Do-it-yourself reverse connection of a single-phase asynchronous motor

Before choosing a connection diagram for a single-phase asynchronous motor, it is important to find out whether to reverse. If for present work For you, it will often be necessary to change the direction of rotation of the rotor, then it is purposeful to organize a reversal with the introduction of a push-button post. If one-sided rotation is enough for you, then the most common circuit without the ability to switch will do. But what if, after connecting through it, you decide that the direction needs to be changed after all?

Formulation of the problem

Let's imagine that for an asynchronous single-phase motor already connected with the introduction of a starting-charging capacity, at first the rotation of the shaft is oriented clockwise, as in the picture below.

Let's clarify the key points:

• Point A marks the beginning of the starting winding, and point B marks its end. A coffee wire is connected to the source terminal A, and a greenish wire to the final terminal.
• Point C marks the beginning of the working winding, and point D marks its end. A reddish wire is connected to the initial contact, and a blue wire is connected to the final contact.
• The direction of rotation of the rotor is indicated by arrows.

We put ourselves in front of the task - to reverse a single-phase motor without opening its case so that the rotor starts spinning in the other direction (in this example, against the movement of the clock). It can be solved by 3 methods. Let's look at them in more detail.

Option 1: reconnecting the working winding

To change the direction of rotation of the motor, you can only swap the beginning and end of the working (unchanged on) winding, as shown in the figure. You might think that for this you will have to open the case, take out the winding and twist it. You do not need to do this, since it is enough to work with contacts from the outside:

1. Four wires should come out of the case. 2 of them correspond to the beginnings of the working and starting windings, and 2 to their ends. Determine which pair belongs only to the working winding.
2. You will see that two strips are connected to this pair: phase and zero. With the engine turned off, reverse by switching the phase from the initial winding contact to the final one, and zero - from the final to the initial one. Or vice versa.

As a result, we get a scheme where points C and D change places among themselves. Now the rotor of the asynchronous motor will spin in the opposite direction.

HOW TO CHANGE THE DIRECTION OF A SHAFT ROTATION IN A SINGLE-PHASE MOTOR

The motor is taken from a household meat grinder. The direction of movement did not suit us, we had to change it. All info.

How to change the direction of rotation of a three-phase asynchronous motor?

Let's figure out how easy it is to change the direction of rotation of a three-phase motor to the opposite.

Option 2: reconnecting the starting winding

The second way to organize the reverse of a 220 Volt asynchronous motor is to swap the beginning and end of the starting winding. This is done by analogy with the first option:

1. From the four wires coming out of the motor box, find out which of them correspond to the starting windings.
2. Initially, the end B of the starting winding was connected to the beginning C of the working winding, and the beginning A was connected to the start-charging capacitor. You can reverse a single-phase motor by connecting the capacitance to terminal B, and the beginning of C with the beginning of A.

After the actions described above, we get a diagram, as in the figure above: points A and B have changed places, which means that the rotor began to turn in the opposite direction.

Option 3: change the starting winding to the working one, and vice versa

It is possible to organize a reverse of a single-phase 220V motor in the ways described above only on the condition that taps from both windings with all beginnings and ends come out of the housing: A, B, C and D. But there are often motors in which the manufacturer deliberately left outside only 3 contacts. By this, he secured the device from various "home-made products". But still there is a way out.

The figure above shows a diagram of such a "problem" motor. It has only three wires coming out of the case. They are labeled in brown, blue and purple. The green and red lines corresponding to the end B of the starting winding and the beginning C of the working winding are interconnected inside. We will not be able to get access to them without disassembling the engine. Therefore, it is not possible to change the rotation of the rotor with one of the first two options.

In this case, do it like this:

1. Remove the capacitor from the initial output A;
2. Connect it to terminal D;
3. From wires A and D, as well as phases, they let off (you can reverse using the key).

Look at the picture above. Now, if you connect the phase to the branch D, then the rotor rotates in one direction. If the phase wire is transferred to branch A, then the direction of rotation can be changed in the opposite direction. The reverse can be done by manually disconnecting and connecting the wires. Using a key will make the job easier.

Important! The last version of the reverse circuit for connecting an asynchronous single-phase motor is incorrect. It can only be used if the following conditions are met:

• The length of the starting and working windings is the same;
• Their area cross section match each other;
• These wires are made from the same material.

All of these quantities affect resistance. It must be constant at the windings. If suddenly the length or thickness of the wires differ from each other, then after you organize the reverse, it turns out that the resistance of the working winding will become the same as it was before with the starting one, and vice versa. This can also cause the engine to fail to start.

Attention! Even if the length, thickness and material of the windings are the same, operation with a changed direction of rotation of the rotor should not be continuous. This is fraught with overheating and engine failure. The efficiency also leaves much to be desired.

It is easy to reverse a 220V asynchronous motor if the ends of the windings are removed from the housing to the outside. It is more difficult to organize it when there are only three conclusions. The third reversing method considered by us is suitable only for short-term inclusion of the engine in the network. If the work with reverse rotation promises to be long, then we recommend opening the box for switching using the methods described in options 1 and 2: this is safe for the unit, and efficiency is maintained.

sis26.ru

How to change the direction of rotation of a single-phase asynchronous motor

Rice. 1 Single-phase motor connection diagram induction motor with start capacitor.

Let us take as a basis the already connected single-phase asynchronous motor, with the direction of rotation clockwise (Fig. 1).

Figure 1

• points A, B conventionally indicate the beginning and end of the starting winding; for clarity, brown and green wires are connected to these points, respectively.
• points C, B conventionally indicate the beginning and end of the working winding, for clarity, red and blue wires are connected to these points, respectively.
• the arrows indicate the direction of rotation of the rotor of the asynchronous motor

Change the direction of rotation of a single-phase asynchronous motor in the other direction - counterclockwise. To do this, it is enough to reconnect one of the windings of a single-phase asynchronous motor - either working or starting.

Option number 1

We change the direction of rotation of a single-phase asynchronous motor by reconnecting the working winding.

