Connecting a three-phase motor to a three-phase network. Connection diagram of a three-phase electric motor to a three-phase network

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

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There are many types of motors, but for all of them, the main characteristic is the voltage supplied to the mechanisms and the power of the motors themselves.

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

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

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

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

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

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

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

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

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

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

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

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

Star-delta circuit

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

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

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

For it to work you need three starters:

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

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

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

How the scheme works

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

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

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

Other motor connections

There are several schemes:

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

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

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

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

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

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

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

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

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

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

Using a magnetic starter

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

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

Connection diagram for a 380V electric asynchronous motor starter:

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

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

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

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

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

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

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

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

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

Connecting a three-phase motor

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

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

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

2. Connecting the engine through a switch or circuit breaker

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Here's what's on the side:

Motor circuit breaker - characteristics on the side wall

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

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

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

Motor connection diagram via magnetic starter

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

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

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

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

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

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

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

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

Connecting a three-phase motor via electronic devices

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

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

1. Solid State Relays ( solid state relay) – in them the power elements are thyristors (triacs), which are controlled input signal from a button or from a controller. There are both single-phase and three-phase. .
2. Soft (soft) starters (soft starters, soft starters) are advanced solid state machines. You can set the protection current, acceleration/deceleration time, turn on reverse, etc. And on this topic. Practical Application soft starters – .Connection of two-speed asynchronous motors. Keywords– Rarity, Retro, USSR.

   I’ll end here, thank you for your attention, I couldn’t cover everything, write questions in the comments!

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

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

   
   

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

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

   1. star;
   2. triangle.

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

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

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

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

   1. the star circuit has reduced currents in the windings, allows you to operate the electric motor for a long time with minimal loads, and provide small torques on the shaft;
   2. The higher currents produced by the delta circuit provide better power output, allowing the motor to be used under extreme loads, so it requires reliable cooling for long-term operation.

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

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

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

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

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

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

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

   Should be done electrical measurements its circuit and check the insulation condition.

   How to determine stator winding connection diagrams

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

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

   Electrical inspection of stator winding ends

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

   Polarity measurements of stator windings

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

   1. short-term supply DC in one winding to create a pulse;
   2. use of a source of variable EMF.

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

   Battery pulse test

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

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

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

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

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

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

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

   Testing with a step-down transformer

   EMF source AC 24 volt is recommended for electrical safety reasons. It is not recommended to neglect this requirement.

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

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

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

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

   Checking the insulation resistance of the stator windings

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

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

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

   Starting an asynchronous motor according to a star circuit

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

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

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

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

   How to choose capacitors

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

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

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

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

   C slave=2800∙I/U.

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

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

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

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

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

   
   Its closed case contains a mechanism consisting of:

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

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

   Starting an asynchronous motor using a triangle pattern

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

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

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

   C slave=4800∙I/U.

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

   Final conclusions

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

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

   
   A variant of such a mechanism is shown in a photograph of an emery board with the protective shield and limit stop removed for clarity. Even with this design, it is difficult to work on it due to power losses.

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

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

   Quite often, three-phase asynchronous motors are used in industrial and household applications. This type of engine is quite common, so most of the devices we are familiar with using propulsion traction operate on exactly this type. This engine consists of only two main parts - a movable rotor and a stator (respectively, stationary). The windings are placed in the stator core at a special angular distance, which is equal to 120 electrical degrees. The beginnings and ends of these windings are led out into a distribution box, where they are secured to special terminals. As a rule, these conclusions are designated by the letter C - C1, C2 and up to C6, respectively. The windings can be connected in two types electrical diagrams- “star” and “triangle”. In a star circuit, the ends of the windings are connected to each other,and the beginnings of the windings are connected to the supply voltage. The triangle diagram is serial connection, that is, the beginning of one winding is connected to the end of each other winding, and so on.

   This is how a three-phase motor is connected, according to a triangle diagram

   
   

   The inside of the engine junction box, with the jumpers set for the delta connection

   Typically, in a distribution box, all contact outputs and their terminals are arranged in a staggered opposite order. That is, C6 is located opposite contact C1, and C4 is located opposite terminal C2.

   

   This is how the contacts in the junction box are arranged:

   
   

   This is how a three-phase motor is connected, according to the “star” circuit

   
   

   In real life, a distribution box with a star connection looks like this:

   By connecting a three-phase motor, respectively, to a three-phase network, a leak begins inside the stator windings at different times. electric current, which in turn creates a rotating magnetic field. This rotating magnetic field drives the motor rotor through magnetic induction, causing it to start rotating. If you connect a three-phase motor to a single-phase network, the machine will not have sufficient torque and it simply will not turn on.

