Speed ​​regulation of an asynchronous motor. How do rotary controls work?

The direction of rotation of the motor shaft sometimes needs to be changed. This requires a reverse connection diagram. Its type depends on what kind of motor you have: direct or alternating current, 220V or 380V. And the reverse of a three-phase motor connected to a single-phase network is arranged in a completely different way.

To reversibly connect a three-phase asynchronous electric motor, we will take as a basis the circuit diagram for connecting it without reversing:

This scheme allows the shaft to rotate only in one direction - forward. To make it turn into another, you need to swap places of any two phases. But in electrics it is customary to change only A and B, despite the fact that changing A to C and B to C would lead to the same result. Schematically it will look like this:

To connect you will additionally need:

• Magnetic starter (or contactor) – KM2;
• Three-button station, consisting of two normally closed and one normally open contacts (a Start2 button has been added).

Important! In electrical engineering, a normally closed contact is a state of a push-button contact that has only two unbalanced states. The first position (normal) is working (closed), and the second is passive (open). The concept of a normally open contact is formulated in the same way. In the first position the button is passive, and in the second it is active. It is clear that such a button will be called “STOP”, while the other two are “FORWARD” and “BACK”.

The reverse connection scheme differs little from the simple one. Its main difference is the electric locking. It is necessary to prevent the motor from starting in two directions at once, which would lead to breakdown. Structurally, the interlock is a block with magnetic starter terminals that are connected in the control circuit.

To start the engine:

1. Turn on the machines AB1 and AB2;
2. Press the Start1 (SB1) button to rotate the shaft clockwise or Start2 (SB2) to rotate the shaft in the opposite direction;
3. The engine is running.

If you need to change direction, you must first press the “STOP” button. Then turn on another start button. An electrical lock prevents it from being activated unless the motor is switched off.

Variable network: electric motor 220 to network 220

Reversing a 220V electric motor is only possible if the winding terminals are located outside the housing. The figure below shows a single-phase switching circuit, when the starting and working windings are located inside and have no outputs to the outside. If this is your option, you will not be able to change the direction of rotation of the shaft.

In any other case, to reverse a single-phase capacitor IM, it is necessary to change the direction of the working winding. For this you will need:

• Machine;
• Push-button post;
• Contactors.

The circuit of a single-phase unit is almost no different from that presented for a three-phase asynchronous motor. Previously, we switched phases: A and B. Now, when changing direction, instead of a phase wire, a neutral wire will be connected on one side of the working winding, and on the other, a phase wire will be connected instead of a zero wire. And vice versa.

A major overhaul of a lathe is in progress. Main engine – two-speed

At a time when frequency converters for asynchronous motors were a luxury (more than 20 years ago), industrial equipment used DC motors, which had the ability to regulate the speed, if necessary.

This method was cumbersome, and along with it another, simpler one was used - two-speed (multi-speed) motors were used, in which the windings are connected and switched in a certain way according to the Dahlander scheme, which allows you to change the rotation speed.

Electronically controlled variable speed DC motors are used in high value industrial equipment.

But two-speed motors are found in machines manufactured in the USSR in the 1980s in the middle price category. And I personally had problems connecting, due to confusion and lack of information.

The latest examples are a special lathe. execution, sawmill. Details will be below.

The design of the windings resembles a delta connection, and therefore the switching can be associated with a star-delta connection. And it's confusing.

The “Star-Delta” circuit is used for easy starting of motors (the speed in both modes is the same!), and two-speed motors with winding switching are used for switching operating speeds.

There are engines not only with two, but also with more speeds But I will talk about what I personally connected and held in my hands:

Dahlander two-speed asynchronous electric motor

Less theory, more practice. And as usual, from simple to complex.

The windings of a two-speed motor look like this:

Diagram of a two-speed Dahlander engine

When connecting the terminals U1, V1, W1 of such a motor to a three-phase voltage, it will be switched into a “delta” at a reduced speed.

And if the terminals U1, V1, W1 are connected to each other, and power is supplied to the terminals U2, V2, W2, then you will get two “stars” (YY), and the speed will be 2 times higher.

