Connection diagram for a 3-phase 220 volt motor. Three-phase motor in a single-phase network. Three-phase motor connection diagram. Motor with magnetic starter

Instructions

As a rule, to connect a three-phase electric motor, three wires and a supply voltage of 380 are used. There are only two wires in a 220 volt network, so in order for the engine to work, voltage must also be applied to the third wire. For this purpose, a capacitor is used, which is called a working capacitor.

The capacitor capacity depends on the engine power and is calculated by the formula:
C=66*P, where C is the capacitance of the capacitor, μF, P is the power of the electric motor, kW.

That is, for every 100 W of engine power it is necessary to select about 7 μF of capacitance. Thus, a 500 watt motor requires a capacitor with a capacity of 35 µF.

The required capacity can be assembled from several capacitors of smaller capacity by connecting them in parallel. Then the total capacity is calculated using the formula:
Ctotal = C1+C2+C3+…..+Cn

It is important to remember that the operating voltage of the capacitor should be 1.5 times the power supply to the electric motor. Therefore, with a supply voltage of 220 volts, the capacitor should be 400 volts. Capacitors can be used of the following types: KBG, MBGCh, BGT.

To connect the motor, two connection schemes are used - “triangle” and “star”.

If in a three-phase network the motor was connected according to a delta circuit, then we connect it to a single-phase network according to the same circuit with the addition of a capacitor.

The star connection of the motor is carried out according to the following diagram.

To operate electric motors with a power of up to 1.5 kW, the capacity of the working capacitor is sufficient. If you connect a higher power engine, then such an engine will accelerate very slowly. Therefore it is necessary to use a starting capacitor. It is connected in parallel with the run capacitor and is used only during engine acceleration. Then the capacitor is turned off. The capacitor capacity to start the engine should be 2-3 times greater than the operating capacity.

After starting the engine, determine the direction of rotation. Typically you want the motor to rotate clockwise. If the rotation occurs in the desired direction, you do not need to do anything. To change direction, it is necessary to remount the engine. Disconnect any two wires, swap them and reconnect. The direction of rotation will change to the opposite.

When performing electrical installation work, follow safety regulations and use personal protective equipment against electric shock.

Three-phase electric does not contain brushes that can wear out and require periodic replacement. It is less efficient than collector, but much more efficient than asynchronous single-phase. Its disadvantage is its significant dimensions.

Instructions

Find the nameplate on the three-phase electric motor. It shows two voltages, for example: 220/380 V. The engine can be powered by any of these voltages, it is only important to connect its windings correctly: for the lower of the indicated voltages - with a triangle, for the higher - with a star.

Asynchronous electric motors, widely used in production, are connected with a “delta” or “star”. The first type is mainly used for motors with prolonged starting and operation. The joint connection is used to start high-power electric motors. The star connection is used at the beginning of the start-up, then switching to delta. A connection diagram for a 220-volt three-phase electric motor is also used.

(ArticleToC: enabled=yes)

There are many types of motors, but for all of them, the main characteristic is the voltage supplied to the mechanisms and the power of the motors themselves.

When connected to 220V, the motor is subject to high starting currents, which reduce its service life. In industry, delta connections are rarely used. Powerful electric motors are connected in a star.

To switch from a 380 to 220 motor connection diagram, there are several options, each of which has advantages and disadvantages.

It is very important to understand how a three-phase electric motor is connected to a 220V network. To connect a three-phase motor to 220V, note that it has six terminals, which corresponds to three windings. Using a tester, the wires are pinged to find the coils. We connect their ends in twos - we get a “triangle” connection (and three ends).

To begin with, we connect the two ends of the network cable (220 V) to any two ends of our “triangle”. The remaining end (the remaining pair of twisted coil wires) is connected to the end of the capacitor, and the remaining capacitor wire is also connected to one of the ends of the power wire and coils.

Whether we choose one or the other will depend on which direction the engine starts to rotate. Having completed all the above steps, we start the engine by applying 220 V to it.

The electric motor should work. If this does not happen, or it does not reach the required power, you need to return to the first stage to swap the wires, i.e. reconnect the windings.

If, when turned on, the motor hums but does not spin, you need to additionally install (via a button) a capacitor. At the moment of starting, it will give the engine a push, forcing it to spin.

Video: How to connect an electric motor from 380 to 220

Calling, i.e. resistance measurement is carried out by a tester. If you don’t have one, you can use a battery and a regular flashlight lamp: the identified wires are connected to the circuit in series with the lamp. If the ends of one winding are found, the lamp lights up.

It is much more difficult to determine the beginning and ends of the windings. You can't do without a voltmeter with an arrow.

You will need to connect a battery to the winding, and a voltmeter to the other.

By breaking the contact of the wire with the battery, observe whether the arrow deviates and in which direction. The same actions are carried out with the remaining windings, changing the polarity if necessary. Make sure that the arrow deviates in the same direction as during the first measurement.

Star-delta circuit

In domestic engines, the “star” is often already assembled, but the triangle needs to be implemented, i.e. connect three phases, and assemble a star from the remaining six ends of the winding. Below is a drawing to make it easier to understand.

