To operate a variety of electrical devices, asynchronous motors are used, which are simple and reliable in operation and installation - you can easily install them yourself. The connection of a three-phase motor to a single-phase and three-phase network is carried out by star and delta.
general information
An asynchronous three-phase motor consists of the following main parts: windings, a moving rotor and a stationary stator. The windings can be connected to each other, and the main power supply of the network is connected to their open contacts or in series, that is, the end of one winding is connected to the beginning of the next.
Photo - star diagram clearlyThe connection can be made to a single-phase, two-phase and three-phase network, while the motors are mainly designed for two voltages - 220/380 V. Switching the type of winding connection allows you to change the rated voltage. Despite the fact that, in principle, it is possible to connect the motor to a single-phase network, it is rarely used, since the capacitor reduces the efficiency of the device. And the consumer receives approximately 60% of the rated power. But if there is no other option, then you need to connect it using a delta circuit, then the motor overload will be less than with a star.
Before connecting the windings in a single-phase network, it is necessary to check the capacitance of the capacitor that will be used. For this you need a formula:
C µF = P W /10
If the initial parameters of the capacitor are unknown, then it is recommended to use a starting model that can “adapt” to the operation of the engine and control its speed. Also, a current relay or a standard magnetic starter is often used to operate a device with a squirrel-cage rotor. This detail of the circuit allows for complete automation of the workflow. Moreover, for household models (with a power from 500 V to 1 kW), you can use a starter from a washing machine or refrigerator, further increasing the capacitor capacity or changing the relay winding.
Video: how to connect a three-phase 220V motor
Connection methods
With a single-phase network, it is necessary to shift the phase using special parts, most often a capacitor. But in some conditions it will be replaced by a thyristor. If you install a thyristor switch in the motor housing, then in the closed position it not only shifts the phases, but also significantly increases the starting torque. This helps to increase efficiency up to 70%, which is an excellent indicator for such a connection. Using only this part, you can avoid using a fan and the main types of capacitors - starting and running.
But this connection is not ideal either. When operating an electric motor with a thyristor, 30% more electric current is consumed than with capacitors. Therefore, this option is used only in production or in the absence of a choice.
Let's consider how a three-phase asynchronous motor is connected to a three-phase network if a triangle circuit is used.
Photo - simple triangle The drawing shows two capacitors - starting and working, a start button, a diode signaling the start of work and a resistor system for braking and stopping completely. Also in this case, a switch is used that has three positions: “hold”, “start”, “stop”. When the handle is installed in the first position, electric current begins to flow to the contacts. It is important here to switch to the “start” mode immediately after the engine starts, otherwise the windings may catch fire due to overload. At the end of the working process, the handle is fixed at the “stop” point.
Photo - connection using electrolyte capacitors Sometimes, when connected in phase, it is more convenient to stop a three-phase motor using the energy stored in the capacitor. Sometimes electrolytes are used instead, but this is a more complex option for installing the device. In this case, the parameters of the capacitor are very important, in particular, its capacity - braking and the time to completely stop the moving parts depend on it. This circuit also uses rectifying diodes and resistors. They will help, if necessary, stop the engine faster. But their technical characteristics should be as follows:
- The resistor's resistance should not exceed 7 kOhm;
- The capacitor must withstand voltages of 350 volts or higher (depending on the mains voltage).
Having at hand a circuit that stops the motor, you can use a capacitor to connect it in reverse. The main difference from the previous drawing is the modernization of the three-phase two-speed motor with a double switch and a magnetic start relay. The switch, as in previous versions, has several main positions, but is fixed only to “start” and “stop” - this is very important.
Photo - reverse using a starter Reversing motor connection is also possible via a magnetic starter. In this case, it is necessary to change the order of the stator phases, then it will be possible to ensure a change in the direction of rotation. To do this, immediately after pressing the “Forward” starter button, press the “Back” button. After this, the blocking contact will turn off the forward coil and transfer the power to reverse - the direction of rotation will change. But you need to be careful when connecting the starter - if the contacts are swapped, then during the transition there will not be a reversal, but a short circuit.
Another unusual way to connect a three-phase motor is the option of using a four-pole RCD. Its feature is the ability to use the network without zero.
