Star and delta connections - what's the difference? Star and delta connection of electric motor windings. Delta motor connection diagram.

Switching the motor from star to delta is used to protect electrical circuits from overloads. Mostly powerful three-phase asynchronous motors from 30-50 kW, and high-speed ones ~3000 rpm, sometimes 1500 rpm, are switched from star to delta.

It is known that when the electric motor starts, its current increases up to 7 times. A squirrel-cage induction motor resembles a transformer with a short-circuited secondary winding.

If the engine is connected in a star, then a voltage of 220 Volts is supplied to each of its windings, and if the engine is connected in a triangle, then a voltage of 380 Volts is supplied to each of its windings. Here Ohm’s law “I=U/R” comes into play; the higher the voltage, the higher the current, but the resistance does not change.

Simply put, when connected to a delta (380), the current will be higher than when connected to a star (220).

When the electric motor accelerates and reaches full speed, the picture completely changes. The fact is that the engine has power that does not depend on whether it is connected to a star or a delta. Engine power depends largely on the iron and wire cross-section. Another law of electrical engineering “W=I*U” applies here.

Power is equal to current multiplied by voltage, that is, the higher the voltage, the lower the current. When connected to a delta (380), the current will be lower than to a star (220).

Let's get to practice

In the engine, the ends of the windings are brought out to the “terminal block” in such a way that, depending on how you place the jumpers, you will get a star or delta connection as shown in the figure. Such a diagram is usually drawn on the lid.

In order to switch from star to delta, we will use magnetic starter contacts instead of jumpers.

Let's look at the power section diagram, shown in thick lines.

Comments and reviews

Star-Triangle: 133 comments

1. Grumm

   Triangle error!
   But that's okay...
   How is phasing carried out (adjusted)?

2. Electrician

   The contents of the article are not true.
   When switching the motor from star to delta, the supply voltage will change accordingly from 380/220 to 220/127.
   The delta-connected engine is switched on at 220/127 V.
   If you turn it on 380/220 it will burn out.

   1. Roman

      We are talking about a 380/660 Y/A engine. You are not right.

      1. Roman

         Confused - correct: 380/660 A/Y

3. admin Post author

   According to the diagram, the motor will rotate in one direction; if you swap the phases on the starter P1, the rotation of the motor will change. The most important thing in this circuit is not to confuse the connection of the magnetic starter P2; its contacts act as JUMPERS for connection in a TRIANGLE.

4. admin Post author

   The contents of the article are completely true. When the motor is connected in a triangle, a voltage of 380 Volts is supplied to each winding, and if the motor is connected to a star, a voltage of 220 Volts is supplied to each winding. According to the scheme, we temporarily supply a reduced voltage of 220V for 10-15 seconds in order to reduce the starting current and reduce the engine jerk at the moment of starting. After this, the engine switches on to normal operation.

5. admin Post author

   Yes, it is worth pointing out that the motor voltage must correspond to the mains voltage; at this voltage it must operate connected in a triangle.

   By the way, I spotted this circuit on Japanese equipment.

6. admin Post author

   Electrician, where did you get the 220/127 from? If the network voltage is 380/220, then this means that when the engine is turned on in a triangle, each of its windings operates at 380 volts, and when the engine is turned on in a star, then 220 volts are supplied to the windings.

7. Eugene

   Guys, a similar scheme is already used in practice. Called “warm start” in pump rooms
   stations, etc. in high-rise construction.

   1. Eugene

      Excuse me, what launch? warm? Why not hot? This starting method is called “combined” in pumping stations. There is a “direct” start (star or triangle).
      However, it is more common today in high-rise construction (when using utility water supply stations - and this is important) to start frequency or frequency-network.
      Now about the subject. This star-delta start provides smoother acceleration on powerful engines to minimize network drawdown.
      However, as everyone knows, with a star we have a “shortage” in power.
      Not fatal during transition. The triangle has maximum power. By the way, this method is used when using powerful pumps at fire extinguishing stations.
      The only thing in the diagram that does not correspond to reality (practice) is the connection in the motor terminal box itself
      spruce.
      An example is Grundfoss pumps. The connection is very simple - U1-W2. V1-U2. W1-V2

      1. Alexander

         Not a lack of power, but of torque. The motor torque depends on the square of the voltage and when connected to a triangle, the torque is almost 3 times higher. A star circuit when starting an engine is used to reduce starting currents.

