which a stationary stator is inserted (can be assembled directly in the housing or inserted there). The stator consists of 3 equal windings, wound in a special way and located on it.

In a star connection, the ends of all three motor windings are connected together, and three phases are supplied to their beginnings. When connecting windings in a triangle, the end of one is connected to the beginning of the next.

Engine operating principle

When an electric motor is operating, connected to a three-phase 380 V network, voltage is sequentially applied to each of its windings and a current flows through each of them, creating an alternating magnetic field that affects the rotor, movably mounted on bearings, which causes it to rotate. To start with this type of operation, no additional elements are needed.

If one of the three-phase asynchronous electric motors is connected to a single-phase 220 V network, then no torque will arise and the motor will not start. To run three-phase devices from a single-phase network, many different options have been invented.

One of the simplest and most common among them is the use of phase shift. For this purpose, various phase-shifting capacitors are used for electric motors, through which the third phase contact is connected.

In addition, there must be one more element. This is the starting capacitor. It is designed to start the engine itself and should only work at the moment of starting for about 2-3 seconds. If it is left on for a long time, the motor windings will quickly overheat and it will fail.

To implement this, you can use a special switch that has two pairs of switchable contacts. When the button is pressed, one pair is fixed until the next press of the Stop button, and the second will be closed only when the Start button is pressed. This prevents motor failure.

Connection diagrams for operating voltage 220 V

Due to the fact that there are two main options for connecting electric motor windings, there will also be two circuits for supplying a household network. Designations:

• “P” – switch that performs the start;
• “P” is a special switch designed to reverse the engine;
• “Sp” and “Cr” are starting and running capacitors, respectively.

When connected to a 220 V network, three-phase electric motors have the opportunity to change the direction of rotation to the opposite. This can be done using the “P” toggle switch.

Attention! The direction of rotation can only be changed when the supply voltage is turned off and the electric motor is completely stopped, so as not to break it.

“Сп” and “Ср” (working and starting capacitors) can be calculated using a special formula: Ср=2800*I/U, where I is the current consumed, U is the rated voltage of the electric motor. After calculating Cp, you can select Sp. The capacity of the starting capacitors should be at least twice as large as that of the Average. For convenience and simplification of choice, the following values ​​can be taken as a basis:

• M = 0.4 kW Av = 40 μF, Sp = 80 μF;
• M = 0.8 kW Av = 80 μF, Sp = 160 μF;
• M = 1.1 kW Av = 100 μF, Sp = 200 μF;
• M = 1.5 kW Av = 150 μF, Sp = 250 μF;
• M = 2.2 kW Av = 230 μF, Sp = 300 μF.

Where M is the rated power of the electric motors used, Cp and Sp are working and starting capacitors.

When using asynchronous electric motors designed for an operating voltage of 380 V in the domestic sphere, by connecting them to a 220 V network, you lose about 50% of the rated power of the motors, but the rotor speed remains unchanged. Keep this in mind when choosing the power needed for the job.

Power losses can be reduced by using a “triangle” connection of the windings; in this case, the efficiency of the electric motor will remain somewhere at the level of 70%, which will be significantly higher than when connecting the windings “star”.

Therefore, if it is technically feasible to change the star connection to a delta connection in the junction box of the electric motor itself, then do it. After all, purchasing an “additional” 20% of power will be a good step and help in your work.

When choosing starting and operating capacitors, keep in mind that their rated voltage must be at least 1.5 times greater than the mains voltage. That is, for a 220 V network, it is advisable to use containers designed for a voltage of 400 - 500 V for startup and stable operation.

Motors with an operating voltage of 220/127 V can only be connected as a star. If you use another connection, you will simply burn it when starting up, and all that remains is to scrap it all.

If you cannot find a capacitor used for start-up and operation, then you can take several of them and connect them in parallel. The total capacity in this case is calculated as follows: Total = C1+C2+....+Sk, where k is the required number.

Sometimes, especially under heavy load, it overheats greatly. In this case, you can try to reduce the degree of heating by changing the capacitance Cp (working capacitor). It is gradually reduced, while checking the engine heating. Conversely, if the operating capacity is insufficient, then the output power produced by the device will be small. In this case, you can try increasing the capacitor capacity.

For a faster and easier start-up of the device, if possible, disconnect the load from it. This applies specifically to those engines that have been converted from a 380 V network to a 220 V network.

Conclusion on the topic

If you want to use an industrial three-phase electric motor for your needs, then you need to assemble an additional connection diagram for it, taking into account all the conditions necessary for this. And be sure to remember that this is electrical equipment and you must comply with all safety standards and regulations when working with it.

