Quite often, three-phase asynchronous motors are used in industrial and household applications. This type of engine is quite common, so most of the devices that are familiar to us that work on engine traction work on just such. This engine consists of only two main parts - a movable rotor and a stator (respectively, stationary). Windings are placed in the stator core at a special angular distance, which is equal to 120 electrical degrees. The beginnings and ends of these windings are brought to the junction box, where they are fixed on special terminals. As a rule, these conclusions are marked with the letter C - C1, C2 and up to C6, respectively. The windings can be connected by two types of electrical circuits - "star" and "triangle". In the star circuit, the ends of the windings are connected to each other,and the beginning of the windings are connected to the supply voltage. The triangle circuit consists in a series connection, that is, the beginning of one winding is connected to the end of each other winding, and so on.
This is how a three-phase motor is connected, according to the triangle diagram
The inside of the motor junction box, with the position of the jumpers for delta connection
Usually, in a junction box, all contact outputs and their terminals are arranged in a shifted order opposite. That is, C6 is located opposite the C1 contact, and C4 is located opposite the C2 terminal.
This is how the contacts are located in the junction box
This is how a three-phase motor is connected, according to the “star” scheme
Live, a star-connected junction box looks like this
By connecting a three-phase motor, respectively, to a three-phase network, an electric current begins to flow inside the stator windings at different times, which in turn creates a rotating magnetic field. This rotating magnetic field, by means of magnetic induction, drives the rotor of the motor, as a result of which it begins to rotate. If you connect a three-phase motor to a single-phase network, there will not be enough torque in the machine, and it simply will not turn on.
Naturally, it will not start if you run it directly. But, there are ways by which the connection of the "three-phase" to the network is still possible. One of the simplest is to connect a phase-shifting capacitor as the third pin.
This is how a three-phase motor is connected at home (single-phase network)
A three-phase motor operating in a single-phase network has almost the same speed as when operating in a three-phase network. But, with this connection, the power of the asynchronous motor is greatly reduced. This is due to insufficient power in the network itself (in comparison with a three-phase one). To say how accurately power is lost with a single-phase connection, you need to know the connection diagram, the operating conditions of the asynchronous motor, as well as the value of the capacitance of the capacitor. But, on average, each three-phase motor connected to a single-phase network can lose up to 30 or even 50% of its own power.
Note that not all three-phase motors can behave normally in a single-phase network. Therefore, if you have connected it and are sure that the connection is correct, but at the same time it completely refuses to work, do not worry. With a high degree of probability, this means that something is wrong with the engine itself. Of course, the vast majority should work fine, regardless of the loss of power. Therefore, asynchronous motors with indices "A" and "AOL", "AO2" and "APN" proved to be the most reliable in working with a single-phase network. All of them have a squirrel-cage rotor.
As a rule, three-phase asynchronous motors have two categories in terms of rated voltage - this is work in 220/127V and 380/220V networks. Motors at lower voltages are used at low power, so they have little distribution. Thus, it is the 380/220V category that is more common. A voltage of 380V is used when connected to a "star", respectively, a voltage of 220V is used in the "triangle" circuit. In the passport of the engine and on its tag, they usually indicate all the main performance characteristics and quantities, including operating voltage, mains frequency, power factor, as well as conditional drawings of the winding connection diagram and what is the possibility of changing it.
This is what the tags look like on the housings of three-phase electric motors
In figure "A", the tag indicates that the windings can be connected in both circuits, as mentioned above. I.e,you can connect both a "triangle" for a voltage of 220V, and a "star" for 380V. Note that when connecting such a motor to a single-phase network, use the “triangle” connection scheme, since when connected to a “star”, the power loss will be insignificantly higher.
In figure "B", the tag indicates that the motor uses a star connection scheme. This corresponds to the possibility of including the "triangle" scheme. If you see such an icon, then know that there are only three outputs in the junction box. Therefore, in order to make a triangle connection, you will need to get inside the engine, find and bring the remaining ends out. This is not so easy to do, so be extremely careful.
