Connection of three-phase electric motors to a single-phase network. Three-phase motor in a single-phase network

The industry produces electric motors designed to operate in various conditions, including for a 220 volt network. However, many people still have 380V three-phase asynchronous electric motors (older people remember such a phenomenon as "brought home from work"). Such devices must not be plugged into a power outlet. To use such devices at home and connect instead of 380 220 volts, the circuit for assembling and connecting the electric machine needs to be improved - switching the windings and connecting the capacitors.

The principle of operation of a three-phase asynchronous electric motor

The windings in the stator of such a machine are wound with an offset of 120 °. When a three-phase voltage is applied to them, a rotating magnetic field appears, which sets the rotor of the electric machine in motion.

When connected to a three-phase electric machine to a single-phase voltage of 220 volts, a pulsating field appears instead of a rotating field. To drive an electric motor in a single-phase network, the pulsating field is converted into a rotating one.

Reference. In devices made for operation in a 220 volt network, starting windings or features of the stator design are used for this.

When the 380 by 220 engine is connected to the network, phase-shifting capacitors are connected to it. Starting a three-phase motor with 220 without capacitors is possible by driving the rotor into rotation. This will create a shift in the magnetic field, and the electric machine, having lost in power, will continue to operate. So include circulars and other similar mechanisms with a low starting torque.

Beginnings and ends of windings

Each winding of an electric machine has a beginning and an end. They are selected conditionally, regardless of the direction of winding, however, they must correspond to the direction of winding of the remaining coils.

Important! In wiring diagrams, the beginning of the coils is marked with a dot.

Connection of coils when connecting a three-phase motor to a 220V network

Most electric motors are designed to operate with 0.4kV line voltage. In these machines, the windings are star-connected. This means that the ends of the windings are connected together, and 3 phases are connected to the beginnings. The voltage on each winding is 220V.

When connected to a network with a line voltage of 220V, a "triangle" connection is used. In this case, the beginning of the next winding is connected to the end of the previous one.

Some devices with a power of more than 30 kW are manufactured for a network with a line voltage of 660V. In such devices, when connected to a 0.4 kV network, the windings are connected with a "triangle".

How to connect a three-phase electric motor to a 220v network

The windings of a three-phase machine, when switched on from 220 volts, are connected in various ways. Synchronous speed and rotation speed do not change from this.

Star connection

When turning on a 220 volt three-phase electric motor, it is easiest to use the existing star connection. Two terminals are supplied with 220V power, and the third is supplied through a phase-shifting capacitor. However, at the same time, not 220V, but 110V is found on each of the coils, which will lead to a drop in power up to 30%. Therefore, such a connection is not used in practice.

Delta connection

The most common scheme for connecting a three-phase electric motor to the 220 network is a triangle. In this case, power is supplied to one side of the triangle, and capacitors are connected in parallel to the other side. The reverse is carried out by changing the side of the triangle on which the container is located.

Changing the connection diagram of the windings of a three-phase electric motor to a delta

The most difficult thing when connecting a three-phase electric machine to a 220 volt household network is to connect its windings with a triangle.

Changing connections on a terminal strip

When connected to a 220 volt network, this operation is easiest to perform if the wires are connected to the terminal block. It has six bolts in two rows.

The connection is made in pairs, with pieces of wire or jumpers supplied with the engine.

Assembling the triangle, according to the marking of the terminals

If there is no terminal strip, and there are markings on the terminals, then the task is also simple. The windings are marked C1-C4, C2-C5, C3-C6, where C1, C2, C3 are the beginning of the windings, and the ends are connected C1-C6, C2-C4, C3-C5.

Interesting. In old electric motors of imported production, the outputs are marked A-X, B-Y, C-Z, and modern designations: U1-U2, V1-V2, W1-W2.

What if there are only three conclusions

The most difficult thing is to assemble a wiring diagram from "star" to "delta" in electric machines, the connection of the windings of which is located inside the case. This operation is performed when the electric machine is completely disassembled. To switch the windings to the triangle, you must:

disassemble the electric motor;
find inside the junction of the windings and disconnect it;
solder pieces of flexible wires to the ends of the windings and bring them out;
assemble the device;
call the output of the coils in pairs;
connect the old terminal of one coil with the new wire of the next;
repeat the operation two more times.

Connection without marking

If there is no marking, and six ends come out of the body, then it is necessary to determine the beginning and end of each winding:

With a tester, determine in pairs the terminals associated with each winding. Flag pairs;
Select a wire in one of the pairs. Mark it as the beginning of the winding, the rest is marked as the end;
Connect the marked winding in series with another pair of wires;
Connect voltage ~ 12-36V to the connected coils;
Measure the voltage on the remaining pair with a voltmeter. Instead of a voltmeter, you can use a control light;
The stator with the windings is a transformer and when the connection is matched, the voltmeter will show the presence of voltage. In this case, the start and end of the coil are marked in the second pair of wires. In the absence of voltage, change the polarity of connecting one of the pairs of terminals and repeat p. 4-5;
Connect one of the marked pairs with the remaining unlabeled one and repeat p. 3-6.

After determining the beginning and ends in all windings, they are connected by a triangle.

Connecting phase-shifting capacitors

For normal operation, an electric machine needs starting and working capacities.