Perhaps the most common and simplest way to connect a three-phase electric motor to a single-phase network in the absence of a supply voltage of ~ 380 V is the method using a phase-shifting capacitor, through which the third winding of the electric motor is powered. Before connecting a three-phase electric motor to a single-phase network, make sure that its windings are connected in a delta (see figure below, option 2), since this connection will give minimal power losses to a 3-phase motor when it is connected to the network ~ 220 V.

The power developed by a three-phase electric motor connected to a single-phase network with such a winding connection diagram can be up to 75% of its rated power. In this case, the engine rotation speed is practically no different from its frequency when operating in three-phase mode.

The figure shows the terminal blocks of electric motors and the corresponding winding connection diagrams. However, the design of the electric motor terminal box may differ from that shown below - instead of terminal blocks, the box may contain two separated bundles of wires (three in each).

These bundles of wires represent the "beginnings" and "ends" of the motor windings. They need to be “ringed” in order to separate the windings from each other and connect them according to the “triangle” pattern we need - in series, when the end of one winding is connected to the beginning of another, etc. (C1-C6, C2-C4, C3-C5).

When a three-phase electric motor is connected to a single-phase network, a starting capacitor Cp is added to the delta circuit, which is used for a short time (only for starting) and a working capacitor Cp.

As a SB button to start the electric. For a low-power engine (up to 1.5 kW), you can use the usual “START” button, used in the control circuits of magnetic starters.

For engines of higher power, it is worth replacing it with a more powerful switching device - for example, an automatic machine. The only inconvenience in this case will be the need to manually turn off the capacitor Sp automatically after the electric motor picks up speed.

Thus, the circuit implements the possibility of two-stage control of the electric motor, reducing the total capacitance of the capacitors when the engine “accelerates”.

If the engine power is small (up to 1 kW), then it will be possible to start it without a starting capacitor, leaving only the running capacitor Cp in the circuit.

• C slave = 2800. I / U, µF - for motors connected to a single-phase network with star-connected windings.

This is the most accurate method, however, it requires measuring the current in the motor circuit. Knowing the rated power of the engine, it is better to use the following formula to determine the capacity of the working capacitor:

C slave = 66·Р nom, μF, where Р nom is the rated power of the engine.

Simplifying the formula, we can say that for a three-phase electric motor to operate in a single-phase network, the capacitance of the capacitor for every 0.1 kW of its power should be about 7 μF.

So, for a 1.1 kW motor, the capacitance of the capacitor should be 77 μF. Such a capacity can be obtained by several capacitors connected to each other in parallel (the total capacity in this case will be equal to the total), using the following types: MBGCh, BGT, KGB with an operating voltage exceeding the network voltage by 1.5 times.

By calculating the capacitance of the working capacitor, you can determine the capacitance of the starting capacitor - it should exceed the capacitance of the working capacitor by 2-3 times. Start-up capacitors should be of the same types as the working ones; in extreme cases and under the condition of a very short-term start-up, you can use electrolytic ones - types K50-3, KE-2, EGC-M, designed for a voltage of at least 450 V.

How to connect a three-phase motor to a single-phase network.

connecting a 380 to 220 volt motor

correct selection of capacitors for the electric motor

The function of stabilizers is that they act as capacitive energy fillers for stabilizer filter rectifiers. They can also transmit signals between amplifiers. To start and operate for a long period of time, capacitors are also used in the AC system for asynchronous motors. The operating time of such a system can be varied using the capacitance of the selected capacitor.

The first and only main parameter of the above-mentioned tool is capacity. It depends on the area of ​​the active connection, which is isolated by a dielectric layer. This layer is practically invisible to the human eye; a small number of atomic layers form the width of the film.

An electrolyte is used if it is necessary to restore the oxide film layer. For proper operation of the device, the system must be connected to a network with alternating current of 220 V and have a clearly defined polarity.

That is, a capacitor is created in order to accumulate, store and transmit a certain amount of energy. So why are they needed if you can connect the power source directly to the engine. It's not that simple. If you connect the motor directly to a power source, then at best it will not work, at worst it will burn out.

In order for a three-phase motor to work in a single-phase circuit, you need a device that can shift the phase by 90° on the working (third) terminal. The capacitor also plays the role of a kind of inductor, due to the fact that alternating current passes through it - its surges are leveled out due to the fact that, before operation, in the capacitor, negative and positive charges are evenly accumulated on the plates, and then transferred to the receiving device.

There are 3 main types of capacitors:

• Electrolytic;
• Non-polar;
• Polar.

