Independently connecting a three-phase motor to a single-phase network is difficult, but doable. Three-phase motor in a single-phase network. Three-phase motor connection diagram

One of the reasons for connection three phase motor to a single-phase circuit is that the supply of electrical energy to industrial facilities and for domestic needs is radically different.

For industrial production, electrical enterprises manufacture electric motors with a three-phase power system, and to start the motor you need to have 3 phases.

What should you do if you purchased motors for industrial production, but need to connect them to a home outlet? Some skilled specialists, with the help of simple electrical diagrams, adapt the electric motor to single-phase network.

Winding connection diagram

To figure it out, a person who has encountered a similar problem for the first time needs to know how a three-phase motor works. If you open the connection cover, you can see the block and wires connected to the terminals, their number will be 6.

A three-phase electric motor has three windings and, accordingly, 6 terminals, they have a beginning and an end, and are connected in electrical configurations called “star and delta”.

This is interesting, but in most cases the standard switching is formed into a “star”, since the connection into a “delta” leads to a loss of power, but the engine speed increases. It happens that the wires are in an arbitrary position and are not connected to the connectors or there is no terminal at all. In this case, you need to use a tester or ohmmeter.

You need to ring each wire and find a pair, these will be the three windings of the motor. Next, we connect it into a “star” configuration as follows: beginning-end-beginning. We clamp three wires under one terminal. There should be three outputs left, and further switching will occur to them.

Important to know: in a household network there is one phase system supply or – “phase and zero”. This configuration must be used to connect the motor. First, we connect one wire from the electric motor to any network wire, then, to the second end of the winding, we connect the network wire and one end of the capacitor unit there.

The last wire from the motor and the unconnected contact of the set of capacitors remain free, we connect them and the circuit for starting a three-phase motor into a single-phase network is ready. They can be represented graphically as follows:

A, B, C - lines of a 3-phase circuit.
F and O – phase and zero.
C – capacitor.

In industrial production, a 3-phase voltage supply system is used. According to PUE standards, all network buses are marked with letter values and have the corresponding color:

A – yellow.

B – green.

C – red.

It is noteworthy that regardless of the location of the phases, in, bus “B”, with green, should always be in the middle. Attention! The interphase voltage is measured by a special device that has passed state testing and is carried out by a worker who has the appropriate tolerance group. Ideally, the phase-to-phase voltage is – 380 volts.

Electric motor device

Most often, we come across electric motors with a three-phase asynchronous operating circuit. What is the engine? This is a shaft on which a squirrel-cage rotor is pressed, at the edges of which there are plain bearings.

The stator is made of transformer steel, with high magnetic permeability, cylindrical in shape with longitudinal grooves for laying wires and a surface insulating layer.

By special technology, the winding wires are laid in the stator channels and insulated from the housing. The symbiosis of stator and rotor is called an asynchronous electric motor.

How to calculate capacitor capacity

To start a 3-phase motor from a household network, it is necessary to perform some manipulations with capacitor blocks. To start an electric motor without a “load”, you need to select the capacitor capacity based on the formula 7-10 mF per 100 W of motor power.

If you look closely at the side of the electric motor, you will find its passport, where the power of the unit is indicated. For example: if the motor has a power of 0.5 kW, then the capacitor capacity should be 35 - 50 mF.

It should be noted that only “permanent” capacitors are used, and in no case “electrolytic”. Pay attention to the inscriptions that are located on the side of the case; they indicate the capacitance of the capacitor, measured in microfarads, and the voltage for which they are designed.

The block of starting capacitors is assembled exactly according to this formula. Using the engine as a power unit: connecting it to a water pump or using it as a circular saw, requires an additional block of capacitors. This design is called working capacitor units.

They start the engine and, by connecting in series or parallel, select the capacitance of the capacitor so that the sound from the electric motor comes from the quietest, but there is more exact method container selections.

To accurately select a capacitor, you need to have a device called a capacitor store. By experimenting with different connection combinations, we achieve same value voltage between all three windings. Then they read the capacitance and select the desired capacitor.

Required materials

In the process of connecting a 3-phase motor to a single-phase network, you will need some materials and devices:

A set of capacitors with different ratings or a “store of capacitors”.
Electrical wires, type PV-2.5.
Voltmeter or tester.
3 position switch.

Basic tools should be at hand: voltage indicator, dielectric pliers, insulating tape, fasteners.