- In most cases, ED only requires 3 phases and 1 ground wire, zero is not necessary, since the load is symmetrical;
- The connection principle is as follows: we take the power phases to the circuit breaker, and connect the zero directly to the RCD terminal - N, after which we do not connect it to anything;
- The cables from the machine are also connected to the RCD in the same way. We ground the engine and that's it.
Most often, our houses, plots, and garages are supplied with a single-phase 220 V network. Therefore, equipment and all homemade products are made so that they work from this power source. In this article we will look at how to correctly connect a single-phase motor.
Asynchronous or collector: how to distinguish
In general, you can distinguish the type of engine by a plate - a nameplate - on which its data and type are written. But this is only if it has not been repaired. After all, anything can be under the casing. So if you are not sure, it is better to determine the type yourself.
How do collector motors work?
You can distinguish between asynchronous and commutator motors by their structure. The collectors must have brushes. They are located near the collector. Another mandatory attribute of this type of engine is the presence of a copper drum, divided into sections.
Such motors are produced only as single-phase ones; they are often installed in household appliances, as they allow one to obtain a large number of revolutions at the start and after acceleration. They are also convenient because they easily allow you to change the direction of rotation - you just need to change the polarity. It is also easy to organize a change in the rotation speed by changing the amplitude of the supply voltage or its cutoff angle. That is why such engines are used in most household and construction equipment.
The disadvantages of commutator motors are high operating noise at high speeds. Remember a drill, an angle grinder, a vacuum cleaner, a washing machine, etc. The noise during their operation is decent. At low speeds, commutator motors are not so noisy (washing machine), but not all tools operate in this mode.
The second unpleasant point is that the presence of brushes and constant friction leads to the need for regular maintenance. If the current collector is not cleaned, contamination with graphite (from brushes being worn out) can cause adjacent sections in the drum to become connected and the motor simply stops working.
Asynchronous
An asynchronous motor has a stator and a rotor, and can be single or three-phase. In this article we consider connecting single-phase motors, so we will only talk about them.
Asynchronous motors are characterized by a low noise level during operation, therefore they are installed in equipment whose operating noise is critical. These are air conditioners, split systems, refrigerators.
There are two types of single-phase asynchronous motors - bifilar (with a starting winding) and capacitor. The whole difference is that in bifilar single-phase motors the starting winding works only until the motor accelerates. Afterwards it is turned off by a special device - a centrifugal switch or a start-up relay (in refrigerators). This is necessary, since after overclocking it only reduces efficiency.
In capacitor single-phase motors, the capacitor winding runs all the time. Two windings - main and auxiliary - are shifted relative to each other by 90°. Thanks to this, you can change the direction of rotation. The capacitor on such engines is usually attached to the housing and is easy to identify by this feature.
You can more accurately determine the bifilar or capacitor motor in front of you by measuring the winding resistance. If the resistance of the auxiliary winding is twice as large (the difference can be even greater), most likely this is a bifilar motor and this auxiliary winding is a starting winding, which means that a switch or starting relay must be present in the circuit. In capacitor motors, both windings are constantly in operation and connecting a single-phase motor is possible through a regular button, toggle switch, or automatic machine.
Connection diagrams for single-phase asynchronous motors
With starting winding
To connect a motor with a starting winding, you will need a button in which one of the contacts opens after switching on. These opening contacts will need to be connected to the starting winding. In stores there is such a button - this is PNDS. Its middle contact closes for the holding time, and the two outer ones remain in a closed state.
Appearance of the PNVS button and the state of the contacts after the “start” button is released"
First, using measurements, we determine which winding is working and which is starting. Typically the output from the motor has three or four wires.
Consider the option with three wires. In this case, the two windings are already combined, that is, one of the wires is common. We take a tester and measure the resistance between all three pairs. The working one has the lowest resistance, the average value is the starting winding, and the highest is the common output (the resistance of two windings connected in series is measured).
If there are four pins, they ring in pairs. Find two pairs. The one with less resistance is the working one, the one with more resistance is the starting one. After this, we connect one wire from the starting and working windings, and bring out the common wire. A total of three wires remain (as in the first option):
- one from the working winding is working;
- from the starting winding;
- general.
With all these 
connecting a single-phase motor
We connect all three wires to the button. It also has three contacts. Be sure to place the starting wire on the middle contact(which is closed only during start-up), the other two are extremelyie (arbitrarily). We connect a power cable (from 220 V) to the extreme input contacts of the PNVS, connect the middle contact with a jumper to the working one ( note! not with the general). That's the whole circuit for switching on a single-phase motor with a starting winding (bifilar) through a button.