Fig. 2 With this connection of the working winding, relative to fig. 1, a single-phase induction motor will rotate in the opposite direction.

Option number 2

We change the direction of rotation of a single-phase asynchronous motor by reconnecting the starting winding.

Fig.3 With this connection of the starting winding, relative to fig. 1, a single-phase induction motor will rotate in the opposite direction.

Important note.

This way to change the direction of rotation of a single-phase asynchronous motor is possible only if the motor has separate taps for the starting and working windings.

Fig. 4 With this connection of the motor windings, reverse is not possible.

On fig. 4 shows a fairly common version of a single-phase asynchronous motor, in which the ends of the windings B and C, the green and red wires, respectively, are connected inside the housing. Such an engine has three outputs, instead of four as in fig. 4 brown, purple, blue wire.

UPD 09/03/2014 Finally, it was possible to check in practice, not very correct, but still used method of changing the direction of rotation of an asynchronous motor. For a single-phase asynchronous motor, which has only three outputs, it is possible to make the rotor rotate in the opposite direction, it is enough to swap the working and starting windings. The principle of such inclusion is shown in Fig. 5

Rice. Non-standard reverse asynchronous motor

zival.ru

How to reduce the speed of the electric motor scheme and description | ProElectrika.com

Adjusting the speed of the electric motor is often necessary both for industrial and for some domestic purposes. In the first case, to reduce or increase the speed, industrial voltage regulators are used - inverter frequency converters. And with the question of how to regulate the speed of the electric motor at home, let's try to figure it out in more detail.

It must be said right away that different power controllers should be used for different types of single-phase and three-phase electrical machines. Those. for asynchronous machines, the use of thyristor controllers, which are the main ones for changing the rotation of collector motors, is unacceptable.

The best way reduce the speed of your device - not in adjusting the speed of the engine itself, but by means of a gearbox or belt drive. At the same time, the most important thing will remain - the power of the device.

A little theory about the device and scope of collector motors

Electric motors of this type can be permanent or alternating current, with serial, parallel or mixed excitation (only the first two types of excitation are used for alternating current).

The commutator motor consists of a rotor, stator, commutator and brushes. The current in the circuit passing through the stator and rotor windings connected in a certain way creates a magnetic field that causes the latter to rotate. The voltage on the rotor is transmitted using brushes made of a soft electrically conductive material, most often it is graphite or a copper-graphite mixture. If you change the direction of the current in the rotor or stator, the shaft will begin to rotate in the opposite direction, and this is always done with the rotor terminals, so that the cores do not remagnetize.

If the connection of both the rotor and the stator is changed at the same time, reversal will not occur. There are also three-phase collector motors, but that's another story.

DC Motors with Parallel Excitation

Excitation winding (stator) in a motor with parallel excitation consists of a large number of turns of thin wire and is connected in parallel to the rotor, the winding resistance of which is much less. Therefore, to reduce the current during the start of electric motors with a power of more than 1 kW, a starting rheostat is included in the rotor circuit. The speed control of the electric motor with such a switching scheme is carried out by changing the current only in the stator circuit, because. the method of lowering the voltage at the terminals is not very economical and requires the use of a high power regulator.

If the load is small, then in the event of an accidental break in the stator winding, when using such a scheme, the rotational speed will exceed the maximum allowable and the electric motor may go "peddling"

DC motors with series excitation

The excitation winding of such an electric motor has no big number turns of thick wire, and when it is connected in series to the armature circuit, the current in the entire circuit will be the same. Electric motors of this type are more resistant to overloads and therefore are most often found in household appliances.

Adjustment of turns of the electric motor direct current with a series-connected stator winding can be done in two ways:

1. By connecting parallel to the stator an adjusting device that changes the magnetic flux. However, this method is quite complicated to implement and is not used in household devices.
2. Regulation (reduction) of revolutions by reducing the voltage. This method is used in almost all electrical devices - household appliances, tool, etc.

AC commutator motors

These single-phase motors have a lower efficiency than DC motors, but due to the ease of manufacture and control circuits, they have found the most wide application v household appliances and power tools. They can be called "universal", because. they are capable of operating both with alternating and direct current. This is due to the fact that when an alternating voltage is connected to the network, the direction of the magnetic field and current will change in the stator and rotor simultaneously, without causing a change in the direction of rotation. The reverse of such devices is carried out by reversing the ends of the rotor.

To improve performance in powerful (industrial) AC collector motors, additional poles and compensation windings are used. There are no such devices in the engines of household appliances.

Electric motor speed controllers

Schemes for changing the speed of electric motors in most cases are built on thyristor controllers, due to their simplicity and reliability.

The principle of operation of the presented circuit is as follows: the capacitor C1 is charged to the breakdown voltage of the dinistor D1 through a variable resistor R2, the dinistor breaks through and opens the triac D2, which controls the load. The load voltage depends on the opening frequency D2, which in turn depends on the position of the variable resistance slider. This scheme not provided with feedback, i.e. when the load changes, the speed will also change and they will have to be adjusted. According to the same scheme, the turnover of imported household vacuum cleaners is controlled.

This is how a good engine speed controller works:

A change in the speed of rotation of the motor shaft in a washing machine, for example, occurs with the use of feedback from the tachometer, so its speed is constant under any load.

proelectrica.com

Speed ​​control of single-phase motors

Single-phase asynchronous motors are powered by a conventional 220 V AC mains.

The most common design of such motors contains two (or more) windings - working and phase-shifting. The working one is fed directly, and the additional one through a capacitor, which shifts the phase by 90 degrees, which creates a rotating magnetic field. Therefore, such motors are also called two-phase or capacitor.

It is necessary to regulate the rotation speed of such motors, for example, for:

• changes in air flow in the ventilation system
• pump performance control
• changes in the speed of moving parts, for example in machine tools, conveyors

In ventilation systems, this allows you to save energy, reduce the level of acoustic noise of the installation, and set the required performance.

Ways of regulation

Consider mechanical methods we will not change the speed of rotation, for example, gearboxes, couplings, gear transmissions. Also, we will not touch on the method of changing the number of winding poles.