Parallel and series connection of capacitors

The capacitor is an electronic component and with different switching combinations, its nominal values may change.

Parallel connection:

Serial connection:

It should be noted that when parallel connection The capacitances of the capacitors will add up, but the voltage will decrease, and vice versa, the series version gives an increase in voltage and a decrease in capacitance.

In conclusion, we can say that there are no hopeless situations, you just need to put in a little effort and the result will not be long in coming. Electrical engineering is an educational and useful science.

How to connect a three-phase motor to a single-phase network, see instructions in the following video:

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” bending of the supply lines) and from short circuit(“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:

What's new in the VK group? SamElectric.ru ?

Subscribe and read the article further:

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

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

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

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

Since motors usually have a high starting current, motor 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 with 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:

Solid State Relays ( solid state relay) – in them the power elements are thyristors (triacs), which are controlled by an input signal from a button or from a controller. There are both single-phase and three-phase. .
Soft starters (soft starters, devices soft start) – improved solid bodies. 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!

Three-phase electric motors have higher efficiency than single-phase 220 volt ones. If you have a 380-volt input in your house or garage, then be sure to buy a compressor or machine with a three-phase electric motor. This will ensure more stable and economical operation of the devices. To start the motor, you will not need various starting devices and windings, because a rotating magnetic field appears in the stator immediately after connecting to a 380-volt power supply.

Selecting a motor switching circuit

3-phase connection diagrams motors using magnetic starters I described in detail in previous articles: “” and ““.

It is also possible to connect a three-phase motor to a 220 Volt network using capacitors. But there will be a significant drop in the power and efficiency of its operation.

In the stator of an asynchronous motor at 380 V there are three separate windings, which are connected to each other in a triangle or star and 3 opposite phases are connected to the three beams or vertices.

You must consider that when connected with a star, the start will be smooth, but in order to achieve full power it is necessary to connect the motor with a triangle. In this case, the power will increase by 1.5 times, but the current when starting powerful or medium-sized motors will be very high, and can even damage the insulation of the windings.

Before connecting electric motor, read its characteristics in the passport and on the nameplate. This is especially important when connecting 3-phase electric motors made in Western Europe, which are designed to operate from a mains voltage of 400/690. An example of such a nameplate is in the picture below. Such motors are connected only in a “delta” configuration to our electrical network. But many installers connect them in the same way as domestic ones in a “star” and the electric motors burn out, especially quickly under load.

In practice all electric motors are domestically produced for 380 Volts they are connected by a star. Example in the picture. In very rare cases, in production, in order to squeeze out all the power, a combined star-delta connection circuit is used. You will learn about this in detail at the very end of the article.

Star-delta motor connection diagram

In some There are only 3 of our electric motors. the end of a stator with windings - this means that a star is already assembled inside the engine. All you have to do is connect 3 phases to them. And in order to assemble a star, both ends of each winding or 6 terminals are needed.

The ends of the windings in the diagrams are numbered from left to right. Numbers 4, 5 and 6 are connected to 3 phases A-B-C from the mains.

When a three-phase electric motor is connected by a star, the beginnings of its stator windings are connected together at one point, and 3 phases of 380 Volt power supply are connected to the ends of the windings.

When connected by a triangle The stator windings are connected to each other in series. In practice, it is necessary to connect the end of one winding to the beginning of the next. 3 power phases are connected to the three points connecting them to each other.

Star-delta connection

To connect the motor according to a rather rare star scheme at launch, with subsequent transfer for operation in operating mode to a triangle scheme. This way we can squeeze out maximum power, but it turns out quite complex circuit without the possibility of reversing or changing the direction of rotation.

For the circuit to operate, 3 starters are required. The first K1 is connected to the power supply on one side, and on the other - the ends of the stator windings. Their origins are connected to K2 and K3. From starter K2, the beginning of the windings are connected respectively to other phases according to a triangle diagram. When K3 is turned on, all 3 phases are short-circuited with each other and a star operating circuit is obtained.

Attention, magnetic starters K2 and K3 should not be turned on at the same time, otherwise an emergency shutdown of the circuit breaker will occur due to the occurrence of an interphase short circuit. Therefore, an electrical interlock is made between them - when one of them is turned on, the block contacts open the control circuit of the other.