Selecting the nominal working capacitor

There are different formulas for determining the required capacity of a working capacitor, taking into account the rated current, cosφ and other parameters, but most often it is simply taken 7mkF per 100W or 70mkF per 1kW of power.

After assembling the circuit, it is advisable to turn on the ammeter in series with the machine and, by increasing and decreasing the working capacity, achieve the minimum value of the instrument readings.

Important! Working capacitors are used for alternating voltages of at least 300V.

Selection and connection of starting capacitors

Starting using only working phase-shifting capacitors is long-term, and with a significant torque on the machine shaft, it is impossible. To facilitate the start-up and reduce its duration for the period of acceleration of the electric machine, starting capacities are connected in parallel with the workers. They are selected 2-3 times more than workers. The rated voltage is also over 300V. The start-up takes a few seconds, therefore it is allowed to connect electrolytic capacitors.

How to connect a 220 volt three-phase motor using starting capacitors

The start-up scheme should provide for the disconnection of the starting capacities after starting the electric machine. If this is not done, the machine will overheat. There are different ways to do this:

Disconnection of starting capacities using a time relay. The shutdown delay is a few seconds and is selected empirically;
The use of a universal switch (key UP) for 3 positions. Its switching diagram is assembled in such a way that in the first position all contacts are open, in the second two are closed: power supply and starting capacitors, and in the third - only power supply. For reverse operation, a 5-position key is used;
Special button station - PNVS (push-button starter with starting contact). These designs have 3 contacts. When you press "Start", all are closed, but the extreme ones are fixed, and the middle one is needed to start the car, and disappears after the button is released. Pressing the "Stop" button disconnects the fixed contacts.

How to convert a rotation scheme to reverse

To reverse the electric motor, it is necessary to change the direction of rotation of the magnetic field. When starting the motor without capacitors, it is first manually given the required direction of rotation, and in the capacitor circuit, the capacitance is switched from the neutral wire to the phase one. This is done with a toggle switch, switch or starters.

Important! Starting capacitors are connected in parallel with the operating ones and switch when the direction of rotation is changed simultaneously with them.

Electronic converters of household voltage into industrial three-phase 380V

These three-phase inverters are used for three-phase motors in the household network. Electric motors are connected directly to the output of the device.

The required inverter power is selected depending on the current of the electrical machine. There are three modes of operation of such devices:

Launcher. Allows short-term (up to 5 seconds) double power excess. This is enough to start the electric motor;
Worker, or nominee;
Reloading. Allows the current to be exceeded by 1.3 times for half an hour.

Advantages of an inverter 220 to 380:

connection of not converted three-phase electrical machines for 220 volts;
obtaining the full power and moment of the electric machine without losses;
energy saving;
smooth start and speed control.

Despite the appearance of electronic converters, capacitor circuits for switching on three-phase electric motors continue to be used in everyday life and small workshops.

Video

For the operation of a variety of electrical devices, asynchronous motors are used, which are simple and reliable in operation and installation - they can be easily installed with your own hands. The connection of a three-phase motor to a single-phase and three-phase network is carried out with a star and a delta.

general information

An asynchronous three-phase motor consists of the following main parts: windings, a movable rotor and a fixed 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 - diagram star clearly

The connection can be carried out 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 connection of the windings 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 with a "triangle" circuit, then the motor overload will be less than with a star.

Before connecting the windings in a single-phase network, it is imperative to check the capacity of the capacitor that will be used. This requires 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 "adjust" 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 schematic detail allows you to fully automate your 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 capacitance of the capacitor or changing the relay winding.

Video: how to connect a three-phase motor at 220V

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 contributes to an increase in efficiency up to 70%, which is an excellent indicator for such a connection. Using only this part, it is possible to abandon the use of a fan and the main types of capacitors - starting and operating.

But this connection is not ideal either. When an ED operates with a thyristor, 30% more electric current is consumed than with capacitors. Therefore, this option only applies in production or in the absence of a choice.

Consider how a three-phase asynchronous motor is connected to a three-phase network, if a delta 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 braking and complete stop system. Also in this case, a switch is used, which has three positions: "hold", "start", "stop". When the handle is installed in the first position, an electric current begins to flow to the contacts. It is important here immediately after the engine starts to go into the "start" mode, otherwise the windings may catch fire due to overload. During the end of the working process, the handle is fixed at the "stop" point.

Photo - connection using electrolyte capacitors

Sometimes, when connected to a phase, it is more convenient to stop a three-phase motor using the energy that is stored in the capacitor. Sometimes electrolytes are used instead, but this is a more difficult option for installing the device. In this case, the parameters of the capacitor are very important, in particular, its capacity - the braking and the time of the complete stop of the moving parts depend on it. This circuit also uses rectifying diodes and resistors. They will help to speed up the stopping of the engine, if necessary. But their technical characteristics should be as follows:

The resistance of the resistor should not exceed 7 kOhm;
The capacitor must withstand a voltage of 350 volts or more (depending on the mains voltage).

Having at hand a circuit with stopping the motor, using a capacitor, you can make a connection with a 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 the previous versions, has several basic positions, but it is fixed only for "start" and "stop" - this is very important.

Photo - reverse with a starter

Reversible 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, you need to press the Back button immediately after pressing the Forward button of the starter. After that, the blocking contact will disconnect the forward coil and transfer the power to the reverse - the direction of rotation will change. But you need to be careful when connecting the starter - if you mix up the contacts, then during the transition there will be not a reversal, but a short circuit.