Consider methods with a change in electrical parameters:

• motor supply voltage change
• changing the frequency of the supply voltage

Voltage regulation

Speed ​​control in this way is associated with a change in the so-called motor slip - the difference between the rotation speed of the magnetic field created by the stationary stator of the motor and its moving rotor:

n1 - magnetic field rotation speed

n2 - rotor speed

In this case, slip energy is necessarily released - because of which the motor windings heat up more.

This method has a small regulation range, approximately 2:1, and can also be carried out only downwards - that is, by reducing the supply voltage.

When adjusting the speed in this way, it is necessary to install oversized motors.

But despite this, this method is used quite often for small power motors with a fan load.

In practice, various schemes of regulators are used for this.

Autotransformer voltage regulation

An autotransformer is an ordinary transformer, but with one winding and with taps from part of the turns. At the same time, there is no galvanic isolation from the network, but in this case it is not needed, therefore, savings are obtained due to the lack of a secondary winding.

The diagram shows the autotransformer T1, the switch SW1, which receives taps with different voltages, and the motor M1.

The adjustment is obtained in steps, usually no more than 5 steps of regulation are used.

The advantages of this scheme:

• undistorted output voltage (pure sine wave)
• good overload capacity of the transformer

Flaws:

• large weight and dimensions of the transformer (depending on the power of the load motor)
• all the disadvantages inherent in voltage regulation

Thyristor engine speed controller

In this circuit, keys are used - two thyristors connected in anti-parallel (variable voltage, therefore each thyristor passes its half-wave of voltage) or a triac.

The control circuit regulates the moment of opening and closing of the thyristors relative to the phase transition through zero, respectively, a piece is "cut off" at the beginning or, more rarely, at the end of the voltage wave.

This changes the RMS value of the voltage.

This circuit is quite widely used to regulate the active load - incandescent lamps and all kinds of heating devices (the so-called dimmers).

Another way to regulate is to skip half-cycles of the voltage wave, but at a network frequency of 50 Hz, this will be noticeable to the engine - noise and jerks during operation.

To control motors, regulators are modified due to the characteristics of the inductive load:

• install protective LRC circuits to protect the power switch (capacitors, resistors, chokes)
• add a capacitor at the output to correct the voltage waveform
• limit the minimum power of voltage regulation - for a guaranteed start of the engine
• use thyristors with a current several times higher than the current of the electric motor

Advantages of thyristor regulators:

• low cost
• small weight and dimensions

Flaws:

• can be used for small motors
• during operation, noise, crackling, engine jerks are possible
• when using triacs, a constant voltage is applied to the motor
• all the disadvantages of voltage regulation

It should be noted that in most modern air conditioners of medium and top level The fan speed is controlled in this way.

Transistor voltage regulator

As the manufacturer himself calls it - an electronic autotransformer or a PWM controller.

The voltage change is carried out according to the PWM principle (pulse width modulation), and transistors are used in the output stage - field-effect or bipolar with an insulated gate (IGBT).

The output transistors are switched at a high frequency (about 50 kHz), if you change the width of the pulses and pauses between them, then the resulting voltage at the load will also change. The shorter the pulse and the longer the pause between them, the lower the resulting voltage and power input.

For an engine, at a frequency of several tens of kHz, a change in the pulse width is equivalent to a change in voltage.

The output stage is the same as that of the frequency converter, only for one phase - a diode rectifier and two transistors instead of six, and the control circuit changes the output voltage.

Advantages of an electronic autotransformer:

• Small dimensions and weight of the device
• low cost
• Pure, undistorted output current waveform
• No noise at low revs
• 0-10 Volt signal control

Weaknesses:

• The distance from the device to the engine is not more than 5 meters (this drawback is eliminated when using remote controller)
• All the disadvantages of voltage regulation

Frequency regulation

More recently (10 years ago), there were a limited number of frequency motor speed controllers on the market, and they were quite expensive. The reason was that there were no cheap high-voltage power transistors and modules.

But developments in the field of solid-state electronics have made it possible to bring IGBT power modules to the market. As a result - the massive appearance on the market of inverter air conditioners, welding inverters, frequency converters.

At the moment, frequency conversion is the main way to control the power, performance, speed of all devices and mechanisms driven by an electric motor.

However, frequency converters are designed to control three-phase motors.

Single-phase motors can be driven:

• specialized single-phase inverters
• three-phase inverters with the exception of the capacitor

Converters for single-phase motors

Currently only one manufacturer claims serial production specialized inverter for capacitor motors - INVERTEK DRIVES.

This is an Optidrive E2 model

For stable start and operation of the engine, special algorithms are used.

At the same time, frequency adjustment is also possible upwards, but in a limited frequency range, this is prevented by a capacitor installed in the phase-shifting winding circuit, since its resistance directly depends on the current frequency:

f - current frequency

C - capacitance of the capacitor

The output stage uses a bridge circuit with four output IGBT transistors:

Optidrive E2 allows you to control the motor without removing the capacitor from the circuit, that is, without changing the design of the motor - in some models this is quite difficult to do.

Advantages of a dedicated frequency converter:

• intelligent motor control
• stable stable operation of the engine
• huge possibilities of modern inverters:
• the ability to control the operation of the engine to maintain certain characteristics (water pressure, air flow, speed with a changing load)
• numerous protections (motor and device itself)
• sensor inputs (digital and analog)
• various outputs
• communication interface (for control, monitoring)
• preset speeds
• PID controller

Cons of using a single-phase inverter:

• limited frequency control
• high price

Use of VSD for three-phase motors

The standard chastotnik has a three-phase voltage output. When a single-phase motor is connected to it, a capacitor is removed from it and connected according to the diagram below:

The geometric arrangement of the windings relative to each other in the stator of an induction motor is 90°:

The phase shift of the three-phase voltage is -120°, as a result of this, the magnetic field will not be circular, but pulsating and its level will be less than when powered with a 90° shift.

In some capacitor motors, the additional winding is carried out with a thinner wire and, accordingly, has a higher resistance.