The scheme works as follows. When the starter K1 is turned on, the time relay turns on K3 and the engine starts according to the star circuit. After a specified period of time has elapsed, sufficient for the engine to fully start, the time relay turns off the starter K3 and turns on K2. The motor switches to operating the windings in a triangle pattern.

Shutdown occurs starter K1. At relaunch everything repeats itself again.

Related materials:
1. Sergey:
  
  Good afternoon. A single-phase motor from an old Soviet washing machine rotates in different sides(no system). The engine has 4 terminals (2 thick, 2 thin. I connected it through a switch with a third outgoing contact. After starting, the engine runs stably (does not heat up). I can’t understand why it rotates in different directions.
  1. Experienced Electrician:
    
    Sergey, hello. The whole point is that single-phase motor no matter where you turn. The field is not circular (as in three-phase network), and pulsating 1/50 of a second at the “plus” phase relative to zero, and 1/50 - “minus”. It's like spinning a battery a hundred times a second. Only after the engine has spun up does it maintain its rotation. In the old washing machine a strict direction of rotation may not have been provided for. If we assume this, then at the moment of launch on the “positive” half-wave of the sine wave it starts in one direction, and with a negative half-wave - in the other. It makes sense to try to set the current bias of the starting winding through the capacitor. The current in the starting winding will begin to lead the voltage and will set the rotation vector. As I understand it, you now have two wires (phase and neutral) going to the motor from the working winding. One of the wires of the starting winding is connected to the phase (conditionally, just actually tightly with one of the wires), and the second wire goes to zero through the third non-latching contact (also conditionally, in fact, to the other of the network wires). So try installing a capacitor with a capacity of 5 to 20 µF between the wire and the non-locking contact and observe the result. In theory, you should rigidly set this direction magnetic field. In fact, this is a capacitor motor (single-phase asynchronous, all capacitor motors) and here only three points are possible: either the capacitor always works and then you need to select the capacitance, or it sets the rotation, or the start occurs without it, but in any direction.
2. Galina:
  
  Hello
3. Sergey:
  
  Good afternoon. I assembled the circuit, as you said, set the capacitor to 10 uF, the engine now starts steadily only in one direction. The direction of rotation can only be changed if the ends of the starting winding are swapped. Therefore, the theory worked flawlessly in practice. Thank you very much for the advice.
4. Galina:
  
  Thanks for the answer, I bought a CNC milling machine in China, a 3-phase motor at 220, and here (I live in Argentina) the network is single-phase at 220, or 3-phase at 380
  I consulted with local specialists - they say that I need to change the engine, but I really don’t want to. Help me with advice on how to connect the machine.
5. Galina:
  
  Hello! Thank you very much for the information! A couple of days later the machine arrives. I’ll see what’s really there, and not just on paper, and I suppose I’ll still have questions for you. Thanks again!
6. Hello! Is this option possible: draw a 3-phase 380v line and install a step-down transformer to have 3-phase 220v? The machine has 4 motors, the main power is 5.5 kw. If this is possible, then what kind of solution is needed?
7. Yura:
  
  Hello!
  Please tell me - is it possible to power an asynchronous three-phase electric motor of 3.5 kW from 12-volt batteries? For example, using three household inverters 12-220 with a pure sine wave.
  1. Experienced Electrician:
    
    Yuri, hello. Purely theoretically this is possible, but in practice you will encounter the fact that when you start asynchronous motor creates a large starting current and you will have to buy an appropriate inverter. The second point is complete phasing (a frequency shift of three inverters by an angle of 120° relative to each other), which cannot be done unless provided by the manufacturer, therefore you will not be able to achieve manual synchronization at a frequency of 50 Hz (50 times per second). Plus the engine power is quite large. Based on this, I would recommend that you pay attention to the “battery-inverter-frequency converter” combination. The frequency converter is capable of producing the required synchronized phases of the voltage that will be at the input. Almost all engines have the ability to switch on 220 and 380 volts. Therefore, having received the desired voltage and received the desired connection diagram, you can use a frequency converter to make a smooth start, avoiding large starting currents.
    1. Yura:
      
      I don’t understand a little - my inverters are 1.5 kW, that is, do you recommend using a battery of batteries and one such inverter in conjunction with a frequency converter? how will he pull it out???
      or do you recommend using an inverter of appropriate power - 3.5 kW? then the need for a frequency converter is unclear...
      1. Experienced Electrician:
        