Description of types of capacitors and calculation of specific capacitance

When choosing the best option, you need to consider several factors. If the connection occurs through a single-phase network with a voltage of 220 V, then a phase-shifting mechanism must be used to start. Moreover, there should be two of them, not only for the capacitor itself, but also for the engine. The formulas used to calculate the specific capacitance of a capacitor depend on the type of connection to the system; there are only two of them: triangle and star.

I 1 – rated motor phase current, A (Amps, most often indicated on the motor packaging);

U network – network voltage (the most standard options are 220 and 380 V). There are also higher voltages, but they require completely different types of connections and more powerful motors.

Sp = Wed + Co

where Cn is the starting capacitance, Cp is the working capacitance, Co is the switched capacitance.

So as not to strain with calculations, smart people derived average, optimal values, knowing the optimal power of electric motors, which is denoted by M. An important rule is that the starting capacity should be greater than the working capacity.

With a power of 0.4 to 0.8 kW: working capacitance – 40 µF, starting power – 80 µF, From 0.8 to 1.1 kW: 80 µF and 160 µF, respectively. From 1.1 to 1.5 kW: Av – 100 µF, Sp – 200 µF. From 1.5-2.2 kW: Av – 150 µF, Sp 250 µF; At 2.2 kW, the operating power should be at least 230 μF, and the starting power should be 300 μF.

When a motor designed to operate at 380 V is connected to an AC network with a voltage of 220 V, half of the rated power is lost, although this does not affect the rotor rotation speed. When calculating power, this is an important factor; these losses can be reduced with a “delta” connection diagram; the engine efficiency in this case will be 70%.

It is better not to use polar capacitors in a system connected to an alternating current network, in this case the dielectric layer is destroyed and the device heats up and, as a result, a short circuit occurs

Connection diagram "Triangle"

The connection itself is relatively easy; the current-carrying wire is connected to and from the motor (or motor) terminals. That is, if we take it more simply, there is a motor; it contains three current-carrying conductors. 1 – zero, 2 – working, 3 – phase.

The power wire is stripped and there are two main wires in a blue and brown winding, the brown one is connected to terminal 1, one of the capacitor wires is also connected to it, the second capacitor wire is connected to the second working terminal, and the blue power wire is connected to the phase.

If the motor power is small, up to one and a half kW, in principle only one capacitor can be used. But when working with loads and high powers, it is mandatory to use two capacitors; they are connected in series, but between them there is a trigger mechanism, popularly called “thermal”, which turns off the capacitor when the required volume is reached.

A quick reminder that the lower wattage starting capacitor will be turned on for a short period of time to increase the starting torque. By the way, it is fashionable to use a mechanical switch, which the user himself will turn on for a given time.

You need to understand that the motor winding itself already has a star connection, but electricians use wires to turn it into a delta. The main thing here is to distribute the wires that go into the junction box.

Connection diagram “Triangle” and “Star”

Connection diagram "Star"

But if the engine has 6 outputs - terminals for connection, then you need to unwind it and see which terminals are interconnected. After that, it is reconnected to the same triangle.

To do this, change the jumpers, let's say there are 2 rows of terminals on the engine, 3 each, they are numbered from left to right (123.456), using wires they are connected in series 1 to 4, 2 to 5, 3 to 6, you first need to find the regulatory documents and look on which relay the winding starts and ends.

In this case, the conditional 456 will become: zero, working and phase - respectively. A capacitor is connected to them, as in the previous circuit.

When the capacitors are connected, all that remains is to test the assembled circuit, the main thing is not to get confused in the sequence of connecting the wires.

What should I do if I need to connect the motor to a source designed for a different type of voltage (for example, a three-phase motor to a single-phase network)? Such a need may arise, in particular, if you need to connect the motor to any equipment (drilling or sanding machine, etc.). In this case, capacitors are used, which, however, can be of different types. Accordingly, you need to have an idea of ​​what capacity a capacitor is needed for an electric motor, and how to correctly calculate it.

What is a capacitor

The capacitor consists of two plates located opposite each other. A dielectric is placed between them. Its task is to remove polarization, i.e. charge of nearby conductors.

There are three types of capacitors:

• Polar. It is not recommended to use them in systems connected to AC power, because Due to the destruction of the dielectric layer, the device heats up, causing a short circuit.
• Non-polar. They work in any switching mode, because their plates interact equally with the dielectric and with the source.
• Electrolytic (oxide). A thin oxide film acts as electrodes. They are considered an ideal option for low-frequency electric motors, because... have the highest possible capacity (up to 100,000 µF).

How to choose a capacitor for a three-phase electric motor

When wondering: how to choose a capacitor for a three-phase electric motor, you need to take into account a number of parameters.