Important point! If the motor tag indicates the operating voltage in the form of 220 / 127V, be aware that when connected to a single-phase network for an operating voltage of 220V, it is possible only with a “star” circuit and nothing more. When you try to connect an engine with a “triangle” circuit to a 220V network, it will simply burn out.
How to understand the beginnings and ends of the windings?
One of the most confusing difficulties when connecting a three-phase motor to a household network is the confusion that arises with the wires that go into the junction box. Moreover, in some cases, the box may be missing, and you yourself will have to figure out where and which wire.
The simplest case is the one in which the windings are connected in a "triangle" circuit at a motor operating voltage of 380/220V. So, it is only necessary to connect the conductive wires from the network by connecting the working and starting capacitors in the junction box to the terminals, according to the starting diagram. When the motor connection circuit is closed to a star, but it is possible to switch it to a delta, you must take advantage of this by changing the circuit using contact jumpers.
Now, as for the definition of the beginning and end of all windings. It is quite difficult when 6 wires simply stick out in the junction box without any markings. In this case, it is difficult to understand which of the winding wires is the beginning, and which is the end. Therefore, you will have to strain a little and solve this problem. Before doing anything with the engine, check the Internet for the make of the engine. Perhaps there are some documents on the network that can decipher the existing wiring. But, if no useful information was found, we act as follows
We determine the pairs of wires that are involved in the same winding;
And we determine which of the conclusions is the beginning, and which is the end.
Determination of pairs of wires is carried out by "dialing" with the help of a tester (resistance measurement mode is set). If there is no such device at hand, you can use the "grandfather" method, and determine the ownership of the ends of the windings using a light bulb and a battery. If the lamp lights up (or the device shows the presence of resistance), this means that the two wires belong to the same winding.Thus, the remaining pairs of winding leads are also determined (in the figure below this is shown in the diagram).
In the second task, you have to find out which of the conclusions is the beginning and which is the end. To do this, we need to take a battery and a pointer voltmeter (an electronic device will not work for this). And then, we determine the beginnings and ends of the windings according to the diagram below.
So, the battery is connected to the ends of one winding (let it beBUT, as in the figure), and to the ends of the windingATconnect the existing voltmeter. When the contacts are broken by a battery wire on the windingBUT, voltmeter pointer onAT, should deviate to one of the sides. Remember which one, and do the same action on the windingWithby connecting a voltmeter to it. Now, make sure that the voltmeter needle on the windingWithdeviated in the same direction as on the windingAT. This can be achieved by changing the polarity (changing the endsC1 and C2). The winding is checked in the same way.BUT. Then, the battery will be connected toWith or AT, and the voltmeter, respectively, toBUT.
Thus, after "ringing" all the windings, you should get some regularity. Breaking the contacts of the battery on any winding, the other two should show the deviation of the voltmeter needle in the same direction (this indicates the same polarity). After that, it remains to make marks on the conclusions (beginnings) on the one hand (A1, B1 and C1), and the conclusions (ends) on the other hand A2, B2 and C2. At the final stage, connect the ends into the appropriate "star" or "triangle" patterns.
How to remove the missing ends of the winding?
This case is perhaps one of the most difficult. So, a motor connected to a "star" does not switch to a "delta". In practice, when you open the junction box, you will see only three outputs (C1, C2 and C3). The remaining three (C4, C5 and C6) will have to be taken out from inside the engine. The figure below shows just such a case.
Motor tag with the case in question
And this is what the inside of the terminal box will look like
First, you need to disassemble the engine to get free access to the stator. To do this, you need to remove the end cover of the engine, which is held on by bolts, and remove its moving part - the rotor. Now, you need to find a place for soldering the remaining ends of the windings, and clean it from insulation. After, disconnect the ends of the leads and solder to them, pre-prepared, stranded wires in flexible insulation. Insulate the soldering point additionally, and fasten the wires with a strong thread on the stator windings. Ultimately, additionally soldered wires are output to the junction box.
Now, you need to determine the beginnings and ends of the windings in the above way, and designate all the available conclusions C1, C2 and so on. After identifying all the wires, you can safely make a triangle connection. Note that such actions require certain experience and skills. In words, there is nothing complicated about this, but in fact, you can get confused in the spikes of wires inside the stator and short-circuit the windings (for example). Therefore, if there is no special need for a delta connection, it is better to leave the connection as it is, that is, a “star”.