        I'll try to explain.
        1. Study information about three-phase current. Three phases are not three voltages at 220 volts. Each phase has a frequency of 50 hertz, that is, it changes its value from plus to minus 100 times per second. In order for an asynchronous motor to start working, it needs a circular field. In this field, three phases are shifted relative to each other by an angle of 120°. In other words, phase A reaches its peak, after 1/3 of the time this peak reaches phase B, after 2/3 of the time phase C, then the process repeats. If the change of peaks of the sine wave occurs chaotically, the engine will not start to rotate, it will simply hum. Therefore, either your inverters must be phased or there is no point in them.
        2. Study information about asynchronous motors. The starting current reaches values of 3-8 times the rated one. Therefore, if we take an approximate value of 5 amperes, then when starting the engine the current can be 15-40 amperes or 3.3 - 8.8 kW per phase. An inverter of less power will burn out immediately, which means you need to take the inverter at maximum power, even if it lasts only half a second or even less, and this will be an expensive pleasure.
        3. Study the information on the frequency converter. The frequency generator can provide both a smooth start and the conversion of one phase into three. A smooth start will allow you to avoid large starting currents (and the purchase of a heavy-duty inverter), and converting one phase into three will allow you to avoid the expensive procedure for phasing inverters (if they are not initially adapted to this, then you definitely cannot do this on your own and you will have to find a good electronics engineer ).
        
        I advise you to take a powerful inverter in conjunction with frequency converter if you really need to get full power from your engine.
8. Valery:
  
  Thank you very much for everything. For your patience, re-explaining everything that has been repeated many times in other comments. I re-read all this, in some places more than once. I read a lot of information. on various sites for converting 3 ph.d. to the 220v network. (from the moment my assistants set fire to the electric motor of a small homemade machine). But I learned a lot more from you, features that I didn’t know about and hadn’t encountered before. Today, after using a search engine, I went to this site, re-read almost all the comments and was amazed at the usefulness and accessibility of the information.
  Regarding my questions. Here's the thing. On my old machine (formerly, my father’s) there is the same old electric. dv. But it has lost power and is “beating” from the housing (probably the burnt winding is shorting). There is no tag, a classic triangle, no terminals - it was probably altered at some point. They offer me a new engine, Polish, it seems, with the given options on the tag. By the way, there is 50 Hz for each option. And after sending the comment, I carefully looked at all 4 options given and understood why the current is higher in the triangle.
  I will take it and turn it on in 220 according to option 1 in a triangle through capacitors with 70% power. The gear ratio can be increased, but the machine could have more power.
  Yes, besides the classic triangle and star, there are other options for connecting 380 to a 220 network. And there is (you know) a simpler way to determine the beginning of the windings using a battery and a switch.
9. Valery:
  
  Today I received a photo of the email nameplate. dv. You're right. There are 3 and 4 options 60Hz. And now it is clear that it could not be otherwise and that at 50Hz - a maximum of 3000 rpm. Another question. How reliably and for a long time do electrolytic capacitors work with one turn on through a powerful diode as a working one? con.?
10. Alexander:
  
  Hello, can you tell me how to attach a file with a photo to ask a question?
11. Sergey:
  
  Good afternoon.
  A little history. On a water heating boiler (a large industrial one - for heating an enterprise) I use two VILO circulation pumps with a German electric motor of 7.5 kW each. When we received both pumps, we connected them in a triangle. We worked for a week (everything was fine). The hot water boiler automation adjusters arrived and told us that the connection diagram for both engines should be switched to a “star” one. We worked for a week and one after another both engines burned out. Tell me, can reconnecting from delta to star be the cause of burnt-out German engines? Thank you.
12. Alexander:
  
  Hello, Experienced Electrician) Tell me your opinion about this motor connection diagram, I came across it on one forum
  
  “Partial counter star, with working capacitors in two windings”
  Link to the diagram and diagram describing the operating principle of such a circuit - https://1drv.ms/f/s!AsqtKLfAMo-VgzgHOledCBOrSua9
  
  It is said that this motor connection diagram was developed for a two-phase network and best results shows when connected to 2 phases. But in a single-phase 220V network it is used because it has best characteristics than the classic ones: star and triangle.
  What can you say about this option for connecting a three-phase motor to a 220V network? Has the right to life? I want to try it on a homemade lawn mower.
  1. Experienced Electrician:
    