The main advantage of connecting a three-phase circuit with a star is that the motor produces the most power.

Nevertheless, such a connection is loved by amateurs, but is not often used in production, since the connection diagram is complex.

For it to work you need three starters:

The first of them, K1, is connected to the stator winding on one side and the current to the other. The remaining ends of the stator are connected to starters K2 and K3, and then to obtain a “triangle”, the winding with K2 is also connected to the phases.

Having connected it to phase K3, slightly shorten the remaining ends to obtain a “star” circuit.

Important: It is unacceptable to turn on K3 and K2 at the same time, so that a short circuit does not occur, which can lead to the shutdown of the electric motor circuit breaker. To avoid this, electrical interlocking is used. It works like this: when one of the starters is turned on, the other is turned off, i.e. its contacts open.

How the scheme works

When K1 is turned on using a time relay, K3 is turned on. The three-phase motor, connected in a star configuration, operates with more power than usual. After some time, the contacts of relay K3 open, but K2 starts. Now the motor operation pattern is “triangle”, and its power becomes less.

When a power cut is required, K1 is started. The pattern is repeated in subsequent cycles.

A very complex connection requires skill and is not recommended for beginners.

Other motor connections

There are several schemes:

1. More often than the option described, a circuit with a capacitor is used, which will help to significantly reduce power. One of the contacts of the working capacitor is connected to zero, the second - to the third output of the electric motor. As a result, we have a low-power unit (1.5 W). If the engine power is high, a starting capacitor will need to be added to the circuit. With a single-phase connection, it simply compensates for the third output.
2. It is easy to connect an asynchronous motor with a star or triangle when moving from 380V to 220V. Such motors have three windings. To change the voltage, it is necessary to swap the outputs going to the tops of the connections.
3. When connecting electric motors, it is important to carefully study the passports, certificates and instructions, because in imported models there is often a “triangle” adapted for our 220V. Such motors, if you ignore this and turn on the “star”, simply burn out. If the power is more than 3 kW, the motor cannot be connected to the household network. This can lead to a short circuit and even failure of the RCD.

Connecting a three-phase motor to a single-phase network

The rotor connected to the three-phase circuit of a three-phase motor rotates due to the magnetic field created by the current flowing at different times through different windings. But, when such a motor is connected to a single-phase circuit, no torque arises that could rotate the rotor. The simplest way to connect three-phase motors to a single-phase circuit is to connect its third contact through a phase-shifting capacitor.

When connected to a single-phase network, such a motor has the same rotation speed as when operating from a three-phase network. But the same cannot be said about power: its losses are significant and they depend on the capacity of the phase-shifting capacitor, the operating conditions of the motor, and the selected connection diagram. Losses approximately reach 30-50%.

The circuits can be two-, three-, or six-phase, but the most commonly used are three-phase. A three-phase circuit is understood as a set of electrical circuits with the same frequency of sinusoidal EMF, which differ in phase, but are created by a common energy source.

If the load in the phases is the same, the circuit is symmetrical. For three-phase asymmetrical circuits it is different. The total power consists of the active power of the three-phase circuit and the reactive power.

Although most motors cope with operation from a single-phase network, not all can work well. Better than others in this sense are asynchronous motors, which are designed for a voltage of 380/220 V (the first is for star, the second is for delta).

This operating voltage is always indicated in the passport and on the plate attached to the engine. It also shows the connection diagram and options for changing it.

If "A" is present, this indicates that either a delta or star circuit can be used. “B” indicates that the windings are connected in a star and cannot be connected in any other way.

The result should be: when the contacts of the winding with the battery are broken, the electric potential of the same polarity (i.e., the arrow deflects in the same direction) should appear on the two remaining windings. The start (A1, B1, C1) and end (A2, B2, C2) terminals are marked and connected according to the diagram.

Using a magnetic starter

The good thing about using a 380 electric motor connection diagram is that it can be started remotely. The advantage of a starter over a switch (or other device) is that the starter can be placed in a cabinet, and the controls can be placed in the work area; the voltage and currents are minimal, therefore, the wires are suitable for a smaller cross-section.

In addition, connection using a starter ensures safety in the event that the voltage “disappears”, since this opens the power contacts, and when the voltage appears again, the starter will not supply it to the equipment without pressing the start button.

Connection diagram for a 380V electric asynchronous motor starter:

At contacts 1,2,3 and start button 1 (open), voltage is present at the initial moment. Then it is supplied through the closed contacts of this button (when you press “Start”) to the contacts of the coil starter K2, closing it. The coil creates a magnetic field, the core is attracted, the contacts of the starter close, driving the motor.

At the same time, the NO contact closes, from which the phase is supplied to the coil through the “Stop” button. It turns out that when the “Start” button is released, the coil circuit remains closed, as do the power contacts.

By pressing “Stop”, the circuit is broken, returning the power contacts to open. The voltage disappears from the conductors and NO supplying the engine.

Video: Connecting an asynchronous motor. Determination of engine type.

The article contains tips on how you can connect such an electric motor to a single-phase network without using a capacitor bank or a frequency converter using a current pulse from an electronic switch. They are supplemented with diagrams and a video.