Condenser
When connecting a single-phase capacitor motor, there are options: there are three connection diagrams and all with capacitors. Without them, the engine hums, but does not start (if you connect it according to the diagram described above).
The first circuit - with a capacitor in the power supply circuit of the starting winding - starts well, but during operation the power it produces is far from rated, but much lower. The connection circuit with a capacitor in the connection circuit of the working winding gives the opposite effect: not very good performance at start-up, but good performance. Accordingly, the first circuit is used in devices with heavy starting (for example), and with a working capacitor - if good performance characteristics are needed.
Circuit with two capacitors
There is a third option for connecting a single-phase motor (asynchronous) - install both capacitors. It turns out something between the options described above. This scheme is implemented most often. It is in the picture above in the middle or in the photo below in more detail. When organizing this circuit, you also need a PNVS type button, which will connect the capacitor only during the start time, until the motor “accelerates”. Then two windings will remain connected, with the auxiliary winding through a capacitor.
Connecting a single-phase motor: circuit with two capacitors - working and starting
When implementing other circuits - with one capacitor - you will need a regular button, machine or toggle switch. Everything connects there simply.
Selection of capacitors
There is a rather complex formula by which you can calculate the required capacity accurately, but it is quite possible to get by with recommendations that are derived from many experiments:
- The working capacitor is taken at the rate of 70-80 uF per 1 kW of engine power;
- starting - 2-3 times more.
The operating voltage of these capacitors should be 1.5 times higher than the network voltage, that is, for a 220 volt network we take capacitors with an operating voltage of 330 V and higher. To make starting easier, look for a special capacitor for the starting circuit. They have the words Start or Starting in their markings, but you can also use regular ones.
Changing the direction of motor movement
If, after connecting, the motor works, but the shaft does not rotate in the direction you want, you can change this direction. This is done by changing the windings of the auxiliary winding. When assembling the circuit, one of the wires was fed to the button, the second was connected to the wire from the working winding and the common one was brought out. This is where you need to switch the conductors.
There are situations in life when you need to connect some industrial equipment to a regular home power supply network. A problem immediately arises with the number of wires. Machines intended for use in enterprises usually have three, but sometimes four, terminals. What to do with them, where to connect them? Those who tried to try various options were convinced that the motors simply did not want to spin. Is it even possible to connect a single-phase three-phase motor? Yes, you can achieve rotation. Unfortunately, in this case, the power drop is inevitable by almost half, but in some situations this is the only way out.
Voltages and their ratio
In order to understand how to connect a three-phase motor to a regular outlet, you need to understand how the voltages in the industrial network relate. The voltage values are well known - 220 and 380 Volts. Previously, there was still 127 V, but in the fifties this parameter was abandoned in favor of a higher one. Where did these “magic numbers” come from? Why not 100, or 200, or 300? It seems that round numbers are easier to count.
Most industrial electrical equipment is designed to be connected to a three-phase network. The voltage of each phase in relation to the neutral wire is 220 Volts, just like in a home socket. Where does 380 V come from? It is very simple, just consider an isosceles triangle with angles of 60, 30 and 30 degrees, which is a vector stress diagram. The length of the longest side will be equal to the length of the thigh multiplied by cos 30°. After some simple calculations, you can make sure that 220 x cos 30° = 380.
Three-phase motor device
Not all types of industrial motors can operate from a single phase. The most common of them are the “workhorses” that make up the majority of electrical machines in any enterprise - asynchronous machines with a power of 1 - 1.5 kVA. How does such a three-phase motor work in the three-phase network for which it is intended?
The inventor of this revolutionary device was the Russian scientist Mikhail Osipovich Dolivo-Dobrovolsky. This outstanding electrical engineer was a proponent of the theory of a three-phase power supply network, which has become dominant in our time. three-phase operates on the principle of induction of currents from the stator windings to closed rotor conductors. As a result of their flow through the short-circuited windings, a magnetic field arises in each of them, interacting with the stator power lines. This produces a torque that leads to circular motion of the motor axis.
The windings are angled 120° so that the rotating field generated by each phase pushes each magnetized side of the rotor in succession.
Triangle or star?
