Hi all. Glad to see you on my website. The topic of today's article: the design and principle of operation of asynchronous electric motors. I would also like to say a little about ways to adjust their rotation speed, and list their main advantages and disadvantages.
Previously, I have already written articles regarding asynchronous electric motors. If anyone is interested, you can read it. Here is the list:
Well, now let's move on to the topic of today's article.
At the present time, it is very difficult to imagine how all industrial enterprises would exist if there were no asynchronous machines. These engines are installed almost everywhere. Even at home, every person has such an engine. It can be on your washing machine, on a fan, on a pumping station, in an extractor hood, and so on.
In general, an asynchronous electric motor is a colossal breakthrough in global industry. Worldwide, they produce more than 90 percent of all engines produced.
An asynchronous electric motor is an electrical machine that converts electrical energy into mechanical energy. That is, it consumes electric current, and in return they provide torque, with which you can rotate many units.
And the word “asynchronous” itself means non-simultaneous or not coinciding in time. Because in such engines the rotor speed is slightly behind the rotation speed of the stator electromagnetic field. This lag is also called sliding.
This sliding is designated by the letter: S
And the slip is calculated using the following formula: S = (n1 - n2)/ n1 - 100%
Where, n1 is the synchronous frequency of the stator magnetic field;
n2 is the shaft rotation speed.
The engine consists of the following parts:
1. Stator with windings. Or a frame inside which there is a stator with windings.
2. Rotor. This is if it is short-circuited. And if it is phase, then we can say that it is an armature or even a collector. I think there will be no mistakes.
3. Bearing shields. On powerful engines, there are also bearing caps with seals at the front.
4. Bearings. They can be sliding or rolling, depending on the design.
5. Cooling fan. Made from plastic or metal.
6. Fan shroud. Has slots for air supply.
7. Borno or terminal box. For connecting cables.
These are all its main details, but depending on the type, type and design it may vary slightly.
Asynchronous electric motors are mainly produced in two types: three-phase and single-phase. In turn, three-phase ones are further divided into subtypes: with a squirrel-cage rotor or a phase rotor.
The most common are three-phase with a squirrel-cage rotor.
The stator has a round shape and is assembled from sheets of special steel, which are insulated with each other, and this assembled structure forms a core with grooves. Windings with a special winding wire insulated with varnish are placed in the grooves of the core. This wire is cast mainly from copper, but also from aluminum. If the engine is very powerful, then I make the windings with a busbar. The windings are laid so that they are shifted relative to each other by 120 degrees. The stator windings are connected in a star or triangle.
The rotor, as I already wrote above, can be short-circuited or phase.
The short-circuited shaft is a shaft onto which sheets of also special steel are placed. These typesetting sheets form a core into the grooves of which molten aluminum is poured. This aluminum flows evenly along the grooves and forms rods. And at the edges of these rods they are closed with aluminum rings. It turns out to be a kind of “squirrel cage”.
The phase rotor is a shaft with a core and three windings. Some ends, which are usually connected in a star, and the second three ends are connected to slip rings. And electric current is supplied to these rings using brushes.
If you add a load rheostat to the circuit of phase windings, and increase the active resistance when starting the engine, then in this way you can reduce large starting currents.
When electric current is applied to the stator windings, an electric current occurs in these windings. As you remember from the words written above, our phases are shifted relative to each other by 120 degrees. And this flow in the windings begins to rotate.
And when the stator magnetic flux rotates, an electric current and its own magnetic field appear in the rotor windings. These two magnetic fields begin to interact and cause the rotor of the electric motor to rotate. This is if the rotor is short-circuited.
Based on the robot principle, watch the video clip.
Well, with a wound rotor, the principle is essentially the same. Voltage is supplied to the stator and rotor. Two magnetic fields appear, which begin to interact and rotate the rotor.
The main advantages of an asynchronous electric motor with a squirrel cage rotor:
1. A very simple device, which reduces the cost of its production.
2. The price is much less compared to other engines.
3. Very simple launch scheme.
4. The shaft rotation speed practically does not change with increasing load.
5. Tolerates short-term overloads well.
6. Possibility of connecting three-phase motors to a single-phase network.
7. Reliability and ability to operate in almost any conditions.
8. Has a very high efficiency and cos φ.
Flaws:
1. It is not possible to control the rotor speed without loss of power.
2. If you increase the load, the torque decreases.
3. The starting torque is very small compared to other machines.
4. When underloaded, the cos φ indicator increases
5. High inrush currents.
Advantages of wound rotor motors:
1. Compared to squirrel-cage motors, it has a fairly large torque. This allows it to run under load.
2. It can work with a slight overload, and at the same time the shaft rotation speed practically does not change.
3. Small starting current.
4. Automatic starting devices can be used.
Flaws:
1. Large dimensions.
2. Efficiency and cos φ indicators are less than those of squirrel-cage motors. And when underloaded, these indicators have a minimum value
3. The brush mechanism needs to be serviced.
This is where I will end my article. If you found it useful, then share it with your friends on social networks. If you have questions, ask them in the comments and subscribe to updates. Bye.
Sincerely, Alexander!