Operating principle of the electronic key

If you assemble the windings of an asynchronous electric motor according to a triangle diagram and connect them to a single-phase network voltage of 220 volts, then the same currents will flow through them, as shown in the graph below.

The angular displacement of any winding relative to the others is 120 degrees. Therefore, the magnetic fields from each of them will add up, eliminating mutual influence.

The resulting stator magnetic field created will not affect the rotor: it will remain at rest.

In order for the electric motor to start rotating, it is necessary to pass currents shifted by 120° through its windings, as is done in a normal three-phase power system or due to. Then the engine will produce power with minimal losses, having the greatest efficiency.

Widespread industrial ones allow it to work, but with lower efficiency and greater losses, which, most often, is quite acceptable.

Alternative methods are:

1. Mechanical spinning of the rotor, for example, due to manually winding the cord on the shaft and sharply twisting it with a jerk when voltage is applied;
2. Phase shift of currents due to short-term use of an electronic switch that switches the electrical resistance of one winding.

Since the first method of “winding and pulling” does not cause difficulties, we immediately analyze the second.

The top diagram shows an electronic switch “k” connected in parallel to winding B. This rather conventional designation is adopted to explain the principle of operation of an electric motor due to the formation of a current pulse.

How the engine starts

The stator windings are connected in a delta circuit. One of them (A) is supplied with 220 volts. Another chain of two serial windings (B+C) is connected in parallel to it.

According to Ohm's law, network voltage creates currents in them. Their value depends on the resistance. All windings are the same. Therefore, in (A) the current is greater, and (B+C) is 2 times less in magnitude. Moreover, they coincide in phase. In this situation, they are not able to create a rotating magnetic field sufficient to start the rotor.

An electronic circuit designated as switch K is connected in parallel to winding (B). It is in an open state, but briefly closes when the maximum voltage on winding C is reached.

The electronic switch short-circuits winding B and the voltage drop on winding C jumps twice, which ultimately ensures a phase shift of the currents in windings A and C. It is important to note that the current in windings (A) and (B + C) at this moment equal to zero.

The phase shift angle φ required to start the engine can be maintained in the range of 50÷70°, although the ideal option is 120.

The design of a phase-shifting electronic key can be assembled from various parts. The most suitable devices for domestic purposes, according to their complexity, are presented below.

Electric motor starting circuit up to 2 kW

Its description can be found in No. 6 of Radio magazine, 1996. The author of the article, V. Golik, proposes the design of a bidirectional (positive and negative semi-harmonics) electronic switch based on two diodes and thyristors with control of a transistor unit.

Description of technology

Power diodes VD1 and VD2 together with thyristors VS1, VS2 form a bridge, which is controlled by forward and reverse bipolar transistors. The position of the trimming resistor R7 affects the opening voltage of VT1, VT2.

The operation of the transistor switch provides a short-term phase shift of the currents in the windings and the creation of a rotating magnetic field that spins the rotor.

Due to the applied moment of magnetic forces to the rotor, the latter begins to rotate. Its energy is constantly replenished at each half-wave with the next impulse.

Installation features

The author made an electronic key on a fiberglass board and placed it in an insulated housing with the ability to connect input and output circuits through contact pins. The option of performing the circuit with wall-mounted installation is also eligible for implementation.

For operation of small-power electric motors, it is permissible to place power diodes and thyristors without radiators. But it is better to ensure good heat removal from them and reliable operation in advance by including these elements in the design of the electronic key.

The ratings of the electronic components are indicated directly on the diagram.

To ensure safety, the housing of the electronic unit should be well insulated to prevent accidental touching of its parts during operation: they are all energized at 220 volts.

Setup principles

The resistor slider R7 “Mode” has two extreme positions:

1. minimal;
2. and maximum resistance.

In the first case, the electronic switch is open and creates a maximum current shift pulse in the winding, and in the second case it is closed: rotor rotation is excluded.

A three-phase motor is started at the maximum permissible phase shift of the current inside the winding. Then position R7 sets its operating speed and power.

Verified models

1. speed 1360 and power 370 watts (AAAM63V4SU1);
2. 1380 rpm, 2 kW.

The results of the experiments satisfied him.

Two triac circuits

The following 2 electronic key designs were described by V Burlako in 1999. They were published in the journal Signal No. 4.

Starting a light motor

The device is designed for engines with power up to 2.2 kW and has a minimum set of electronic parts.

Capacitor C, having capacitive reactance, under the influence of voltage applied to its plates, shifts the current vector forward by 90 degrees, directing it to control dinistor VS2.

The potential difference across the capacitor is regulated by the total resistance R1, R2. The dinistor pulse is supplied to the control electrode of triac VS1, which injects current into the motor winding.

Engine starting circuit under load

For machines and mechanisms that create great resistance to rotor spin-up, it is recommended to switch the windings to an open-star circuit with the creation of two spin-up torques.

The polarity of the motor windings is indicated by dots in the diagram. Phase-shifting chains of current pulses work using the same technology as in previous cases. The ratings of electrical parts are indicated next to their graphic symbols.

Setup features

All three contacts of this starter close simultaneously when you press the “Start” button, and when released:

• the two extreme ones remain in a closed state;
• middle - breaks, turning off the starting winding circuit.