8. Dmitriy

   The diagram is absolutely correct, and everything is described correctly.

9. Megavolt

   Has anyone noticed that the RT and P3 relays are connected bypassing the “Start” button?
   They will work as soon as you connect the circuit to the network.

10. admin Post author

    Megavolt, you are right, thanks for the comment. They need to be connected on the other side of the start button or through an additional normally open contact P1

11. admin Post author

    The diagram has been corrected. If you click on the diagram you can see the old diagram.

    In the diagram at the top on the left, dotted lines show the possibility of connecting starter coils and time relays for 220 and 380 Volts. This common wire is connected to phase 380 volts, or to zero 220V. It is not advisable to connect along the dotted line to both phase and zero at the same time; it may result in a “short one”.

12. Michael

    Thanks for the diagram. Please, if possible, provide a diagram when the starter coils are designed for different voltages. For example, P2 is 220V and P3 is 380V. The STOP button in this case for some reason does not work. Thank you.

13. admin Post author

    If the starter coils are for different voltages, then instead of connecting to a common wire, the 220V coils are connected to zero, and the 380V coils to the phase. The rest of the scheme is unchanged.

14. Michael

    The Stop button does not work in this version. Installed a two-contact Stop button. I am breaking the two phases.

15. admin Post author

    And this button opens exactly two phases. We have two-contact buttons: one contact opens the circuit, the other closes it, turning on the signal lights.
    How it doesn't work, doesn't turn on or off.

16. Impedance

    Thank you admina for the brief, correct explanation of the operating principle of this scheme!!!

17. Bach

    There are starters together with a temporary relay. They can be easily removed and connected

18. Eugene
19. admin Post author

    Evgeniy, Ohm’s law is valid for active loads.
    Ohm's law is preserved, only on a rotating motor, in addition to the active resistance of the windings, inductive resistance appears. And with an inductive load, as the voltage increases, the inductive reactance increases, and accordingly the current decreases

    Yes, for reliable operation of the circuit, you should use a 660/380 motor if the network voltage is 380/220

20. Pamir

    Why was no one confused by the statement that “When connected to a delta (380), the current will be lower than to a star (220),” which directly contradicts what was written a few paragraphs above.
    Why are you afraid, one might ask, the power in the star and in the triangle are equal, then what is the point of switching to the triangle if the engine in the star also operates at rated power?
    admin, inductive (reactive) resistance depends only on frequency and not on voltage. And Ohm's law also works in this case; the higher the voltage, the greater the current.

21. admin Post author

    The circuit reduces the starting current, the engine turns on for a short time, during star starting. The jerk that the engine makes when starting is also reduced, this is especially true if the engine is under load.
    And in a triangle, less current is more power when the engine is running.

    The engine power does not depend on whether the engine is connected to a star or a delta. Engine power depends largely on the load

22. Pamir

    The power that the engine can develop is written on the nameplate, and it is determined by the engine parameters and the connection method, and only the currently consumed power depends on the load and it cannot exceed the declared one.
    When connected to a star, a lower voltage is applied to the motor windings (not linear 380 but phase 220), and accordingly lower starting and operating current (Ohm's law). From here it is clear that in a star, the power that the engine is capable of developing will be less than the rated one.
    Admin, you are confusing sources (generators, transformers) with loads. For a generator or transformer, the power will be the same for any type of connection, and the phase current in a delta is less than in a star. For the load, engine type, everything will be as I described above.

