Connection diagram for a three-phase delta motor. Connecting the motor windings according to the star and delta circuits

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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.

On 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 to be a rather 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 predetermined interval 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. When you restart it, everything repeats again.

Related materials:

I also tried this option. Star connection. I start a 3 kilowatt engine using a 160 microfarad capacitor. And then I remove it from the network (if you do not remove it from the network, the capacitor begins to heat up). And the engine runs independently at quite good speeds. Is it possible to use it in this way? Is it not dangerous?

Novel:

Hello! There is a 1.5 kW Vesper Frequency Drive, which transforms from a single phase 220 volt network into 3 phases at the output with interphase 220V to power an asynchronous 1.1 kW. dv. 1500 rpm However, when the 220 volt network is turned off, it is necessary to power it from a direct current inverter, which uses the battery as a backup power source. The question is, is it possible to do this through an ABB changeover switch (i.e. manually switch to powering the Vesper from a direct current inverter) and will the direct current inverter not be damaged?

Experienced Electrician:

Roman, hello. To do this, you need to read the instructions or ask questions to the inverter manufacturer, namely, whether the inverter is capable of connecting to the load (or in other words, its overload capacity for a short time). If you don’t take risks, then it’s easier (when 220 volts disappear) to turn off the electric motor using an automatic switch or switch, turn on the power from the inverter with a changeover switch (thus powering the frequency switch) and then turn on the engine. Or make a scheme for uninterrupted operation - constantly supply mains voltage to the inverter, and take it from the inverter to the frequency converter. In the event of a power outage, the inverter remains in operation thanks to the battery and there is no interruption in the power supply.

Sergey:

Good afternoon. A single-phase motor from an old Soviet washing machine rotates in different directions every time it starts (there is 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 thing is that a single-phase motor does not care where it rotates. The field is not circular (as in a three-phase network), but pulsating for 1/50 of a second at the “plus” phase relative to zero, and 1/50 for the “minus” phase. It's like spinning a battery a hundred times a second. Only after the engine has spun up does it maintain its rotation. An old washing machine may not have had a strict direction of rotation. 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 another 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 the direction of the magnetic field with this. 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.
Galina:

Hello
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.
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.
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!
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?
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 starting, an asynchronous motor creates a large starting current and you will have to use 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. Learn 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 recommend getting a powerful inverter coupled with a frequency converter if you really need to get full power from your engine.

Valery:

Hello. Please tell me, is it possible to use this motor (imported) to be connected to our 220V network for a woodworking machine?
There are 4 options on the nameplate:
— 230, triangle, 1.5kw, 2820 /min., 5.7A, 81.3%
— 400, star, 1.5kw, 2800/min., 3.3A, 81.3%
— 265, triangle, 1.74kw, 3380/min, 5.7A, 84%
— 460, evezda, 1.74kw, 3380/min, 3.3A, 84%
Judging by this, this engine is very well suited for d.o. machine (according to option 1). There are probably 6 contacts in the box? Good (relatively) speed. 230V is confusing - how will it behave in a 220V network? Why is the maximum current according to options 1, 3?
Is it possible to use this motor for the machine and how to connect it to a 220V network?

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.
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.?
Alexander:

Hello, can you tell me how to attach a file with a photo to ask a question?
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.
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 shows the best results when connected to 2 phases. But in a single-phase 220V network it is used because it has better 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, well, or if they give me an engine and say - 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 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. I'll try to ask him one of these days.
      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 was 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 performance visually, by ear and by my own feelings) since I have nothing with which to measure the same currents on different circuits. I’m far from a serious electrician, I can basically use a ready-made circuit with already known parts to twist something into a bunch, 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 happen with currents, voltages and what should lag behind or lead 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 have engines of about 2.5 kW connected in a triangle, they stalled if you put a little more load on them, as if they had no more than a kilowatt. Now it’s just all this in the workshop, which has 380. I’ll mow it a couple or three more times, and If everything goes well, I’ll design 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.

The entire load in three-phase circuits is connected according to a star or delta circuit. Depending on the type of electricity consumers and the voltage in the electrical network, the appropriate option is selected. If we talk about electric motors, then the choice of winding connection option determines the possibility of its operation in a specific network with nominal characteristics. In the article we will look at the difference between a star and a triangle in an electric motor, what they influence and what is the principle of connecting wires in the terminal block of a three-phase motor.

Theory

As already mentioned, star and delta connection diagrams are typical not only for an electric motor, but also for transformer windings, heating elements (for example, electric boiler heating elements) and other loads.