A current pulse is supplied through this middle contact in both circuits. The circuit operates only for the time necessary to spin up the engine, after which it is taken out of operation and disconnected from the supply voltage.

The engine starting moment in each circuit is selected after applying voltage by changing resistance R2. At the same time, large currents pass in the triangle until the rotor spins up, causing strong vibrations of the structure. To reduce them, it is recommended to select the phase-shifting pulse in steps, rather than smoothly.

At the optimal position of R2, the engine starts without vibration.

For low-power engines, it is possible to install triacs without cooling radiators, but the latter still increase the reliability of the circuit.

My opinion about the method

In the three considered circuits, the operating mode current flows through all connected windings. The full consumption of the applied energy is not spent profitably. Only about 30% of its power is generated by the rotation of the rotor. The rest, about 70%, are irrecoverable losses.

If someone is satisfied with starting a three-phase motor in a single-phase network according to this scheme, then this is your choice. I reviewed these schemes to show their positive and negative sides, without imposing my own opinion.

This topic began to be widely used by the creators of videos on YouTube, gaining the number of views and subscribers, like YUKA LAKHT, in his video “Without capacitor starting a three-phase motor.”

Make your choice consciously, and if you still have questions on the topic, now it’s convenient for you to ask them in the comments.

Three-phase asynchronous motors are deservedly the most popular in the world, due to the fact that they are very reliable, require minimal maintenance, are easy to manufacture and do not require any complex and expensive devices when connecting, unless adjustment of the rotation speed is required. Most of the machines in the world are driven by three-phase asynchronous motors; they also drive pumps and electric drives of various useful and necessary mechanisms.

But what about those who do not have a three-phase power supply in their personal household, and in most cases this is exactly the case. What if you want to install a stationary circular saw, electric jointer or lathe in your home workshop? I would like to please the readers of our portal that there is a way out of this difficult situation, and one that is quite simple to implement. In this article we intend to tell you how to connect a three-phase motor to a 220 V network.

Let us briefly consider the principle of operation of an asynchronous motor in its “native” three-phase 380 V networks. This will greatly help in later adapting the motor for operation in other, “non-native” conditions - single-phase 220 V networks.

Asynchronous motor device

Most of the three-phase motors produced in the world are squirrel-cage induction motors (SCMC), which do not have any electrical contact between the stator and the rotor. This is their main advantage, since brushes and commutators are the weakest point of any electric motor; they are subject to intense wear and require maintenance and periodic replacement.

Let's consider the ADKZ device. The engine is shown in cross-section in the figure.

The cast housing (7) houses the entire electric motor mechanism, which includes two main parts - a stationary stator and a movable rotor. The stator has a core (3), which is made of sheets of special electrical steel (an alloy of iron and silicon), which has good magnetic properties. The core is made of sheets due to the fact that under conditions of an alternating magnetic field, Foucault eddy currents can arise in the conductors, which we absolutely do not need in the stator. Additionally, each core sheet is coated on both sides with a special varnish to completely eliminate the flow of currents. We only need from the core its magnetic properties, and not the properties of an electric current conductor.

A winding (2) made of enameled copper wire is laid in the grooves of the core. To be precise, there are at least three windings in a three-phase asynchronous motor - one for each phase. Moreover, these windings are laid in the grooves of the core with a certain order - each is located so that it is at an angular distance of 120° to the other. The ends of the windings are led out into the terminal box (in the figure it is located at the bottom of the motor).

The rotor is placed inside the stator core and rotates freely on the shaft (1). To increase efficiency, they try to make the gap between the stator and rotor minimal - from half a millimeter to 3 mm. The rotor core (5) is also made of electrical steel and it also has grooves, but they are not intended for wire winding, but for short-circuited conductors, which are located in space so that they resemble a squirrel wheel (4), for which they received their Name.

The squirrel wheel consists of longitudinal conductors that are connected both mechanically and electrically to the end rings. Typically, the squirrel wheel is made by pouring molten aluminum into the grooves of the core, and at the same time, both rings and fan impellers (6) are molded as a monolith. In high-power ADKZ, copper rods welded with end copper rings are used as cell conductors.

What is three-phase current

In order to understand what forces make the ADKZ rotor rotate, we need to consider what a three-phase power supply system is, then everything will fall into place. We are all accustomed to the usual single-phase system, when the socket has only two or three contacts, one of which is (L), the second is a working zero (N), and the third is a protective zero (PE). The rms phase voltage in a single-phase system (the voltage between phase and zero) is 220 V. The voltage (and when a load is connected, the current) in single-phase networks varies according to a sinusoidal law.

From the above graph of the amplitude-time characteristic it is clear that the amplitude value of the voltage is not 220 V, but 310 V. So that readers do not have any “misunderstandings” or doubts, the authors consider it their duty to inform that 220 V is not the amplitude value, but the root mean square or current. It is equal to U=U max /√2=310/1.414≈220 V. Why is this done? For convenience of calculations only. Constant voltage is taken as the standard, based on its ability to produce some kind of work. We can say that a sinusoidal voltage with an amplitude value of 310 V in a certain period of time will produce the same work that a constant voltage of 220 V would do in the same period of time.