To select the capacitance for the working capacitor, you need to apply the following calculation formula: Work = k*Iph / U network, where:

• k – special coefficient equal to 4800 for a “triangle” connection and 2800 for a “star” connection;
• Iph is the rated value of the stator current, this value is usually indicated on the electric motor itself, but if it is erased or illegible, then it is measured with special pliers;
• U mains – mains supply voltage, i.e. 220 volt.

This way you will calculate the capacitance of the working capacitor in microfarads.

Another calculation option is to take into account the engine power value. 100 watts of power corresponds to approximately 7 µF of capacitor capacity. When making calculations, do not forget to monitor the value of the current supplied to the stator phase winding. It should not have a greater value than the nominal value.

In the case when the engine is started under load, i.e. its starting characteristics reach maximum values; a starting capacitor is added to the working capacitor. Its peculiarity is that it operates for approximately three seconds during the start-up period of the unit and turns off when the rotor reaches the rated speed level. The operating voltage of the starting capacitor should be one and a half times higher than the network voltage, and its capacity should be 2.5-3 times greater than the working capacitor. To create the required capacitance, you can connect capacitors either in series or in parallel.

How to choose a capacitor for a single-phase electric motor

Asynchronous motors, designed to operate in a single-phase network, are usually connected to 220 volts. However, if in a three-phase motor the connection torque is specified constructively (location of the windings, phase displacement of the three-phase network), then in a single-phase motor it is necessary to create a rotary displacement torque of the rotor, for which an additional starting winding is used at startup. Its current phase is shifted using a capacitor.

So, how to choose a capacitor for a single-phase electric motor?

Most often, the value of the total capacitance Srab + Drain (not a separate capacitor) is as follows: 1 µF for every 100 watts.

There are several operating modes for engines of this type:

• Starting capacitor + additional winding (connected during startup). Capacitor capacity: 70 µF per 1 kW of engine power.
• Working capacitor (capacity 23-35 μF) + additional winding, which is connected during the entire operating time.
• Running capacitor + starting capacitor (connected in parallel).

If you are thinking: how to choose a capacitor for a 220V electric motor, you should proceed from the proportions given above. However, it is necessary to monitor the operation and heating of the engine after connecting it. For example, if the unit noticeably heats up in mode with a working capacitor, the capacitance of the latter should be reduced. In general, it is recommended to select capacitors with an operating voltage of 450 V or more.

How to choose a capacitor for an electric motor is a difficult question. To ensure efficient operation of the unit, it is necessary to carefully calculate all parameters and proceed from the specific conditions of its operation and load.

Many owners quite often find themselves in a situation where they need to connect a device such as a three-phase asynchronous motor to various equipment in the garage or country house, which can be a sanding or drilling machine. This poses a problem, since the source is designed for single-phase voltage. What to do here? In fact, this problem is quite easy to solve by connecting the unit according to the circuits used for capacitors. To realize this idea, you will need a working and starting device, often referred to as a phase shifter.

Selection of capacity

To ensure proper operation of the electric motor, certain parameters must be calculated.

For run capacitor

To select the effective capacity of the device, it is necessary to perform calculations using the formula:

• I1 is the nominal value of the stator current, for measuring which special clamps are used;
• Umains – single-phase network voltage, (V).

After performing the calculations, you will get the capacitance of the working capacitor in microfarads.

It may be difficult for some to calculate this parameter using the above formula. However, in this case, you can use another scheme for calculating capacity, where you do not need to carry out such complex operations. This method allows you to quite simply determine the required parameter based only on the power of the asynchronous motor.

Here it is enough to remember that 100 watts of power of a three-phase unit should correspond to about 7 µF of the working capacitor capacity.

When making calculations, you need to monitor the current that flows to the stator phase winding in the selected mode. It is considered unacceptable if the current is greater than the nominal value.

For starting capacitor

There are situations when the electric motor has to be turned on under conditions of heavy load on the shaft. Then one running capacitor will not be enough, so you will have to add a starting capacitor to it. The peculiarity of its operation is that it will only work during the startup period of the device for no more than 3 seconds, for which the SA key is used. When the rotor reaches the rated speed level, the device turns off.

If, through an oversight, the owner left the starting devices turned on, this will lead to the formation of a significant imbalance in the currents in the phases. In such situations, there is a high probability of engine overheating. When determining the capacitance, it should be assumed that the value of this parameter should be 2.5-3 times greater than the capacitance of the working capacitor. By acting in this way, it is possible to ensure that the starting torque of the engine reaches the nominal value, as a result of which no complications arise during its startup.