    Alexander, hello. Well, what can I tell you? Firstly, the literacy of both the presentation of the material and the literacy of the language of the article are incredibly impressive. Secondly, for some reason very few people know about this method. Thirdly, if this method were effective and better, it would have long been included in educational literature. Fourthly, there is no theoretical explanation of this method anywhere. Fifthly, there are proportions, but there are no formulas for calculating the capacitance (that is, conditionally, you can take 1000 μF or 0.1 μF as a reference point - the main thing is to maintain the proportions???). Sixth, the topic was not written by an electrician. Seventh, I personally can’t wrap my head around the first winding, which is connected backwards and through a capacitor - all this makes me think that someone came up with something and wants to pass something off as an invention that supposedly works better for two-phase networks. Theoretically, this can be allowed, but there is little theoretical data for reflection. In theory, if you somehow obtain one or the other half-wave from one or the other phase, but the circuit should then have a different form (when using two phases, it is definitely a star, but using a neutral wire and two capacitors to it or from him... and again, it turns out to be garbage. In general, experiment, and then write back - I’m interested in what happens, but I personally don’t want to conduct such experiments, or if they give me an engine and tell me that it can be killed, then I’ll experiment. I have already written about the selection of capacitors both in the comments and in the links to the article “Capacitor for a three-phase motor” on this site and on the site of the “hereditary master” - there is no need to thoughtlessly install a capacitor according to the formula. You need to take into account the motor load and select a capacitor according to the working one. current in a specific operating cycle.
    1. Alexander:
      
      Thanks for the answer.
      On the forum where I came across this, several people tried this scheme on their engines (including the person who posted it) and they say that they are very pleased with the results of its work. Regarding the competence of the person who proposed it, as I understand it, he seems to be on topic (and the moderator of that forum), the diagram is not his, as he said, he found it in some old books on engines. But that’s it, I have an engine suitable for experiments , I'll try it on it.
      Regarding the formulas, I just didn’t present all the entries from that thread, a lot of things are written there, I added more from the main one if you’re interested, look at the same link.
      1. Experienced Electrician:
        
        Alexander, experiment and write the result. I can say one thing - I am an inquisitive comrade, but I have not heard about such a scheme either from textbooks or from the lips of many authoritative senior comrades. My neighbor, an even more inquisitive electronics engineer with a focus on electricity, hasn’t heard either. One of these days I'll try to ask him.
        Competence is such a... questionable thing when it comes to the Internet. You never know who is sitting on the other side of the screen and what he is like, and whether he has the diploma he is talking about hanging on his wall, or whether he knows any of the subjects that are indicated on the diploma. I’m not trying to criticize the person at all, I’m just trying to say that you don’t always have to believe one hundred percent of the person on the other side of the screen. If something happens, you won’t be able to push him to the wall for harmful advice, and this gives rise to complete irresponsibility.
        There is another “dark” point - forums are often created in order to generate income and all means are good for this, as an option, to propose some kind of tricky topic, promote it, even if it is not entirely working, but unique, that is, only on his website. And “several” people, this could just be a moderator, talk to themselves under several nicknames to promote the topic. Again, I don’t criticize that particular person, but I’ve already seen this type of black PR on the forum.
        Now let's touch on old books and the Soviet Union. There were few fools in the USSR (among those who were involved in development) and if the scheme had proven itself, it would probably have been included in the textbooks I studied from, at least for mention and for general development that such an option is possible. And our teachers were not fools, and on electrical machines the guy generally gave a lot of interesting information beyond the curriculum, but he had never heard of this scheme.
        Conclusion, I don’t believe that this circuit is better (it’s possible that it’s better for two phases, but you still need to look at it and draw the “correct” circuit so that the effect of currents and their displacement is clear), although I admit that it works. There are plenty of such options, when someone has cleverly done something, but it works :) As a rule, the person himself does not understand what he has done and does not delve into the essence, but is trying hard to modernize something.
        Well, one more conclusion: if this scheme were really better, then it would at least be known, but I only learned about it from you, with all my insatiable curiosity.
        In general, I’m waiting for your opinions and results, and then you’ll see, I’ll conduct an experiment with my neighbor on a practical and theoretical basis.
    2. Alexander:
      
