Crane and metallurgical electric motors. Design features, types of rotors. Operation of crane motors with a frequency converter

Crane and metallurgical electric motors (CMEs) are asynchronous electric motors specially designed for operation in lifting, moving and rotating mechanisms of cranes, as well as in other difficult industrial conditions. They are distinguished by a number of features that make them indispensable in areas where high power, reliability and resistance to adverse factors are required.

Application of KME:

●      Crane lifting mechanisms: CMEs are used in crane lifting mechanisms to ensure vertical movement of loads.

●      Mechanisms of movement of cranes: KME drive the mechanisms of movement of cranes on rail tracks.

●      Crane rotation mechanisms: KME provide rotation of the crane boom for accurate positioning of the load.

●      Other industrial mechanisms: CMEs are used in conveyors, conveyors, crushing machines and other industrial mechanisms where high power and resistance to adverse factors are required.

Choice of KME:

A number of factors must be taken into account when choosing a CME, such as:

●      Power: the power of the electric motor must correspond to the power of the mechanism that it will set in motion.

●      Frequency of rotation: the frequency of rotation of the rotor of the electric motor must correspond to the nominal frequency of rotation of the mechanism.

●      Starting torque: The starting torque of the electric motor must be sufficient to accelerate the mechanism with the load.

●      Operating conditions: the electric motor must be designed to work in specific conditions

CMEs are produced in two main types: with a short-circuited rotor and with a phase rotor.

CME with a short-circuited rotor:

●      Design: The rotor has a simple design with a honeycomb of copper or aluminum rods connected by rings.

●      Advantages:

○      Simple and reliable design

○      Low cost

○      Resistance to overloads

○      Low losses in copper

○      Does not require maintenance

●      Disadvantages:

○      Low starting torque

○      The impossibility of adjusting the rotation frequency without a state of emergency

○      Higher sliding, which can lead to overheating

CME with a phase rotor:

●      Design: The rotor has a three-phase winding connected to a starting rheostat.

●      Advantages:

○      High starting torque

○      The possibility of adjusting the rotation frequency

○      Less slip, resulting in less overheating

●      Disadvantages:

○      A more complex design

○      Needs maintenance

○      More susceptible to overloads

Selection of the type of CME:

The choice of the type of CME depends on the specific requirements for the mechanism.

●      KME with a short-circuited rotor: suitable for mechanisms where high starting torque is not required, but simplicity, reliability and low cost are important.

●      KME with a phase rotor: recommended for mechanisms where a high starting torque is required, smoothness of operation is important, or the ability to adjust the rotation frequency.

Construction of KME:

KME consists of the following main components:

●      Stator: The stationary part of an electric motor consisting of a housing, a core, and a winding. The stator winding creates a rotating magnetic field that induces emf in the rotor.

●      Rotor: the moving part of an electric motor, consisting of a core and a short-circuited white cage. The white cage is a set of copper or aluminum rods connected to each other at the ends.

●      Bearings: ensure the rotation of the rotor in the stator housing.

●      Fan: used to cool the electric motor.

●      Thermal sensors: monitor the temperature of the electric motor to prevent overheating.

The principle of KME operation:

When a three-phase voltage is applied to the stator winding, a rotating magnetic field arises in it. This field induces an emf in the rotor winding, which causes it to rotate in the same direction as the magnetic field. The speed of rotation of the rotor is slightly less than the speed of rotation of the magnetic field, which is called slip.

Classification of KME:

KME are classified according to several parameters:

●      Cooling method:

○      With natural cooling

○      With self-blowing

○      With forced cooling

●      Number of speeds:

○      Single speed

○      Two-speed

○      Multi-speed

●      Installation method:

○      On paws

○      On the flank

○      Built-in

●      Protection class:

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