A three-phase motor in a three-phase network can be switched on in two ways - with or without a neutral wire. The first method is called “star”, in this case each of the windings is under (between phase and zero), equal in our conditions to 220 V. The connection diagram of a three-phase motor with a “triangle” involves connecting three windings in series and applying linear (380 V) voltage to switching nodes. In the second case, the engine will produce about one and a half times more power.
How to turn the motor in reverse?
Control of a three-phase motor may require changing the direction of rotation to the opposite, that is, reverse. To achieve this, you just need to swap two of the three wires.
To make it easier to change the circuit, jumpers are provided in the motor terminal box, usually made of copper. For star switching, gently connect the three output wires of the windings together. The “triangle” turns out to be a little more complicated, but any average qualified electrician can handle it.
Phase shifting tanks
So, sometimes the question arises about how to connect a three-phase motor to a regular home outlet. If you just try to connect two wires to the plug, it will not rotate. In order for things to work, you need to simulate the phase by shifting the supplied voltage by some angle (preferably 120°). This effect can be achieved by using a phase-shifting element. Theoretically, this could be inductance or even resistance, but most often a three-phase motor in a single-phase network is switched on using electrical circuits designated by the Latin letter C on the diagrams.
As for the use of chokes, it is difficult due to the difficulty of determining their value (if it is not indicated on the device body). To measure the value of L, a special device or a circuit assembled for this purpose is required. In addition, the choice of available chokes is usually limited. However, any phase-shifting element can be selected experimentally, but this is a troublesome task.
What happens when you turn on the engine? Zero is applied to one of the connection points, phase is applied to the other, and a certain voltage is applied to the third, shifted by a certain angle relative to the phase. It is clear to a non-specialist that the operation of the engine will not be complete in terms of mechanical power on the shaft, but in some cases the very fact of rotation is sufficient. However, already at startup, some problems may arise, for example, the lack of an initial torque capable of moving the rotor from its place. What to do in this case?
Start capacitor
At the moment of starting, the shaft requires additional efforts to overcome the forces of inertia and static friction. To increase the torque, you should install an additional capacitor, connected to the circuit only at the moment of start, and then turned off. For these purposes, the best option is to use a locking button without fixing the position. The connection diagram for a three-phase motor with a starting capacitor is shown below, it is simple and understandable. At the moment the voltage is applied, press the “Start” button, and it will create an additional phase shift. After the engine spins up to the required speed, the button can (and even should) be released, and only the working capacity will remain in the circuit.
Calculation of container sizes
So, we found out that in order to turn on a three-phase motor in a single-phase network, an additional connection circuit is required, which, in addition to the start button, includes two capacitors. You need to know their value, otherwise the system will not work. First, let's determine the amount of electrical capacitance required to make the rotor move. When connected in parallel, it is the sum:
C = C st + Wed, where:
C st - starting additional capacity that can be switched off after takeoff;
C p is a working capacitor that provides rotation.
We also need the value of the rated current I n (it is indicated on the plate attached to the engine at the manufacturer). This parameter can also be determined using a simple formula:
I n = P / (3 x U), where:
U - voltage, when connected as a “star” - 220 V, and if connected as a “triangle”, then 380 V;
P is the power of a three-phase motor; sometimes, if the plate is lost, it is determined by eye.
So, the dependencies of the required operating power are calculated using the formulas:
C p = Wed = 2800 I n / U - for the “star”;
C p = 4800 I n / U - for a “triangle”;
The starting capacitor should be 2-3 times larger than the working capacitor. The unit of measurement is microfarads.
There is also a very simple way to calculate capacity: C = P /10, but this formula gives the order of the number rather than its value. However, in any case you will have to tinker.
Why adjustment is needed
The calculation method given above is approximate. Firstly, the nominal value indicated on the body of the electrical capacitance may differ significantly from the actual one. Secondly, paper capacitors (generally speaking, an expensive thing) are often second-hand, and they, like any other items, are subject to aging, which leads to an even greater deviation from the specified parameter. Thirdly, the current that will be consumed by the motor depends on the magnitude of the mechanical load on the shaft, and therefore it can only be assessed experimentally. How to do it?
This requires a little patience. The result can be a rather voluminous set of capacitors. The main thing is to secure everything well after finishing the work so that the soldered ends do not fall off due to vibrations emanating from the motor. And then it would be a good idea to analyze the result again and, perhaps, simplify the design.