      Hello. You are right) I immediately connected it with a triangle in the workshop, although I didn’t mow it, and I can only evaluate the engine’s operation visually, by ear and by my own feelings) since measuring the same currents on different schemes I have nothing. I am far from a serious electrician, I can basically twist something together using a ready-made circuit with already known parts, ring it and check it with a 220-380 voltmeter). In the description of the circuit it was said that its advantage is in lower engine power losses and in its operating mode close to the nominal one. I will say that it was easier for me to brake the shaft on the engine using a triangle than using this diagram. Yes, and he rotated on it, I would say faster. It works for me on this engine and I liked how the engine itself works, so I didn’t bother collecting and stuffing two circuits one by one into one box and checking how it works. For now, I stuffed the capacitors into a temporary box to see how it would work (maybe I’ll have to add or remove something else), and then I thought I’d arrange the whole thing beautifully and compactly with some kind of protection. I’m wondering where I came across this diagram, people used it to connect low-power motors and no one wrote about connecting at least 1.5 or 2 kW. As far as I understand, for them you need a lot of capacitors (compared to a triangle), and there should also be ones for high voltage. I’m here and decided to ask around about this scheme, since I really hadn’t heard about it anywhere before and thought maybe the experts would tell me from the point of view of theory and science whether it should work or not.
      I can say for sure that the engine is spinning and, as for me, it’s very good, but what should be there with currents, voltages and what should be behind or ahead according to this scheme and I would like to hear from someone who knows. Maybe this scheme is just a scam? and it is no different from the same triangle (except for the extra wires and capacitors. At my house now there is no need for powerful motors, so I could try connecting them through capacitors according to this circuit and see how they would work. Previously, I had both a circular saw and a jointer , so they had motors of about 2.5 kW connected in a triangle, they stalled if a little more load give it, as if they had no more than a kilowatt. Now it’s just all this in the workshop, which has 380. I’ll mow a couple more times, and if everything goes well, I’ll decorate my miracle mower correctly and post a photo, it might be useful to someone.
      
      Vladimir:
      
      Good evening, tell me how to change the direction of rotation of the shaft of a 380V synchronous electric motor connected from star to triangle.
There are several types of electric motors - three-phase and single-phase. The main difference between three-phase electric motors and single-phase ones is that they are more efficient. If you have a 380 V outlet at home, then it is best to buy equipment with a three-phase electric motor.
Using this type of engine will allow you to save on electricity and gain more power. Also you won't have to use various devices to start the engine, since thanks to a voltage of 380 V, a rotating magnetic field appears immediately after connecting to the electrical network.
380 volt electric motor wiring diagrams
If you don't have a 380V network, you can still connect three phase electric motor into a standard 220 V electrical network. To do this, you will need capacitors, which must be connected according to this diagram. But when connected to a regular power grid, you will observe a loss of power. You might want to read about this.
380 V electric motors are designed in such a way that they have three windings in the stator, which are connected like a triangle or star, and three different phases are connected to their tops.
You need to remember that using a star connection, your electric motor will not work at full power, but it will start smoothly. When using a triangle circuit, you will receive a power increase of one and a half times compared to a star, but with such a connection the chance of damaging the winding during startup increases.
Before using an electric motor, you must first become familiar with its characteristics. All necessary information can be found in the data sheet and on the engine nameplate. Particular attention should be paid to three-phase motors of Western European type, as they are designed to operate at a voltage of 400 or 690 volts. In order to connect such an electric motor to domestic networks, it is necessary to use only a triangle connection.
If you want to make a triangle circuit, then you need to connect the windings in series. You need to connect the end of one winding to the beginning of the next and then you need to connect three phases of the electrical network to the three connection points.
Connecting a star-delta circuit.
Thanks to this scheme we can get maximum power, but we will not be able to change the direction of rotation. In order for the circuit to work, three starters will be needed. The first (K1) is connected to power on one side, and the ends of the windings are connected to the other. Their origins are connected to K2 and K3. From the K2 starter, the windings are connected to other phases using a triangle connection. When K3 turns on, all three phases are short-circuited and, as a result, the electric motor operates in a star circuit.
It is important that K2 and K3 are not started at the same time, as this can lead to an emergency shutdown. This scheme works as follows. When K1 starts, the relay temporarily turns on K3 and the engine starts as a star. After starting the engine, K3 is turned off and K2 is started. And the electric motor starts working in a triangle pattern. Stopping work occurs by turning off K1.