When operating without a capacitor, this will result in:

• stronger heating of the winding (service life is reduced, short circuits and interturn short circuits are possible)
• different current in the windings

Many inverters have protection against current asymmetry in the windings, if it is impossible to disable this function in the device, operation according to this circuit will be impossible

Advantages:

• lower cost compared to specialized inverters
• huge selection by capacity and manufacturers
• wider frequency control range
• all the advantages of the inverter (inputs / outputs, intelligent operation algorithms, communication interfaces)

Disadvantages of the method:

• the need for preliminary selection of the inverter and motor for joint operation
• pulsating and reduced torque
• increased heat
• no warranty in case of failure, tk. three-phase inverters are not designed to work with single-phase motors

masterxoloda.com

Ways to control the speed of an asynchronous motor

Asynchronous AC motors are the most used electric motors in absolutely all economic areas. Their advantages include constructive simplicity and low price. In this case, the regulation of the speed of an asynchronous motor is of no small importance. Existing methods shown below.

According to the block diagram, the speed of the electric motor can be controlled in two directions, that is, by changing the values:

1. stator electromagnetic field speed;
2. engine slip.

The first correction option, used for models with a squirrel-cage rotor, is carried out by changing:

• frequency,
• number of pole pairs,
• voltage.

The second option, used for modification with a phase rotor, is based on:

• change in supply voltage;
• connection of a resistance element to the rotor circuit;
• use of a valve cascade;
• use of dual power.

Due to the development of power converter technology, various types of frequency drives are currently being manufactured on a large scale, which has determined the active use of a frequency-controlled drive. Consider the most common methods.

Frequency regulation

Just ten years ago, there were a small number of ED speed controllers in the distribution network. The reason for this was that cheap power high-voltage transistors and modules were not yet produced at that time.

Today, frequency conversion is the most common way to control the speed of motors. Three-phase frequency converters are designed to control 3-phase electric motors.

Single-phase motors are controlled by:

• special single-phase frequency converters;
• 3-phase frequency converters with capacitor elimination.

Schemes of speed controllers of an asynchronous motor

For everyday engines, you can easily perform the necessary calculations and assemble the device on a semiconductor chip with your own hands. An example of a motor controller circuit is shown below. Such a scheme can achieve control of the parameters of the drive system, maintenance costs, and reduce electricity consumption by half.

The schematic diagram of the ED rotation speed controller for everyday needs is greatly simplified if the so-called triac is used.

The rotation speed of the ED is controlled by a potentiometer that determines the phase of the input pulse signal that opens the triac. The image shows that two thyristors connected in anti-parallel are used as keys. The thyristor speed controller ED 220 V is often used to control loads such as dimmers, fans and heating equipment. The technical performance and efficiency of the propulsion equipment depend on the rotation speed of the asynchronous EM.

Conclusion

The technomarket today offers a wide range of controllers and frequency converters for asynchronous AC motors.

Controlling the frequency variation method at the moment is the most optimal method, since it allows you to smoothly adjust the speed of an asynchronous EM in the widest range, without significant losses and a decrease in overload capabilities.

However, based on the calculation, you can independently assemble a simple and efficient device with regulation of revolutions of rotation of single-phase electric motors with the help of thyristors.

electricdoma.ru

Of the large number of types of AC motors used in modern electrical engineering, the most widespread, convenient and economical is the motor with a rotating magnetic field based on the use of three-phase current.

To understand the basic idea underlying the design of these engines, let us return again to the experiment depicted in Fig. 264. We saw there that a metal ring placed in a rotating magnetic field begins to rotate in the same direction as the field rotates. The reason for this rotation is the fact that when the field rotates, the magnetic flux through the ring changes and, at the same time, currents are induced in the ring, on which the field acts with forces already familiar to us that create a torque.

In the presence of a three-phase current, i.e., a system of three currents shifted in phase relative to each other by (a third of a period), it is very easy to obtain a rotating magnetic field without mechanical rotation of the magnet and without any additional devices. Rice. 351a shows how this is done. We have here three coils put on iron cores, located relative to each other at an angle of 120 °. Through each of these coils passes one of the currents of the system, constituting a three-phase current. Magnetic fields are created in the coils, the directions of which are marked with arrows. The magnetic induction of each of these fields changes over time according to the same sinusoidal law as the corresponding current (Fig. 351, b). Thus, the magnetic field in the space between the coils is the result of the superposition of three alternating magnetic fields, which, on the one hand, are directed at an angle of 120 ° relative to each other, and on the other hand, are out of phase by . The instantaneous value of the resulting magnetic induction is the vector sum of the three components of the fields at a given time:

.

If we now begin to look for how the resulting magnetic induction changes over time, then the calculation shows that the absolute value of the magnetic induction of the resulting field does not change (keeps a constant value), but the direction of the vector rotates uniformly, describing a full revolution during one current period.

Rice. 351. Obtaining a rotating magnetic field by adding three sinusoidal fields directed at an angle of 120 ° relative to each other and displaced in phase by: a) the location of the coils that create a rotating field; b) graph of changes in field induction over time; c) the resulting induction is constant in absolute value and rotates on a circle in a period

Without going into the details of the calculation, let us explain how the addition of three fields gives a rotating field that is constant in absolute value. On fig. 351b, the arrows mark the values ​​of the magnetic induction of the three fields at the moment when , at the moment when , and at the moment when , and in fig. 351,c, addition is made according to the parallelogram rule of magnetic inductions and at these three moments, and the directions of the arrows and , and , and correspond to Fig. 351 a. We see that the resulting magnetic induction has the same module at all three indicated moments, but its direction is rotated for each third of the period by one third of the circle.

If a metal ring (or, even better, a coil) is placed in such a rotating field, then currents will be induced in it in the same way as if the ring (coil) rotated in a fixed field. The interaction of the magnetic field with these currents creates forces that cause the ring (coil) to rotate. This is the main idea of ​​a three-phase motor with a rotating field, first implemented by M. O. Dolivo-Dobrovolsky.