What happens if the windings of the vertices of the triangle U1, V1, W1 and the midpoints of the sides U2, V2, W2 are swapped? I think nothing will change, it's just a matter of names. Although, I haven't tried it. If anyone knows, write in the comments to the article.

Connection diagrams

For those who are a little unfamiliar with how asynchronous electric motors are connected to a three-phase network, I strongly recommend that you read my article. I assume that the reader knows how the electric motor turns on, why and what kind of motor protection is needed, so in this article I omit these questions.

In theory everything is simple, but in practice you have to rack your brains.

Obviously, turning on the Dahlander motor windings can be done in two ways - through a switch and through contactors.

Changing speeds using a switch

Let's first consider a simpler circuit - through a PKP-25-2 type switch. Moreover, these are the only schematic diagrams that I have come across.

The switch must have three positions, one of which (middle) corresponds to the engine being turned off. About the switch device - a little later.

Connecting a two-speed motor. Diagram on the control panel switch.

Crosses on the dotted lines of the SA1 switch position indicate the closed states of the contacts. That is, in position 1 power from L1, L2, L3 is supplied to the triangle (pins U1, V1, W1). Pins U2, V2, W2 remain unconnected. The engine rotates at the first, reduced speed.

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When switching SA1 to position 2 pins U1, V1, W1 are connected to each other, and power is supplied to U2, V2, W2.

Switching speeds using contactors

When started using contactors, the circuit will look similar:

Engine connection diagram for different speeds on contactors

Here, the motor turns on the contactor KM1 at the first speed, and KM2 at the second speed. It is obvious that physically KM2 must consist of two contactors, since it is necessary to close five power contacts at once.

Practical implementation of a two-speed electric motor connection diagram

In practice, I only came across circuits on PKP-25-2 switches. This is a universal miracle of Soviet switching, which can have a million possible combinations of contacts. There is a cam inside (there are also several variations in shape) that can be rearranged.

This is a real puzzle and rebus that requires high concentration of consciousness. It’s good that each contact is visible through a small slot, and you can see when it is closed or open. In addition, contacts can be cleaned through these slots in the housing.

There can be several positions, their number is limited by the stops shown in the photo:

PKP switch 25. A puzzle for everyone.

Batch switch PKP-25-2 – contacts

Practical Application

As I already said, I came across such engines in Soviet machines that I restored.

Namely, a circular woodworking machine TsA-2A-1, it uses a two-speed asynchronous motor 4AM100L8/4U3. Its main parameters are first speed (triangle) 700 rpm, current 5.0 A, power 1.4 kW, stars - 1410 rpm, current 5.0 A, power 2.4 kW.

I was asked to do several speeds, for different woods and for different sharpness of the circular saw. But alas, you can’t do this without a frequency converter.

Another old man is a special-design lathe UT16P, it has an engine of 720/1440 rpm, 8.9/11 A, 3.2/5.3 kW:

Nameplate of two-speed electric motor 11 kW lathe

Switching is also done with a switch, and the machine diagram looks like this:

There is an error in this diagram, exactly on the topic of the article. Firstly, speed switching is carried out not by relay P2, but by switch B2. And second (and most importantly) – the switching diagram absolutely does not correspond to reality. And she confused me, I tried to connect using it. Until I created this diagram:

Additionally – appearance and arrangement of electrical circuit elements.

lathe diagram - appearance

electrical diagram of a lathe - arrangement of elements

That's all.

Friends! Anyone who comes across such machines and engines, write, share your experience, ask questions, I will be glad!

Update March 2017

I am posting photos and diagrams of the practical activation of a two-speed electric motor.

The engine runs on hydraulic power. At reduced speed, it produces low pressure, allowing hydraulically driven machinery to be controlled more accurately. At increased speed, the pressure increases approximately 2 times, and the speed of movement accordingly.

Borno two-speed motor - 6 wires come to the terminals

Two-speed motor contactors. The left one engages in a triangle (low speed), the right ones – a double star

Automatic motors. It can be seen that the delta current is up to 8A, the star current is up to 13A

Video of engine operation according to Dahlander's scheme

Unfortunately, there is no video in Russian on this topic.