Three-phase motor stator
Soldering additional wires
In this way, the wires are tightly screwed
Conclusion of conductors in the junction box
Connecting conductors in a "triangle" circuit
Schemes that are used when connecting a three-phase motor to a household network
Triangle pattern.
This scheme is the most appropriate and suitable for a household network, since the output power of a three-phase motor in this case will be somewhat greater than with other schemes. So, the power of the "triangular" connection can be 70% of the nominal. engine power. In the junction box, it looks like this: two contacts are connected to the network, and the third is connected to the working capacitor Cp, then to any of the network contacts.
This is how the diagram is depicted on paper
And this is how it looks in practice
Launching
Starting a three-phase motor at idle is possible using a working capacitor. But, if there is even a slight load on it, it may not start, or it may turn on and work at low, insufficient speeds. Therefore, in such cases, additional equipment is used, namely the starting capacitor Sp. Calculations for determining the required capacitance of the capacitor can be found below. For reference, such capacitors (in other cases it can be a group of capacitors) serve only to start the engine. Consequently, their operating time is very short - usually milliseconds, but can be up to 2 seconds. In such a short period, the engine must have time to gain the necessary power.
Circuit with starting capacitor Sp
For more convenient operation of the engine, a switch can be added to the start-up and operation circuit. It works on a simple principle, in which one pair of contacts closes when the Start button is pressed. The whole circuit works in this mode until the “Stop” button is pressed and the contacts open.
Switch made in the USSR
Application of reverse
The rotation of the rotor in one direction or another depends on which phase the third winding is connected to.
reverse circuit
Therefore, by connecting an additional capacitor with a switch (tumbler) to the third winding, which is connected to the contacts of the first and second windings, we can change the direction of rotation of the rotor of a three-phase electric motor. Below, a diagram using all three of the above methods is clearly demonstrated, which will help make it more convenient to work with a three-phase motor.
Star connection
This scheme is used when connecting "three-phase" to the household network, if their windings operate at a voltage of 220/127V.
Connection of a three-phase electric motor "star"
Calculation of the required capacitances of capacitors. So, the calculation of the capacitance of working capacitors is made, based on the motor connection diagram and many other parameters. In the case of a star connection, the calculation is carried out as follows:
Wed=2800∙I/U;
Connecting the windings with a triangle, calculate the working capacity as follows:
Cp=4800∙I/U;
Here, the working capacitance of the capacitor is denoted Cp and is measured in microfarads, andIandUare current and voltage, respectively. WhereinU= 220V, otherwise we calculate by the expression:
I=P/(1.73∙U∙n∙cosϕ);
P- indicates the power of the engine;
N - efficiency of the "three-phase";
Cosϕ is the power factor;
1.73 - shows the relationship between linear and phase current.
Efficiency and power factor values can be found on the motor tag. As a rule, these values approximately fluctuate within 0.8-0.9.
Practice shows that the value of the capacitance of the working capacitors can be calculated according to the equationC=70∙ Pn; where Rn is the rated power. This formula is consistent when connecting the windings to the "delta", and according to it, for every 100 watts, about 7 microfarads of capacitance will be required. The stable operation of the electric motor depends on how correctly the capacitor is selected. If the capacity is selected slightly higher than necessary, the engine will experience overheating. If the starting capacityturned out to be less than necessary, the engine power will be somewhat underestimated. Capacitors can be selected by the selection method. So, starting with small capacitors, move on to more powerful ones until the optimal choice. If it is possible to measure the current in the network and on the working capacitor, then there is a chance to select the most accurate capacitor. It is necessary to carry out this measurement in the operating mode of the engine.
Starting capacity is calculated based on the requirement to generate sufficient starting torque. Do not confuse the capacitance of the starting capacitor with the value of the starting capacitance. For example, in the diagrams above, the starting capacitance is the sum of the two capacitances Cp and Sp.