    1. Eugene

       “if you look through a telescope”... or better yet, at the engine nameplate, you can see... what? right... answers to questions... and they are written in the form In=...
       Example - P=1.5 kW. then I(380)=1500/380*1.732=2.3 (Simplified, without coefficients)
       For I(220)=1500/220=6.8.
       Ohm's Law is great. U=IxR. To put it simply, Voltage is directly proportional to Current.
       Accordingly, power is directly proportional to... voltage... and current.... Output - less voltage (or current, which is proportional) on the winding - less power. And here the point arises... DO NOT OVERLOAD THE NETWORK. BUT we are losing power.
       Well, and, as a result, the customer’s question: “why is the passport data 3 cubic meters per hour, but this shit pumps only 1 cubic meter?”

23. Kostantin

    switching from star to triangle ensures a smooth start. When you press the start button, the windings are switched to star (for our voltage 380\220) and in star it works at 660, after a certain time the windings switch to triangle and already operate at a rated voltage of 380 volts .

24. EVgen

    Engine AIR132 M2 11 Kw/3000 rpm. Is it possible to connect such a star-delta motor?

25. admin Post author

    EVgen, yes if it is 660/380

26. Dmitriy

    Good afternoon
    I’m a beginner, help me figure this out: “If the motor is connected in a star, then a voltage of 220 Volts is supplied to each of its windings, and if the motor is connected in a triangle, then a voltage of 380 Volts is supplied to each of its windings.”
    As I heard, when connecting the windings “star” - 380 V, and “triangle” - 220 V.
    Maybe I misunderstood something, or there was a typo in the article?

27. admin Post author

    Dmitry, Everything is written correctly in the article about the voltage on the motor windings. You have heard about phase-to-phase voltage in a network.
    If there is 380V between the phases in the network and the motor is connected “in a star”, then a voltage of 220V will be supplied to each motor winding.

    We take a 660/380 motor, in such an engine each winding is designed for 380 Volts, that is, it must be connected in a triangle.
    And at the moment of starting we connect it to the star and supply a reduced voltage of 220V to the windings. Accordingly, the starting current will be less.
    And when the engine accelerates, switch it to triangle.

28. vital
29. admin Post author
30. Yuri

    Interesting read.
    Switching from star to delta is used a) to reduce inrush currents; b) to increase the power factor of the electric motor and its load level. In the first case, for a 380/220 V network, it is necessary to take an electric motor whose voltage is written on the passport as 660/380 V. In the second case, the torque on the motor shaft, in addition to what has been said, should not exceed 30%. As for the diagram, it must be brought in accordance with GOST for designations, but a mixture of current and long-unused designations is given.

31. vik

    Hello everyone! I’ll say right away that for me the concepts of phase and linear current are elusive. In general, I will be grateful to anyone who can explain whether this circuit is suitable for (and what options I have) connecting the AIR90L2U3 electric motor (3 kW, approx. 3000 rpm, 380v). The network is three-phase - four wires enter the house. On the shield, the neutral is connected to the ground loop.
    Thank you in advance.

32. vik

    To forestall questions regarding 220/380 and 380/660, I’ll say right away that the nameplate simply says 380v. (without fractions)

33. admin Post author

    vik, the engine is low-power and can be connected without this circuit.
    Just through one starter and start-stop buttons.

34. vik

    thanks, there are three wires under the cover, does that mean it's just a star? I still need reverse.

35. admin Post author

    vik, If there are three wires under the cover, it means a star.
    To reverse, you need to swap two phases. They install two starters with simultaneous activation blocking (required electrical and additionally mechanical).

    An article with diagrams about connecting motors is currently being prepared and will appear on the website soon.

36. vik

    admin, please tell me whether the TRN-10U3 thermal relay is suitable for my engine (and how necessary it is)?
    Thank you.

37. admin Post author

    vik, What brand of thermal relay is not important, the main thing is what current.
    If a separate machine is installed on the engine, then there is no special need for a thermal relay, since the machine already has thermal protection.
    But protection is never superfluous, so it is better to install a thermal relay.

38. vik

    How do you know what current it is at? There is a stamp (TRN-10U3) stamped on one side of the contact, and the number 10 on the other.
    Or is the current regulated by a smooth regulator?
    Thank you.

    1. admin Post author

       It's probably 10 amps. The regulator can be used to smoothly adjust the current. Try installing it, it will work often, so it won’t work.