Another unusual way how a three-phase motor can be connected is the option using a four-pole RCD. Its feature is the ability to use the network without scratch.

In most cases, ED only needs 3 phases and 1 ground wire, zero is optional, since the load is symmetrical;
The connection principle is as follows: we divert the power supply phases to the circuit breaker, and connect zero directly to the RCD-N terminal, after which we do not connect it to anything;
From the machine, the cables are also connected in the same way to the RCD. We ground the engine and that's it.

The theoretical material outlined in the first part of the topic, dedicated to the single-phase connection of a three-phase electric motor, is intended so that the home craftsman can consciously transfer the industrial devices of the 380 volt network to household electrical wiring 220.

Thanks to her, you will not only mechanically repeat our recommendations, but will carry them out consciously.

Optimal schemes for connecting a three-phase motor to a single-phase household network

Among the many ways to connect an electric motor in practice, only two have become widespread, referred to for short as:

star;
triangle.

The name is given by the method of connecting the windings in the electrical circuit inside the stator. Both methods differ in that they apply a voltage of different magnitude to each phase of the motor.

In a star circuit, the line voltage is applied directly to two windings connected in series. Their electrical resistance adds up, provides greater resistance to the passing current.

In a triangle, a line voltage is applied to each winding individually and therefore has less resistance. Currents are created higher in amplitude.

We draw attention to these two differences and draw practical conclusions for their use:

the star circuit has reduced currents in the windings, allows you to operate the electric motor for a long time with minimal loads, to provide small torques on the shaft;
the higher delta currents provide better power output, allow the motor to handle extreme loads, and therefore require reliable cooling for continuous operation.

These two differences are explained in detail in the picture. Take a good look at her. For clarity, red arrows specially marked the incoming voltages from the line (linear) and applied to the windings (phase). For a triangle circuit, they coincide, and for a star, they are reduced by connecting two windings through a neutral.

These methods should be analyzed in relation to the operating conditions of your future mechanism at the design stage, before starting to create it. Otherwise, the star circuit motor may not cope with the connected loads and will stop, and at the triangle it will overheat and eventually burn out. The motor current load can be considered by choosing the wiring diagram.

How to find out the connection diagram of the stator windings in an asynchronous motor

At each plant, it is customary to place information plates on the body of electrical equipment. An example of its execution for a three-phase electric motor is shown in the photo.

The home craftsman can pay attention not to all the information, but only to:

power consumption: its value is used to judge the operability of the connected drive;
winding connection diagram - the question has just been sorted out;
the number of revolutions that may require the connection of the gearbox;
currents in phases - windings are created for them;
environmental protection class - determines the operating conditions, including protection against atmospheric moisture.

Factory data can usually be trusted, but it was written for a new engine being shipped to the market. During the entire period of operation, this scheme can be reconstructed several times, having lost its original appearance. An old engine, if stored improperly, can become ineffective.

Electrical measurements should be made of its circuit and the condition of the insulation should be checked.

How to determine the connection diagrams of the stator windings

To carry out electrical measurements, it is necessary to have access to each end of all three windings. Usually six of their leads are connected to their bolts inside the terminal box.

But, among the methods of factory installation, there is one when special asynchronous models are made according to a star scheme so that the neutral point is assembled by the ends of the windings inside the case, and one core assembly is connected to the lead-in box. This unsuccessful option for us will require untwisting the cover studs on the body to remove the latter. Then you need to get close to the junction of the windings and disconnect their ends.

Electrical check of the ends of the stator windings

After finding both ends for one winding, they must be marked with their own marking for subsequent checks and connections.

Polarity measurements at the stator windings

Since the windings are wound in a strictly defined way, we need to accurately find the beginning and end of them. There are two simple electrical methods for this:

short-term supply of direct current to one winding to create a pulse;
using a source of variable EMF.

In both cases, the principle of electromagnetic induction works. After all, the windings are assembled inside the magnetic circuit, which is good for the transformation of electricity.

Battery impulse test

The work is done on two windings at once. The picture shows this process for three - draw less this way.

The process consists of two stages. First, unipolar windings are determined, and then a control check is carried out to eliminate a possible error in the measurements performed.

To search for unipolar clamps, a DC voltmeter is connected to any free winding, switched to the limit of the sensitive scale. We will use it to implement the impulse that appears due to the transformation.

The negative terminal of the battery is rigidly connected to an arbitrary end of the second winding, and the plus is briefly touched to its second end. This moment is shown in the picture by the contact of the Kn button.

Observe the behavior of the voltmeter needle, which responds to the supply of an impulse in its circuit. It can move towards plus or minus. The coincidence of the polarities of both windings will be indicated by a positive deviation, and the difference - negative.

When the impulse is removed, the arrow will go in the opposite direction. Pay attention to this too. Then the ends are marked.

After that, the measurement is performed on the third winding, and the control check is carried out by switching the battery to another chain.

Step-down transformer check

A 24 volt AC EMF source is recommended for electrical safety. It is not recommended to neglect this requirement.

First, take two arbitrary windings, for example, # 2 and # 3. In pairs, their outputs are connected together and a voltmeter is connected to these places, but already of an alternating current. The remaining winding No. 1 is supplied with voltage from a step-down transformer and the appearance of readings from it on a voltmeter is observed.