Composing a battery of containers
If the master does not have at his disposal special electrolytic clamps that allow you to measure the current without opening the circuits, then you should connect an ammeter in series to each wire that enters the three-phase motor. In a single-phase network, the total value will flow, and by selecting capacitors one should strive for the most uniform loading of the windings. It should be remembered that when connected in series, the total capacitance decreases according to the law:
It is also necessary not to forget about such an important parameter as the voltage for which the capacitor is designed. It must be no less than the nominal value of the network, or better yet, with a margin.
Discharge resistor
The circuit of a three-phase motor connected between one phase and a neutral wire is sometimes supplemented with resistance. It serves to prevent the charge remaining on the starting capacitor from accumulating after the machine has already been turned off. This energy can cause an electric shock, which is not dangerous, but extremely unpleasant. In order to protect yourself, you should connect a resistor in parallel with the starting capacitance (electricians call this “bypassing”). The value of its resistance is large - from half a megohm to a megohm, and it is small in size, so half a watt of power is enough. However, if the user is not afraid of being “pinched,” then this detail can be completely dispensed with.
Using Electrolytes
As already noted, film or paper electrical containers are expensive, and purchasing them is not as easy as we would like. It is possible to make a single-phase connection to a three-phase motor using inexpensive and readily available electrolytic capacitors. At the same time, they won’t be very cheap either, since they must withstand 300 Volts of DC. For safety, they should be bypassed with semiconductor diodes (D 245 or D 248, for example), but it would be useful to remember that when these devices break through, alternating voltage will reach the electrolyte, and it will first heat up very much, and then explode, loudly and effectively. Therefore, unless absolutely necessary, it is still better to use paper-type capacitors that operate under either constant or alternating voltage. Some craftsmen completely allow the use of electrolytes in starting circuits. Due to short-term exposure to alternating voltage, they may not have time to explode. It's better not to experiment.
If there are no capacitors
Where do ordinary citizens who do not have access to in-demand electrical and electronic parts purchase them? At flea markets and flea markets. There they lie, carefully soldered by someone’s (usually elderly) hands from old washing machines, televisions and other household and industrial equipment that are out of use and out of use. They ask a lot for these Soviet-made products: sellers know that if a part is needed, they will buy it, and if not, they will not take it for nothing. It happens that just the most necessary thing (in this case, a capacitor) is just not there. So what should we do? No problem! Resistors will also do, you just need powerful ones, preferably ceramic and vitrified ones. Of course, ideal resistance (active) does not shift the phase, but nothing is ideal in this world, and in our case this is good. Every physical body has its own inductance, electrical power and resistivity, whether it is a tiny speck of dust or a huge mountain. Connecting a three-phase motor to a power outlet becomes possible if in the above diagrams you replace the capacitor with a resistance, the value of which is calculated by the formula:
R = (0.86 x U) / kI, where:
kI - current value for three-phase connection, A;
U - our trusty 220 Volts.
What engines are suitable?
Before purchasing a motor for a lot of money, which a zealous owner intends to use as a drive for a grinding wheel, circular saw, drilling machine or any other useful household device, it would not hurt to think about its applicability for these purposes. Not every three-phase motor in a single-phase network will be able to operate at all. For example, the MA series (it has a squirrel-cage rotor with a double cage) should be excluded so that you do not have to carry considerable and useless weight home. In general, it is best to experiment first or invite an experienced person, an electrician, for example, and consult with him before purchasing. A three-phase asynchronous motor of the UAD, APN, AO2, AO and, of course, A series is quite suitable. These indices are indicated on the nameplates.
Of all types of electric drives, the most widespread are the ones. They are unpretentious in maintenance, there is no brush-collector unit. If you don't overload them, don't get them wet, and periodically service or change the bearings, then it will last almost forever. But there is one problem - most of the asynchronous motors that you can buy at the nearest flea market are three-phase, as they are intended for industrial use. Despite the trend towards switching to three-phase power supply in our country, the vast majority of houses still have single-phase input. Therefore, let's figure out how to connect a three-phase motor to a single-phase and three-phase network.
What is a star and triangle in an electric motor?
First, let's figure out what the winding connection diagrams are. It is known that a single-speed three-phase asynchronous electric motor has three windings. They are connected in two ways, according to the diagrams:
- star;
- triangle.