If the electric motor is used at idle, then the starting capacity can be taken as a working one, moreover, the starting capacitor is no longer required. In such cases, the scheme is largely simplified and cheaper.Such measures will help to disconnect the load, with the ability to quickly and conveniently change the position of the engine, for example, to loosen the belt drive, or to make a pressure roller for it.
An example of a V-belt transmission of a walk-behind tractor
Starting the engine requires additional capacitance Sp, which is required only for starting. If you increase the disconnected capacity, this will lead to an increase in the starting torque, and at some value the starting torque will reach its peak value. But, with a further increase in capacity, the starting torque will only fall, and this must be taken into account.
Based on all the calculations and conditions for starting the electric motor under a load that is close to the nominal one, the value of the starting capacity should exceed the operating one by 2 or even 3 times. For example, if the capacitance on the working capacitor is 80 microfarads, then the starting capacitor will have this capacitance of 80-160 microfarads. This will add up to a starting capacitance (which as mentioned is the sum of Cp and Cn) of 160-240 uF. However, if the load during start-up is insignificant, the capacitance of the starting capacitor will be somewhat less, if not completely absent. Capacitors working to start the engine actually work for milliseconds, so they are used for a long time, and, as a rule, budget models are enough.
Where the best option is to use not one capacitor, but a group combined into a capacitor bridge. This is more convenient in the sense that by connecting a group, you can more accurately adjust the required capacitance by disconnecting or connecting capacitors. Small capacitors that form a bridge are connected in parallel because with such a connection, the capacitances are adjusted: Ctot = C1 +C2 +C3 +…+Cn.
This is what a parallel connection looks like
Metallized paper capacitors serve as working capacitors, and film capacitors such as MBGO, K78-17, BGT, etc. are also excellent. The voltage in the permissible value should exceed the mains voltage during operation of the electric motor by at least 1.5-2 times.
Thus, connecting a three-phase motor to a single-phase network requires careful mathematical analysis and some experience with electrical equipment.
More about electrical:
We are going to consider how a three-phase motor is connected to a single-phase network, to give recommendations on controlling the unit. More often people want to vary the rotation speed or direction. How to do it? We described vaguely earlier how to connect a 230 volt three-phase motor, now let's take care of the details.
Standard scheme for connecting a three-phase motor to a single-phase network
The process of connecting a three-phase motor to a voltage of 230 volts is simple. Usually the branch carries a sinusoid, the difference is 120 degrees. A phase shift is formed, uniform, ensures smooth rotation of the stator electromagnetic field. The effective value of each wave is 230 volts. This will allow you to connect a three-phase motor to your home outlet. Circus trick: get three sine waves using one. The phase shift is 120 degrees.
In practice, this can be done by enlisting the help of special devices of phase shifters. Not those that are used by high-frequency paths of waveguides, but special filters formed by passive, less often active elements. Fans of troubles prefer the use of a real capacitor. If the motor windings are connected in a triangle, forming a single ring, we get phase shifts of 45 and 90 degrees, more or less enough for the uncertain operation of the shaft:
Wiring diagram of a three-phase motor by switching the windings in a triangle
- The socket phase is supplied to one winding. Wires catch the potential difference.
- The second winding is powered by a capacitor. A phase shift of 90 degrees relative to the first is formed.
- At the third, due to the applied voltages, an oscillation weakly similar to a sinusoid is formed with a shift of another 90 degrees.
In total, the third winding is 180 degrees out of phase with the first. Practice shows that the alignment is enough to work normally. Of course, the engine sometimes “sticks”, gets very hot, the power drops, the efficiency is lame. Users put up when the connection of an asynchronous motor to a three-phase network is excluded.
From purely technical nuances, we add: a diagram of the correct layout of the wires is given on the device case. More often it decorates the inside of the casing that hides the block, or is drawn nearby on the nameplate. Guided by the diagram, we will understand how to connect an electric motor with 6 wires (a pair for each winding). When the network is three-phase (often referred to as 380 volts), the windings are connected by a star. One common point is formed for the coils, where the neutral is joined (conditional circuit electrical zero). Phases are fed to the other ends. It turns out three - according to the number of windings.
How to handle a triangle to connect a three-phase 230 volt motor is understandable. Additionally, here is a picture showing:
- Wiring diagram of the windings.