If the vectors are directed in the same way, then they will not affect each other and the voltmeter will show their total value - 24 volts. When the polarity is reversed, then on the voltmeter the opposite vectors will add up, give the total number 0, which will be displayed on the scale by the arrow reading. The ends should also be marked immediately after measurement.

Then you need to check the polarity for the remaining pair and take a control measurement.

With such simple electrical experiments, it is possible to reliably determine whether the ends belong to the windings and their polarity. This will help you assemble them correctly for the capacitor start circuit.

Insulation resistance test of stator windings

If the engine was stored in an unheated room, then it came into contact with humid air and became damp. Its insulation has broken, it is capable of creating leakage currents. Therefore, its quality must be assessed by electrical measurements.

A tester in ohmmeter mode is not always able to detect such a violation. It will show only an obvious defect: too little power of its current source does not provide an accurate measurement result. To check the condition of the insulation, it is necessary to use a megohmmeter - a special device with a powerful power source that can apply an overvoltage of 500 or 1000 volts to the measuring circuit.

Insulation should be assessed before applying operating voltage to the windings. If leakage currents are detected, you can try to dry the motor in a warm, well-ventilated environment. Often this technique allows you to restore the functionality of the electrical circuit assembled inside the stator core.

Star-starting an induction motor

For this method, the ends of all windings K1, K2, K3 are connected at the neutral point and isolated, and a line voltage is applied to their beginning.

The working zero of the network is rigidly connected to one beginning, and the phase potential is rigidly connected to the other two in the following way:

any first winding is connected rigidly;
the second cuts through the capacitor assembly.

For a stationary connection of an asynchronous motor, it is necessary to first determine the phase and operating zero of the supply network.

How to choose capacitors

In the electric motor starting circuit, two chains are used to connect the winding through capacitor assemblies:

working - connected in all modes;
starting - used only for intensive spinning of the rotor.

At the moment of start-up, both of these circuits work in parallel, and when brought to the operating mode, the start chain is disabled.

The capacity of the working capacitors must correspond to the power consumption of the electric motor. To calculate it, use the empirical formula:

C slave = 2800 ∙ I / U.

The values of the rated current I and voltage U included in it just introduce the correction for the electric power of the engine.

The capacity of starting capacitors is usually 2 ÷ 3 krats higher than the operating one.

The correct selection of capacitors affects the formation of currents in the windings. They should be checked after starting the engine under load. To do this, measure the currents in each winding and compare them in magnitude and angle. Good operation is carried out with the lowest possible misalignment. Otherwise, the motor is unstable, and some winding or two will overheat.

The starting diagram shows the SA switch, which brings into operation the starting capacitor for a short start-up time. There are many button designs that allow this operation.

However, I would like to draw your attention to a special device produced in Soviet times by the industry for washing machines with an activator - a centrifuge.

In its closed case, a mechanism is hidden, consisting of:

two contacts working on closure from pressing the upper "Start" button;
one contact opening the entire circuit from the Stop button.

When you press the Start button, the phase of the circuit is supplied to the engine through the working capacitors in one chain and starting capacitors in the other. When the button is released, one contact is broken. It is connected to starting capacitors.

Starting an asynchronous motor in a delta pattern

There are practically no big differences between this method and the previous one. The starting and working chains work according to the same algorithms.

In this scheme, it is necessary to take into account the increased currents flowing in the windings and other methods of selecting capacitors for them.

Their calculation is performed according to a formula similar to the previous one, but different:

C slave = 4800 ∙ I / U.

The relationship between starting and running capacitors does not change. Do not forget to evaluate their selection by test measurements of currents under rated load.

Final conclusions

Existing technical methods make it possible to connect three-phase asynchronous motors to a single-phase 220 volt network. Numerous researchers offer their experimental schemes for this in a large assortment.
However, this method does not provide efficient use of the electrical power resource due to large energy losses associated with poor-quality voltage conversion for connection to the stator phases. Therefore, the engine operates with low efficiency and increased costs.
Long-term operation of machines with similar motors is not economically justified.
The method can be recommended only for connecting irresponsible mechanisms for a short period of time.
In order to effectively use an asynchronous electric motor, it is necessary to use a full-fledged three-phase connection or a modern expensive inverter converter of appropriate power.
A single-phase electric motor with the same power in a household network is better able to cope with all tasks, and its operation will be cheaper.

Thus, the designs of asynchronous motors, previously massively connected to home wiring, are now not popular, and the method of connecting them is morally outdated and rarely used.

A variant of such a mechanism is shown by a photograph of emery with a protective shield and a limit stop removed for clarity. Even with this design, it is difficult to work on it due to power losses.

The practical advice of Alexander Shenrok, set out in his video, visually complements the material of the article, allows you to better comprehend this topic. I recommend viewing it, but be critical about measuring the insulation resistance with a tester.

Ask questions in the comments, share the article with your friends through the buttons of social networks.

The owner of a garage or a private house often needs the work of a machine or emery with an asynchronous electric motor for processing metals, wood. And only 220 volts is available.

In this case, connecting a three-phase motor to a single-phase network can be done in several ways. Here I will be looking at three available and common capacitor starting circuits.

All of them have been repeatedly tested on personal experience.

