The most popular of the existing electric motors is still the asynchronous motor, created in the XIX century. Its design turned out to be ingeniously simple and so successful that all further transformations did not concern the principle of operation, affecting only the technology of manufacturing certain parts. For example, the bearings on which the motor shaft was attached could be modified, the shape of the rotor and stator windings changed, but the principle of operation of the induction motor remained the same.
- 1 How does an asynchronous engine
- 2 Different engine types
- 3 Advantages of asynchronous motors
- 4 Disadvantages of asynchronous motors
- 5 Single-phase motor connection
How does an asynchronous engine
Regardless of what size this type of electric motor has, its structure will be the same. Easier for an example to consider three phase electric motor. Such motors work in factory workshops - on a conveyor belt and in machine tools; they set in motion an elevator cabin - in houses. and in the mines, pumping water, turning the pump turbine - and in a small well, and on the powerful water intake stations. The scope of application of three-phase devices is wide.
Different engine types
Unlike the three-phase, single-phase asynchronous motor is often used in household appliances - vacuum cleaners, washing machines. machines, fans, food processors, blenders, etc. They are also used in tape recorders and turntables. drives. Even as part of a personal computer, you can find more than one asynchronous motor. But we will return to the device of this version of the engine a little later.
The first was born precisely a three-phase electric motor, the principle of which was built on the interaction of electromagnetic fields. The main parts of the asynchronous motor are the stator and the rotor. Accordingly, the stator was called the part that remains stationary. That it is located directly under the outer shell of the device and has the shape of a cylinder. In this part in a circle are three windings - at an angle of 120 ° to each other.
In modern engines you can count a lot of windings, however, they are connected to each other so that each subsequent phase differed from the previous one, and the phase shift between adjacent windings was 120°. The windings are wound with a copper wire, and the voltage from its own phase is connected to each of the groups. Thus, it turns out that the magnetic field moves along these windings, as if closing into a ring.
The stator also has its own windings. Since no electricity is supplied to the stator, it is entitled to closed conductorwhich sometimes instead of windings is formed in the form of a so-called squirrel cell. If we compare more precisely, then this detail does not resemble the cage itself for an agile rodent, but a squirrel wheel, designed so that the animal throws out its irrepressible energy. In the rotor of the device "squirrel cage" is formed by pouring molten aluminum into the grooves of the core, made of recruited steel sheets. Such a device is called a short-circuited rotor.
If the stator is made with real windings, then it is usually made multipolar. This rotor is called phase. The windings of this rotor are closed with a star or a triangle.
The rotor has its own shaft, which rests on the rear and front bearings. They in turn secured to the motor housing so that the rotor inside the stator can rotate freely. The principle of operation of asynchronous motors is based on the fact that the stator induces a magnetic field in the windings or “squirrel wheel”. Under its action, a current appears in the conductors of the rotor, and with it - its own magnetic field.
The variable magnetic field of the stator carries the rotor behind it, and the rotor begins to rotate. But the magnetic field of the rotor is always delayed relative to the stator field, and the rotation of both fields cannot occur synchronously. This causes the rotor to overcome many forces acting on it:
- force of force;
- rolling friction (if ball or roller bearing is used);
- sliding friction (if a bronze bushing is used as a bearing);
- counter force driven equipment.
The latter force depends on many moments, therefore it cannot be reduced to any simplest physical parameter. If you need to move the tram, the engine has to take gearbox load, which must be unwound, from the car itself, which must be shifted, besides, we must not forget also about the rolling friction force experienced by the wheels of the vehicle.
In the case when there is a description of the work of a professional meat grinder, which is powered by an asynchronous motor, then the resistance of the gearbox itself and that piece of meat or even bone that is to be grind up
Since there is a gap between the stator and the rotor, the rotor under load simply lags behind the stator in angular velocity. Therefore, the rotor speed depends on the load on the motor shaft. The principle of synchronicity is violated, and from there the name of the device itself: “asynchronous motor”.
Advantages of asynchronous motors
The principle of operation embedded in an asynchronous motor gives a number of advantages this device:
- A simple device makes it economical in production.
- Low energy consumption leads to efficiency devices equipped with this engine.
- Versatility of application in devices where exact maintenance of rotational speed is not required or there is a control circuit with feedback that ensures rotation with a given frequency.
- High reliability in work.
- Asynchronous motor can work with single-phase connection.
Disadvantages of asynchronous motors
Electric motors of this design have their disadvantages. These include heat losses. They really can overheat, especially - under load. To do this, their bodies are often made ribbed - so that they better radiate heat into the surrounding space. Also, an asynchronous device is often supplied with a fan to blow the rotor sitting on the same shaft, because the case can only dissipate heat from the stator, since there is no air gap between them, which can't be said about rotor.
The inability to stably hold the rotational speed makes the asynchronous motor inapplicable in some devices.
Single-phase motor connection
In our home appliances most often you can find all the same asynchronous device. But how does he "understand", in which direction does he start to rotate when it starts, if only one phase and zero wind up on it? In such an asynchronous motor, the principle of operation is the same as that of a three-phase one. magnetic field rotation. To do this, each engine has another contact - start.
The stator has two windings between which the angle of 90 ° is maintained. Both groups of coils are connected to the same phase, however, in order to provide a shift of the same 90 ° between the windings, one of them is connected through a capacitor. This causes the magnetic field to rotate.
Similar engines are used, for example, in coffee grinders or juice extractors. You can hear how it changes asynchronous engine sound in these devices when they work under load. At idle speed of the rotor they have clearly higher.
Summing up, it is important to say that asynchronous electric motors have become very popular. Of course, we can not forget about some of the shortcomings. However, they all overlap due to the great variety of advantages.