To understand why these connection diagrams for the elements of a three-phase circuit are called that way, you need to modify them somewhat.

In a “star”, the load of each phase is connected to each other by one of the terminals, this is called the neutral point. In a “triangle”, each of the load terminals is connected to opposite phases.

Let's consider this issue using the example of connecting the windings of a three-phase transformer or a three-phase motor (in this context it does not matter).

In this figure, the differences are more noticeable; in a “star,” the beginnings of the windings are connected to the phase conductors, and the ends are connected together; in most cases, the neutral wire from the supply generator or transformer is connected to the same load point.

The dots indicate the beginning of the windings.

That is, in a “triangle” the end of the previous winding and the beginning of the next are connected, and the supply phase is connected to this point. If you confuse the end and the beginning, the connected machine will not work.

What is the difference

If we talk about connecting single-phase consumers, let’s briefly look at the example of three electric heaters, then in a “star”, if one of them burns out, the remaining two will continue to work. If two out of three burn out, none of them will work at all, since they are connected in pairs to line voltage.

In a triangle circuit, even if 2 heating elements burn out, the third one will continue to work. There is no neutral wire in it, there is simply nowhere to connect it. And in the “star” it is connected to the neutral point, and it is needed to equalize the phase currents and their symmetry in the case of different loads across the phases (for example, in one of the branches there is 1 heating element connected, and in the rest there are 2 in parallel).

But if with such a connection (with different loads in phases) the zero burns out, then the voltages will be unequal (where the load is greater, it will sag, and where it is less, it will increase). We wrote more about this in the article about

It should be taken into account that it is impossible to connect ordinary single-phase devices (220V) between phases at 380V. Either the devices must be designed for such power, or the network must be with Ulinear 220V (as in electrical networks from some specific objects, for example, ships).

But, at , zero is often not connected to the midpoint of the star, since this is a symmetrical load.

Formulas for power, current and voltage

Let's start with the fact that in a star circuit there are two different voltages - linear (between linear or phase wires) and phase (between phase and zero). Ulinear is 1.73 (root of 3) times greater than Uphase. In this case, the linear and phase currents are equal.

That is, they are correlated in such a way that with linear 380V, phase is equal to 220V.

In a “triangle”, Ulinear and Uphase are equal, and the currents differ by a factor of 1.73.

In both cases, they are calculated using the same formulas:

full S = 3*Sф = 3*(Uл/√3)*I = √3*Uл*I;
active P = √3*Uл*I*cos φ;
reactive Q = √3*Uл*I*sin φ.

When connecting the same load to the same Uphase and Ulinear, the power of the connected devices will differ by 3 times.

Let's say there is a motor that operates from a three-phase network of 380/220V, and its windings are designed for a star connection to an electrical network with a linear voltage of 660V. Then, when connected in a “triangle”, the supply Ulinear should be 1.73 times less, that is, 380V, which is suitable for connecting to our network.

Let us present calculations to show what differences will occur for the motor when switching the windings from one circuit to another.

Let’s assume that the stator current when connected in a triangle to a 380V network was 5A, then its total power is equal to:

S=1.73*380*5=3287 VA

Let's switch the electric motor to a "star" and the power will decrease by 3 times, since the voltage on each winding has decreased by 1.73 times (it was 380 per winding, and now it is 220), and the current is also 1.73 times: 1.73 * 1 .73=3. This means that taking into account the reduced values, we will calculate the total power.

S=1.73*380*(5/3)=1.73*380*1.67=1070 VA

As you can see, the power has dropped by 3 times!

But what will happen if there is another electric motor and it worked in a “star” in a 380V network and the stator current is the same 5A, respectively, and the windings are designed to be connected to a “triangle” at 220V (3 phases), but for some reason they connected exactly in a “triangle” and connected to 380V?

In this case, the power will increase 3 times, since the voltage on the winding has now, on the contrary, increased by 1.73 times and the current by the same amount.

S=1.73*380*5*(3)=9861 VA

The engine power has become more than rated by these same 3 times. So it will just burn out!

Therefore, you need to connect the electric motor according to the winding connection diagram that corresponds to their rated voltage.

Practice - how to choose a scheme for a specific case

Most often, electricians work with a 380/220V network, so let’s look at how to connect an electric motor, star or delta, to such a three-phase electrical network.

In most electric motors, the winding connection diagram can be changed; for this purpose, there are six terminals in the Brno, they are located in such a way that with the help of a minimum set of jumpers you can assemble the circuit you need. In simple words: the terminal of the beginning of the first winding is located above the end of the third, the beginning of the second, above the end of the first, the beginning of the third above the end of the second.