I immediately warn the experienced electricians who have opened this article: the material has been prepared for novice craftsmen. Therefore, it is voluminous. If you don't want to read everything, then here are some quick tips:

use the triangle diagram, having previously checked the serviceability of the engine;
choose working capacitors at the rate of 70 microfarads per 1 kilowatt of power, and increase the starting capacitors by 2-3 times;
in the process of setting up, correct the capacitances according to the load and the heating of the windings;
remember to observe safety precautions with electric current and tools.

From my own experience, I was convinced more than once that an initial check of the technical condition of the equipment eliminates many errors, saves the total time of work, and significantly prevents injuries and accidents.

Three-phase asynchronous motor: what to look for before connecting it

With a few exceptions, we get the asynchronous device in an unknown state. It is very rare for it to have a test certificate and a certified warranty from the electrical laboratory.

Mechanical condition of the stator and rotor: what can interfere with the operation of the motor

The stationary stator consists of three parts: a middle housing and two side covers, tightened with pins. Pay attention to the gap between them, tightening force with nuts.

The body must be tightly compressed. Inside it, the rotor rotates on bearings. Try to twist it by hand. Evaluate the applied force: how the bearings are working, whether there are no beats.

Without proper experience, minor defects cannot be detected in this way, but a case of gross jamming will immediately appear. Listen to the noises: is there any rubbing of the stator elements by the rotor during rotation.

After starting the engine to idle and running for a short time, listen to the sounds of rotating parts again.

Ideally, it is better to disassemble the stator, visually assess its condition, wash out the contaminated rotor bearings and completely replace their grease.

Electrical characteristics of stator windings: how to check the assembly diagram

The manufacturer indicates all the main parameters of the electric motor on a special plate attached to the stator housing.

These factory characteristics can only be trusted if you are sure that after the factory none of the electricians changed the winding connection diagram or made any involuntary mistakes. And such cases came across to me.

And the plate itself can be erased or lost over time. Therefore, I propose to deal with the rotor spinning technology.

To understand the electrical processes taking place inside the stator of the motor, it is convenient to imagine it in the form of an ordinary toroidal transformer, when three equivalent windings are symmetrically located on the circular core of the magnetic circuit.

The stator circuit is assembled inside a closed housing, from which only six ends of the windings are brought out.

They are labeled and connected on a lid-covered terminal block for star or delta wiring by means of a typical jumper changeover.

The right side of the picture shows the assembly of the triangle. The layout of the jumpers for the star is published below.

Electrical techniques for checking the winding assembly diagram

But not everything is as simple as it might seem at first glance. There are a number of engines that deviate from these rules.

For example, a manufacturer may produce electric motors not for universal use, but for work in specific conditions with star-connected windings.

In this case, he can collect three ends of the windings inside the stator housing, and only four wires can be brought out to connect to the potentials of the phases and zero.

The mounting of these ends is usually done in the area of the back cover. To switch the windings to the triangle, you will need to open the case and draw additional conclusions.

It's not a hard job. But it requires careful handling of the lacquered copper wire. If the wire is bent, it may be damaged, which will lead to a violation of the insulation and create an interturn short circuit.

What to do if there is no pin marking

On an old induction motor, the wires can be removed from the terminals, and the factory markings are lost. There were also such instances when six ends simply stuck out of the body. They need to be called and labeled.

We carry out the work in two stages:

We check the belonging of the ends to the windings.
We define and label each pin.

If an interturn short circuit occurs in the winding, then it, as a rule, can be determined by measuring a multimeter in ohmmeter mode. To do this, carefully analyze and compare the active resistances of each chain.

How the stator magnetic field is checked at the factory

When voltage is applied to a working electric motor, a rotating magnetic field is created. It is visually assessed using a metal ball that repeats the rotation.

I am not encouraging you to repeat this experience. This example is intended to help understand that the operation of an induction motor is based on the interaction of the magnetic fields of the stator and rotor.

Only the correct connection of the windings ensures the rotation of the ball or rotor.

Motor power and winding wire diameter

These are two interrelated quantities because the cross-section of a conductor is selected for its ability to withstand heat from the current flowing through it.

The thicker the wire, the more power can be transmitted through it with acceptable heating.

If there is no nameplate on the engine, then its power can be judged by two signs:

The diameter of the winding wire.
Dimensions of the core of the magnetic circuit.

After opening the stator cover, analyze it visually.

Star connection of a three-phase motor to a single-phase network

I'll start with a warning: even experienced electricians make mistakes during their work, which are called the "human factor". What can we say about home craftsmen ...

The star connection diagram is shown in the picture.

The ends of the windings are collected at one point by horizontal jumpers inside the terminal box. No external wires are connected to it.

The phase (through the circuit breaker) and zero of the household wiring are fed to two different terminals of the winding beginnings. A parallel chain of two capacitors is connected to a free terminal (in figure H2): Cp - working, Cn - starting.

The working capacitor is rigidly connected by the second plate to the phase wire, and the starting capacitor is connected through an additional SA switch.

When starting the electric motor, the rotor must be unscrewed from rest. It overcomes the forces of friction of bearings, resistance of the environment. For this period, it is required to increase the magnitude of the stator magnetic flux.

This is done by increasing the current through the additional chain of the starting capacitor. After the rotor reaches the operating mode, it must be turned off. Otherwise, the starting current will overheat the motor winding.