Control diagram for the stand shown above:

Another diagram, switching speeds - through Stop:

Sharpening machine on Dahlander engine

I recently came across a machine with a two-speed motor, I am posting its diagram.

Scheme of a sharpening machine on a two-speed Dahlander motor

I am often asked what kind of protection should be given to this engine? Here, in the diagram, is a simple thermal relay (PT1), configured for a higher current (about 11 A).

Here is the engine nameplate:

Parameters of two-speed sharpening machine motor

And here are his pin designations:

Why do you think the rectangle PS (speed switch) is shown instead of the connection diagram? That's right, the circuit would then be 2 times larger and more complex.

You have to deal with the issue of adjusting speed when working with power tools, drives sewing machines and other devices in everyday life and at work Regulating speed by simply lowering the supply voltage does not make sense - the electric motor sharply reduces speed, loses power and stops. The optimal option for adjusting speed is to regulate voltage with feedback by motor load current

In most cases, power tools and other devices use universal commutator electric motors with sequential excitation. They work well on both AC and DC current. A feature of the operation of a commutator electric motor is that when switching the armature windings on the commutator lamellas during opening, pulses of self-induction counter-EMF occur. They are equal to the supply ones in amplitude, but opposite to them in phase. The back-EMF displacement angle is determined external characteristics electric motor, its load and other factors. The harmful effect of back-EMF is expressed in sparking on the collector, loss of engine power, and additional heating of the windings. Some of the back-EMF is suppressed by capacitors that shunt the brush assembly.

Let's consider the processes occurring in the regulation mode with the OS, using the example of a universal scheme (Figure 1). The resistive-capacitive circuit R2-R3-C2 provides the formation of a reference voltage that determines the rotation speed of the electric motor.

As the load increases, the rotation speed of the electric motor drops, and its torque decreases. The back-EMF arising on the electric motor and applied between the cathode of the thyristor VS1 and its control electrode decreases. As a result, the voltage at the control electrode of the thyristor increases in proportion to the decrease in back-EMF. The additional voltage on the control electrode of the thyristor causes it to turn on at a smaller phase angle (cut-off angle) and pass more current to the electric motor, thereby compensating for the decrease in rotation speed under load. There is a balance of pulse voltage on the control electrode of the thyristor, composed of the supply voltage and the self-induction voltage of the motor. Switch SA1 allows you to switch to full voltage power if necessary, without adjustment Special attention attention should be paid to selecting a thyristor based on the minimum switching current, which will ensure better stabilization of the motor rotation speed

The second scheme (Fig. 2) is designed for more powerful electric motors used in woodworking machines, grinders, and drills. In it, the principle of adjustment remains the same. The thyristor in this circuit should be installed on a radiator with an area of ​​at least 25 cm2.

For low-power electric motors and, if it is necessary to obtain very low rotation speeds, the circuit on an IC can be successfully applied (Fig. 3). It is designed for 12V DC power supply. In the case of a higher voltage, the microcircuit should be powered through a parametric stabilizer with a stabilization voltage no higher than 15V.

Speed ​​control is carried out by changing the average voltage of the pulses supplied to the electric motor. Such pulses effectively regulate very low rotation speeds, as if continuously “pushing” the electric motor rotor. At high rotation speeds, the electric motor operates normally.

A very simple scheme (Fig. 4) will allow you to avoid emergency situations on line railway(toy) and will open up new possibilities for managing squads. An incandescent lamp in the external circuit protects and signals a short circuit on the line, while limiting the output current.

When it is necessary to regulate the speed of electric motors with high torque on the shaft, for example in an electric winch, a full-wave bridge circuit (Fig. 5) can be useful, providing full power to the electric motor, which significantly distinguishes it from the previous ones, where only one half-wave of the supply voltage worked.

Diodes VD2 and VD6 and quenching resistor R2 are used to power the trigger circuit. The phase delay in opening the thyristors is ensured by the charging of capacitor C1 through resistors R3 and R4 from a voltage source, the level of which is determined by the zener diode VD8. When capacitor C1 is charged to the operating threshold of the unijunction transistor VT1, it opens and starts the thyristor at the anode of which there is a positive voltage. When the capacitor discharges, the unijunction transistor turns off. The value of resistor R5 depends on the type of electric motor and the desired depth of feedback. Its value is calculated using the formula

where Im is the effective value of the maximum load current for a given electric motor. The proposed schemes are highly repeatable, but require the selection of some elements depending on the characteristics of the motor used (it is almost impossible to find electric motors similar in all parameters, even within the same series).