39. vik

    I have a reversible MP with three normally open contacts and one normally closed. I don't understand how to connect it. If normally closed contacts are used for blocking (to duplicate the mechanical one), then how to fix three power ones? It turns out that if you release the “start” button, the engine will stop rotating, right?

40. admin Post author

    vik, there are not enough contacts, there should be four normally open and one normally closed contacts.

    The coil of the second starter is connected through a normally closed contact for blocking.

    One normally open contact is used to block the “Start” button, and three power contacts.

    Additional contacts must be installed on the starters.

41. vik

    admin, thanks for your help. You won't be able to add contacts. I see the solution as follows: convert the main section of the starter into four normally open ones, reverse by holding the button (this completely covers my needs). The only lock remains mechanical. How critical is this?
    Thanks again.

42. vik

    Yes, there are still a couple of normally closed contacts on the second starter. Will it be useful if it opens the main section while holding the reverse button?

43. vik

    And another question: on the one hand, somewhere it was said that from a safety point of view it is better to isolate the engine from a metal structure, and in the circuit the neutral is grounded to the metal case in which it is assembled. Which is more appropriate?
    Thank you.

44. admin Post author

    vik, the mechanical lock is not very reliable, over time it can break and have to be removed. Well, if there is no other way out, you can do it this way.

    It has never been possible to isolate an engine from a metal structure. This structure and the engine itself must be grounded.
    The neutral is grounded to the metal body just for safety. In the event of a breakdown of the insulation on the housing, a short circuit will occur and the machine will turn off the engine.

45. vik

    admin, thank you very much for your help.
    The device I'm trying to build is a garden shredder. 99% of the time the engine will run in one direction. The reverse will only turn on if the crushed mass is wound around the cutting unit, so holding the button will be even preferable.
    I don’t think that this device (if it works out) will be used by anyone other than me. Well, I will try to refrain from pressing two buttons at the same time, so there is hope that the load on the mechanical lock will not be very shocking.
    Thanks again.

46. Andrey

    HELLO, I WANT TO KNOW WHETHER THIS DIAGRAM WILL SUIT IN MY CASE: 130 KW INDUCTION MOTOR, 5 VELECTRON STARTERS, “CLAPPERS”, I THINK THEY WILL WITHstand.

47. admin Post author

    Andrey, yes, if the voltage matches.

48. Completely confused...

    It's different on all sites. There is an engine (vacuum, water cooling), on the nameplate 380 volts, 5.5 kW. The terminal block on it is connected into a triangle.
    http://s018.radikal.ru/i516/1203/44/1f6335630318.jpg

    If I connect 380 will it be correct, or will it be correct to switch the terminals to star?

    Thank you in advance!

49. admin Post author

    Usually they write 380/220 or 660/380. If only 380 is written, then it is correct to connect it to a star.

    It’s safer to try connecting it to a star, see how it works, whether it produces the required power, and measure the current.
    If something goes wrong, you can switch to a triangle.

50. vik

    2admin:
    Good afternoon, I want to connect this device to protect against phase loss:
    http://www.kriwan.com/en/Protection_and_Controls-Products–25,productID__182.htm
    What is not clear is that the contacts that break the circuit (M2, M1) do not ring. This is fine? Perhaps they will close when voltage is applied?
    Thank you.

51. admin Post author

    vik, the contacts are probably open; if you apply voltage, they should close.
    It should turn off when at least one phase fails, but here all three phases are missing.

52. vik

    Logical, thanks.

53. Glory

    Here's a question. An asynchronous motor connected by a star (three terminals) must be connected to a single-phase network, there is a starting circuit with a resistance or capacitance, and the capacitance is starting and working, or only starting or only working. If the tank is only working, will the engine start with the button or not? If you use nichrome at start-up, the engine starts and the resistance is discarded. The question is, is it possible to use nichrome in one circuit for acceleration, and a capacitance (working) to increase engine power in operation? If yes, what is the scheme? I hope I didn't confuse you too much. Thank you very much in advance!