We are going to look at how a three-phase motor is connected to a single-phase network and give recommendations on how to control the unit. More often than not, people want to vary the rotation speed or direction. How to do this? We described vaguely earlier how to connect a three-phase 230 volt motor, now let’s worry about the details.
Standard diagram for connecting a three-phase motor to a single-phase network
The process of connecting a three-phase motor to 230 volts is simple. Usually the branch carries a sine wave, the difference is 120 degrees. A uniform phase shift is formed, ensuring smooth rotation of the electromagnetic field of the stator. Effective value each wave is 230 volts. This will allow you to connect a three-phase motor to a household outlet. Circus trick: get three sine waves using one. The phase shift is 120 degrees.
In practice, this can be done with the help of special phase shifters. Not those used by high-frequency waveguide paths, but special filters formed by passive, less often active, elements. Fans of troubles prefer to use a real capacitor. If the motor windings are connected in a triangle, forming a single ring, we get phase shifts of 45 and 90 degrees, at least enough for unstable shaft operation:
Connection diagram for a three-phase motor using delta winding switching
1. One winding is supplied with the socket phase. The wires pick up the potential difference.
2. The second winding is powered by a capacitor. A phase shift of 90 degrees relative to the first is formed.
3. On the third, due to the applied voltages, an oscillation slightly similar to a sinusoid is formed with a shift of another 90 degrees.
In total, the third winding is 180 degrees out of phase from the first. Practice shows that the layout is enough to work normally. Of course, the engine sometimes “sticks”, gets very hot, power drops, and efficiency suffers. Users put up with it when connecting an asynchronous motor to a three-phase network is excluded.
From purely technical nuances, let us add: a diagram of the correct wiring layout is given on the device body. More often decorates inner side casing that hides the block, or is drawn nearby on the nameplate. Using the diagram as a guide, we will understand how to connect an electric motor with 6 wires (a pair for each winding). When the network is three-phase (often called 380 volts), the windings are connected in a star. A single point common to the coils is formed, where the neutral (conventional circuit electrical zero) is connected. Phases are supplied to the other ends. It turns out three - according to the number of windings.
It is clear how to handle a triangle for connecting a three-phase 230 volt motor. Additionally, we provide a picture depicting:
- Electrical connection diagram of the windings.
- A working capacitor that serves the purpose of creating the correct phase distribution.
- A starting capacitor that facilitates spin-up of the shaft at initial speeds. Subsequently, it is disconnected from the circuit with a button and discharged with a shunt resistor (for safety and to be ready for a new start cycle).
Connecting a three-phase 230 volt motor with a triangle
The picture shows: winding A is energized at 230 volts. At C it is supplied with a phase shift of 90 degrees. Due to the potential difference, the ends of winding B generate a voltage shifted by 90 degrees. The outlines are far from the sinusoid familiar to school physicists. The starting capacitor and shunt resistor have been omitted for simplicity. We believe the location is obvious from the above. Such a technique will at the very least allow you to achieve from the engine normal operation. Using the key, the starting capacitor is closed, performing a start, disconnected from the phase, and discharged by a shunt.
The time has come to say: the capacitance indicated by the drawing 100 µF is practically selected taking into account:
1. Shaft rotation speed.
2. Engine power.
3. Loads placed on the rotor.
You need to select a capacitor experimentally. According to our figure, the voltage of windings B and C will be the same. We remind you: the tester shows the actual value. The voltage phases will be different, the waveform of winding B is non-sinusoidal. The effective value shows: equal power is delivered to the shoulders. Provides less stable operation of the installation. The motor heats up less and is optimized Engine efficiency. Each winding is formed inductive reactance, which also affects the phase shift between voltage and current. This is why it is important to choose the correct capacitance value. Ideal engine operating conditions can be achieved.
Make the engine spin in reverse
Three phase voltage 380 volts
When connected to three phases, changing the direction of shaft rotation is ensured by correct signal switching. Special contactors are used (three pieces). 1 per phase. In our case, only one circuit is subject to switching. Moreover (guided by the guru’s statements) it is enough to swap any two wires. Whether it's power supply or where the capacitor connects. Let's check the rule before issuing instructions to readers. The results are demonstrated by the second figure, which schematically shows diagrams showing the phase distribution of the indicated case.
When making diagrams, we assumed: winding C is connected in series to a capacitor, which gives the voltage a positive phase increase. According to the vector diagram, to maintain balance, winding C must have a negative sign relative to the main voltage. On the other hand, the capacitor, coil B are connected in parallel. One branch provides a positive increase in voltage (capacitor), the other - in current. Similar to parallel oscillatory circuit, the branch currents flow almost in the opposite direction. Taking into account the above, we adopted the law of changing the sinusoid out of phase with respect to winding C.
The diagrams show: the maximums, according to the diagram, bypass the windings counterclockwise. The previous review showed a similar context: the rotation is in a different direction. It turns out that when the power polarity is changed, the shaft rotates in the opposite direction. We will not draw the distribution of magnetic fields; we consider it unnecessary to repeat ourselves.
More precisely, such things will allow us to calculate special computer programs. The explanation was given on the fingers. It turns out that the practitioners are right: by changing the polarity of the power supply, the direction of movement of the shaft will be reversed. Surely a similar statement is valid for the case of connecting a capacitor with a branch of another winding. For those hungry for detailed graphs, we recommend studying specialized software packages like the free Electronics Workbench. Enter any number in the application control points, trace the laws of changes in currents and voltages. Those who like to make fun of their brain will have the opportunity to view the spectrum of signals.