You can see how to distinguish the two options for connecting an electric motor in the figure below.

Let's talk about which scheme to choose. The connection diagram of the electric motor coils does not have a particular influence on the operating mode of the engine, provided that the nominal parameters of the engine comply with the supply network. To do this, look at the nameplate and determine what voltages your particular electrical machine is designed for.

Typically the marking looks like:

It deciphers like this:

If the phase-to-phase voltage is 220, assemble the windings in a triangle, and if 380, assemble them in a star.

To simply answer the question “How to connect the windings of a motor?” We have made a connection diagram selection table for you:

Star-delta changeover for smooth starting

When starting the electric motor, high starting currents are observed. Therefore, to reduce the starting currents of asynchronous motors, a starting circuit is used with switching the windings from star to delta. In this case, as mentioned above, the electric motor must be designed to be connected in a “triangle” and work under the Ulinear of your network.

Thus, in our three-phase electrical networks (380/220V), for such cases we use motors with a nominal “380/660” Volt, for “Δ/Y”, respectively.

When starting, the windings are switched on as a star to a reduced voltage of 380V (relative to the nominal 660V), the engine begins to pick up speed and at a certain point in time (usually by a timer, in more complicated versions - by a signal from current and speed sensors) the windings switch to delta and operate already at its nominal 380 volts.

The illustration above describes this method of starting engines, but a changeover switch is shown as an example; in practice, two additional contactors (KM2 and KM3) are used; although it is more complicated than the usual electric motor connection circuit, this is not its drawback. But it has a number of advantages:

Less load on the electrical network from inrush currents.
Accordingly, there are smaller voltage drops and the likelihood of stopping related equipment is reduced.
Soft start of the engine.

There are two main drawbacks to this solution:

It is necessary to lay two three-core cables from the location of the contactors directly to the motor terminals.
The starting torque drops.

Conclusion

As such, there are no differences in performance characteristics when connecting the same electric motor in a star or delta configuration (it will simply burn out if you make the wrong choice). Just as there are no advantages or disadvantages of any of the schemes. Some authors argue that there is less current in the star. But with the same power of two different motors, one of which is designed to be connected in a “star” and the second in a “delta” to a network, for example, 380V, the current will be the same. And the same engine cannot be switched “at random” and “for unknown reasons”, as it will simply burn out. The main thing is to choose the option that matches the supply voltage.

We hope that now you have become more clear about what a star and delta circuit is in an electric motor, what the difference is in connecting in each method, and how to choose a circuit for a particular case. We hope the information provided was useful and interesting for you!

Materials

When creating any device, it is important not only to select the necessary parts, but also to connect them all correctly. And within the framework of this article we will talk about the connection with a star and a triangle. Where is this applied? What does this action look like schematically? These, as well as other questions, will be answered within the article.

What is a three-phase power supply system?

It is a special case of multiphase systems for constructing electrical circuits for alternating current. They operate using sinusoidal EMFs created using a common energy source and having the same frequency. But at the same time they are shifted relative to each other by a certain phase angle. In a three-phase system it is equal to 120 degrees. The six-wire (often also called multi-wire) design for alternating current was invented at one time by Nikola Tesla. Also, a significant contribution to its development was made by Dolivo-Dobrovolsky, who was the first to propose making three- and four-wire systems. He also discovered a number of advantages that three-phase designs have. What are switching circuits?

Star diagram

This is the name for a connection in which the ends of the phases of the generator windings are connected to a common point. It is called neutral. The ends of the phases of the consumer windings are also connected to one common point. Now to the wires that connect them. If it is located between the beginning of the consumer and generator phases, it is called linear. The wire that connects the neutrals is designated as neutral. The name of the chain also depends on it. If there is a neutral, the circuit is called four-wire. Otherwise it will be three-wire.

Triangle

This is a type of connection in which the beginning (H) and end (K) of the circuit are at the same point. So, K of the first phase is connected to H of the second. Her K connects to the third N. And its end is connected to the beginning of the first. Such a scheme could be called a circle, if not for the peculiarity of its installation, when placement in the form of a triangle is more ergonomic. To find out all the features of the connection, check out the types of connections below. But before that, a little more information. What is the difference between a star and delta connection? The difference between them is that the phases are connected differently. There are also certain differences in ergonomics.