The design of such an engine is clear from Fig. 352. Its fixed part - the stator - is a cylinder assembled from sheet steel, on the inner surface of which there are grooves parallel to the axis of the cylinder. Wires are placed in these grooves, interconnected along the end sides of the stator so that they form three coils rotated relative to each other by 120 °, which were discussed in the previous paragraph. The beginnings of these coils 1, 2, 3 and their ends 1", 2", 3" are connected to six clamps located on a shield mounted on the machine frame. The location of the clamps is shown in Fig. 353.

Rice. 352. Disassembled three-phase AC motor: 1 - stator, 2 - rotor, 3 - end shields, 4 - fans, 5 - ventilation holes

Rice. 353. The location of the clamps on the engine shield

Inside the stator is placed the rotating part of the engine - its rotor. This is also dialed from individual sheets a steel cylinder mounted on a shaft, with which it can rotate in bearings located in the side plates (covers) of the engine. At the edges of this cylinder there are ventilation blades, which, when the rotor rotates, create a strong stream of air in the engine, cooling it. On the cylindrical surface of the rotor, in grooves parallel to its axis, there is a row of wires connected by rings at the ends of the cylinder. Such a rotor, shown separately in Fig. 354, is called "short-circuited" (sometimes called "squirrel wheel"). It comes into rotation when a rotating magnetic field arises in the space inside the stator.

Rice. 354. Squirrel-cage rotor of a three-phase motor

The rotating field is created by a three-phase system of currents supplied to the stator windings, which can be interconnected either by a star (Fig. 355) or a triangle (Fig. 356). In the first case (§ 170), the voltage on each winding is several times less than the line voltage of the network, and in the second, it is equal to it. If, for example, the voltage between each pair of wires three-phase network(linear voltage) is 220 V, then when the windings are connected in a triangle, each of them is energized with 220 V, and if they are connected with a star, then each winding is energized with 127 V.

Rice. 355. Turning on the stator windings with a star: a) the circuit for turning on the engine; b) connection of clamps on the shield. Terminals 1", 2", 3" are connected "short" by metal busbars; wires of a three-phase network are connected to terminals 1, 2, 3

Rice. 356. Turning on the stator windings with a triangle: a) the circuit for turning on the engine; b) connection of clamps on the shield. Terminals 1 and 3", 2 and 1", 3 and 2" are connected by metal busbars; wires of a three-phase network are connected to terminals 1, 2, 3

Thus, if the motor windings are designed for a voltage of 127 V, then the motor can operate with normal power both from a 220 V network when its windings are connected in a star, and from a 127 V network when its windings are connected in a triangle. The plate attached to the frame of each motor therefore indicates two mains voltages at which this motor can operate, for example 127/220 V or 220/380 V. When connected to a network with a lower linear voltage, the motor windings are connected in a triangle, and when powered by networks with a higher voltage are connected by a star.

The torque of the engine is created by the interaction forces of the magnetic field and the currents induced by it in the rotor, and the strength of these currents (or the corresponding emf) is determined by the relative frequency of rotation of the field with respect to the rotor, which itself rotates in the same direction as field. Therefore, if the rotor rotated with the same frequency as the field, then there would be no relative motion between them. Then the rotor would be at rest with respect to the field and no induced e would arise in it. d.s., i.e., there would be no current in the rotor and forces could not arise, causing it to rotate. From this it is clear that the motor of the described type can only operate at a rotor speed that is somewhat different from the field speed, i.e., from the current frequency. Therefore, such engines in technology are usually called "asynchronous" (from the Greek word "synchronous" - coinciding or coordinated in time, the particle "a" means negation).

Thus, if the field rotates with a frequency , and the rotor with a frequency , then the rotation of the field relative to the rotor occurs with a frequency , and it is this frequency that determines the e. d.s. and current.

Value called in the technique of "sliding". It plays a very important role in all calculations. The slip is usually expressed as a percentage.

When we turn on an unloaded engine in the network, then in the first moments it is equal to or close to zero, the frequency of rotation of the field relative to the rotor is large and induced in the rotor e. d.s. accordingly, it is also large - it is 20 times greater than that e. d.s., which occurs in the rotor when the engine is running at normal power. In this case, the current in the rotor also significantly exceeds the normal one. The engine develops a rather significant torque at the moment of starting, and since its inertia is relatively small, the rotor speed quickly increases and almost equals the field speed, so that their relative frequency becomes almost equal to zero and the current in the rotor quickly drops. For motors of low and medium power, their short-term overload during start-up is not dangerous, while starting very powerful motors (tens and hundreds of kilowatts), special starting rheostats are used that weaken the current in the winding; as the normal rotor speed is reached, these rheostats are gradually turned off.

As the engine load increases, the rotor speed decreases somewhat, the field rotation frequency relative to the rotor increases, and at the same time, the current in the rotor and the torque developed by the engine increase. However, to change the engine power from zero to the normal value, a very small change in the rotor speed is required, up to about 6% of the maximum value. Thus, an asynchronous three-phase motor maintains an almost constant rotor speed with very wide load fluctuations. In principle, it is possible to regulate this frequency, but the corresponding devices are complex and uneconomical, and therefore they are used very rarely in practice. If the machines driven by the engine require a different speed than this engine gives, then gears or belt drives with different gear ratios are preferred.

It goes without saying that with an increase in the load of the engine, i.e., the mechanical power given off by it, not only the current in the rotor must increase, but also the current in the stator so that the engine can absorb the corresponding electrical power from the network. This is done automatically due to the fact that the current in the rotor also creates its own magnetic field in the surrounding space, which acts on the stator windings and induces some e in them. d.s. The connection between the magnetic flux of the rotor and the stator, or, as they say, "armature reaction", causes changes in the current in the stator and ensures that the electrical power taken from the network is matched with the mechanical power given by the motor. The details of this process are quite complex and we will not go into them.