Take the trouble to correctly set the inductance of the windings. Of course, the load that prevents startup contributes to the influence. It is difficult to account for losses with such programs. Practitioners recommend avoiding focusing on the indicated sharpener and selecting capacitor values (empirically) experimentally. Thus, the exact connection diagram of a three-phase motor is determined by the design and intended purpose. Let's say lathe will differ from the bread crusher in its developing loads.
Three-phase motor starting capacitor
More often, a three-phase motor must be connected to a single-phase network using a starting capacitor. This aspect especially concerns powerful models, motors under significant load at the start. In this case, the intrinsic reactance increases, which will have to be compensated using capacitors. It’s easier to choose again experimentally. It is necessary to assemble a stand on which it is possible to “hot” switch on and exclude individual containers from the circuit.
Avoid helping the engine start with your hand, as “experienced” mechanics demonstrate. Just find the battery value at which the shaft rotates vigorously, and as it spins up, begin to remove capacitors from the circuit one by one. While there will be a set below which the engine does not rotate. The selected elements form the starting capacity. And the correctness of your choice must be monitored using a tester: the voltage in the arms of the phase-shifted windings (in our case C and B) should be the same. This means that approximately equal power is delivered.
Three-phase motor with starting capacitor
As for estimates and estimates, battery capacity increases with increasing power and speed. And if we talk about the load, it has a big impact at the start. When the shaft spins, in most cases small obstacles are overcome due to inertia. The more massive the shaft, the higher the chance that the engine will not “notice” the difficulty that has arisen.
Please note that an asynchronous motor is usually connected through a circuit breaker. A device that stops rotation when the current exceeds a certain value. This not only protects the local network plugs from burning out, but also saves the motor windings when the shaft is jammed. In this case, the current will increase sharply and the operation of the device will stop. The circuit breaker is also useful when selecting the required capacity rating. Eyewitnesses claim that if a 3-phase motor is connected to a single-phase network through capacitors that are too weak, the load increases sharply. If you have a powerful motor, this is very important, because even in normal mode, consumption exceeds the nominal by 3-4 times.
And a few words about how to estimate the starting current in advance. Let's say you need to connect a 230 asynchronous motor with a power of 4 kW. But this is for three phases. In the case of standard wiring, the current flows through each of them separately. For us, all this will add up. Therefore, we safely divide the power by the network voltage and get 18 A. It is clear that such a current is unlikely to be consumed without a load, but for stable operation When the engine is running at full speed, you need a protective circuit breaker of amazing power. As for a simple test run, a 16 ampere device will do just fine. And there is even a chance that the launch will take place without incident.
We hope readers now know how to connect a three-phase motor to home network at 230 volts. It remains to add to this that the capabilities of a standard apartment do not exceed, in terms of power delivery to the consumer, about 5 kW. This means that it is simply dangerous to turn on the engine described above at home. Please note that even grinders are rarely more powerful than 2 kW. At the same time, the engine is optimized for operation in a single-phase 220 volt network. Simply put, too powerful devices will not only cause the lights to flicker, but will most likely provoke other emergency situations. IN best case scenario will knock out the plugs, in the worst case, the wiring will catch fire.
With this we say “goodbye” and want to note: knowledge of theory is sometimes useful for practitioners. Especially when it comes to powerful technology that can cause considerable harm.