It is not always convenient to disconnect the start chain with a simple switch. To automate this process, circuits with relays or timed starters are used.

Among the home-made craftsmen, the start button from Soviet activator-type washing machines is popular. It has two built-in contacts, one of which, after switching on, turns off automatically with a delay: what is needed in our case.

If you look closely at the principle of supplying single-phase voltage, you will see that 220 volts are applied to two series-connected windings. Their total electrical resistance adds up, weakening the amount of current flowing.

Connecting a three-phase motor to a single-phase network in a star scheme is used for low-power devices, it is characterized by increased energy losses up to 50% from a three-phase power system.

Triangle diagram: advantages and disadvantages

Connecting an electric motor using this method assumes the use of the same external chain as that of the star. The phase, zero and midpoint of the lower plates of the capacitors are mounted in series on three jumpers of the terminal box.

By switching the terminals of the windings in a delta pattern, the applied voltage 220 creates a greater current in each winding than that of the star. There are less energy losses, higher efficiency.

Connecting the motor in a delta circuit in a single-phase network allows you to use up to 70-80% of the power consumption.

To form a phase-shifting chain, it is required to use a smaller capacity of working and starting capacitors.

When the engine is turned on, it may start rotating in the wrong direction. We need to reverse it.

To do this, it is enough in both circuits (star or triangle) to swap the wires coming from the network on the terminal block. The current will flow through the winding in the opposite direction. The rotor will change its direction of rotation.

How to choose capacitors: 3 important criteria

A three-phase motor creates a rotating magnetic field of the stator due to the uniform passage of sinusoidal currents through each winding, spaced 120 degrees apart in space.

In a single-phase network, this is not possible. If you connect one voltage to all 3 windings at once, then there will be no rotation - the magnetic fields will be balanced. Therefore, voltage is applied to one part of the circuit, as it is, and to the other, the current is shifted along the angle of rotation by capacitors.

The addition of two magnetic fields creates an impulse of moments that spin the rotor.

The performance of the created circuit depends on the characteristics of the capacitors (the value of the capacitance and the permissible voltage).

For low-power motors with easy starting at idle, in some cases, it is permissible to do only with working capacitors. All other engines will need a launch block.

I would like to draw your attention to three important parameters:

capacity;
permissible operating voltage;
type of construction.

How to choose capacitors by capacity and voltage

There are empirical formulas that allow you to perform a simple calculation based on the magnitude of the rated current and voltage.

However, people often get confused in formulas. Therefore, when checking the calculation, I recommend taking into account that for a power of 1 kilowatt, it is required to select a capacity of 70 microfarads for the working chain. The dependence is linear. Feel free to use it.

It is possible and necessary to trust all these methods, but theoretical calculations must be verified in practice. The specific design of the engine and the applied loads always require adjustments.

Capacitors are calculated for the maximum current value allowed by the heating conditions of the wire. This consumes a lot of electricity.

If the electric motor overcomes loads of lesser magnitude, then it is desirable to reduce the capacitance of the capacitors. This is done empirically when setting up, measuring and comparing the currents in each phase with an ammeter.

Most often, metal-paper capacitors are used to start an asynchronous electric motor.

They work well, but have low ratings. When assembled into a capacitor bank, a rather dimensional structure is obtained, which is not always convenient even for a stationary machine.

Now
the industry produces small-sized electrolytic capacitors adapted to work with AC motors.

Their internal construction of insulating materials is adapted to work under different voltages. For a working chain, it is at least 450 volts.

In the starting circuit with the conditions of short-term switching on under load, it is reduced to 330 by reducing the thickness of the dielectric layer. These capacitors are smaller.

This important condition should be well understood and applied in practice. Otherwise, the 330 volt capacitors will explode during prolonged use.

Most likely, for a particular engine, one capacitor will not get rid of. You will need to collect the battery using a serial and parallel connection of them.

When connected in parallel, the total capacitance is added up, and the voltage does not change.

Series connection of capacitors reduces the total capacitance and divides the applied voltage into parts between them.

What types of capacitors can be used

The rated voltage of the network is 220 volts. Its peak value is 310 volts. Therefore, the minimum limit for short-term operation at start-up is 330 V.

The voltage reserve of up to 450 V for working capacitors takes into account surges and impulses that are created in the network. It cannot be underestimated, and the use of containers with a large reserve significantly increases the dimensions of the battery, which is irrational.

For a phase-shifting circuit, it is permissible to use polar electrolytic capacitors, which are designed to allow current to flow in only one direction. The circuit for their connection must contain a current-limiting resistor of several ohms.

Without using it, they quickly fail.

Before installing any capacitor, it is necessary to check its real capacity with a multimeter and not rely on the factory markings. This is especially true for electrolytes: they often dry out prematurely.

Phase shift circuit of currents by capacitors and a choke: what I did not like

This is the third construction promised in the title, which I implemented two decades ago, tested it in operation, and then abandoned it. It allows you to use up to 90% of the three-phase motor power, but has disadvantages. More about them later.

I assembled a three-phase voltage converter for a power of 1 kilowatt.

It includes:

choke with an inductive resistance of 140 ohms;
capacitor bank for 80 and 40 microfarads;
adjustable rheostat for 140 ohms with a power of 1000 watts.

