Three-phase motor - into a single-phase network. Purpose and connection of starting capacitors for electric motors Capacitor capacity per 1 kW single-phase

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.

Each object is initially supplied with three-phase current. The main reason is the use in power plants of generators with three-phase windings, out of phase with each other by 120 degrees and generating three sinusoidal voltages. However, with further distribution of current, only one phase is supplied to the consumer, to which all existing electrical equipment is connected.

Sometimes there is a need to use non-standard devices, so you have to solve the problem of how to choose a capacitor for a three-phase motor. As a rule, it is necessary to calculate the capacity of a given element that ensures stable operation of the unit.

The principle of connecting a three-phase device to one phase

In all apartments and most private houses, all internal energy supply is carried out through single-phase networks. Under these conditions, it is sometimes necessary to perform . This operation is quite possible from a physical point of view, since individual phases differ from each other only by a time shift. Such a shift can be easily organized by including any reactive elements in the circuit - capacitive or inductive. It is they who perform the function of phase-shifting devices when working and starting elements are used.

It should be taken into account that the stator winding itself has inductance. In this regard, it is quite enough to connect a capacitor with a certain capacitance outside the engine. At the same time, the stator windings are connected in such a way that the first of them shifts the phase of the other winding in one direction, and in the third winding the capacitor performs the same procedure, only in the other direction. As a result, the required phases are formed in the amount of three, extracted from a single-phase supply wire.

Thus, the three-phase motor acts as a load for only one phase of the connected power supply. As a result, an imbalance is formed in the energy consumed, which negatively affects the overall operation of the network. Therefore, this mode is recommended to be used for a short time for low-power electric motors. Connecting the windings to a single-phase network can be done.

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

When a three-phase electric motor is planned to be connected to a single-phase network, it is recommended to give preference to a delta connection. An information plate attached to the housing warns about this. In some cases there is a “Y” designation here, which means a star connection. It is recommended to reconnect the windings in a delta configuration to avoid large power losses.

The electric motor is connected to one of the phases of a single-phase network, and the other two phases are created artificially. For this, a working capacitor (Cp) and a starting capacitor (Sp) are used. At the very beginning of starting the engine, a high level of starting current is required, which cannot be provided by the running capacitor alone. A starting or starting capacitor, connected in parallel with the working capacitor, comes to the rescue. With low engine power, their performance is equal. Specially produced starting capacitors are marked “Starting”.

These devices operate only during start-up periods in order to accelerate the engine to the required power. It is subsequently turned off using a push-button or double switch.

Types of starting capacitors

Small electric motors, the power of which does not exceed 200-400 watts, can operate without a starting device. For them, one working capacitor is quite enough. However, if there are significant loads at the start, additional starting capacitors are necessarily used. It is connected in parallel with the working capacitor and during the acceleration period is kept in the on position using a special button or relay.

To calculate the capacitance of the starting element, it is necessary to multiply the capacitance of the working capacitor by a factor equal to 2 or 2.5. During acceleration, the engine requires less and less capacity. In this regard, you should not keep the starting capacitor constantly on. High capacity at high speeds will lead to overheating and failure of the unit.

The standard capacitor design consists of two plates located opposite each other and separated by a dielectric layer. When choosing a particular element, it is necessary to take into account its parameters and technical characteristics.

All capacitors are presented in three main types:

Polar. Cannot operate electric motors connected to alternating current. A collapsing dielectric layer can lead to heating of the unit and subsequent short circuit.
Non-polar. Received the greatest distribution. They can operate in any connection options due to the identical interaction of the plates with the dielectric and the current source.
Electrolytic. In this case, the electrodes are a thin oxide film. They can reach a maximum possible capacity of up to 100 thousand uF, ideal for low-frequency motors.

Selecting a capacitor for a three-phase motor

Capacitors intended for a three-phase motor must have a fairly high capacity - from tens to hundreds of microfarads. Electrolytic capacitors are not suitable for these purposes because they require a unipolar connection. That is, specifically for these devices it will be necessary to create a rectifier with diodes and resistances.

Gradually, the electrolyte in such capacitors dries out, which leads to loss of capacity. In addition, during operation, these elements sometimes explode. If you still decide to use electrolytic devices, you must take these features into account.

Classic examples are the elements presented in the figure. The working capacitor is shown on the left, and the starting capacitor on the right.

The selection of a capacitor for a three-phase motor is carried out experimentally. The capacity of the working device is selected at the rate of 7 μF per 100 W of power. Therefore, 600 W will correspond to 42 µF. The starting capacitor is at least 2 times the operating capacitance. Thus 2 x 45 = 90 uF would be the most appropriate figure.