It is very important, however, to remember that although an underloaded motor takes away from the network such an amount of energy that corresponds to the work it does, but if it is underloaded, when the current in the stator drops, this is due to an increase in the stator inductive resistance, i.e., a decrease in power factor (§ 163), which spoils the operating conditions of the network as a whole. If, for example, a machine has enough power of 3 kW, and we install a 10 kW motor on it, then this enterprise will suffer almost no damage - the motor will still take only the power that is required for its operation, plus losses in the engine itself. But such an underloaded motor has a large inductive resistance and reduces the power factor of the network. It is unprofitable from the point of view of the national economy as a whole. In order to stimulate the struggle for increasing the power factor, organizations that sell electricity to consumers apply a system of fines for a power factor that is too low compared to the established norm and incentives for increasing it.

Therefore, when working with engines, the following rules must be strictly observed:

1. It is always necessary to select an engine of such power as the machine driven by it actually requires.

2. If the motor load does not reach 40% of normal, and the stator windings are connected in a delta, then it is advisable to switch them to a star. In this case, the voltage on the windings decreases by a factor, and the magnetizing current - by almost three times. In cases where such switching has to be done frequently, the engine is connected to the network using a toggle switch according to the diagram shown in fig. 357. In one position of the switch, the windings are connected by a triangle, in the other - by a star.

Rice. 357. Scheme for switching the motor windings from a triangle (switch position I, I, I) to a star (switch position II, II, II)

In order to reverse the direction of rotation of the motor shaft, it is necessary to swap two line wires connected to the motor. This is easily done with a two-pole switch, as shown in fig. 358. By moving the switch from position I-I to position II-II, we change the direction of rotation of the magnetic field and at the same time the direction of rotation of the motor shaft.

Rice. 358. Switching circuit for changing the direction of rotation of a three-phase motor

We have seen that if there are three coils in the motor stator, displaced relative to each other by 120 °, the magnetic field rotates with the frequency of the current, that is, it makes one revolution per fraction of a second, or 3000 revolutions per minute. The motor shaft will also rotate at almost the same frequency. In many cases, this rotational speed is excessively high. To reduce it, not three coils, but six or twelve are placed in the motor stator and connected so that the north and south poles alternate around the stator circumference. In this case, the field rotates for each current period only by half or a quarter of a turn, i.e., the machine shaft rotates at a frequency of about 1500 or 750 revolutions per minute.

Finally, one more practically important remark. In case of damage (breakdown) of the insulation of the frame and casings of electrical machines and transformers, they are energized relative to the Earth. Touching these machine parts can be dangerous for people under such conditions. To prevent this danger, at voltages above 150 V relative to the Earth, the frames and casings of electrical machines and transformers should be grounded, that is, they should be reliably connected with metal wires or rods to the Earth. This is done according to special rules that must be strictly observed in order to avoid accidents.

Changing the direction of rotation in an asynchronous motor by changing two phases in the windings is possible only for THREE-PHASE motors (intended for inclusion in a three-phase network)!

The main principle of changing the direction of an induction motor is to change the direction of rotation

field stator.

Single-phase induction motors have several principles for creating a rotating magnetic field.

There are single-phase capacitor motors: one of the two windings is connected through a phase-shifting capacitor: here, to change the rotation, it is necessary to change the direction of switching on any of the two windings (for this, 4 wires must come out of the motor, i.e. the connection point of the windings should not be inside).

There are single-phase motors with a short-circuited coil: here the direction of rotation is determined by the installation of short-circuited turns on the poles (they create a phase shift) - here the direction of rotation cannot be changed.

There are single-phase motors with working and starting windings (these are often put on refrigerator compressors) the starting one turns on for a short time at the time of start (this produces a start-up relay): here it is also possible to change the rotation by changing the inclusion of one of the windings (it is necessary that all 4 ends of the windings come out of the engine) .

If there are only three ends (or the starting winding does not work), then with a small power - about a kilowatt - such an engine can be started in any direction by turning on the working winding and sharply turning the shaft in the right direction.

If the power is greater, the launch can be carried out with a rope wound around the shaft.

There are other designs of induction motors and changing the rotation of each of the designs must be considered separately.

Therefore, the rotation of the electric motor does not change when replacing two phases, that the starting torque of an asynchronous two-phase motor with a symmetrical winding is zero. To change the rotation of an asynchronous motor, use the following advice-instruction:

Changing the rotation of an induction motor is not so difficult. The main thing is to understand at least a little in this matter. Turn off the power, read the instructions, swap the wires and turn it on again. This will change the rotation. More details can be read here.





In an asynchronous motor, rotation is possible both in one direction and in the other. And it depends on where the magnetic field rotates around the stator. There are several ways to change the rotation of a magnetic field. One of them is like this. If a three-phase network feeds the motor, then you need to swap any two phase wires.

An asynchronous motor can indeed change direction. Clockwise or counterclockwise. Sometimes it helps a lot at work. I don't want to buy an engine for every job. The main thing when working with changing the direction of movement of the motor is to disconnect it from the mains.

This type of motor can rotate in two directions: clockwise and counterclockwise. There are many ways to change the rotation of an induction motor, you can do it in one of the following ways:

Because the starting torque of an asynchronous two-phase motor with a symmetrical winding is zero.

The winding of a two-phase asynchronous circuit consists of two - starting and working, and they create two magnetic moments, structurally offset one relative to the other. There can be a capacitor in the starting winding, which also provides a phase shift. If it is rearranged in the working winding, then the direction of rotation will change. Only here the working winding is designed for a larger current. Indeed, in the circuit of the starting winding there is resistance, which, again, provides the phase shift of the current necessary for the starting torque. You will change the direction of rotation in this way, but it will not work for a long time.

Experienced electricians will tell you that a three-phase (it is symmetrical) can be started with a winding the cord around the shaft and pulling sharply on it. That is, creating a starting external moment.

An asynchronous motor can be connected to the network in several ways:

• directly from a three-phase network (in this case, you need to swap any two of the three phase wires in places);
• the electric motor is powered by a capacitor from a single-phase network (here we need to disconnect the output of the capacitor, which is connected to one of the wires that feeds it, and then switch to another);
• the electric motor is powered by a three-phase inverter (here it is better to trust the instructions for use).