The efficiency and reliability of equipment directly depend on the electric motor, so its selection requires a serious approach.
By means of an electric motor, electrical energy is converted into mechanical energy. Power, revolutions per minute, voltage and type of power supply are the main indicators of electric motors. Also, weight, size and energy indicators are of great importance.
Electric motors have great advantages. Thus, compared to heat engines of comparable power, electric engines are much more compact in size. They are perfect for installation in small areas, for example in the equipment of trams, electric locomotives and on machine tools for various purposes.
When using them, no steam or decomposition products are released, which ensures environmental cleanliness. Electric motors are divided into DC and AC motors, stepper motors, servo motors and linear motors.
AC electric motors, in turn, are divided into synchronous and asynchronous.
They are used to create adjustable electric drives with high dynamic and performance indicators. These indicators include high uniformity of rotation and reloading ability. They are used to complete paper-making, dyeing and finishing and material handling machines, for polymer equipment, drilling rigs and auxiliary units of excavators. They are often used to equip all types of electric vehicles.
They are in higher demand than DC motors. They are often used in everyday life and in industry. Their production is much cheaper, the design is simpler and more reliable, and operation is quite simple. Almost all household appliances are equipped with AC motors. They are used in washing machines, kitchen hoods, etc. In large industries, they are used to drive machine tools, winches for moving heavy loads, compressors, hydraulic and pneumatic pumps and industrial fans.
They operate on the principle of converting electrical impulses into mechanical movement of a discrete nature. Most office and computer equipment is equipped with them. Such engines are very small but highly productive. Sometimes they are in demand in certain industries.
Refers to DC motors. They are high tech. Their work is carried out through the use of negative feedback. Such an engine is particularly powerful and is capable of developing a high shaft rotation speed, the adjustment of which is carried out using computer software. This function makes it popular when equipping production lines and in modern industrial machines.
They have the unique ability of rectilinear movement of the rotor and stator relative to each other. Such engines are indispensable for the operation of mechanisms whose operation is based on the forward and reciprocating movement of the working bodies. The use of a linear electric motor can increase the reliability and efficiency of the mechanism due to the fact that it significantly simplifies its operation and almost completely eliminates mechanical transmission.
They are a type of AC electric motors. The rotation frequency of their rotor is equal to the rotation frequency of the magnetic field in the air gap. They are used for compressors, large fans, pumps and DC generators as they operate at a constant speed.
Also, they belong to the category of AC electric motors. The rotational speed of their rotor differs from the rotational frequency of the magnetic field, which is created by the current in the stator winding. Asynchronous motors are divided into two types, depending on the rotor design: squirrel cage and wound rotor. The stator design is the same in both types, the only difference is in the winding.
Electric motors are indispensable in the modern world. Thanks to them, people's work is greatly facilitated. Their use helps reduce the cost of human energy and make everyday life much more comfortable.
Comparison of internal combustion engines and electric motors - page No. 1/1
Comparison of internal combustion engines and electric motors
Advantages of internal combustion engines
1. High range of movement on one gas station;
2. Low weight and volume of the energy source (fuel tank).
1. Low average efficiency during operation;
2. High environmental pollution;
3. Mandatory presence of a checkpoint;
4. No energy recovery mode;
5. The internal combustion engine operates most of the time with underload.
1. Light weight;
2. Maximum torque available at 0 rpm;
3. There is no need for a checkpoint;
4. High efficiency;
5. Possibility of energy recovery.
Disadvantages of the electric motor:
1. Small shoulder per charge;
2. Long charging time;
3. Short battery life;
4. Large volume and weight of the battery.
The hybrid combines the advantages and minimizes the disadvantages of both types of engines.
Advantages of a hybrid:
1. Possibility of recovery;
2. Long mileage per fill;
4. Maximum torque available at 0 rpm;
5. The internal combustion engine operates with a high degree of uniformity and a high degree of loading;
6. High average efficiency;
7. Lack of checkpoint;
8. High environmental performance.
1. The car essentially has two power plants installed in parallel (though each of them is in a truncated version).
2. The problems with electric vehicles also lie in winter. For existing batteries, low temperatures are not very useful. If we take into account this driving mode: Summer, the car owner lives in his house or in a parking lot, he has the opportunity to charge the batteries. Overnight charging up to 100%. The charge lasts for 200 km. mileage For the city, in most cases, it is quite enough. Although most electric vehicle projects were designed for approximately 400 km. How long will the charge last? In the summer, there are lights, air conditioning, and a radio in the cabin, and they all consume energy; in winter, there is a problem with heating.
3. Low weight and volume of the energy source (fuel tank and fuel tank);
However, a battery weighing 80 kg is still a lot, especially considering that its capacity is small.
All hardware was invented about 100 years ago. Since then, news has appeared ONLY in electronics - the progress here is impressive. But practically nothing happens in mechanics and electrical engineering.
Breakthroughs occur at the intersection of disciplines. For example, just fifteen years ago, industrial products appeared - IGBT transistors (an insulated gate bipolar transistor is also a kind of hybrid, combining the qualities of a bipolar transistor (the ability to transmit high power) and a field transistor (control of the field (voltage), not current). Appearance These transistors made a small revolution - an asynchronous electric drive (the most common) can now be made controllable! Previously, only DC motors were controlled, and they must have brushes, which reduced their use, for example, on cars, to zero.