The choice is made gradually, based on the operation of the engine, since its real power directly depends on the capacity of the capacitors used. In addition, this can be done using a special table. If there is insufficient capacity, the engine will lose its power, and if there is excess capacity, overheating will occur from excessive current. If the capacitor is selected correctly, the engine will operate normally, without jerking or extraneous noise. We select the device more accurately through calculations performed using special formulas.

Capacity calculation

The capacitance of the capacitor for the electric motor is calculated based on the winding connection diagram - star or triangle.

In both cases, the general calculation formula is applied: C slave = k x I f /U network, to which all parameters have the following designations:

k - is a special coefficient. Its value is 2800 for the star circuit and 4800 for the delta circuit.
If - rated stator current indicated on the information plate. If it is impossible to read, measurements are taken using special measuring clamps.
Umains is the supply voltage of 220 volts.

By substituting all the necessary values, you can easily calculate what capacity the working capacitor will have (μF). During calculations, it is necessary to take into account the current supplied to the stator phase winding. It should not exceed the rated value, just as the load on a motor with a capacitor should not exceed 60-80% of the rated power indicated on the information plate.

How to connect starting and running capacitors

The figure shows the simplest diagram of connecting the starting and working elements. The first of them is installed at the top, and the second at the bottom. At the same time, an on and off button is connected to the engine. The most important thing is to carefully understand the wires so as not to mix up the ends.

This scheme allows you to perform a preliminary check with an inaccurate estimate. It is also used after the final selection of the most optimal value.

This selection is carried out experimentally using several capacitors of different capacities. When connected in parallel, their total power will increase. At this time, you need to monitor the operation of the engine. If the operation is stable and smooth, in this case you can buy a capacitor with a capacitance equal to the sum of the capacitances of the test elements.

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 operate 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 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 alternating current network with a voltage of 220 V, half of the rated power is lost, although this does not affect the speed of rotation of the rotor.

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.

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.

If there is a need to connect an asynchronous three-phase electric motor to a household network, you may encounter a problem - it seems completely impossible to do this. But if you know the basics of electrical engineering, you can connect a capacitor to start an electric motor in a single-phase network. But there are also capacitorless connection options; they are also worth considering when designing an installation with an electric motor.

The easiest way is to connect the motor using a frequency converter. There are models of these devices that convert single-phase voltage to three-phase. The advantage of this method is obvious - there is no power loss in the electric motor. But the cost of such a frequency converter is quite high - the cheapest copy will cost 5-7 thousand rubles.

There is another method that is used less frequently - the use of a three-phase asynchronous winding to convert voltage. In this case, the entire structure will be much larger and more massive. Therefore, it will be easier to calculate which capacitors are needed to start the electric motor and install them by connecting them according to the diagram. The main thing is not to lose power, since the operation of the mechanism will be much worse.

Features of the circuit with capacitors

The windings of all three-phase electric motors can be connected according to two schemes:

“Star” - in this case, the ends of all windings are connected at one point. And the beginnings of the windings are connected to the supply network.
“Triangle” - the beginning of the winding is connected to the end of the adjacent one. The result is that the connection points of the two windings are connected to the power supply.

The choice of circuit depends on what voltage the motor is supplied with. Typically, when connected to a 380 V AC network, the windings are connected in a “star”, and when operating under a voltage of 220 V - in a “delta”.

In the picture above:

a) star connection diagram;

b) triangle connection diagram.

Since a single-phase network clearly lacks one supply wire, it needs to be made artificially. For this purpose, capacitors are used that shift the phase by 120 degrees. These are working capacitors; they are not enough when starting electric motors with a power of over 1500 W. To start powerful engines, you will need to additionally include another container, which will facilitate work during the start.

Working capacitor capacity

In order to find out what capacitors are needed to start an electric motor when operating on a 220 V network, you need to use the following formulas:

When connected in a star configuration C (slave) = (2800 * I1) / U (network).
When connected in a "triangle" C (slave) = (4800 * I1) / U (network).

Current I1 can be measured independently using clamps. But you can also use this formula: I1 = P / (1.73 U (network) cosφ η).

The value of power P, supply voltage, power factor cosφ, efficiency η can be found on the tag, which is riveted on the motor housing.

A simplified version of calculating a working capacitor

If all these formulas seem a little complicated to you, you can use their simplified version: C (slave) = 66 * P (motor).

And if we simplify the calculation as much as possible, then for every 100 W of electric motor power a capacitance of about 7 μF is required. In other words, if you have a 0.75 kW motor, then you will need a run capacitor with a capacity of at least 52.5 uF. After selection, be sure to measure the current when the motor is running - its value should not exceed the permissible values.