It must be said right away that almost all generated electrical energy in the world is three-phase. It’s just that single-phase energy is easier to manage in everyday life; most electricity consumers only need one phase to operate, and single-phase wiring is much cheaper. Therefore, one phase and neutral conductor are “pulled out” from a three-phase system and sent to consumers - apartments or houses. This is clearly visible in the entrance panels, where you can see how the wire goes from one phase to one apartment, from another to a second, from a third to a third. This is also clearly visible on the poles from which the lines go to private households.

Three-phase voltage, unlike single-phase, has not one phase wire, but three: phase A, phase B and phase C. Phases can also be designated L1, L2, L3. In addition to the phase wires, of course, there is also a working zero (N) and a protective zero (PE) common to all phases. Let's consider the amplitude-time characteristic of three-phase voltage.

It is clear from the graphs that three-phase voltage is a combination of three single-phase ones, with an amplitude of 310 V and an rms value of the phase (between phase and working zero) voltage of 220 V, and the phases are shifted relative to each other with an angular distance of 2 * π / 3 or 120 ° . The potential difference between the two phases is called linear voltage and is equal to 380 V, since the vector sum of the two voltages will be U l =2*U f *sin(60°)=2*220*√3/2=220* √3=220*1.73=380.6 V, Where U l– linear voltage between two phases, and U f– phase voltage between phase and zero.

Three-phase current is easy to generate, transmit to its destination and subsequently convert it into any desired type of energy. Including the mechanical energy of rotation of the ADKZ.

How does a three-phase asynchronous motor work?

If you apply an alternating three-phase voltage to the stator windings, currents will begin to flow through them. They, in turn, will cause magnetic fluxes, also varying according to a sinusoidal law and also shifted in phase by 2*π/3=120°. Considering that the stator windings are located in space at the same angular distance - 120°, a rotating magnetic field is formed inside the stator core.

This constantly changing field crosses the “squirrel wheel” of the rotor and causes an EMF (electromotive force) in it, which will also be proportional to the rate of change of the magnetic flux, which in mathematical language means the derivative of the magnetic flux with respect to time. Since the magnetic flux changes according to a sinusoidal law, this means that the EMF will change according to the cosine law, because (sin x)’= cos x. From the school mathematics course it is known that the cosine “leads” the sine by π/2 = 90°, that is, when the cosine reaches its maximum, the sine will reach it after π/2 - after a quarter of the period.

Under the influence of EMF, large currents will arise in the rotor, or more precisely, in the squirrel wheel, given that the conductors are short-circuited and have low electrical resistance. These currents form their own magnetic field, which spreads along the rotor core and begins to interact with the stator field. Opposite poles, as is known, attract, and like poles repel each other. The resulting forces create a torque causing the rotor to rotate.

The stator's magnetic field rotates at a certain frequency, which depends on the supply network and the number of pole pairs of the windings. The frequency is calculated using the following formula:

n 1 =f 1 *60/p, Where

• f 1 – alternating current frequency.
• p – number of pole pairs of stator windings.

Everything is clear with the frequency of alternating current - in our power supply networks it is 50 Hz. The number of pole pairs reflects how many pairs of poles there are on the winding or windings belonging to the same phase. If one winding is connected to each phase, spaced 120° from the others, then the number of pole pairs will be equal to one. If two windings are connected to one phase, then the number of pole pairs will be equal to two, and so on. Accordingly, the angular distance between the windings changes. For example, when the number of pole pairs is two, the stator contains a winding of phase A, which occupies a sector of not 120°, but 60°. Then it is followed by the winding of phase B, occupying the same sector, and then phase C. Then the alternation is repeated. As the pole pairs increase, the sectors of the windings decrease accordingly. Such measures make it possible to reduce the rotation frequency of the magnetic field of the stator and, accordingly, the rotor.

Let's give an example. Let's say a three-phase motor has one pair of poles and is connected to a three-phase network with a frequency of 50 Hz. Then the stator magnetic field will rotate with a frequency n 1 =50*60/1=3000 rpm. If you increase the number of pole pairs, the rotation speed will decrease by the same amount. To increase the engine speed, you need to increase the frequency supplying the windings. To change the direction of rotation of the rotor, you need to swap two phases on the windings

It should be noted that the rotor speed always lags behind the rotation speed of the stator magnetic field, which is why the motor is called asynchronous. Why is this happening? Let's imagine that the rotor rotates at the same speed as the stator's magnetic field. Then the squirrel wheel will not “pierce” the alternating magnetic field, but it will be constant for the rotor. Accordingly, no EMF will be induced and currents will stop flowing, there will be no interaction of magnetic fluxes and the moment driving the rotor in motion will disappear. That is why the rotor is “in a constant quest” to catch up with the stator, but will never catch up, since the energy causing the motor shaft to rotate will disappear.

The difference in the rotation frequencies of the magnetic field of the stator and the rotor shaft is called the slip frequency, and it is calculated by the formula:

∆ n=n 1 -n 2, Where

• n1 – rotation frequency of the stator magnetic field.
• n2 – rotor speed.