- A run capacitor that serves the purpose of creating the correct phase distribution.
- Starting capacitor, which facilitates the unwinding of the shaft at initial speed. Subsequently, it is disconnected from the circuit with a button, discharged by a shunt resistor (for safety and being ready for a new start cycle).
Connecting a three-phase motor 230 volts in a triangle
The picture shows: winding A is energized with 230 volts. C is supplied with a phase shift of 90 degrees. Due to the potential difference, the ends of the winding B form a voltage shifted by 90 degrees. The outlines are far from the sinusoid familiar to school physicists. Omitted for simplicity are the start capacitor, shunt resistor. We believe the location is obvious from the above. At the very least, this technique will allow you to achieve normal operation from the engine. With the key, the starting capacitor is closed, starting, disconnected from the phase, discharged by the shunt.
It's time to say: the capacitance indicated by the 100 uF drawing is practically chosen, given:
- Shaft speed.
- Engine power.
- Loads placed on the rotor.
You need to select a capacitor experimentally. According to our drawing, the voltage of windings B and C will be the same. We remind you: the tester shows the effective value. The voltage phases will be different, the waveform of the winding B is non-sinusoidal. The effective value shows: the same power is given to the shoulders. More or less stable operation of the installation is provided. The motor heats up less, the efficiency of the motor is optimized. Each winding is formed by an inductive reactance, which also affects the phase shift between voltage and current. That is why it is important to choose the right capacitance value. You can achieve ideal engine operating conditions.
Make the engine turn in the opposite direction
Three phase voltage 380 volts
When connected to three phases, the change in the direction of rotation of the shaft is ensured by the correct switching of the signal. Special contactors (three pieces) are used. 1 for each phase. In our case, only one circuit is subject to switching. Moreover (guided by the statements of the guru) it is enough to swap any two wires. Whether it's power, the place where the capacitor is docked. Let's check the rule before issuing parting words to readers. The results are shown in the second figure, which schematically shows diagrams showing the distribution of the phases of the indicated case.
When making diagrams, it was assumed that the winding C is connected in series to a capacitor, which gives the voltage a positive phase increase. According to the vector diagram, in order to maintain balance, winding C must have a negative sign relative to the main voltage. On the other side of the capacitor, coil B is connected in parallel. One branch provides a positive increase in voltage (capacitor), the other - to current. Akin to a parallel oscillating circuit, the branch currents flow in almost the opposite direction. Given the above, we adopted the law of changing the sinusoid in antiphase with respect to the winding C.
The diagrams show: the maxima, according to the scheme, bypass the windings counterclockwise. The last review showed a similar context: the rotation is in a different direction. It turns out that when the polarity of the power supply is reversed, the shaft rotates in the opposite direction. We will not draw the distribution of magnetic fields, we consider it unnecessary to repeat ourselves.
More precisely, such things will allow you to calculate special computer programs. The explanation was given on the fingers. It turned out that the practitioners are right: by changing the polarity of the supply, the direction of movement of the shaft is reversed. Surely a similar statement is suitable for the case of switching on a capacitor by a branch of another winding. Thirsty for detailed graphs, we recommend studying specialized software packages like the free Electronics Workbench. In the application, put down the desired number of control points, track the laws of changes in currents and voltages. Those who like to mock their brain will be able to view the spectrum of signals.
Take the trouble to correctly set the inductance of the windings. Of course, the influence is introduced by the load that prevents the launch. It is difficult to take into account the losses of such programs. Practitioners recommend avoiding focusing on the specified sharpener, selecting capacitor values (empirically) empirically. Thus, the exact connection diagram of a three-phase motor is determined by the design, the intended purpose. Suppose a lathe will differ from a bread machine in developing loads.
Starting capacitor of a three-phase motor
More often, the connection of a three-phase motor to a single-phase network must be carried out with the participation of a starting capacitor. Especially the aspect concerns powerful models, motors under significant load at the start. In this case, its own reactance increases, which will have to be compensated with the help of capacitances. It's easier to choose again experimentally. It is necessary to assemble a stand on which it is possible to “hot” turn on, exclude individual containers from the circuit.