54. admin Post author
55. Glory

    admin
    Thanks, I'll try, but I don't want to disassemble the engine to add a fourth wire.

56. vik

    2admin:
    good afternoon, I bought a used three-phase electric motor on the market as 1.5 kW (the nameplate is illegible), I went online, and it looks like it is 0.75 kW. I was going to use it in a device that had a 1.1 kW single-phase power supply. How critical is the difference and what can you come up with? Can I connect it in a triangle?
    Thank you very much in advance.

57. vik

    2admin:
    Still waiting for your answer...

58. admin Post author

    vik, well, if you already bought it, then put the difference is not very critical. It will simply produce less power.
    For example, if you put it on a pump, a 0.75 kW motor will pump a smaller volume of water per unit of time than a 1.5 kW motor. And it will get hotter.
    You should not connect it to a triangle; it may burn out.

59. vik
60. vik

    2admin:
    Christ is Risen!
    I apologize in advance for bothering you on such a day - when connecting to a star, is it necessary to connect the common point to the engine housing or only the neutral?

61. admin Post author

    vik, when connecting to a star, you don’t have to connect the common point to anything at all. And connect the zero to the motor housing, and in another place the motor is still connected to ground. This is how we usually do it.
    If you wish, you can connect the middle point to the body.

62. vik

    Thank you.

63. Dimon

    Good afternoon! I’m finishing university right now, I have a special question in my diploma, the regulation of asynchronous motors by changing the winding connection diagrams from star to delta, it is necessary to calculate losses at different loads and connection diagrams. engine 4a315s6 110 kW, 380/660. can anyone help???

64. admin Post author

    Dimon, the engine engages in a star only when starting for just a few seconds. Then he switches to a triangle.

    It even became interesting that if the engine is switched to a star at low loads, and to a triangle when the load increases.
    Can this reduce losses?
    I think not, otherwise such schemes would be used everywhere.

65. PASS

    Can you please tell me if a three-phase 220V motor is connected to 380V, will it not burn out? and how to do it right
    admin writes:
    31 Jan 2012 at 20:08

    vital, Such an engine needs to be connected only in a star, but if connected in a triangle it will burn out.

    Fucked up!!! It will burn anyway! Admin, where did you study?!
    Three-phase voltage 380V (linear!) and three-phase voltage 220V (linear!) are different values!!!
    Three-phase 220V motors are easier to connect via a converter. The simplest is a three-phase motor connected to a single-phase 220V network.

    1. Eugene

       Excuse me, but where did you see 220V three-phase?) In the house? Sorry, the interphase is 380 with a line of 220...
       No, well, if 127 V is considered linear, then yeah.
       So, the Admin is not so wrong as he did not ask for the full parameters. What did Vitalya mean? 220/380? Or 127/220?

       1. admin Post author

          Eugene,
          Line voltage is the voltage between phases. A Phase voltage is the voltage between phase and zero.
          Although I agree it is necessary to clarify what kind of engine it is.

          And it often happens that the motor has only three terminals in a star or triangle; it is soldered inside. and is designed for only one voltage, for example, 380V or 220V

          The 220/380 motor for a 220/380 voltage network is connected to a star. And for a 220/127 network in a triangle.

          I haven’t come across 127/220 engines, and why would such an engine be everywhere in the 220/380 network.

66. admin Post author

    PASS, and three-phase voltage 380V (linear!) and three-phase voltage 220V (phase!) are almost the same values.
    If the engine is 220/127. The easiest way is to rewind it.

67. PASS

    It clearly says “3-phase 220V motor.” I have three of these and they work perfectly from the converter motor. And there’s no need for the extra hassle of rewinding!
    And I MYSELF know the difference between phase and line voltages.

68. DIMA

    SHEMA RABOTAET MALAKA

69. Plague

    “Switching a motor from star to delta is used to protect electrical circuits from overloads.” Hmmm...Actually, all the fuss is due to the increased starting torque, which can hardly be called smooth, “warm” and fluffy. That is, we deliberately overload the engine with current for a short time along the triangle and after gaining speed we switch to long-term star mode.