Kinds

As can be understood from the figures, there are quite a few options for implementing the inclusion of parts. The resistances that arise in such cases are called load phases. There are five types of connections through which the generator can be connected to the load. This:

Star-star. The second is used with a neutral wire.
Star-star. The second is used without a neutral wire.
Triangle-triangle.
Star-triangle.
Triangle-star.

What are these reservations in the first and second paragraphs? If you have already asked yourself this question, read the information that comes with the star diagram: there is an answer there. But here I would like to make a small addition: the beginnings of the generator phases are indicated using capital letters, and the loads are indicated in capital letters. This is relative to the schematic representation. Now, based on the experience of use: when choosing the direction of current flow, in the linear wires they make it so that it is directed from the generator to the load. With the zeros they do the exact opposite. See what a star-delta connection diagram looks like. The drawings very well clearly show how and what should be. The star/delta winding connection diagram is presented from different angles, and there should be no problems understanding them.

Advantages

Each EMF operates in a certain phase of the periodic process. To designate conductors, the Latin letters A, B, C, L and numbers 1, 2, 3 are used. Speaking about three-phase systems, their advantages are usually highlighted:

Cost-effective when transmitting electricity over long distances, which provides a star-delta connection.
Low material consumption of three-phase transformers.
Balance of the system. This point is one of the most important, since it allows you to avoid uneven mechanical load on the power generating installation. This results in a longer service life.
Power cables have low material consumption. Thanks to this, with the same power consumption, the currents required to maintain a star-delta connection are reduced compared to single-phase circuits.
It is possible, without significant effort, to obtain a circular rotating magnetic field, which is necessary for the operation of an electric motor and a number of other electrical devices that operate on a similar principle. This is achieved due to the possibility of creating a simpler and at the same time effective design, which, in turn, follows from the efficiency indicators. This is another significant advantage that the star and delta connection has.
In one installation you can obtain two operating voltages - phase and linear. It is also possible to make two power levels when there is a delta or star connection.
You can dramatically reduce the flickering and stroboscopic effect of lamps operating on fluorescent lamps by following the path of placing devices powered from different phases in it.

Thanks to the above seven advantages, three-phase systems are now the most common in modern electronics. The star/delta connection of the transformer windings allows you to select the optimal options for each specific case. In addition, the ability to influence the voltage transmitted through networks to residents’ homes is invaluable.

Conclusion

These connection systems are the most popular due to their efficiency. But it should be remembered that the work is carried out with high voltage, and extreme caution must be taken.

Asynchronous motors have a whole range of undoubted advantages. Among the advantages of asynchronous motors, first of all, I would like to mention the high performance and reliability of their operation, the very low cost and unpretentiousness of motor repair and maintenance, as well as the ability to withstand fairly high mechanical overloads. All these advantages that asynchronous motors have are due to the fact that this type of motor has a very simple design. But, despite the large number of advantages, asynchronous motors also have certain negative aspects.

In practical work, it is customary to use two main methods of connecting three-phase electric motors to the electrical network. These connection methods are called: “star connection” and “delta connection”.

When a three-phase electric motor is connected using the star connection type, then the ends of the stator windings of the electric motor are connected at one point. In this case, three-phase voltage is supplied to the beginning of the windings. Below, in Figure 1, the connection diagram for a star asynchronous motor is clearly illustrated.

When a three-phase electric motor is connected using the “delta” connection type, then the stator windings of the electric motor are connected in series one after another. In this case, the beginning of the subsequent winding is connected to the end of the previous winding, and so on. Below, in Figure 2, the connection diagram of a delta asynchronous motor is clearly illustrated.

If you do not go into the theoretical and technical foundations of electrical engineering, then you can take for granted the fact that the operation of those electric motors whose windings are connected in a star configuration is softer and smoother than that of electric motors whose windings are connected in a delta configuration ". But here it is worth paying attention to the fact that electric motors, the windings of which are connected in a star configuration, are not capable of developing the full power declared in the passport characteristics. In the event that the windings are connected according to a delta circuit, the electric motor operates at the maximum power stated in the technical data sheet, but at the same time there are very high starting currents. If we make a comparison in terms of power, then electric motors whose windings are connected in a delta configuration are capable of delivering power one and a half times higher than those electric motors whose windings are connected in a star configuration.

Based on all of the above, in order to reduce currents during startup, it is advisable to use a combined delta-star connection of the windings. This type of connection is especially relevant for electric motors with greater power. Thus, due to the delta-star connection, the starting is initially carried out in the star configuration, and after the electric motor has gained momentum, switching is carried out in automatic delta mode.