One phase works in the usual way. The second with a capacitor shifts the current forward by 90 degrees in the direction of rotation of the electromagnetic field, and the third with a choke forms its lag by the same angle.

The currents of all three phases of the stator are involved in the creation of the phase-shifting magnetic moment.

The throttle body had to be assembled with a mechanical structure made of wood on springs with a threaded air gap adjustment to adjust its characteristics.

The design of the rheostat is generally "tin". Now it can be assembled from powerful resistances purchased in China.

I even got the idea to use a water rheostat.

But I refused it: it is too dangerous a construction. I just wound a thick steel wire on an asbestos pipe for the experiment, put it on the bricks.

When I started the circular saw motor, it worked fine, withstood the applied loads, and sawed fairly thick pads normally.

Everything would be fine, but the meter has doubled the rate: this converter takes on the same power as the motor. The choke and wire are hot enough.

Due to the high power consumption, low safety, complex design, I do not recommend such a converter.

Safety precautions when connecting a three-phase motor: reminder

Trained persons must carry out the adjustment work on the energized circuit. Knowledge of safety is a prerequisite.

The use of an isolation transformer significantly reduces the risk of being affected by current. Therefore, use it for any energized commissioning work.

The electrician's special tool with dielectric handles not only makes work easier, but also keeps you healthy. Don't neglect it!

If you have any questions or noticed inaccuracies, then use the comments section.

In a household, sometimes it becomes necessary to start a 3-phase asynchronous electric motor (AM). With a 3-phase network, this is not difficult. In the absence of a 3-phase network, the engine can be started from a single-phase network by adding capacitors to the circuit.

Structurally, the IM consists of a fixed part - a stator, and a movable part - a rotor. The windings are laid in the grooves on the stator. The stator winding is a three-phase winding, the conductors of which are evenly distributed around the stator circumference and are laid in slots in phases with an angular distance of 120 el. degrees. The ends and the beginning of the windings are brought out into the junction box. The windings form a pair of poles. The nominal rotor speed of the motor depends on the number of pole pairs. Most common industrial motors have 1-3 pole pairs, less often 4. AMs with a large number of pole pairs have low efficiency, larger dimensions, and therefore are rarely used. The more pole pairs, the lower the rotor speed of the motor. General industrial ADs are produced with a number of standard rotor speeds: 300, 1000, 1500, 3000 rpm.

The rotor of the AD is a shaft on which there is a short-circuited winding. In low and medium-power AM, the winding is usually made by pouring molten aluminum alloy into the grooves of the rotor core. Short-circuited rings and end blades are cast together with the rods, which ventilate the machine. In high-power machines, the winding is made of copper rods, the ends of which are connected to short-circuited rings by welding.

When the blood pressure is turned on in a 3-phase network, current begins to flow through the windings in turn at different times. In one period of time, the current passes through the pole of phase A, in the other along the pole of phase B, in the third along the pole of the face C. Passing through the poles of the windings, the current alternately creates a rotating magnetic field, which interacts with the rotor winding and makes it rotate, as if pushing it in different planes at different times.

If you turn on the blood pressure in the 1ph network, the torque will be generated by only one winding. Such a moment will act on the rotor in one plane. This moment is not enough to move and rotate the rotor. To create a phase shift of the pole current relative to the supply phase, phase-shifting capacitors are used in Fig. 1.

All types of capacitors can be used, except for electrolytic ones. Capacitors such as MBGO, MBG4, K75-12, K78-17 are well suited. Some capacitor data are shown in table 1.

If it is necessary to gain a certain capacity, then the capacitors should be connected in parallel.

The main electrical characteristics of the blood pressure are given in the passport of Fig. 2.

Fig. 2

The passport shows that the motor is three-phase, with a power of 0.25 kW, 1370 rpm, it is possible to change the connection diagram of the windings. Connection diagram of windings "triangle" at a voltage of 220V, "star" at a voltage of 380V, respectively, a current of 2.0 / 1.16A.

The star connection is shown in Fig. 3. With this connection, a voltage is applied to the motor windings between the points AB (line voltage U l) that is times greater than the voltage between the points AO (phase voltage U f).

Fig.3 Wiring diagram "star".

Thus, the line voltage is times the phase voltage:. In this case, the phase current I f is equal to the linear current I l.

Let's consider the connection diagram "triangle" fig. 4:

Fig.4 Connection diagram "delta"

With such a connection, the line voltage U L is equal to the phase voltage U f., And the current in the line I l is times greater than the phase current I f:.

Thus, if the AD is designed for a voltage of 220/380 V, then to connect it to a phase voltage of 220 V, a "triangle" stator winding connection is used. And for connection to line voltage 380 V - star connection.

To start this AM from a single-phase 220V network, we should turn on the windings according to the "triangle" scheme, Fig. 5.

Fig.5 Connection diagram of EM windings according to the "triangle" scheme

The connection diagram of the windings in the terminal box is shown in Fig. 6

Fig. 6 Connection in the ED outlet box according to the "delta" scheme

To connect an electric motor according to the "star" scheme, it is necessary to connect two phase windings directly to a single-phase network, and the third through a working capacitor C p to any of the wires of the network fig. 6.

The connection in the terminal box for the "star" circuit is shown in fig. 7.