70. admin Post author

    The plague, if you need a smooth start, switch from star to delta, but you need starting torque, then vice versa.
    In practice, I have not encountered switching circuits from triangle to star; the circuit from star to triangle is more often used.

71. Don Migeli

    Why engine

72. Don Migeli

    380/220 660/380 - does this mean if it is a triangle then the first value of the fraction, and if it is a star then the second?

    Why can only 660/380 be connected to a star-delta circuit?

73. admin Post author

    Don Migeli,
    The less voltage in the fraction is phase and the greater is linear.

    Because the electric motor only switches on to low voltage for a few seconds at the moment of starting, and after starting it switches to normal operation.

    For a 220/380 engine, the usual connection diagram is star; if you connect it in a triangle, it will burn out.
    And for a 380/660 engine, the usual circuit is a triangle.
    This is at a network voltage of 220/380

74. Don Migeli

    Thanks for the answer, can you help me choose a cable? What is the basis for starting from the current on the nameplate or is a calculation needed?

    1. admin Post author

       Don Migeli, from nameplate current or power

75. Don Migeli

    if 22 kW, 46.2 A - how is it that each phase has 46A or 46 should be divided into 3 phases, can you be more specific?

    1. admin Post author

       Don Migeli, 46A on each phase.

76. Don Migeli
77. Andron

    Good afternoon. Tell me how can I find out which winding connection of the motor is “star” or “delta”?? There are three wires coming out of it, but how is it connected? I want to start it, but I don’t know which capacitor to install??

78. Nick

    on the nameplate 220/380 the triangle is only 220. The star 380 can be 220 with a reduction in torque. It all depends on what you want to get, high torque or limit the starting current. Do not burn the engines.

79. Sergey

    Good afternoon, I have the same problem: the engine nameplate says 380/660, but when switching from star to triangle, the automatic switches out instantly. The motor worked fine after rewinding and before rewinding, is it possible that it was rewinded incorrectly and how can I check this?

    1. admin Post author

       Maybe it was rewound 220/380, but this is more difficult, it’s easier to count the number of turns on a burnt-out motor and rewind the same number.
       It is necessary to measure the current in the star and compare it with the current on the nameplate to see if it is much different.

80. Sergey

    I tried to start it without load, the circuit works fine, the currents are below the nominal value. I changed the size of the pulley to reduce the load, now it does not knock out and the currents are normal. Thank you very much for your help.

81. Sergey

    Compressor with 7.5 kW motor.
    The line drops a lot and the engine does not fully accelerate.
    I propose to change the diameter of the engine pulley, increase the cross-section of the cable from the meter to the compressor, and connect it to a star.
    Will these measures be enough, and what else can be done?

    1. admin Post author

       Sergey, First of all, increase the cable cross-section.

82. Sergey

    That's where I thought I'd start.
    But there is also interest in why they installed three thousand units for the compressor.
    Usually we used to see compressors with motors of 900 or one and a half thousand, but this???

    1. admin Post author

       Maybe his blood pressure is higher?

83. Arthur

    The old 75 kV motor was started from a star to a delta, but for some reason the new one indicated the connection with a triangle D-D. Is it possible to start it like the old motor?

    1. admin Post author

       Yes you can

84. Alexander

    Help me figure it out, we bought an engine on the cheap with the overall dimensions of an AIR 180M but there are 6 ends inside, there is no sign. How to figure out its connection diagram, triangle or star, and how many revolutions it will give us and what power?

Connection diagrams for power sources and windings of consuming devices are used for various purposes. With their help, they increase the power of voltage transmission, reduce surges and failures. They also allow you to avoid using a large number of wires to connect the load to the network. In physics, several methods are used to connect resistors: parallel, series, combined, delta and star connections.

Features of the circuits

Serial, parallel and mixed connections are most often used for single-phase networks. The windings of consuming devices and the power source in a three-phase network are connected with a star or delta. Chains vary in load on electricity, so before use you need to find out the strengths and weaknesses of each type of connection.

In parallel circuits, the ends and ends of the resistors are tied to different points, and a separate current flows through each component.