The electric motor control circuit is shown in Figure 3.

Rice. 3 Control circuit

Another version of the electric motor control circuit is as follows (Fig. 4).

Rice. 4 Engine control circuit

The NC (normally closed) contact of time relay K1, as well as the NC contact of relay K2, in the circuit of the short-circuit starter coil, is supplied with supply voltage.

After the short-circuit starter is turned on, the normally closed short-circuit contacts disengage the circuits of the K2 starter coil (prohibition of accidental activation). The short circuit contact in the power supply circuit of the starter coil K1 closes.

When the magnetic starter K1 starts, the K1 contacts close in the power circuit of its coil. The time relay turns on at the same time, the contact of this relay K1 in the short circuit starter coil circuit opens. And in the starter coil circuit K2 it closes.

When the short circuit starter winding is disconnected, the short circuit contact in the starter coil circuit K2 will close. After the K2 starter turns on, it opens the power circuit of the short-circuit starter coil with its K2 contacts.

Three-phase supply voltage is supplied to the beginning of each of the windings W1, U1 and V1 using the power contacts of the starter K1. When the short-circuit magnetic starter is triggered, then with the help of its short-circuit contacts a short circuit is made, through which the ends of each of the electric motor windings W2, V2 and U2 are connected to each other. Thus, the motor windings are connected using a star connection.

A time relay combined with a magnetic starter K1 will operate after a certain time. In this case, the short-circuit magnetic starter is turned off and the magnetic starter K2 is simultaneously turned on. Thus, the power contacts of the starter K2 will be closed and the supply voltage will be supplied to the ends of each of the windings U2, W2 and V2 of the electric motor. In other words, the electric motor is switched on according to the “delta” connection diagram.

In order to start the electric motor using a delta-star connection, various manufacturers produce special starting relays. These relays can have various names, for example, “start-delta” relay or “start time relay”, as well as some others. But the purpose of all these relays is the same.

A typical circuit made with a time relay designed for starting, that is, a delta-star relay, to control the starting of a three-phase asynchronous type electric motor is shown in Figure 5.

Fig. 5 Typical circuit with a starting time relay (star/delta relay) for controlling the start of a three-phase asynchronous motor.

So, let's summarize all of the above. In order to reduce starting currents, starting the electric motor is required in a certain sequence, namely:

first, the electric motor is started at low speeds connected in a star configuration;
then the electric motor is connected in a delta pattern.

The initial start according to the "triangle" circuit will create the maximum torque, and the subsequent connection according to the "star" circuit (for which the starting torque is 2 times less) with continued operation in the nominal mode, when the engine has "picked up speed", there will be a switch to the "delta" connection circuit "in automatic mode. But do not forget about the load that is created on the shaft before starting, since the torque is weakened when connecting in a star configuration. For this reason, it is unlikely that this starting method will be suitable for electric motors with high loads, since they may then lose their functionality.

To increase the transmission power without increasing the network voltage, to reduce voltage ripple in power supplies, to reduce the number of wires when connecting the load to the power supply, various circuits for connecting the windings of power sources and consumers (star and delta) are used.

Scheme

The windings of generators and receivers when working with 3-phase networks can be connected using two circuits: star and triangle. Such circuits have several differences among themselves; they also differ in current load. Therefore, before connecting electrical machines, it is necessary to find out the difference in these two circuits - star and triangle.

Star diagram

Connecting different windings according to a star circuit involves connecting them at one point, which is called zero (neutral), and is designated on the diagrams “O”, or x, y, z. The neutral point may have a connection to the power supply neutral point, but not all cases have such a connection. If there is such a connection, then such a system is considered 4-wire, and if there is no such connection, then it is considered 3-wire.

Triangle diagram

With this scheme, the ends of the windings are not combined into one point, but are connected to another winding. That is, the result is a circuit similar in appearance to a triangle, and the windings in it are connected in series with each other. It should be noted that the difference from the star circuit is that in the delta circuit the system is only 3-wire, since there is no common point.

In a triangle circuit, when the load is off and the EMF is symmetrical, it is 0.

Phase and linear quantities

In 3-phase power networks there are two types of current and voltage - phase and linear. Phase voltage is its value between the end and beginning of the receiver phase. Phase current flows in one phase of the receiver.

When using a star circuit, the phase voltages are Ua,Ub,Uc, and the phase currents are I a, I b, I c. When using a delta circuit for load or generator windings, the phase voltages are - U aв, U bс, U са, phase currents – I ac, I bс, I са.