All manipulations must be carried out, of course, when the electric motor is disconnected from the network.

I can offer you two solutions to your question:

1) in order to change the direction of rotation of a single-phase asynchronous motor, you need to reconnect the working winding.

2) or reconnect the starting winding.

An induction motor can indeed move both clockwise and counterclockwise. There is different ways change its rotation. In any case, first you need to disconnect it from the power supply. It is important to know that the connection method does not affect the direction of rotation, so nothing needs to be changed in this regard. If the power comes directly from a three-phase network, you need to swap two of the three phase wires going to it, and any. If the power goes through a three-phase inverter, then the instructions for the device itself will help change the direction. In other conditions, everything is a little more complicated, perhaps experts will tell you.

8. The principle of operation and reverse (changing the direction of rotation) of a three-phase asynchronous motor.

The figure shows the electromagnetic circuit of the IM with a short-circuited rotor winding in the section, including the stator (1), in the grooves of which there are three phase stator windings (2), represented by one turn. The beginnings of the phase windings are A, B, C, and the ends are X, Y, Z, respectively. In the cylindrical rotor (3) of the engine, there are rods (4) of short-circuited windings closed at the ends of the rotor by plates.

When a three-phase voltage is applied to the phase windings of the stator, stator currents flow in the turns of the stator winding iA, iB, iC, creating a rotating magnetic field with a rotation frequency n1. This field crosses the rods of the short-circuited rotor winding and EMF is induced in them, the direction of which is determined by the right hand rule. The EMF in the rotor bars is created by the rotor currents i2 and the rotor magnetic field, which rotates with the frequency of the stator magnetic field. The resulting magnetic field of the IM is equal to the sum of the magnetic fields of the stator and rotor. Electromagnetic forces act on conductors with current i2 located in the resulting magnetic field, the direction of which is determined by the left hand rule. The total gain Fres applied to all conductors of the rotor forms a rotating electromagnetic moment M of the induction motor.

The rotating electromagnetic moment M, overcoming the moment of resistance Ms on the shaft, forces the rotor to rotate with a frequency n2. The rotor rotates with acceleration if the moment M is greater than the moment of resistance Ms, or at a constant frequency if the moments are equal.

The rotational speed of the rotor n2 is always less than the rotational speed of the magnetic field of the machine n1, because only in this case does a rotating electromagnetic moment occur. If the rotor speed is equal to the stator MF rotation frequency, then the EM moment is zero (the rotor rods do not cross the motor MF, and the current is zero). The difference in the rotational speeds of the MT of the stator and rotor in relative units is called motor slip:

s = n 1 − n 2. n 1

Slip is measured in relative units or percentages relative to n1. In the operating mode, close to the nominal, the motor slip is 0.01-0.06. Rotor speed n 2 = n 1 (1− s ) .

Thus, a characteristic feature of an asynchronous machine is the presence of slip - the inequality of the frequencies of rotation of the magnetic field of the motor and the rotor. Therefore, the machine is called asynchronous.

When the asynchronous machine is operating in the motor mode, the rotor speed is less than the speed of the MP and 0< s < 1. в этом режиме обмотка статора питается от сети, а вал ротора передает механический момент на исполнительный орган механизма. Электрическая энергия преобразуется в механическую.

If the IM rotor is inhibited (s = 1), this is a short circuit mode. If the rotational speed of the rotor coincides with the frequency of rotation of the MP, then the engine torque does not occur. This is the ideal idle mode.

To change the direction of rotation of the rotor (reverse the motor), you need to change the direction of rotation of the MP. To reverse the motor, you need to change the order of the phases of the supplied voltage, that is, switch two phases.

9. Equivalent circuit and mechanical characteristics of a three-phase asynchronous motor.

In the scheme, an asynchronous machine with electromagnetic coupling of the stator and rotor circuits is replaced by an equivalent equivalent circuit. In this case, the parameters of the rotor winding R2 and x2 are reduced to the stator winding, provided that E1 = E2 ". E2", R2 ", x2" are the reduced rotor parameters.

included in the winding of the fixed rotor, i.e. the machine has an active load.

The value of this resistance is determined by the slip, and, consequently, by the mechanical load on the motor shaft. If the moment of resistance on the motor shaft Ms = 0, then slip s = 0; in this case, the value of R n =∞ and I2 " = 0, which corresponds to the work

engine at idle.

In idle mode, the stator current is equal to the magnetizing current I 1 \u003d I 0. The magnetic circuit of the machine is represented by a magnetizing circuit with the parameters x0, R0 are the inductive and active resistances of the stator winding magnetization. If the moment of resistance on the motor shaft exceeds its torque, the rotor stops. In this case, the value of Rн = 0, which corresponds to the short circuit mode.

The first circuit is called the T-shaped IM equivalent circuit. It can be converted to a simpler form. For this purpose, the magnetizing circuit Z 0 = R 0 + jx 0

taken out on common clamps. So that at the same time the magnetizing current I 0 does not change its value, resistors R1 and x1 are connected in series in this circuit. In the resulting L-shaped equivalent circuit, the resistance of the stator and rotor circuits are connected in series. They form a working circuit, in parallel to which a magnetizing circuit is connected.

The magnitude of the current in the working circuit of the equivalent circuit:

mains voltage.

The electromagnetic moment of the IM is created by the interaction of the current in the rotor winding with the rotating MF of the machine. The electromagnetic moment M is determined through the electromagnetic power:

Assuming in the equation the number of motor phases m1 = 3; x1 + x2 " = xk , we examine it for an extremum. To do this, we equate the derivative dM / ds to zero and obtain two extreme points. At these points, the moment Mk and slip sk are called critical and are respectively equal:

The dependence of the EM torque on the slip M(s) or on the rotor speed M(n2) is called the mechanical characteristic of the IM.

If we divide M by Mk, we get a convenient form of writing the equation for the mechanical characteristic of IM:

Most often, a single-phase 220 V network is connected to our houses, plots, garages. Therefore, equipment and all home-made products are made so that they work from this power source. In this article, we will consider how to properly connect a single-phase motor.