Such connection methods are typical for any type of three-phase load, and not just for electric motors. Below is how they look in the diagram:
The power wires are connected to the terminal block, which is located in a special box. It is called Brno or Borno. Wires from the windings are routed into it and secured to terminal blocks. The box itself is removed from the motor housing, as are the terminal blocks located in it.
Depending on the design of the engine, there may be 3 wires, or there may be 6 wires. If there are 3 wires, then the windings are already connected according to a star or delta circuit and, if necessary, it will not be possible to quickly reconnect them; to do this, you need to open the case, look for the connection point, disconnect it and make taps.
If there are 6 wires in the brno, which is more common, then depending on the characteristics of the engine and the voltage of the supply network (read about this below), you can connect the windings as you see fit. Below you see the brno and the terminal blocks that are installed in it. For a 3-wire version there will be 3 pins in the terminal block, and for a 6-wire version there will be 6 pins.
The beginnings and ends of the windings are connected to the studs not just “at random” or “as convenient”, but in a strictly defined order, so that with one set of jumpers you can connect both a triangle and a star. That is, the beginning of the first winding is above the end of the third, the beginning of the second is the end of the first, and the beginning of the third is above the end of the second.
Thus, if you install jumpers on the lower contacts of the terminal block in line, you get a star connection of the windings, and by installing three jumpers vertically parallel to each other, you get a delta connection. On “factory equipped” engines, copper bars are used as jumpers, which is convenient to use for connection - no need to bend wires. 
By the way, on the covers of the electric motor, the location of the jumpers is often marked in accordance with these diagrams.
Connection to a three-phase network
Now that we have figured out how the windings are connected, let's figure out how they connect to the network.
Motors with 6 wires allow the windings to be switched for different supply voltages. This is how electric motors with supply voltages became widespread:
- 380/220;
- 660/380;
- 220/127.
Moreover, the higher voltage is for the star connection circuit, and the lower voltage is for the delta connection.
The fact is that a three-phase network does not always have the usual voltage of 380V. For example, on ships there is a network with an isolated neutral (without zero) for 220V, and in old Soviet buildings of the first half of the last century, a 127/220V network is sometimes found now. While a network with a linear voltage of 660V is rare, it is more common in production.
You can read about the differences between phase and line voltage in the corresponding article on our website:.
So, if you need to connect a three-phase electric motor to a 380/220V network, inspect its nameplate and find the supply voltage.
Electric motors on the nameplate that indicate 380/220 can only be connected with a star to our networks. If instead of 380/220 it says 660/380, connect the windings with a triangle. If you are unlucky and have an old 220/127 engine, you need either a step-down transformer or a single-phase one with a three-phase output (3x220). Otherwise, connecting it to three phases 380/220 will not work.
The worst case scenario is when the rated voltage of the motor is three wires with an unknown winding connection diagram. In this case, you need to open the case and look for the point of their connection and, if possible, and they are connected in a triangle pattern, convert them into a star circuit.
We’ve sorted out the connection of the windings, now let’s talk about what types of connections there are for a three-phase electric motor to a 380V network. The diagrams are shown for contactors with coils with a rated voltage of 380V; if you have 220V coils, connect them between phase and zero, that is, the second wire to zero, and not to phase “B”.
Electric motors are almost always connected via (or). You can see the connection diagram without reverse and self-retaining below. It works in such a way that the motor will rotate only when the button on the control panel is pressed. In this case, the button is selected without fixing, i.e. makes or opens contacts while held down, like those used in keyboards, mice, and doorbells.
The principle of operation of this circuit: when you press the “START” button, current begins to flow through the coil of the KM-1 contactor, as a result the contactor armature is attracted and the power contacts of KM-1 are closed, the engine begins to work. When you release the START button, the engine will stop. QF-1 is one that de-energizes both the power circuit and the control circuit.
If you need to press a button and the shaft starts to rotate, instead of the button, install a toggle switch or a button with a locking mechanism, that is, the contacts of which, after pressing, remain closed or open until the next press.
But this is not done often. Much more often, electric motors are started from remote controls with buttons without locking. Therefore, one more element is added to the previous circuit - the block contact of the starter (or contactor), connected in parallel to the “START” button. This circuit can be used to connect electric fans, hoods, machine tools and any other equipment whose mechanisms rotate in only one direction.