Avoid helping the engine start by hand, as demonstrated by "experienced" masters. Just find the value of the battery at which the shaft rotates vigorously, as you spin up, start excluding capacitors from the circuit one by one. Until such a set remains, below which the engine does not rotate. The selected elements form the starting capacity. And the correctness of your choice must be controlled with the help of a tester: the voltage in the arms of the phase-shifted windings (in our case, C and B) should be the same. This means that approximately equal power is delivered.
Three-phase motor with starting capacitor
As for estimates and estimates, battery capacity grows with increasing power, speed. And if we talk about the load, it has a big impact at the start. When the shaft spins, in most cases small obstacles are overcome due to inertia. The more massive the shaft, the higher the chance that the engine will not "notice" the difficulty that has arisen.
Please note that the connection of an asynchronous motor is usually carried out through a circuit breaker. A device that will stop rotation when the current exceeds a certain value. This not only saves the local network plugs from burning out, but also saves the motor windings when the shaft is jammed. In this case, the current will rise sharply, and the device will stop working. The circuit breaker is also useful when selecting the desired capacitance rating. Eyewitnesses say that if a 3-phase motor is connected to a single-phase network through too weak capacitors, then the load increases dramatically. In the case of a powerful motor, this is very important, because even in normal mode, the consumption exceeds the nominal by 3-4 times.
And a few words about how to estimate the starting current in advance. Let's say you need to connect an asynchronous motor for 230 with a power of 4 kW. But this is for three phases. In the case of standard wiring, the current flows through each of them separately. We will put it all together. Therefore, we boldly divide the power by the mains voltage and get 18 A. It is clear that without a load, such a current is unlikely to be consumed, but for the stable operation of the engine to its fullest, a circuit breaker of amazing power is needed. As for a simple test run, a 16 amp device will do just fine. And there is even a chance that the start will take place without excesses.
We hope readers now know how to connect a three-phase motor to a 230 volt home network. It remains to add to this that the capabilities of a standard apartment do not exceed, in terms of power output to the consumer, values of the order of 5 kW. This means that the engine described above at home is simply dangerous to turn on. Please note that even grinders are rarely more powerful than 2 kW. At the same time, the motor is optimized for operation in a single-phase 220 volt network. Simply put, too powerful devices will not only cause the blinking of the light, but most likely will provoke the occurrence of other emergency situations. At best, it will knock out plugs, at worst, a wiring fire will occur.
On this we say “goodbye” and want to note: knowledge of the theory is sometimes useful for practitioners. Especially when it comes to powerful equipment that can cause considerable harm.
It happens that a three-phase electric motor falls into the hands. It is from such engines that home-made circular saws, emery machines and various kinds of grinders are made. In general, a good owner knows what can be done with him. But the trouble is, a three-phase network in private homes is very rare, and it is not always possible to conduct it. But there are several ways to connect such a motor to a 220v network.
It should be understood that the engine power with such a connection, no matter how hard you try, will noticeably drop. So, the “triangle” connection uses only 70% of the engine power, and the “star” connection is even less - only 50%.
In this regard, the engine is desirable to have more powerful.
Important! When connecting the engine, be extremely careful. Do everything slowly. When changing the circuit, turn off the power supply and discharge the capacitor with an electric lamp. Do the work with at least two people.
So, in any connection scheme, capacitors are used. In fact, they play the role of the third phase. Thanks to him, the phase to which one terminal of the capacitor is connected shifts exactly as much as is necessary to simulate the third phase. Moreover, for the operation of the engine, one capacity (working) is used, and for starting, another one (starting) is used in parallel with the working one. Although this is not always necessary.
For example, for a lawn mower with a blade in the form of a sharpened blade, a 1 kW unit and only working capacitors will be enough, without the need for start-up tanks. This is due to the fact that the engine is idling at startup and it has enough energy to spin the shaft.
If you take a circular saw, hood or other device that gives the initial load on the shaft, then you can’t do without additional cans of capacitors to start. Someone may say: “why not connect the maximum capacity so that there is not enough?” But not everything is so simple. With this connection, the motor will overheat and may fail. Don't risk your equipment.