Literature

1. Electronics Todays. Int N6

2. RCA Corp Manual

3.IOI Electronic Projects. 1977p93

5. G. E. Semiconductor Data Hand book 3. Ed

6.Count P. Electronic circuits. -M World, 1989

7. Semenov I.P. Power regulator with feedback. - Radio Amateur, 1997, N12, C 21.

Hello. With my review I will continue the series of reviews of components for the “smart home”. And today I’ll tell you about the electric motor rotation direction switch from ITEAD. The switch connects to your home Wi-Fi network, and you can control it over the Internet from anywhere in the world. In the review, I will test its operation and express my thoughts on improving and expanding the capabilities of the switch. If you are interested, welcome to cat.

The switch is supplied in an antistatic bag:

His brief characteristics from the website of the manufacturer ITEAD, who is also the seller:

Overview

This WiFi switch supports to control 7-32V DC or 125-250V AC motor’s clockwise/anticlockwise running. The switch adopts PSA 1-channel wifi module to realize motor clockwise/anticlockwise running control. Reversible status will be synchronously feedback to your phone! Input voltage: usb 5V or DC 7-32V.

The power supply switch uses a pulsed DC-BC converter:

Therefore, to power the switch it is possible to apply to the input constant voltage from 7 to 32 Volts:

Or the switch can be powered with 5 volts from micro USB:

Let's turn the board over and look at it from below:

I can’t help but notice that the flux from the relays and power contacts is poorly washed off.

A matrix of seven Darlington transistors, a linear regulator with a low voltage drop, and an unnamed microcircuit are installed here:

Let's connect a DC motor to the switch for testing:

You can connect motors with power from 7 to 32 volts. Power is connected according to the connection diagram:

The main thing is to keep the color of the wires, otherwise it won’t work)))

We supply power, in our case 7.5V and now it’s time to connect the switch to the smartphone application:

I described in detail how to install and configure the application in my review. Since the release of that review, the application has only gotten better and acquired a Russian-language interface.

Open the application and select add device. Adding devices has become even easier and is now done in four simple steps.

Step one. Press the button on the switch and hold it pressed for five seconds:

Step two. Select a Wi-Fi network and enter its password. If you have already used this application, you will no longer have to enter anything:

In the third step, the application searches for and connects the switch:

The fourth and final step is to give the switch a name:

Switch connected:

We go into the switch management and we are asked to update the firmware on it:

Click on settings and update the firmware:

Notice how the switch settings menu has changed after the firmware update:

Now here it is possible to select actions after turning off the power to the switch. There are three options. After power is restored, the motor continues to rotate in the same direction, the motor stops, or the motor starts to rotate in the other direction.

It is also possible to set countdown timers:

Single or repeating timers:

Cyclic timers:

Manual control of changing the direction of rotation occurs by pressing this button on the screen:

The key is on - the engine rotates in one direction, off - it rotates in the other direction.

It is also possible to control the direction of rotation by briefly pressing the button on the switch itself. LEDs on the relays indicate their operation:

The LED next to the button indicates connection to the network. When Wi-Fi is connected, it lights up. The connection is fast enough. 2-3 seconds. Until the LED lights up - remote control impossible.

I illustrated the operation of the switch with a short video:

You can also connect 125-250 Volt AC motors to the switch. Only powering the switch itself needs to be done separately. As I wrote, there are two options for connecting the power supply:

And now let’s talk about how ITEAD could improve its product, which would undoubtedly expand its scope of application.

First, and most significant. The switch does not have a STOP button. Stopping the process requires the use of limit switches that momentarily interrupt the power supply to the switch. But sometimes the process does not need to be completed... And here a problem arises. Although, if the power to the switch is interrupted, it is possible to turn off two relays at once to stop the engine. You saw this in the switch settings. I would also like to be able to automatically turn off the engine when the load on it increases, in contrast to normal. But this will require complication of the scheme. But I am sure that such a function would be in demand.