The principle of operation of the circuit:
When the QF-1 circuit breaker is switched to the on state, voltage appears on the power contacts of the contactor and the control circuit. The “STOP” button is normally closed, i.e. its contacts open when it is pressed. Through “STOP”, voltage is supplied to the normally open “START” button, the block contact and, ultimately, the coil, so when you press it, the coil control circuit will be de-energized and the contactor will turn off.
In practice, in a push-button post, each button has a normally open and normally closed pair of contacts, the terminals of which are located on different sides of the button (see photo below).
When you press the “START” button, current begins to flow through the coil of the contactor or starter KM-1 (on modern contactors designated as A1 and A2), as a result its armature is attracted and the power contacts of KM-1 are closed. KM-1.1 is a normally open (NO) block contact of the contactor; when voltage is applied to the coil, it closes simultaneously with the power contacts and bypasses the “START” button.
After you release the “START” button, the engine will continue to operate, since current is now supplied to the contactor coil through the KM-1.1 block contact.
This is called “self-recovery”.
The main difficulty that beginners have in understanding this basic circuit is that it is not immediately clear that the push-button station is located in one place, and the contactors in another. At the same time, KM-1.1, which is connected parallel to the “START” button, can actually be located tens of meters away.
If you need the electric motor shaft to rotate in both directions, for example, on a winch or other lifting mechanism, as well as on various machines (lathes, etc.) - use a connection diagram for a three-phase motor with reverse.
By the way, this circuit is often called a “reversing starter circuit.”
A reversible connection diagram consists of two non-reversible diagrams with some modifications. KM-1.2 and KM-2.2 are normally closed (NC) block contacts of contactors. They are included in the control circuit of the coil of the opposite contactor, this is the so-called “fool protection”, it is needed to prevent this from happening in the power circuit.
Between the “FORWARD” or “BACK” button (their purpose is the same as in the previous diagram for “START”) and the coil of the first contactor (KM-1), a normally closed (NC) block contact of the second contactor (KM-2) is connected. . Thus, when KM-2 turns on, the normally closed contact opens accordingly and KM-1 will no longer turn on, even if you press “FORWARD”.
Conversely, the NC from KM-2 is installed in the control circuit of KM-1 to prevent their simultaneous activation.
To start the motor in the opposite direction, that is, turn on the second contactor, you need to turn off the existing contactor. To do this, press the “STOP” button, and the control circuit of the two contactors is de-energized, and after that press the start button in the opposite direction of rotation.
This is necessary to prevent a short circuit in the power circuit. Pay attention to the left side of the diagram; the differences in connecting the power contacts KM-1 and KM-2 are in the order of connecting the phases. As you know, to change the direction of rotation of an asynchronous motor (reverse), you need to swap 2 of the 3 phases (any), here the 1st and 3rd phases were swapped.
Otherwise, the operation of the circuit is similar to the previous one.
By the way, Soviet starters and contactors had combined block contacts, i.e. one of them was closed, and the second was open; in most modern contactors you need to install a block contact attachment on top, which has 2-4 pairs of additional contacts just for these purposes.
Connection to a single-phase network
To connect a three-phase 380V electric motor to a single-phase 220V network, a circuit with phase-shifting capacitors (starting and running) is most often used. Without capacitors, the engine may start, but only without a load, and you will have to turn its shaft by hand when starting.
The problem is that for the IM to operate, it requires a rotating magnetic field, which cannot be obtained from a single-phase network without additional elements. But by connecting one of the windings through, you can shift the voltage phase to -90˚ and with the help of +90˚ relative to the phase in the network. We discussed the issue of phase shift in more detail in the article:.
Most often, capacitors are used for phase shifting, rather than chokes. In this way, not a rotating one is obtained, but an elliptical one. As a result, you lose about half of the nominal power. Single-phase IMs work better with this connection, due to the fact that their windings are initially designed and located on the stator for such a connection.
You can see typical motor connection diagrams without reverse for star or delta circuits below.
In the diagram below, it is needed to discharge the capacitors, since after turning off the power, voltage will remain at its terminals and you may get an electric shock.
You can select the capacitor capacity for connecting a three-phase motor to a single-phase network based on the table below. If you observe a difficult and lengthy startup, you often need to increase the starting (and sometimes working) capacity.
If the engine is powerful or starts under load (for example, in a compressor), you also need to connect a starting capacitor.