   Naturally, it will not start if you launch it directly. But, there are ways in which connecting a “three-phase network” to the network is still possible. One of the simplest is to connect a phase-shifting capacitor as a third contact.

   

   This is how a three-phase motor is connected at home (single-phase network)

   A three-phase motor operating in a single-phase network has almost the same speed as when operating in a three-phase network. But, with such a connection, the power of the asynchronous motor is significantly reduced. This is due to insufficient power in the network itself (compared to three-phase). To say exactly how much power is lost during a single-phase connection, you need to know the connection diagram, operating conditions of the asynchronous motor, as well as the capacitance value of the capacitor. But, on average, each three-phase motor connected to a single-phase network can lose up to 30 and even 50% of its own power.

   Note that not all three-phase motors can behave normally in a single-phase network. Therefore, if you have connected it and are sure that the connection is correct, but it completely refuses to work, do not worry. With a high degree of probability, this means that something is wrong with the engine itself. Of course, the vast majority should work fine, regardless of the loss of power. Therefore, asynchronous motors with the indices “A” and “AOL”, “AO2” and “APN” have proven to be the most reliable in working with a single-phase network. All of them have a squirrel-cage rotor.

   As a rule, three-phase asynchronous motors have two categories according to rated voltage - this is operation in 220/127V and 380/220V networks. Lower voltage motors are used at low power levels and therefore have limited distribution. Thus, it is the 380/220V category that is more common. A voltage of 380V is used for a star connection, respectively, a voltage of 220V is used for a delta connection. In the engine passport and on its tag, all the main operating characteristics and values ​​are usually indicated, including operating voltage, network frequency, power factor, and also the connection diagram of the windings and the possibility of changing it are shown in symbolic drawings.

   

   This is what the tags on the housings of three-phase electric motors look like

   In Figure “A” the tag indicates that the windings can be connected in both circuits, as mentioned above. That is,You can connect both a “delta” voltage of 220V and a “star” voltage of 380V. Note that when connecting such a motor to a single-phase network, use a “delta” connection diagram, since when connected to a “star” the power loss will besignificantly higher.

   In Figure “B” the tag indicates that the engine uses a “star” connection. In this case, it is possible to switch on the “triangle” circuit. If you see such an icon, then know that there are only three outputs in the distribution box. Therefore, in order to make a “triangle” connection, you will need to get inside the engine, find and bring the remaining ends out. This is not so easy to do, so be extremely careful.

   Important point! If the engine tag indicates the operating voltage as 220/127V, be aware that when connecting to a single-phase network with an operating voltage of 220V, it can only be used with a “star” circuit and nothing more. If you try to connect a motor with a delta circuit to a 220V network, it will simply burn out.

   How to understand the beginnings and ends of the windings?

   One of the most confusing difficulties when connecting a three-phase motor to a household network is the confusion that arises with the wires that go into the junction box. Moreover, in some cases the box may be missing, and you will have to figure out which wire is where and on your own.

   The simplest case is the one in which the windings are connected in a “delta” circuit at an operating voltage of the engine of 380/220V. So, you only need to connect the current-carrying wires from the network by connecting the working and starting capacitors in the junction box to the terminals, according to the starting diagram. When the motor connection circuit is closed to star, but it is possible to switch it to delta, you need to take advantage of this by changing the circuit using contact jumpers.

   Now, as for determining the beginning and ends of all windings. It’s quite difficult when there are simply 6 wires sticking out in the junction box without any markings. In this case, it is difficult to understand which of the winding wires is the beginning and which is the end. Therefore, you will have to work a little harder and solve this problem. Before doing anything to the engine, check the Internet for the brand of the engine. Perhaps there are some documents on the network that can decipher the existing wiring. But, if no useful information was found, we proceed as follows

   We identify pairs of wires that are connected to the same winding;

   And we determine which of the conclusions is the beginning and which is the end.

   The determination of pairs of wires is carried out by “diagnosis” using a tester (the resistance measurement mode is set). If you don’t have such a device at hand, you can use the “old-fashioned” method and determine the identity of the ends of the windings using a light bulb and battery. If the light comes on (or the device shows the presence of resistance), this means that the two wires belong to the same winding.Thus, the remaining pairs of winding terminals are determined (the figure below shows this in the diagram).

   

   In the second task, you have to find out which of the conclusions is the beginning and which is the end. To do this, we will need to take a battery and a dial voltmeter (an electronic device will not be suitable for this). And then, we determine the beginnings and ends of the windings according to the diagram below.