Asynchronous or collector: how to distinguish

In general, you can distinguish the type of engine by the plate - nameplate - on which its data and type are written. But this is only if it has not been repaired. After all, under the casing can be anything. So if you're not sure, it's best to determine the type yourself.

How collector engines are arranged

It is possible to distinguish between asynchronous and collector motors by structure. Collectors must have brushes. They are located near the collector. Another obligatory attribute of this type of engine is the presence of a copper drum divided into sections.

Such motors are produced only single-phase, they are often installed in household appliances, as they allow you to get a large number of revolutions at the start and after acceleration. They are also convenient in that they easily allow you to change the direction of rotation - you just need to change the polarity. It is also easy to organize a change in the rotation speed - by changing the amplitude of the supply voltage or its cutoff angle. Therefore, such engines are used in most household and construction equipment.

The disadvantages of collector motors are high noise at high speeds. Remember a drill, a grinder, a vacuum cleaner, a washing machine, etc. The noise during their work is decent. At low speeds, collector motors are not so noisy ( washing machine), but not all tools work in this mode.

The second unpleasant moment - the presence of brushes and constant friction leads to the need for regular maintenance. If the current collector is not cleaned, graphite contamination (from wearable brushes) can cause adjacent sections in the drum to connect, the motor simply stops working.

Asynchronous

An asynchronous motor has a starter and a rotor, it can be one or three phase. In this article, we consider the connection of single-phase motors, because we will only talk about them.

Asynchronous motors are distinguished by a low level of noise during operation, therefore they are installed in equipment whose operation noise is critical. These are air conditioners, split systems, refrigerators.

There are two types of single-phase asynchronous motors - bifilar (with a starting winding) and capacitor. The whole difference is that in bifilar single-phase motors, the starting winding only works until the motor accelerates. After that, it is turned off by a special device - a centrifugal switch or a start-up relay (in refrigerators). This is necessary, because after overclocking, it only reduces efficiency.

In capacitor single-phase motors, the capacitor winding operates all the time. Two windings - main and auxiliary - are offset relative to each other by 90 °. Thanks to this, you can change the direction of rotation. The capacitor on such engines is usually attached to the case and is easy to identify by this sign.

You can more accurately determine the bifolar or capacitor motor in front of you by measuring the windings. If the resistance of the auxiliary winding is less than half (the difference can be even more significant), most likely it is a bifolar motor and this auxiliary winding is a starting one, which means that there must be a switch or a starting relay in the circuit. In capacitor motors, both windings are constantly in operation and the connection of a single-phase motor is possible through a conventional button, toggle switch, automatic machine.

Wiring diagrams for single-phase asynchronous motors

With start winding

To connect a motor with a starting winding, you will need a button, in which one of the contacts opens after switching on. These opening contacts will need to be connected to the starting winding. In stores there is such a button - this is PNVS. Her middle contact closes for the holding time, and the two extreme ones remain in the closed state.

The appearance of the PNVS button and the state of the contacts after the "start" button is released "

First, using measurements, we determine which winding is working, which is starting. Usually the output from the motor has three or four wires.

Consider the option with three wires. In this case, the two windings are already combined, that is, one of the wires is common. We take a tester, measure the resistance between all three pairs. The working one has the smallest resistance, the average value is the starting winding, and the largest is the total output (the resistance of two windings connected in series is measured).

If there are four leads, they are called in pairs. Find two pairs. The one in which the resistance is less - working, in which more - starting. After that, we connect one wire from the starting and working windings, we output a common wire. In total, three wires remain (as in the first option):

• one from the working winding - working;
• from the starting winding;
• general.

With all these

connection of a single-phase motor

We connect all three wires to the button. It also has three contacts. Be sure to start the wire "we put on the middle contact(which closes only during start-up), the other two are extremeie (optional). We connect a power cable (from 220 V) to the extreme input contacts of the PNVS, connect the middle contact with a jumper to the working one ( note! not with common). That's the whole scheme for switching on a single-phase motor with a starting winding (bifolar) through a button.

condenser

When connecting a single-phase capacitor motor, there are options: there are three connection schemes and all with capacitors. Without them, the motor hums, but does not start (if you connect it according to the scheme described above).

The first circuit - with a capacitor in the power supply circuit of the starting winding - starts up well, but during operation, the power is given out far from the nominal, but much lower. The switching circuit with a capacitor in the working winding connection circuit has the opposite effect: not very good start-up performance, but good performance. Accordingly, the first circuit is used in devices with a difficult start (, for example), and with a working condenser - if good performance is needed.

Circuit with two capacitors

There is a third option for connecting a single-phase motor (asynchronous) - install both capacitors. It turns out something in between the options described above. This scheme is implemented most often. It is in the picture above in the middle or in the photo below in more detail. When organizing this circuit, a button of the PNVS type is also needed, which will connect the capacitor only not at the start time, until the motor “accelerates”. Then two windings will remain connected, and the auxiliary winding through the capacitor.

Connecting a single-phase motor: a circuit with two capacitors - working and starting

When implementing other circuits - with one capacitor - you will need a regular button, automatic machine or toggle switch. Everything just connects there.

Selection of capacitors

There is a rather complicated formula by which you can accurately calculate the required capacity, but it is quite possible to get by with recommendations that are derived from many experiments:

• a working capacitor is taken at the rate of 70-80 microfarads per 1 kW of engine power;
• launcher - 2-3 times more.

The operating voltage of these capacitors should be 1.5 times higher than the mains voltage, that is, for a 220 V network, we take capacities with an operating voltage of 330 V and higher. And to make the start easier, look for a special capacitor in the starting circuit. They have the words Start or Starting in the marking, but you can take the usual ones.

Changing the direction of the motor

If, after connecting, the motor works, but the shaft rotates in the wrong direction that you need, you can change this direction. This is done by changing the windings of the auxiliary winding. When the circuit was assembled, one of the wires was applied to the button, the second was connected to the wire from the working winding and a common one was brought out. This is where you need to throw the conductors.