Slip is the ratio of the sliding frequency to the rotation frequency of the stator magnetic field, it is calculated by the formula: S=∆n/n 1 =(n 1 —n 2)/n 1.

Methods for connecting windings of asynchronous motors

Most ADKZ has three windings, each of which corresponds to its own phase and has a beginning and an end. Winding designation systems may vary. In modern electric motors, a system has been adopted for designating windings U, V and W, and their terminals are designated by number 1 as the beginning of the winding and by number 2 as its end, that is, winding U has two terminals U1 and U2, winding V-V1 and V2, and winding W - W1 and W2.

However, asynchronous motors made during the Soviet era and having the old marking system are still in use. In them, the beginnings of the windings are designated C1, C2, C3, and the ends are C4, C5, C6. This means that the first winding has terminals C1 and C4, the second winding C2 and C5, and the third winding C3 and C6. The correspondence between the old and new notation systems is presented in the figure.

Let's consider how windings can be connected in an ADKZ.

Star connection

With this connection, all ends of the windings are combined at one point, and phases are connected to their beginnings. In the circuit diagram, this connection method really resembles a star, which is why it got its name.

When connected by a star, a phase voltage of 220 V is applied to each winding individually, and a linear voltage of 380 V is applied to two windings connected in series. The main advantage of this connection method is small starting currents, since the linear voltage is applied to two windings, and not to one. This allows the engine to start “softly,” but its power will be limited, since the currents flowing in the windings will be less than with another connection method.

Delta connection

With this connection, the windings are combined into a triangle, when the beginning of one winding is connected to the end of the next - and so on in a circle. If the linear voltage in a three-phase network is 380 V, then much larger currents will flow through the windings than with a star connection. Therefore, the power of the electric motor will be higher.

When connected by a delta at the moment of starting, the ADKZ consumes large starting currents, which can be 7-8 times higher than the rated ones and can cause network overload, so in practice, engineers have found a compromise - the engine starts and spins up to rated speed using a star circuit, and then automatic switching to triangle.

How to determine which circuit the motor windings are connected to?

Before connecting a three-phase motor to a single-phase 220 V network, it is necessary to find out what circuit the windings are connected to and at what operating voltage the ADKZ can operate. To do this, you need to study the plate with technical characteristics - the “nameplate”, which should be on each engine.

You can find out a lot of useful information on such a “nameplate”

The plate contains all the necessary information that will help connect the motor to a single-phase network. The presented nameplate shows that the engine has a power of 0.25 kW and a speed of 1370 rpm, which indicates the presence of two pairs of winding poles. The ∆/Y symbol means that the windings can be connected either by a triangle or a star, and the following indicator 220/380 V indicates that when connected by a triangle, the supply voltage should be 220 V, and when connected by a star - 380 V. If such Connect the motor to a 380 V network in a triangle, then its windings will burn out.

On the next nameplate you can see that such a motor can only be connected with a star and only to a 380 V network. Most likely, such an ADKZ will have only three terminals in the terminal box. Experienced electricians will be able to connect such a motor to a 220 V network, but to do this they will need to open the back cover to get to the winding terminals, then find the beginning and end of each winding and make the necessary switching. The task becomes much more complicated, so the authors do not recommend connecting such motors to a 220 V network, especially since most modern ADKZ can be connected in different ways.

Each motor has a terminal box, most often located on the top. This box has inputs for power cables, and on top it is closed with a lid that must be removed with a screwdriver.

As electricians and pathologists say: “An autopsy will tell.”

Under the cover you can see six terminals, each of which corresponds to either the beginning or the end of the winding. In addition, the terminals are connected by jumpers, and by their location you can determine by what scheme the windings are connected.

Opening the terminal box showed that the “patient” had obvious “star fever”

The photo of the “opened” box shows that the wires leading to the windings are labeled and the ends of all windings – V2, U2, W2 – are connected to one point by jumpers. This indicates that a star connection is taking place. At first glance, it may seem that the ends of the windings are located in the logical order V2, U2, W2, and the beginnings are “confused” - W1, V1, U1. However, this is done for a specific purpose. To do this, consider the ADKZ terminal box with connected windings according to a triangle diagram.

The figure shows that the position of the jumpers changes - the beginnings and ends of the windings are connected, and the terminals are located so that the same jumpers are used for reconnection. Then it becomes clear why the terminals are “mixed up” - this makes it easier to transfer jumpers. The photo shows that terminals W2 and U1 are connected by a piece of wire, but in the basic configuration of new engines there are always exactly three jumpers.

If, after “opening” the terminal box, a picture like the one in the photograph is revealed, this means that the motor is intended for a star and a three-phase 380 V network.

It is better for such an engine to return to its “native element” - in a three-phase alternating current circuit

Video: An excellent film about three-phase synchronous motors, which has not yet been painted

It is possible to connect a three-phase motor to a single-phase 220 V network, but you must be prepared to sacrifice a significant reduction in its power - in the best case, it will be 70% of the nameplate, but for most purposes this is quite acceptable.