Important! Whatever the capacity of the capacitors, their operating voltage must be at least 400V, otherwise they will not work for a long time and may explode.
Let's first consider how a three-phase motor is connected to a 380v network.
Three-phase motors come in both with three leads - for connecting only to a "star", and with six connections, with the choice of a star or delta circuit. The classic scheme can be seen in the figure. The figure on the left here shows a star connection. The photo on the right shows how it looks on a real motor brand.
It can be seen that for this it is necessary to install special jumpers on the desired outputs. These jumpers are included with the motor. In the case when there are only 3 outputs, then the star connection is already made inside the motor housing. In this case, it is simply impossible to change the connection scheme of the windings.
Some say that they did this so that the workers would not steal the units from home for their own needs. Be that as it may, such engine options can be successfully used for garage purposes, but their power will be noticeably lower than those connected by a triangle.
Scheme of connecting a 3-phase motor to a 220v network connected by a star.
As you can see, the voltage of 220V is distributed into two series-connected windings, where each is designed for such a voltage. Therefore, power is lost almost twice, but such an engine can be used in many low-power devices.
The maximum power of a 380v motor in a 220v network can only be achieved using a delta connection. In addition to minimal power losses, the engine speed remains unchanged. Here, each winding is used for its operating voltage, hence the power. The connection diagram of such an electric motor is shown in Figure 1.
In Fig. 2, a brno is shown with a 6-pin terminal for the possibility of connecting with a triangle. The three resulting outputs are supplied: phase, zero and one output of the capacitor. The direction of rotation of the electric motor depends on where the second output of the capacitor is connected - phase or zero.
In the photo: an electric motor with only working capacitors without start-up tanks.
If there will be an initial load on the shaft, capacitors must be used to start. They are connected in parallel with the workers using a button or switch at the time of switching on. As soon as the engine reaches maximum speed, the start containers must be disconnected from the workers. If it's a button, just release it, and if it's a switch, then turn it off. Further, the engine uses only the working capacitors. Such a connection is shown in the photo.
How to choose capacitors for a three-phase motor using it in a 220v network.
The first thing to know is that capacitors must be non-polar, that is, not electrolytic. It is best to use brand containers - MBGO. They were successfully used in the USSR and in our time. They perfectly withstand voltage, current surges and the damaging effects of the environment.
They also have eyelets for mounting, helping to easily place them anywhere in the body of the device. Unfortunately, it is problematic to get them now, but there are many other modern capacitors that are no worse than the first ones. The main thing is that, as mentioned above, their operating voltage should not be less than 400V.
Calculation of capacitors. Capacitance of the working capacitor.
In order not to resort to long formulas and torture your brain, there is an easy way to calculate a capacitor for a 380v motor. For every 100 W (0.1 kW), 7 microfarads are taken. For example, if the engine is 1 kW, then we calculate as follows: 7 * 10 \u003d 70 microfarads. It is extremely difficult to find such a capacity in one bank, and it is also expensive. Therefore, most often the containers are connected in parallel, gaining the desired capacity.
starting capacitor capacity.
This value is taken from the calculation of 2-3 times more than the capacity of the working capacitor. It should be borne in mind that this capacitance is taken in total with the working one, that is, for a 1 kW engine, the working one is equal to 70 microfarads, we multiply it by 2 or 3, and we get the required value. This is 70-140 microfarads of additional capacitance - starting. At the moment of switching on, it is connected to the working one and in total it turns out - 140-210 microfarads.
Features of the selection of capacitors.
Capacitors, both working and starting, can be selected by the method from smaller to larger. So, having selected an average capacity, you can gradually add and monitor the engine's operating mode so that it does not overheat and has enough power on the shaft. Also, the starting capacitor is selected by adding until it starts smoothly without delay.
There are several types of electric motors - three-phase and single-phase. The main difference between three-phase electric motors and single-phase electric motors is that they are more productive. If you have a 380 V outlet at home, then it is best to buy equipment with a three-phase electric motor.
Using this type of engine will allow you to save on electricity and get an increase in power. Also, you do not have to use various devices to start the engine, because thanks to a voltage of 380 V, a rotating magnetic field appears immediately after connecting to the mains.