Second. There are very few seconds in the timer settings. Sometimes a minute is too much.

And third. Manual control in the application is very uninformative. When changing the direction of rotation, the switch button shows the on or off state. I would like to see the rotation control buttons in the form of arrows, for greater clarity.

Well, in general, the switch is a very useful thing in process automation. And with the above modifications, there would be no price for it at all. In the meantime, the possibility and scope of its application are somewhat limited.

Thank you for your attention.

The product was provided for writing a review by the store. The review was published in accordance with clause 18 of the Site Rules.

I'm planning to buy +33 Add to favorites I liked the review +30 +56

In various industries there are many different production mechanisms that perform a limited number of operations that do not require smooth control of the rotation speed and can only be satisfied with a limited number of speeds. Such machines include woodworking and metal-cutting machines, oil well winches, centrifugal separators and other mechanisms. Limited quantity rotation speeds can well be provided by multi-speed squirrel-cage asynchronous electric motors. In this case, two designs of electric motors are possible: with several windings on the stator placed in the same slots, or with one winding that can be switched to obtain a different number of pairs of poles.

The interaction of the MMF of the rotor and stator is possible only if the number of pole pairs of the stator and rotor windings is equal. Therefore, when changing the number of pole pairs of the stator winding, it is necessary not to forget to change the number of pole pairs on the rotor winding. If we consider an asynchronous machine with a wound rotor, then to fulfill this condition it is necessary to have additional slip rings, which greatly increases the dimensions and cost of the electric machine. The squirrel cage rotor has the very valuable property of automatically generating the number of pole pairs, equal number pairs of poles MMF of the stator winding. It is this property that determined the use of squirrel-cage rotors in multi-speed asynchronous electric motors.

Multi-speed motors with several independent windings on the stator are inferior to single-winding motors in terms of economic and technical indicators. In multi-winding machines, the stator winding is poorly used, filling the stator slot is impractical, and the efficiency and cos φ values ​​are below optimal. Therefore, in recent times, multi-speed single-winding electrical machines with switching to a different number of pole pairs have become more widespread. The essence this method lies in the fact that by switching the direction of the current in part of the winding, the distribution of the magnetomotive force inside the stator bore is changed, resulting in a change in the rotation speed of the magnetomotive force, and therefore the magnetic flux in space. Most often, switching is carried out in a ratio of 1:2. In this case, the windings of each phase are made in the form of two sections. Changing the direction of the current in one of them allows you to change the number of pole pairs by 2 times. Let's consider this in relation to a motor switched between 8 and 4 poles.

For simplicity, the figure below shows the winding of one phase, consisting of two sections:

When connecting sections in series, that is, when connecting the end of the first section 1K to the beginning of the second 2H, we get 8 poles or 4 pairs. If the direction of the current in the second section is reversed, then the number of poles formed by the winding will decrease by 2 times. Changing the direction of the current in the second section can be done by breaking the jumper between 1K - 2K. The number of poles formed in this case is indicated in Figure b).

The same change in the number of poles can be obtained by changing the direction of the current in the second section by connecting in parallel with the first (Figure c)). In this case, just like in the previous one, the winding forms 4 poles, which corresponds to twice the rotation speed of the electric machine.

When comparing winding circuits of multi-speed electric motors, preference should be given to circuits that provide the right character depending on the permissible heating torque on the speed and having the smallest number of leads and contacts.

Let us establish a criterion that makes it possible to classify the connection of windings into one group or another. The torque developed by an asynchronous motor with a squirrel-cage rotor is equal to:

• p – number of pole pairs of the stator winding;
• N 2 – full number rotor winding rods (squirrel cage);
• I 2 – rotor rod current;
• Ψ 2 – angle of shift of the current vector relative to the rotor EMF vector;
• Ф – magnetic flux of one pair of poles;

According to the conditions for heating the rotor (if neglected), the current I 2 when working with a different number of pole pairs should remain the same; cos ψ 2 in the range from idle to nominal torque remains close to unity. Under such conditions, the moment of the electric machine will be expressed by the equality:

On the other hand, the electromagnetic moment in joules will be equal to:

Equating equations (2) and (3) to each other and solving for P, we obtain P = 314c 1 F.