(And now the Prius has brushless three-phase motors with permanent magnets on the rotor (permanent magnets on rare earth elements are also news at the intersection of physics and chemistry) and are controlled by an IGBT-based inverter controlled by a microprocessor...)
About thirty years ago, analog electronics became so reliable that they began to be widely used in ignition systems. Then everything developed gradually and suddenly it turned out that the microprocessor copes much better with controlling internal combustion engine modes than any analog automation. Also a small revolution, only from brainless automation of the “hook-and-spring” type they smoothly moved to program control - which means that the engine MODES are determined not by the designer, but by the programmer, and accordingly, development/tuning/adjustment is dramatically simplified and cheaper
And on the Prius there are already five to seven of these controllers, and on the 20k they are connected via a standard bus for exchanging information between control controllers (CAN), and control not only the internal combustion engine, but also the rotation of each wheel - and immediately the possibility of a simple (cheap to develop) ) software implementation of traction control / anti-lock braking / directional stability, etc. etc... - that is, ensuring ACTIVE SAFETY of the car.
There is no need to compare an electric car and a hybrid - it is wrong. Obviously, the fossil fuel car will die. But YET he can't die. Simply because there will be nothing to ride. Because there are NO electric vehicles of acceptable consumer qualities - mileage, refueling time, comfort, cost...
Electrification, which began in the 20th century, led to the emergence of a huge number of useful inventions. One of them was an electric motor.
The motor lost mechanically rubbing and sparking components, surpassing many types of drives popular at that time. Today, there are various types of electric motors, which allows you to implement the best option in a particular machine. Which units are considered in demand, and what are their key features?
It is immediately worth noting that motors are roughly divided into two types: direct and alternating current. Therefore, we will consider the characteristic features of each of them.
Such units make it possible to create adjustable electric drives with excellent performance properties. There are two categories of DC motors: brushed and valve-type.
The first are characterized by the presence of a brush-collector unit, which facilitates the electrical connection of the stationary and rotating parts of the unit. Brushless (valve) motors are electric motors with a closed system. They work the same way as synchronous ones. Such units can have any dimensions. The smallest ones are equipped with PCs, toys and other devices.
DC electric motors are used in various fields due to the huge number of positive aspects:
However, collector devices require labor-intensive preventive maintenance. And the cost of producing the units is quite high, which is reflected in their price.
These units are divided into synchronous and asynchronous. The key difference is that in the first electric motors, the 1st harmonic of the starter's magnetomotive force moves in a manner similar to the rotor speed. With asynchronous ones, the field rotates faster. And since AC motors are used especially often, they are worth considering in more detail.
Many types of computer equipment are equipped with these engines. The advantages of using them are obvious:
Of course, there are some disadvantages in the form of difficulties with starting, complexity of the design and speed adjustment.
Here the rotor speed differs from the torque field indicators. Based on their design features, devices with phase-wound and squirrel-cage rotors are distinguished. There are practically no other differences in the design. They only affect the number of windings, according to which the devices are divided into single-, two- and three-phase.
Today, asynchronous units are included in a huge number of electrical machines. Due to the variety of physical and technical characteristics of the device, you can choose the optimal one (depending on operating conditions).
For example, a three-phase electric motor 1.1 kW 3,000 rpm is suitable for equipping concrete mixers, compressors, pumps, etc. A single-phase unit is applicable in low-power devices, including small room fans.
Among the advantages of asynchronous electric motors it is worth highlighting:
However, such devices depend on the mains voltage, have a small starting torque and cause difficulties in accurately adjusting the speed. This is important to consider when purchasing.
Electric motors are used literally everywhere. Without them it is impossible to imagine the operation of most machines. Their use helps reduce human labor costs and make everyday life as comfortable as possible.
The electric motor has many advantages over the internal combustion engine:
The electric motor itself has no significant disadvantages. But there are great difficulties in his nutrition. The imperfection of current sources has so far prevented the widespread use of electric motors in the automotive industry.
The quality of operation of a modern electric drive is largely determined by the correct choice of the electric motor used, which in turn ensures long-term reliable operation of the electric drive and high efficiency of technological and production processes in industry, transport, construction and other areas.
When choosing an electric motor to drive a production mechanism, follow the following recommendations:
Based on technological requirements, an electric motor is selected according to its technical characteristics (type of current, rated voltage and power, rotational speed, type of mechanical characteristics, duration of operation, overload capacity, starting, regulating and braking properties, etc.), as well as design engine according to the method of installation and fastening.
Based on economic considerations, the most simple, economical and reliable engine is selected, which does not require high operating costs and has the smallest dimensions, weight and cost.
Based on the environmental conditions in which the engine will operate, as well as the safety requirements for working in an explosive environment, the design of the engine is selected according to the method of protection.
The correct choice of the type, design and power of the electric motor determines not only the safety, reliability and efficiency of operation and the service life of the engine, but also the technical and economic indicators of the entire electric drive as a whole.