Fig.7 Connection diagram of EM windings according to the "star" scheme

The connection diagram of the windings in the terminal box is shown in Fig. eight

Fig.8 Connection in the ED outlet box according to the "star" scheme

The capacity of the working capacitor C p for these circuits is calculated by the formula:
,
where I n - rated current, U n - rated operating voltage.

In our case, for switching on according to the "triangle" scheme, the capacitance of the working capacitor C p = 25 μF.

The operating voltage of the capacitor must be 1.15 times the rated voltage of the supply network.

To start a low-power IM, a working capacitor is usually sufficient, but at a power of more than 1.5 kW, the engine either does not start or picks up speed very slowly, therefore it is necessary to use a starting capacitor C p. The capacity of the starting capacitor should be 2.5-3 times larger than the working capacitor capacitor.

The connection diagram of the motor windings connected according to the "triangle" scheme using starting capacitors C p is shown in Fig. nine.

Fig.9 Connection diagram of EM windings according to the "triangle" scheme with the use of starting condensates

The connection diagram of the "star" motor windings using starting capacitors is shown in Fig. ten.

Fig.10 Connection diagram of the EM windings according to the "star" scheme with the use of starting capacitors.

Starting capacitors C p are connected in parallel to the working capacitors using the KN button for 2-3 s. In this case, the speed of rotation of the rotor of the electric motor must reach 0.7 ... 0.8 of the rated speed.

To start the blood pressure using starting capacitors, it is convenient to use the button in Fig. 11.

Fig. 11

Structurally, the button is a three-pole switch, one pair of contacts of which is closed when the button is pressed. When released, the contacts open and the remaining pair of contacts remain on until the stop button is pressed. The middle pair of contacts performs the function of the KH button (Fig. 9, Fig. 10), through which the starting capacitors are connected, the other two pairs work as a switch.

It may happen that in the electric motor junction box the ends of the phase windings are made inside the motor. Then the AD can only be connected according to the diagrams in Fig. 7, Fig. 10, depending on the power.

There is also a diagram for connecting the stator windings of a three-phase electric motor - an incomplete star in Fig. 12. The connection according to this scheme is possible if the beginnings and ends of the phase stator windings are brought out into the junction box.

Fig. 12

It is advisable to connect EM according to such a scheme when it is necessary to create a starting torque exceeding the nominal one. Such a need arises in drives of mechanisms with severe starting conditions, when starting mechanisms under load. It should be noted that the resulting current in the supply wires exceeds the rated current by 70-75%. This must be taken into account when choosing a wire cross-section for connecting an electric motor.

The capacity of the working capacitor C p for the circuit in Fig. 12 is calculated by the formula:
.

The capacitances of the starting capacitors should be 2.5-3 times greater than the capacitance C p. The operating voltage of the capacitors in both circuits must be 2.2 times the rated voltage.

Usually, the terminals of the stator windings of electric motors are marked with metal or cardboard tags with the designation of the beginnings and ends of the windings. If there are no tags for some reason, proceed as follows. First, the belonging of the wires to the individual phases of the stator winding is determined. To do this, take any of the 6 external terminals of the electric motor and connect it to some power source, and connect the second terminal of the source to the control lamp and with the second wire from the lamp, alternately touch the remaining 5 terminals of the stator winding until the lamp lights up. If the light comes on, it means that 2 outputs belong to the same phase. Let's conditionally mark with tags the beginning of the first wire C1, and its end - C4. Similarly, we find the beginning and end of the second winding and designate them C2 and C5, and the beginning and end of the third - C3 and C6.

The next and main step will be to determine the beginning and end of the stator windings. To do this, we will use the selection method, which is used for electric motors up to 5 kW. We connect all the beginnings of the phase windings of the electric motors according to the previously attached tags to one point (using the "star" scheme) and turn on the electric motor in a single-phase network using capacitors.

If the motor immediately picks up the rated speed without a strong hum, this means that all the beginnings or all the ends of the winding have hit the common point. If, when turned on, the engine hums strongly and the rotor cannot reach the rated speed, then in the first winding, the terminals C1 and C4 should be swapped. If this does not help, the ends of the first winding must be returned to their original position and now the terminals C2 and C5 are reversed. Do the same; for the third pair if the engine continues to hum.

When determining the beginnings and ends of the windings, strictly adhere to the safety rules. In particular, when touching the terminals of the stator winding, only hold the wires by the insulated part. This must also be done because the electric motor has a common steel magnetic circuit and a large voltage may appear at the terminals of other windings.

To change the direction of rotation of the IM rotor connected to a single-phase network according to the "delta" scheme (see Fig. 5), it is enough to connect the third phase stator winding (W) through a capacitor to the terminal of the second phase stator winding (V).

To change the direction of rotation of the AM connected to a single-phase network according to the "star" scheme (see Fig. 7), you need to connect the third phase stator winding (W) through a capacitor to the terminal of the second winding (V).

When checking the technical condition of electric motors, it is often possible to notice with chagrin that after prolonged operation, extraneous noise and vibration appear, and it is difficult to turn the rotor manually. Poor bearing condition may be the reason for this: treadmills are covered with rust, deep scratches and dents, individual balls and cage are damaged. In all cases, it is necessary to inspect the electric motor and eliminate the existing faults. In case of minor damage, it is enough to wash the bearings with gasoline and lubricate them.