In the resulting expression we substitute the value of the magnetic flux from the expression for the emf of the stator and rotor windings:

Thus, electromagnetic power of an electric machine for any number of pairs of poles of the stator winding is determined by the ratio of the phase voltage of the stator to the number of turns connected in series in the phase winding. Using this feature, let us analyze the methods discussed above for switching the number of pole pairs. For greater clarity, we will use simplified three-phase images for cases of switching from a larger number of pole pairs to a smaller number, in our case from 8 to 4. The figure below shows a diagram with the serial connection of the windings retained for both speeds:

It can be seen that the left diagram (Figure a)), in which both sections are flown by currents of the same direction, corresponds to more pairs of poles. In the right diagram (Figure b)), the opposite direction of the currents indicates a smaller number of pole pairs. In both cases, the number of series-connected turns in the winding of one phase remains the same, and the same phase voltage is applied to them. The power ratio for both connections is equal to unity, which means working with constant power P = const.

The figure below shows the mechanical characteristics of a two-speed electric motor operating at P = const:

In this case, to maintain constant power when moving to twice the speed, the torque must change in inverse proportion to the speed.

Pole switching diagram using a transition from series connection of sections to lowest speed to parallel for a larger one, shown in the figure below:

It's easy to see that parallel connection winding sections ensures a change in the direction of current in one of the sections. The latter corresponds to a transition to a smaller number of pole pairs. In this case, the winding forms two parallel stars connected to line voltage. Using the above criterion (4) we see that when switching to top speed power doubles, namely:

This corresponds to work at M = const. Mechanical characteristics two-speed electric motor at M = const is shown in the figure below:

Comparing the circuits with respect to the required number of pins and contacts per control device (controller, switch, etc.), we see that when connected according to the circuit, it requires nine pins and twelve contacts. The circuit allows you to reduce the number of pins to 6 and the number of contacts to 8.

In the considered circuits, at both speeds, the windings were connected either in series or in parallel. If it is necessary to change the voltage per winding of one phase, they use winding pairing, double triangle, and in some cases mixed star-delta. In the latter case, three sections of the winding form a triangle, and the three remaining sections are attached to the vertices of the triangle, thus forming the rays of the star. An example of such connections is a circuit that has become widespread in the drive of metal-cutting machines and makes the transition from a series connection with a triangle to two parallel stars.

When operating at low speed, two winding sections of each phase connected in series form the sides of a triangle, to the vertices of which power is supplied. In this case, both sections of the phase winding are flown by the same current, which corresponds to a larger number of pole pairs. To obtain greater speed, the vertices of the triangle formed by the phase windings are short-circuited, and the supply wires are transferred to the middle points of connection of the winding sections of each phase, thus forming two parallel stars. Below are diagrams for switching on windings at two speeds:

In this circuit, when operating at low speed, line voltage is applied to two sections connected in series with total number turns 2 w c.

In a double star connection, the phase voltage is applied to one section. From relation (4) we obtain the power ratio:

Thus, the circuit for switching the number of pole pairs is a serial triangle - double star when operating on high speed power is 15.5% more than at low. Usually this increase in power is neglected and the circuit is referred to as P = const. Electric motors with pole-changing speeds 3 and 4 are manufactured with two windings on the stator. Each of the windings can be made with pole switching according to the triangle-double star circuit.

In this case, each of the switched windings represents an open triangle. This is done to eliminate the heating of the idle winding by the current created by the EMF induced magnetic flux. Due to this, the number of leads for a three-speed motor is 10 and contacts are 12, for a four-speed motor it is 14 and 18, respectively.

It is worth noting that the labor intensity of manufacturing the windings of multi-speed single-winding electrical machines is significantly lower than that of double-winding ones. So, taking the complexity of manufacturing the winding of a single-speed electric motor as 100%, the complexity of manufacturing a two-winding four-speed motor will be 180%, while for a single-winding four-speed it is only 120%.