Linear voltage values are measured between the beginnings of phases or between linear conductors. Line current flows in the conductors between the power source and the load.

In the case of a star circuit, line currents are equal to phase currents, and line voltages are equal U ab, U bc, U ca. In a triangle circuit, everything turns out the other way around - phase and linear voltages are equal, and linear currents are equal I a, I b, I c.

Great importance is given to the direction of the EMF of voltages and currents in the analysis and calculation of 3-phase circuits, since its direction affects the relationship between the vectors on the diagram.

Features of the circuits

There is a significant difference between these schemes. Let's figure out why different circuits are used in different electrical installations, and what their features are.

When starting an electric motor, the starting current has an increased value, which is several times greater than its rated value. If this is a low-power mechanism, then the protection may not work. When a powerful electric motor is turned on, the protection will definitely work, turning off the power, which will cause a voltage drop for some time and blown fuses, or turn off the electrical circuit breakers. The electric motor will operate at a low speed, which is less than the rated speed.

It can be seen that there are many problems arising due to the high inrush current. It is necessary to somehow reduce its value.

To do this, you can use some methods:

Connect to start the electric motor, throttle, or.
Change the type of connection of the electric motor rotor windings.

In industry, the second method is mainly used, since it is the simplest and gives high efficiency. The principle of switching the windings of an electric motor to circuits such as star and triangle works here. That is, when the motor is started, its windings have a “star” connection, after a set of operating speeds, the connection diagram changes to “triangle”. They have learned to automate this switching process in industrial settings.

It is advisable to use two schemes at once - star and triangle. It is necessary to connect the neutral of the power source to the zero point, since when using such circuits there is an increased likelihood of phase amplitude distortion. The source neutral compensates for this asymmetry, which arises due to different inductive resistances of the stator windings.

Advantages of the schemes

Star connection has important advantages:

Smooth start of the electric motor.
Allows the electric motor to operate with the declared rated power corresponding to the passport.
The electric motor will have a normal operating mode in various situations: with high short-term overloads, with long-term minor overloads.
During operation, the motor housing will not overheat.

The main advantage of the triangle circuit is to obtain the highest possible operating power from the electric motor. It is advisable to maintain operating modes according to the engine passport. When studying electric motors with a triangle circuit, it turned out that its power increases 3 times compared to a star circuit.

When considering generators, the star and delta circuits are similar in parameters to the operation of electric motors. The output voltage of the generator will be higher in a delta circuit than in a star circuit. However, as the voltage increases, the current decreases, since according to Ohm's law these parameters are inversely proportional to each other.

Therefore, we can conclude that with different connections of the ends of the generator windings, two different voltage ratings can be obtained. In modern powerful electric motors, when starting the circuit, star and delta switch automatically, as this makes it possible to reduce the current load that occurs when starting the motor.

Processes that occur when the star and delta circuits change in different cases

Here, changing the circuit means switching on switchboards and in terminal boxes of electrical devices, provided that there are winding terminals.

Generator and transformer windings

When moving from star to triangle, the voltage decreases from 380 to 220 volts, the power remains the same, since the phase voltage does not change, although the line current increases by 1.73 times.

When switching back, the opposite phenomena occur: the linear voltage increases from 220 to 380 volts, and the phase currents do not change, but the linear currents decrease by 1.73 times. Therefore, we can conclude that if there is an output of all ends of the windings, then the secondary windings of the transformer and generators can be used for two types of voltage, which differ by 1.73 times.

Lighting lamps

When moving from a star to a triangle, the lamps will burn out. If the switch is reversed, provided that the lamps at the triangle were lit normally, then the lamps will glow dimly. Without a neutral wire, lamps can be connected in a star, provided that their power is the same and is distributed evenly between the phases. This connection is used in theater chandeliers.

Connection diagram for a three-phase delta motor. Connecting the motor windings according to the star and delta circuits

Selecting a motor switching circuit

Star-delta motor connection diagram

Star-delta connection

Theory

What is the difference

Formulas for power, current and voltage

Practice - how to choose a scheme for a specific case

Star-delta changeover for smooth starting

Conclusion

What is a three-phase power supply system?

Star diagram

Triangle

Kinds

Advantages

Conclusion

Scheme

Star diagram

Triangle diagram

Phase and linear quantities

Features of the circuits

To do this, you can use some methods:

Advantages of the schemes

Star connection has important advantages:

Processes that occur when the star and delta circuits change in different cases

Generator and transformer windings

Lighting lamps

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