Asynchronous electric motor: design and principle of operation
Surely everyone knows what an asynchronous electric motor. And someone can even name the area of its application. It is worth noting that this particular electric machine is currently the most common in the industry. About 96% of all electric motors that are used in factories and plants are asynchronous. There are several reasons for this, but among the main ones - this is the fact that they have a simple construction, their repair is easy to perform, and also they have high efficiency. But there is a drawback - it is necessary to power the three-phase network. True, in factories this is not a problem.
Asynchronous motor design
The base is a stator, which is made of a variety of thin plates from a special grade of steel. These plates are all the same and assembled in such a way that all the slots are the same. Due to this, it is possible to wind the wire, which during operation generates a magnetic field.About what requirements are imposed on the winding will be described below. Covers are located on both sides of the stator. They can be made of different metals - both from aluminum and from black. It all depends on the specific model of the motor.
Without exception, all the asynchronics have bearings in the covers. They ensure the smooth rotation of the rotor. But the latter should be described in more detail, as it is a key feature of the electric motor. The rotor in asynchronous machines is short-circuited. If it is easier to say, then it has several turns of a very thick wire, the ends of which are connected. This principle allows the magnetic field created by the stator to begin rotating the rotor. This phenomenon was noticed for a long time - the first asynchronous electric motor was manufactured in the middle of the 19th century.
Stator motor winding
It serves to create a magnetic field. In fact, the stator has three windings - according to the number of phases of the mains supply. The most common is an asynchronous three-phase electric motor, since its parameters are ideal for any drive.The lack of winding - it can fail, and in simple terms, burn. True, this happens when overheating or exceeding the permissible load on the shaft. To avoid overheating, you need to ensure that the impeller is mounted on the back, which allows air to blow in.
Over it the protective casing is necessarily mounted, which will prevent the ingress of foreign objects, and will also secure the use of the engine. The stator windings are checked with an instrument called a megohmmeter. It allows you to check the winding for the presence of open circuit and short circuit. But if it is not available, then it is quite possible to use a simple tester. Knowing the reference characteristics of asynchronous electric motors, namely the resistance of the windings, we can determine the fault. Yes, and use the electronic tester is much safer.
Ways to turn on the motor in the network
If the electric machine is connected to the network, then it is allowed to connect the windings in two circuits - into a star and a triangle. Each of them has its own characteristics.In order for an asynchronous motor to work in normal mode when powered from 380 V three-phase voltage, it is necessary to use a star connection. The triangle circuit is used much less frequently, it is necessary for connecting electric motors to some models of frequency converters, as well as when powered from 220 volts. When connecting with a star, you must install jumpers so that they are located parallel to the axis of the rotor.
To connect with a triangle it is necessary that the jumpers be perpendicularly located to this axis. For clarity, look at the wiring diagram. In addition, in order to use the asynchronous motor safely, it is necessary to apply protection - automatic switches. They need to be selected based on engine power. And it is necessary to take into account the starting current. Magnetic starters are used to control the motor. They allow you to connect two buttons - start and stop. A more complex design of the two starters will help to make a reverse movement (change the order of connecting the phases to the windings).
All data of the electric motor are applied to the bar, which is attached to the stator housing. It indicates not only the model and emblem of the manufacturer, but also the rotational speed, current consumption, supply voltage, and sometimes the switching circuit. Consequently, there will be no problems with how to install and connect a three-phase asynchronous electric motor. Its characteristics are all known, it remains only to compare with the real load. Care must be taken to ensure that the engine power is comparable to that required for the operation of a particular mechanism.
Otherwise, the failure of the windings is inevitable. Fortunately, this procedure takes a little time (subject to the availability of all the tools and accessories). But you need to use copper wire, the cross section of which is exactly the same as it was before. To check how the motor works on the mechanism, you need to use the measuring pliers. With their help, you can see which current is consumed by each phase. The value of all three should be almost equal. If not, then the winding is out of order.
Should I use the drive?
You can give a definite answer - not just worth it, but you must use frequency converters, because with its help, the three-phase asynchronous motor can work in perfect mode. Chastotnik characteristics only should be selected based on the power of the motor. If the motor has a power of 0.75 kW, then the inverter should ensure operation with a margin - install better than 1.5 kW, reliability will be higher.
True, the cost of such a device is much higher. With the help of frequency converters, you can change many parameters of the drive, plus everything, it is an additional protection. Even use a single-phase network will get an asynchronous motor. There are models of the inverter, which are included in such a network, but at the output they have three phases that are necessary for the operation of the engine.