IM with a phase rotor: principle of operation, design and scope of application of an asynchronous motor

An asynchronous motor (IM) with a wound rotor is a multifunctional power plant that supports regulation by introducing additional resistances into the rotor circuit. The unit differs from the classic models with a squirrel-cage rotor in a higher starting torque and low starting current. The classification of devices is carried out taking into account their properties and design.

general information

To understand how an asynchronous motor with a wound rotor works, it is necessary to carefully study the features of its start. When the installation is started, its rotor passes in parallel from a state of rest to a slow and uniform rotation. In this case, the system balances the moment of resistance forces by means of its own shaft.

During start-up, an increased consumption of energy resources begins, which is associated with overcoming the braking torque and compensating for losses inside the power plant. Often, the parameters of the initial starting torque are far from the required ones, therefore, the asynchronous motor is not able to go into full-fledged operation. In this case, the acceleration is suspended, and the constant exposure to excessive current leads to overheating of the internal components of the installation.

For this reason, the frequency of starting the engine is limited to a few starts. If the unit was operated from a low power electrical network, then a similar phenomenon can reduce the overall voltage and disrupt the operation of other devices connected to this line.

The presence of starting resistors in the rotor circuit reduces the electric current, but at the same time raises the initial starting torque until it reaches the peak level. Starting the power plant is easy, normal, or hard.

Depending on this factor, you can determine the optimal parameters of the resistance of the resistors.

After a successful start, it remains to maintain a stable torque during the acceleration phase of the rotor, which will shorten the duration of the transition from a calm state to the stage of rotation and reduce the likelihood heating. To do this, it is necessary to reduce the resistance values ​​of the resistors.

The switching of different resistors is due to the connection of the acceleration contactors in sequential order. It is possible to disconnect the motor from the electrical network only with a short-circuited rotor circuit. If this requirement is ignored, then there will be a risk of significant overvoltage in the stator winding phases.

Specifications

There are established requirements that guarantee the high-quality operation of induction motors with a wound rotor. The basic parameters and characteristics of the system depend on them, including:

1. The dimensions and power of the installation are in accordance with the technical regulations.
2. Protection from external influences. Its degree is determined by the environmental conditions in which the machine will be located. The fact is that some installations are designed to work indoors, while others are able to function outdoors. In addition, the units available on the market differ in climatic conditions. For example, there are engines that can withstand extreme cold or extreme heat. They have a characteristic design and protection, depending on the conditions of use.
3. Isolation degree. Asynchronous motors with a wound rotor must be resistant to high temperature indicators and possible heating of internal mechanisms. To prevent fires, they are protected with special insulating layers.
4. Compliance with established standards and modes of operation.
5. The presence of a powerful cooling system that matches the operating mode of the engine.
6. Noise level during idle start. It corresponds to the second grade or below.

Device and design

Wanting to buy an asynchronous electric motor with a wound rotor, you need to be well versed in its structure and design features. First of all, you need to know that the main parts of the installation are the stator, which is stationary, and the rotor is a rotating mechanism within the stator. An air gap is located between both elements, and their surface is covered with a special winding.

The stator winding is connected to an alternating voltage network, which is transmitted to the rotor winding. The interaction of the nodes is due to the magnetic flux.

As for the stator housing, the motor housing is used as it, inside which the pressed-in core is located. The latter contains the winding conductors protected against short-circuit by insulation. The core winding consists of several sections enclosed in coils.

The rotor has a shaft and a core made of assembled plates. The last element is created on the basis of high-tech steel and has symmetrical grooves with conductors. During operation, the rotor shaft transmits torque to the unit drive. Depending on the type of rotor there are two types of engines:

1. Squirrel cage rotor.
2. With phase rotor.

In the first type of rotors, there are aluminum rods that are inside the core and are closed at the ends with rings. They are also called the "squirrel wheel". Usually, the grooves of the installation are processed with aluminum, which increases their strength.

The phase rotor of an induction motor differs significantly from the previous version. The number of coils installed at a specific angle in such models is determined by the number of paired poles. In this case, the pairs of poles in a rotor of this type are always comparable to similar stator pairs.

Principle of operation

Having studied the IM device with a phase rotor and its start-up, one can proceed to a more detailed examination of the operation of such an installation. It can be divided into several points:

1. The triple-wound stator is supplied with three-phase voltage from an AC mains.
2. Then the formation of a magnetic field begins, which leads to the rotation of the rotor. As the rotational movements accelerate, the rotor speed increases significantly.
3. Upon reaching certain indicators, the individual lines of the fields of both nodes intersect, which causes the appearance of an electromotive force. It acts on the rotor winding, due to which an electric current is formed in it.
4. At a certain point in time, an interaction begins between the stator magnetic field and the current in the rotor, forming a torque. It is due to him that the work of the asynchronous motor is carried out.

Advantages and disadvantages

Asynchronous aggregates have been gaining popularity lately. It is associated with a host of advantages that they have. Among them:

1. High values ​​at initial torque.
2. Ability to accept any mechanical overload without significant change in efficiency or disruption of stable operation of the installation. Even if various overloads occur in the system, the unit continues to operate at a given speed and practically does not deviate from the basic mode.
3. Reduced starting current. Unlike other asynchronous models, for example, with a squirrel-cage rotor, these motors have relatively low starting currents.
4. Possibility of full automation of work.
5. Simplicity of design.
6. Simple startup scheme.
7. Relatively low price.
8. No need for complex and expensive maintenance.

In addition to many advantages, engines of this type also have disadvantages. The key disadvantages include rather large dimensions, due to which the installation and further operation of the system are complicated, as well as reduced efficiency in comparison with many analogues.

According to the latter indicator, devices with a squirrel-cage rotor are more productive.

Applications

Nowadays, many industrial motors are induction motors. Their popularity is due to the above advantages and availability. The areas of application of such units are very extensive, therefore they are actively used for work automated devices from the telemechanical sphere, household and medical equipment and sound recording installations. The induction motor is a useful invention of the present time, which simplifies human life and provides good efficiency with minimal energy consumption.