   

   So, the battery is connected to the ends of one winding (let it beA, as in the figure), and to the ends of the windingINLet's connect the existing voltmeter. When the contacts are broken by the battery wire on the windingA, voltmeter needle onIN, must deviate in one of the directions. Remember which one, and do the same action on the windingWITHby connecting a voltmeter to it. Now, make sure that the voltmeter needle is on the windingWITHdeviated in the same direction as on the windingIN. This can be achieved by changing the polarity (switching endsC1 And C2). The winding is checked in the same wayA. Then, the battery will be connected toWITH or IN, and the voltmeter, respectively, toA.

   Thus, after “testing” all the windings, you should get some pattern. By breaking the battery contacts on any winding, the other two should show a deviation of the voltmeter needle in the same direction (this indicates the same polarity). After that, all that remains is to make marks on the terminals (starts) on one side (A1, B1 and C1), and the terminals (ends) on the other side A2, B2 and C2. At the final stage, connect the ends in the appropriate star or triangle patterns.

   How to remove the missing ends of the winding?

   This case is perhaps one of the most difficult. Thus, a motor connected in a “star” does not switch into a “delta”. In practice, when you open the junction box, you will see only three terminals (C1, C2 and C3). The remaining three (C4, C5 and C6) will have to be removed from inside the engine. The figure below clearly shows just such a case.

   

   Electric motor tag with the case in question

   
   

   This is what the inside of the terminal box will look like

   First, it is necessary to disassemble the engine to provide free access to the stator. To do this, you need to remove the end cover of the engine, which is held on by bolts, and remove its moving part - the rotor. Now, you need to find the soldering point of the remaining ends of the windings and clean it of insulation. Afterwards, disconnect the ends of the leads and solder pre-prepared stranded wires in flexible insulation to them. Insulate the soldering area additionally, and secure the wires with a strong thread to the stator windings. Ultimately, additional soldered wires are led out into the junction box.

   Now, you need to determine the beginnings and ends of the windings in the above-mentioned way, and designate all the available terminals C1, C2 and so on. After identifying all the wires, you can safely make a delta connection. Please note that such actions require certain experience and skills. In words, there is nothing complicated about this, but in fact, you can get confused in the soldered wires inside the stator and short-circuit the windings (for example). Therefore, if there is no special need for a triangle connection, it is better to leave the connection as is, that is, a “star”.

   

   Three-phase motor stator

   
   

   
   

   Soldering additional wires

   
   

   
   

   In this method, the wires are tightly screwed

   
   

   
   

   Output of conductors to the junction box

   
   

   
   

   Connecting conductors in a triangle pattern

   
   

   Schemes that are used when connecting a three-phase motor to a household network

   Triangle pattern.

   This scheme is the most appropriate and suitable for a household network, since output power three-phase motor in in this case will be slightly greater than with other schemes. Thus, the power of a “triangular” connection can be 70% of the rated value. engine power. In the distribution box it looks like this: two contacts are connected to the network, and the third is connected to the working capacitor Cp, then to any of the network contacts.

   

   This is how the diagram is depicted on paper

   And this is how it looks in practice

   
   

   Start-up

   Starting a three-phase motor at idle is possible using a run capacitor. But, if there is even a slight load on it, it may not start, or it may turn on and operate at low, insufficient speeds. Therefore, in such cases, additional equipment is used, namely the starting capacitor Sp. Calculations for determining the required capacitor capacity can be found below. For reference, such capacitors (in other cases it may be a group of capacitors) serve only to start the engine. Consequently, their operating time is very short - usually milliseconds, but can reach up to 2 seconds. In such a short period, the engine must have time to gain the necessary power.

   

   Circuit with starting capacitor Sp

   For more convenient operation of the engine, a switch can be added to the start-up and operation circuit. It works according to simple principle, in which one pair of contacts closes when the “Start” button is pressed. The entire circuit operates in this mode until the “Stop” button is pressed and the contacts open.

   

   Switch made in the USSR

   Application of reverse

   Rotation of the rotor in one direction or another depends on which phase the third winding is connected to.

   

   Reversible circuit

   Therefore, by connecting an additional capacitor with a switch (toggle switch) to the third winding, which is connected to the contacts of the first and second windings, we can change the direction of rotation of the rotor of a three-phase electric motor. Below, a diagram using all three of the above methods is clearly demonstrated, which will help make more convenient work with three-phase motor.

   

   Connection with star circuit

   This circuit is used when connecting “three-phase circuits” to a household network if their windings operate at a voltage of 220/127V.