380 volt electric motor connection diagrams
If you do not have a 380 V network, then you can still connect a three-phase electric motor to a standard 220 V electrical network. To do this, you need capacitors that need to be connected according to this scheme. But when connected to a conventional power grid, you will observe a loss of power. You could read about this.Electric motors for 380 V are arranged in such a way that they have three windings in the stator, which are connected in a triangle or star type, and three different phases are already connected to their tops.
It must be remembered that using a star connection, your electric motor will not run at full capacity, but it will start smoothly. When using a triangle circuit, you will get an increase in power compared to a star by one and a half times, but with this connection, the chance of damaging the winding at startup increases.
Before using an electric motor, you must first familiarize yourself with its characteristics. All the necessary information can be found in the data sheet and on the nameplate of the engine. Particular attention should be paid to three-phase Western European-style motors, as they are designed to operate on a voltage of 400 or 690 volts. In order to connect such an electric motor to domestic networks, it is necessary to use only a triangle-type connection.
If you want to make a triangle circuit, then you need to connect the windings in series. It is necessary to connect the end of one winding to the beginning of the next, and then three phases of the mains must be connected to the three connections.
Connecting the star-delta circuit.
Thanks to this scheme, we can get maximum power, but we will not be able to change the direction of rotation. In order for the circuit to work, three starters will be needed. On the first (K1), power is connected on one side, and the ends of the windings are connected on the other. Their beginnings are connected to K2 and K3. From the K2 starter, the beginning of the windings are connected to other phases according to the triangle connection type. When K3 turns on, all three phases are shorted and, as a result, the electric motor operates in a star circuit.
It is important that K2 and K3 are not started at the same time, as this may lead to an emergency shutdown. This scheme works as follows. When K1 starts, the relay temporarily turns on K3 and the engine starts as a star. After starting the engine, K3 turns off and K2 starts. And the electric motor starts to work according to the triangle scheme. Termination of work occurs by turning off K1.
Homegrown "kulibins" use whatever comes to hand for electromechanical crafts. When choosing an electric motor, three-phase asynchronous ones usually come across. This type has become widespread due to its successful design, good balance and economy.
This is especially true in powerful industrial units. Outside a private house or apartment, there are no problems with three-phase power. And how to organize the connection of a three-phase motor to a single-phase network if your meter has two wires?
Consider the option of regular connection
Three-phase motor, has three windings at an angle of 120°. Three pairs of contacts are displayed on the contact block. The connection can be established in two ways:
Connection according to the scheme "star" and "delta"
Each winding is connected at one end to two other windings, forming the so-called neutral. The remaining ends are connected to three phases. Thus, 380 volts are supplied to each pair of windings:
In the distribution block, the jumpers are connected accordingly, it is impossible to mix up the contacts. There is no concept of polarity in alternating current, therefore it does not matter which phase, which wire to apply.
With this method, the end of each winding is connected to the next, resulting in a vicious circle, more precisely a triangle. Each winding has a voltage of 380 volts.
Wiring diagram:
Accordingly, jumpers are installed differently on the terminal block. Similarly with the first option, there is no polarity as a class.
For each group of contacts, current flows at a different time, following the concept of "phase shift". Therefore, the magnetic field consistently drags the rotor along with it, creating a continuous torque. This is how the engine works with its “native” three-phase power supply.
And if you got an engine in excellent condition, and you need to connect it to a single-phase network? Do not be upset, the connection diagram of a three-phase motor has long been worked out by engineers. We will share with you the secrets of several popular options.
Connecting a three-phase motor to a 220 volt network (single phase)
At first glance, the operation of a three-phase motor when connected to one phase is no different from the correct inclusion. The rotor rotates, practically without losing speed, no jerks and slowdowns are observed.
However, it is impossible to achieve nominal power with such a power supply. This is a forced loss, there is no way to fix it, you have to reckon with it. Depending on the control circuit, the power reduction ranges from 20% to 50%.
In this case, electricity is consumed in the same way as if you were using all the power. To choose the most profitable option, we suggest that you familiarize yourself with various methods.