In a series connection, the components are on the same line; the beginning of the second component is connected to the end of the first. In mixed circuits, both types of connections are used. But separately it is necessary to analyze the features of triangular schemes.

Star and triangle

Resistors in a star circuit are connected to one point - zero or neutral. It is connected to the same point on the power source. But such a connection is not always possible. The circuit is called four-wire in the event that the connection is possible, and three-wire when the automatic current supply device does not have a neutral point.

When connected in the form of a triangle, the ends of the resistors are not combined at one point, but are connected to the ends of other windings. The circuit looks like an equilateral triangle, and the components in it are connected in series.

The main difference from the star-shaped circuit is the absence of a zero point. Therefore the circuit is three-wire.

In three-phase networks, there are two types of voltage and electricity - linear and phase. The latter type is calculated as the difference between the end and beginning of the consumer phase. This current passes only in one phase of the device. Features of quantities in different circuits:

Between the beginnings of phases or linear conductors there are corresponding quantities. Electricity flows in the components between the load and its source. In the star circuit, the currents are equal to the phase ones, and the linear voltages are equal to Uab, Ubc, Uca. For a triangular circuit, everything is the other way around: phase voltages are equal to values ​​of another type, and electricity is Ia, Ib, Ic.

It is also necessary to take into account the electromotive force of the voltage, since without it it will not be possible to carry out calculations and analysis in a three-phase network. This quantity affects the vector ratio in diagrams.

Advantages of the chain

Both schemes have significant differences and are used differently in practice. When the electric motor is started, the current will be greater than its rated value. The protection may not turn on if the mechanism has a low power level. Otherwise, the protective device will work, but the power will be turned off, the voltage will drop, and some fuses will burn out. Due to such a number of problems, it is necessary to reduce the amount of electricity.

To do this, a choke, transformer or rheostat is connected to the electric motor. Additionally, you can change the connection diagram of the rotor resistors, which is quite simple to do in practice. Switching the circuits to star or delta will be effective. That is, when the motor is turned on, the resistors will be connected in the form of the first figure, and after gaining speed, the connection will be changed to a triangular one. In industrial production conditions, changes in connections occur automatically.

Both types of circuits can be used simultaneously. The electrical network zero is connected to the neutral point of the motor. This protects against the risk of phase amplitude distortions. The neutral of the power supply restores the asymmetry that occurs due to the different inductive reactances of the resistors.

The star design has several advantages:

• the engine starts smoothly;
• the engine operates with the power stated in its passport;
• the operating mode is maintained during voltage surges or overloads;
• The device body does not overheat during operation.

The triangle allows you to squeeze the maximum possible power out of the electric motor. But the modes must be maintained in accordance with operating conditions. The use of this chain allows you to increase the capabilities of the motor three times compared to a star. Different connections of the ends of the resistors make it possible to obtain two voltage ratings. The electrical load when starting an electrical appliance is reduced by switching connections.

The current-carrying windings of the electric motor are led out into the distribution box. The terminals of the windings form two parallel rows, each marked with the letter C and numbers from 1 to 6. This is done in order to mark the beginning and end of all three windings.
The connections are quite complicated. This can be found out using a simple tester. Calling the terminals of the windings, we will find that only two of them are connected along a large diagonal. The rest are connected along small diagonals.
Ringing the windings is necessary when using an old electric motor; in a new one, such work is unlikely to be required. After checking, the motor can be connected either in a star or delta configuration.
Note: a combined star-delta circuit is also used to connect electric motors with a power of more than 5 kW.

Turning on the windings with a star

Switching on the motor windings with a triangle

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:

1. Star-star. The second is used with a neutral wire.
2. Star-star. The second is used without a neutral wire.
3. Triangle-triangle.
4. Star-triangle.
5. 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:

1. Cost-effective when transmitting electricity over long distances, which provides a star-delta connection.
2. Low material consumption of three-phase transformers.
3. 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.
4. 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.
5. 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.
6. 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.
7. 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:

1. first, the electric motor is started at low speeds connected in a star configuration;
2. 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.