   

   Connecting a three-phase electric motor with a star

   
   

   Calculation of the required capacitor capacities. So, the calculation of the capacity of the working capacitors is made based on the motor connection diagram and many other parameters. In the case of a star connection, the calculation is carried out as follows:

   Wed=2800∙I/U;

   Connecting the windings with a triangle, calculate the working capacitance as follows:

   Cp=4800∙I/U;

   Here, the working capacitance of the capacitor is denoted Cp and measured in μF, andIAndU– current and voltage, respectively. At the same timeU= 220V, otherwise we calculate it using the expression:

   I=P/(1.73∙U∙n∙cosϕ);

   P– indicates engine power;

   N – efficiency of “three-phase”;

   Cosϕ – power factor;

   1.73 – shows the relationship between linear and phase current.

   The efficiency and power factor values ​​can be found on the electric motor label. As a rule, these values ​​approximately fluctuate between 0.8-0.9.

   Practice shows that the capacitance value of working capacitors can be calculated using the equationC=70∙ Pn; where Rn is the rated power. This formula is consistent when connecting the windings to a “triangle”, and according to it, for every 100 W you will need about 7 µF of capacitance. The stable operation of the electric motor depends on how correctly the capacitor is selected. If the capacity is selected slightly higher than necessary, the engine will experience overheating. If the starting capacityturned out to be less than necessary, the engine power will be somewhat underestimated. Capacitors can be selected using the selection method. So, starting with small capacitors, move on to more powerful ones. optimal choice. If it is possible to measure the current in the network and on the working capacitor, then it is possible to select the most accurate capacitor. This measurement must be carried out in engine operating mode.

   The starting capacity is calculated based on the requirement to create sufficient starting torque. Do not confuse the capacity of the starting capacitor with the size of the starting capacitance. For example, in the diagrams above, the starting capacitance is the sum of two capacitances Cp and Sp.

   If the electric motor is used at idle speed, then the working capacitance can be taken as the starting capacitance, despite the fact that the starting capacitor is no longer required. In such cases, the scheme is greatly simplified and cheaper.Such measures will help turn off the load, with the ability to quickly and conveniently change the position of the engine, for example, to loosen the belt drive, or make a pressure roller for it.

   

   An example of a V-belt transmission of a walk-behind tractor

   Starting the engine requires additional capacity Sp, which is required only for starting. If you increase the switch-off capacitance, this will lead to an increase in the starting torque, and at a certain value the starting torque will reach a peak value. But, with a further increase in capacity, the starting torque will only fall, and this must be taken into account.

   Based on all calculations and conditions for starting an electric motor under a load that is close to the rated load, the value of the starting capacitance should exceed the working capacity by 2 or even 3 times. For example, if the capacitance on the working capacitor is 80 µF, then the starting capacitor will have this capacitance of 80-160 µF. This will give a total starting capacitance (which, as mentioned, is the sum of Cp and Cp) of 160-240 µF. However, if the load during startup is insignificant, the capacitance of the starting capacitor will be slightly smaller, or even completely absent. The capacitors that work to start the engine actually work for milliseconds, so they last a long time, and, as a rule, budget models are quite sufficient.

   A much better option is to use not one capacitor, but a group combined into a capacitor bridge. This is more convenient in the sense that by connecting a group, you can more accurately adjust the required capacitance by disconnecting or connecting capacitors. Small capacitors forming a bridge are connected in parallel because with this connection the capacitances are coordinated: Ct = C1 +C2 +C3 +…+Sn.

   

   This is what a parallel connection looks like

   Metallized paper capacitors serve as working capacitors, and film capacitors such as MBGO, K78-17, BGT, etc. are also excellent. The permissible voltage must exceed the mains voltage when the electric motor is operating by at least 1.5-2 times.

   

   Thus, connecting a three-phase motor to a single-phase network requires careful mathematical analysis and some experience with electrical equipment.

   Something more about electrics:

   Content:

   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. There is no need to add any starting devices to the connection diagram, 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, electrical 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. Star circuit provides more soft start unit, however, the engine power drops by about 30% of the nominal. 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 negative impact for wire insulation. The insulation may be broken and the motor 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

   A combined connection diagram known as “star-delta” is used relatively rarely. It allows for a smooth start with a star circuit, and during the main operation a triangle is turned on, providing maximum power 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. Simultaneous activation of the second and third starters is strictly prohibited. This will lead to short circuit between the phases connected to them. To prevent such situations, an interlock is installed between these starters. When one MP turns on, the contacts of the other open.

   The entire system operates according to the following principle: simultaneously with MP-1 being turned on, MP-3, connected by a star, is turned 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 a 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, the magnetic starter is equipped with another 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.

   In this way, 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.