To simplify switching on, instead of the “ACceleration” button, use “PNVS”. This is a button for starting motors with a starting capacitor. It has three contacts, phase and zero are connected to two of them, and a starting capacitor is connected through the third. There are two keys on the front panel - “START” and “STOP” (as on AP-50 machines).
When you turn on the engine and press the first key all the way, three contacts close, after the engine has spun up and you release “START”, the middle contact opens, and the two outer ones remain closed, and the starting capacitor is removed from the circuit. When you press the “STOP” button, all contacts open. The connection diagram is almost the same.
You can watch the following video for details about what it is and how to properly connect the NVDS:
The connection diagram for a 380V electric motor to a single-phase 220V network with reverse is shown below. Switch SA1 is responsible for reverse.
The windings of a 380/220 motor are connected in a triangle, and for motors 220/127 – in a star, so that the supply voltage (220 volts) corresponds to the rated voltage of the windings. If there are only three outputs, and not six, then you will not be able to change the winding connection diagrams without opening them. There are two options here:
- Rated voltage 3x220V - you're in luck and use the circuits above.
- Rated voltage 3x380V - you are less lucky, since the engine may start poorly or not start at all if you connect it to a 220V network, but it’s worth a try, it might work!
But when connecting a 380V electric motor to 1 phase 220V through capacitors, there is one big problem - power loss. They can reach 40-50%.
The main and effective way to connect without losing power is to use a frequency converter. Single-phase frequency converters output 3 phases with a linear voltage of 220V without zero. In this way you can connect motors up to 5 kW; for higher power, it is simply very rare to find converters that can work with single-phase input. In this case, you will not only receive full engine power, but will also be able to fully regulate its speed and reverse it.
Now you know how to connect a three-phase motor for 220 and 380 Volts, as well as what is needed for this. We hope the information provided helped you understand the issue!
Materials
Home-grown “kulibins” use whatever they can get their hands on for electromechanical crafts. When choosing an electric motor, you usually come across three-phase asynchronous ones. This type has become widespread due to its successful design, good balancing and efficiency.
This is especially true in powerful industrial units. Outside a private house or apartment, there are no problems with three-phase power. How to organize the connection of a three-phase motor to a single-phase network if your meter has two wires?
Let's consider the standard connection option
Three-phase motor, has three windings at an angle of 120°. Three pairs of contacts are output to the terminal block. The connection can be organized in two ways:
Star and delta connection
Each winding is connected at one end to two other windings, forming the so-called neutral. The remaining ends are connected to the 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, so it does not matter which phase or wire is applied to.
With this method, the end of each winding is connected to the next, resulting in a closed circle, or rather a triangle. Each winding has a voltage of 380 volts.
Connection diagram:
Accordingly, the jumpers on the terminal block are installed differently. Similar to the first option, there is no polarity as a class.
Each group of contacts receives current at different times, following the concept of “phase shift”. Therefore, the magnetic field consistently pulls the rotor along with it, creating a continuous torque. This is how the engine works with its “native” three-phase power supply.
What if you received an engine in excellent condition, but you need to connect it to a single-phase network? Don’t be upset; the connection diagram for a three-phase motor has been worked out by engineers a long time ago. 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 being turned on correctly. The rotor rotates, practically without losing speed, no jerks or slowdowns are observed.
However, it is impossible to achieve standard 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%.
At the same time, 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 the various methods:
Capacitor switching method
Since we need to ensure that “phase shift”, we use the natural abilities of capacitors. We have two supply wires; we connect them respectively to both points of the standard terminal block.
A third contact remains, to which current is supplied from one of the already connected ones. And not directly (otherwise the motor will not start rotating), but through a capacitor circuit.
Two capacitors are used (they are called phase-shifting).
The diagram above shows that one capacitor is constantly on, and the second through a non-latching button. The first element is working, its task is to simulate the standard phase shift for the third winding.
The second container is intended for the first revolution of the rotor, then it rotates by inertia, each time falling between false “phases”. The starting capacitor cannot be left on constantly, as it will cause confusion in the relatively orderly rhythm of rotation.
note
The above diagram for connecting a three-phase motor to a single-phase network is theoretical. For real work, it is necessary to correctly calculate the capacitances of both elements and select the type of capacitors.
Formula for calculating the working “capacitor”:
- When connected as a star, C=(2800*I)/U;
- When connected in a triangle, C=(4800*I)/U;