The main connection problem is the creation of a rotating magnetic field, which induces an emf in the squirrel-cage rotor. This is easy to implement in three-phase networks. When generating three-phase electricity, an EMF is induced in the stator windings due to the fact that a magnetized rotor rotates inside the core, which is driven by the energy of falling water at a hydroelectric power station or a steam turbine at hydroelectric power stations and nuclear power plants. It creates a rotating magnetic field. In engines, the reverse transformation occurs - a changing magnetic field causes the rotor to rotate.

In single-phase networks, it is more difficult to obtain a rotating magnetic field - you need to resort to some “tricks”. To do this, you need to shift the phases in the windings relative to each other. Ideally, you need to make sure that the phases are shifted relative to each other by 120°, but in practice this is difficult to implement, since such devices have complex circuits, are quite expensive, and their manufacture and configuration require certain qualifications. Therefore, in most cases, simple circuits are used, while somewhat sacrificing power.

Phase shift using capacitors

An electric capacitor is known for its unique property of not passing direct current, but passing alternating current. The dependence of the currents flowing through the capacitor on the applied voltage is shown in the graph.

The current in the capacitor will always “lead” for a quarter of the period

As soon as a voltage increasing along a sinusoid is applied to the capacitor, it immediately “pounces” on it and begins to charge, since it was initially discharged. The current will be maximum at this moment, but as it charges, it will decrease and reach a minimum at the moment when the voltage reaches its peak.

As soon as the voltage decreases, the capacitor will react to this and will begin to discharge, but the current will flow in the opposite direction, as it discharges it will increase (with a minus sign) as long as the voltage decreases. By the time the voltage is zero, the current reaches its maximum.

When the voltage begins to increase with a minus sign, the capacitor is recharged and the current gradually approaches zero from its negative maximum. As the negative voltage decreases and it approaches zero, the capacitor discharges with an increase in the current through it. Next, the cycle repeats again.

The graph shows that during one period of alternating sinusoidal voltage, the capacitor is charged twice and discharged twice. The current flowing through the capacitor leads the voltage by a quarter of a period, that is - 2* π/4=π/2=90°. In this simple way you can obtain a phase shift in the windings of an asynchronous motor. A phase shift of 90° is not ideal at 120°, but it is quite sufficient for the necessary torque to appear on the rotor.

Phase shift can also be obtained by using an inductor. In this case, everything will happen the other way around - the voltage will lead the current by 90°. But in practice, more capacitive phase shift is used due to simpler implementation and lower losses.

Schemes for connecting three-phase motors to a single-phase network

There are many options for connecting ADKZ, but we will consider only the most commonly used and easiest to implement. As discussed earlier, to shift the phase, it is enough to connect a capacitor in parallel with any of the windings. The designation C p indicates that this is a working capacitor.

It should be noted that connecting the windings in a triangle is preferable, since more useful power can be “removed” from such an ADKZ than from a star. But there are motors designed to operate in networks with a voltage of 127/220 V. There must be information about this on the nameplate.

If readers come across such an engine, then this can be considered good luck, since it can be connected to a 220 V network using a star circuit, and this will ensure a smooth start and up to 90% of the nameplate rated power. The industry produces ADKZs specially designed for operation in 220 V networks, which can be called capacitor motors.

Whatever you call the engine, it’s still asynchronous with a squirrel-cage rotor

Please note that the nameplate indicates an operating voltage of 220 V and parameters of the operating capacitor of 90 μF (microfarad, 1 μF = 10 -6 F) and a voltage of 250 V. It is safe to say that this motor is actually three-phase, but adapted for single-phase voltage.

To facilitate the start-up of powerful ADSCs in 220 V networks, in addition to the working capacitor, they also use a starting capacitor, which is turned on for a short time. After the start and a set of rated speeds, the starting capacitor is turned off, and only the working capacitor supports rotor rotation.

The starting capacitor “gives a kick” when the engine starts

The starting capacitor is C p, connected in parallel to the working capacitor C p. It is known from electrical engineering that when connected in parallel, the capacitances of the capacitors add up. To “activate” it, use the SB push-button switch, held down for several seconds. The capacity of the starting capacitor is usually at least two and a half times higher than that of the working capacitor, and it can retain its charge for quite a long time. If you accidentally touch its terminals, you can get a fairly noticeable discharge through the body. In order to discharge C p, a resistor connected in parallel is used. Then, after disconnecting the starting capacitor from the network, it will be discharged through a resistor. It is selected with a sufficiently high resistance of 300 kOhm-1 mOhm and a power dissipation of at least 2 W.

Calculation of the capacity of the working and starting capacitor

For reliable start-up and stable operation of the ADKZ in 220 V networks, you should most accurately select the capacitances of the working and starting capacitors. If the capacitance C p is insufficient, insufficient torque will be created on the rotor to connect any mechanical load, and excess capacitance can lead to the flow of too high currents, which can result in an interturn short circuit of the windings, which can only be “treated” by very expensive rewinding.