To create the required capacitance, capacitors can be connected in parallel or series circuits. It should be borne in mind that the operation of three-phase units with a power of no more than 1 kW is permitted if they are connected to a single-phase network with a working device. Moreover, here you can do without a starting capacitor.

Type

After calculations, you need to determine what type of capacitor can be used for the selected circuit

The best option is to use the same type for both capacitors. Typically, the operation of a three-phase motor is ensured by paper starting capacitors, enclosed in a sealed steel housing such as MPGO, MBGP, KBP or MBGO.

Most of these devices are made in the form of a rectangle. If you look at the case, their characteristics are given there:

• Capacitance (uF);
• Operating voltage (V).

Application of electrolytic devices

When using paper starting capacitors, you need to remember the following negative point: they are quite large in size, while providing a small capacity. For this reason, for efficient operation of a small-power three-phase motor, it is necessary to use a fairly large number of capacitors. If desired, paper ones can be replaced with electrolytic ones. In this case, they must be connected in a slightly different way, where additional elements must be present, represented by diodes and resistors.

However, experts do not recommend using electrolytic starting capacitors. This is due to the presence of a serious drawback in them, which manifests itself in the following: if the diode does not cope with its task, alternating current will begin to be supplied to the device, and this is fraught with its heating and subsequent explosion.

Another reason is that today on the market you can find improved polypropylene AC starting models of the SVV type with a metallized coating.

Most often, they are designed to operate with a voltage of 400-450 V. They should be given preference, given that they have repeatedly shown themselves to be good.

Voltage

When considering various types of starting rectifiers for a three-phase motor connected to a single-phase network, one should also take into account such a parameter as the operating voltage.

It would be a mistake to use a rectifier whose voltage is an order of magnitude higher than required. In addition to the high costs of purchasing it, you will have to allocate more space for it due to its large dimensions.

At the same time, you should not consider models in which the voltage has a lower value than the network voltage. Devices with such characteristics will not be able to effectively perform their functions and will soon fail.

To avoid making mistakes when choosing the operating voltage, you should adhere to the following calculation scheme: the final parameter must correspond to the product of the actual network voltage and a coefficient of 1.15, and the calculated value must be at least 300 V.

If paper rectifiers are selected for operation in an alternating voltage network, then their operating voltage must be divided by 1.5-2. Therefore, the operating voltage for a paper capacitor, for which the manufacturer specified a voltage of 180 V, under operating conditions in an AC network will be 90-120 V.

In order to understand how the idea of ​​connecting a three-phase electric motor to a single-phase network is implemented in practice, let’s perform an experiment using an AOL 22-4 unit with a power of 400 (W). The main task that must be solved is starting the engine from a single-phase network with a voltage of 220 V.

The electric motor used has the following characteristics:

Keeping in mind that the electric motor used has little power, when connecting it to a single-phase network, you can only buy a working capacitor.

Calculation of the capacity of the working rectifier:

Using the above formulas, we take the average value of the capacitance of the working rectifier to be 25 μF. Here a slightly larger capacitance was chosen, equal to 10 μF. So we will try to find out how such a change affects the launch of the device.

Now we need to buy rectifiers, the latter will be MBGO type capacitors. Next, based on the prepared rectifiers, the required capacity is assembled.

During operation, it should be remembered that each such rectifier has a capacity of 10 μF.

If you take two capacitors and connect them to each other in a parallel circuit, the resulting capacitance will be 20 µF. In this case, the operating voltage will be equal to 160V. To achieve the required level of 320 V, you need to take these two rectifiers and connect them to another pair of capacitors connected in parallel, but using a series circuit. As a result, the total capacitance will be 10 μF. When the battery of working capacitors is ready, connect it to the engine. Then all that remains is to run it in a single-phase network.

During the experiment with connecting the motor to a single-phase network, the work required less time and effort. When using a similar unit with a selected battery of rectifiers, it should be taken into account that its useful power will be at a level of up to 70-80% of the rated power, while the rotor speed will correspond to the rated value.

Important: if the motor used is designed for a 380/220 V network, then when connecting to the network you should use a “triangle” circuit.

Pay attention to the contents of the tag: it happens that there is an image of a star with a voltage of 380 V. In this case, correct operation of the motor in the network can be ensured by fulfilling the following conditions. First you will have to “gut” the common star, and then connect 6 ends to the terminal block. You should look for a common point in the frontal part of the engine.

Video: connecting a single-phase motor to a single-phase network

The decision to use a starting capacitor should be made based on specific conditions; most often, a working capacitor is sufficient. However, if the engine being used is subjected to increased load, it is recommended to stop operation. In this case, it is necessary to correctly determine the required capacity of the device to ensure efficient operation of the unit.