Start capacitor

In the event that the motor is subject to heavy loads or its power exceeds 1500 W, a phase shift alone cannot be done. You will need to know what other capacitors are needed to start an electric motor of 2.2 kW and higher. The starter is connected in parallel with the worker, but only it is excluded from the circuit when the idle speed is reached.

Be sure to turn off the starting capacitors - otherwise phase imbalance and overheating of the electric motor occurs. The starting capacitor should be 2.5-3 times larger in capacity than the working capacitor. If you consider that a capacitance of 80 μF is required for normal operation of the motor, then to start you need to connect another block of capacitors of 240 μF. You can hardly find capacitors with such a capacitance on sale, so you need to make a connection:

When the capacitances are added in parallel, the operating voltage remains the same as indicated on the element.
In a series connection, the voltages are added, and the total capacitance will be equal to C (total) = (C1*C2*..*CX)/(C1+C2+..+CX).

It is advisable to install starting capacitors on electric motors whose power is over 1 kW. It is better to reduce the power rating a little to increase the degree of reliability.

What type of capacitors to use

Now you know how to select capacitors to start an electric motor when operating on a 220 V AC network. After calculating the capacitance, you can begin to select a specific type of element. It is recommended to use elements of the same type as working and starting elements. Paper capacitors perform well; their designations are as follows: MBGP, MPGO, MBGO, KBP. You can also use foreign elements that are installed in computer power supplies.

The operating voltage and capacitance must be indicated on the body of any capacitor. One drawback of paper cells is that they are large in size, so to operate a powerful engine you will need a rather large battery of cells. It is much better to use foreign capacitors, since they are smaller in size and have a larger capacity.

Using Electrolytic Capacitors

You can even use electrolytic capacitors, but they have a peculiarity - they must operate on direct current. Therefore, to install them in the structure, you will need to use semiconductor diodes. It is undesirable to use electrolytic capacitors without them - they tend to explode.

But even if you install diodes and resistors, this cannot guarantee complete safety. If the semiconductor breaks through, then alternating current will flow to the capacitors, resulting in an explosion. The modern element base allows the use of high-quality products, for example, polypropylene capacitors for operation on alternating current with the designation SVV.

For example, the designation of elements SVV60 indicates that the capacitor is designed in a cylindrical housing. But SVV61 has a rectangular body. These elements operate under a voltage of 400... 450 V. Therefore, they can be used without problems in the design of any device that requires connecting an asynchronous three-phase electric motor to a household network.

Operating voltage

One important parameter of capacitors must be taken into account - operating voltage. If you use capacitors to start an electric motor with a very large voltage reserve, this will lead to an increase in the dimensions of the structure. But if you use elements designed to operate with a lower voltage (for example, 160 V), this will lead to rapid failure. In order for capacitors to function normally, their operating voltage must be approximately 1.15 times greater than the network voltage.

Moreover, one feature must be taken into account - if you use paper capacitors, then when working in alternating current circuits their voltage must be reduced by 2 times. In other words, if the housing indicates that the element is designed for a voltage of 300 V, then this characteristic is relevant for direct current. Such an element can be used in an alternating current circuit with a voltage of no more than 150 V. Therefore, it is better to assemble batteries from paper capacitors, the total voltage of which is about 600 V.

Connecting an electric motor: a practical example

Let's say you have an asynchronous electric motor designed to be connected to a three-phase AC network. Power - 0.4 kW, motor type - AOL 22-4. Main characteristics for connection:

Power - 0.4 kW.
Supply voltage - 220 V.
The current when operating from a three-phase network is 1.9 A.
The motor windings are connected using a star circuit.

Now it remains to calculate the capacitors to start the electric motor. The motor power is relatively small, therefore, to use it in a household network, you only need to select a working capacitor; there is no need for a starting capacitor. Using the formula, calculate the capacitance of the capacitor: C (slave) = 66*P (motor) = 66*0.4 = 26.4 µF.

You can use more complex formulas; the capacity value will differ slightly from this. But if there is no capacitor suitable for the capacitance, you need to connect several elements. When connected in parallel, the containers are folded.

note

Now you know which capacitors are best to use to start an electric motor. But the power will drop by about 20-30%. If a simple mechanism is set in motion, it will not be felt. The rotor speed will remain approximately the same as indicated in the passport. Please note that if the motor is designed to operate from a 220 and 380 V network, then it is connected to a household network only if the windings are connected in a triangle. Carefully study the tag; if it only has the designation of a “star” circuit, then in order to work in a single-phase network you will have to make changes to the design of the electric motor.

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.