Scheme	What is calculated	Formula	What is needed for calculations
	Capacitance of the working capacitor for connecting star windings – Cp, µF	Cр=2800*I/U; I=P/(√3*U*η*cosϕ); Cр=(2800/√3)*P/(U^2*n* cosϕ)=1616.6*P/(U^2*n* cosϕ)	For everyone: I – current in amperes, A; U – network voltage, V; P – electric motor power; η – engine efficiency expressed in values ​​from 0 to 1 (if it is indicated on the engine nameplate as a percentage, then this indicator must be divided by 100); cosϕ – power factor (cosine of the angle between the voltage and current vector), it is always indicated in the passport and on the nameplate.
	Capacity of the starting capacitor for connecting star windings – Cp, µF	Cп=(2-3)*Cр≈2.5*Ср
	Capacitance of the working capacitor for connecting the windings in a triangle – Cp, µF	Cр=4800*I/U; I=P/(√3*U*η*cosϕ); Cр=(4800/√3)*P/(U^2*n* cosϕ)=2771.3*P/(U^2*n* cosϕ)
	Capacity of the starting capacitor for connecting windings in a triangle – Cn, µF	Cп=(2-3)*Cр≈2.5*Ср

The formulas given in the table are quite sufficient to calculate the required capacitor capacity. Passports and nameplates may indicate efficiency or operating current. Depending on this, you can calculate the necessary parameters. In any case, that data will be enough. For the convenience of our readers, you can use a calculator that will quickly calculate the required working and starting capacity.

It happens that a three-phase electric motor falls into your hands. It is from such engines that homemade circular saws, emery machines and various types of shredders are made. In general, a good owner knows what can be done with it. But the trouble is, a three-phase network in private homes is very rare, and it is not always possible to install 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 drop noticeably. Thus, a delta connection uses only 70% of the engine power, and a star connection uses even less - only 50%.

In this regard, it is desirable to have a more powerful engine.

Important! When connecting the motor, be extremely careful. Take your time. When changing the circuit, turn off the power supply and discharge the capacitor with an electric lamp. Work with at least two people.

So, in any connection scheme, capacitors are used. In essence, they act as the third phase. Thanks to it, the phase to which one terminal of the capacitor is connected shifts exactly as much as necessary to simulate the third phase. Moreover, to operate the engine, one tank is used (working), and for starting, another (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 sufficient, without the need for containers for starting. This is due to the fact that the engine is idling when starting and it has enough energy to spin the shaft.

If you take a circular saw, a hood or another device that puts an initial load on the shaft, then you cannot do without additional banks of capacitors for starting. Someone may say: “why not connect the maximum capacity so that there is not enough?” But it's not that simple. With such a connection, the motor will overheat and may fail. Don't risk your equipment.

Important! Whatever the capacitance 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 with either three terminals - for connection to a star only - or with six connections, with the ability to select a circuit - star or delta. The classic scheme can be seen in the figure. Here in the picture on the left there is a star connection. The photo on the right shows how it looks on a real engine frame.

It can be seen that for this it is necessary to install special jumpers on the required pins. These jumpers come with the motor. In the case where there are only 3 terminals, the star connection is already made inside the motor housing. In this case, it is simply impossible to change the winding connection diagram.

Some say that they did this to prevent workers from stealing 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.

Connection diagram for a 3-phase motor in a 220V network connected by a star.

As you can see, the 220V voltage is distributed over two series-connected windings, where each is designed for such a voltage. Therefore, the 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 also remains unchanged. Here, each winding is used for its own operating voltage, hence the power. The connection diagram for such an electric motor is shown in Figure 1.

Fig. 2 shows a terminal with a 6-pin terminal for delta connection. The three resulting outputs are supplied with: phase, zero and one terminal of the capacitor. The direction of rotation of the electric motor depends on where the second terminal of the capacitor is connected - phase or zero.

In the photo: an electric motor with only working capacitors and no capacitors for starting.

If there is an initial load on the shaft, it is necessary to use capacitors for starting. 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 starting tanks should be disconnected from the workers. If it is a button, we simply release it, and if it is a switch, then we turn it off. Then the engine uses only working capacitors. Such a connection is shown in the photo.

How to select capacitors for a three-phase motor using it in a 220V network.

The first thing you need to know is that the capacitors must be non-polar, that is, not electrolytic. It is best to use containers of the brand ― 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 mounting eyes that help you easily place them at any point on the device’s body. Unfortunately, getting them now is problematic, 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 is not less than 400V.

Calculation of capacitors. Capacity of the working capacitor.

In order not to resort to long formulas and torture your brain, there is a simple way to calculate a capacitor for a 380V motor. For every 100 W (0.1 kW) 7 µF is taken. For example, if the motor is 1 kW, then we calculate it like this: 7 * 10 = 70 µF. It is extremely difficult to find such a capacity in one jar, and it is also expensive. Therefore, most often the containers are connected in parallel, gaining the required capacity.

Starting capacitor capacity.

This value is taken at the rate of 2-3 times greater than the capacity of the working capacitor. It should be taken into account that this capacity is taken in total with the working capacity, that is, for a 1 kW motor, the working capacity is equal to 70 μF, multiply it by 2 or 3, and get the required value. This is 70-140 µF of additional capacitance - starting. At the moment of switching on, it is connected to the working one and the total is 140-210 µF.

Features of the selection of capacitors.

Capacitors, both working and starting, can be selected using the method from smallest to largest. Having thus selected the average capacity, you can gradually add and monitor the operating mode of the engine 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 delays.