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Advantages of cast aluminum rotor slots in motors
source：未知 time：2024-06-03 10:19nbsp; click：
For most electric motors, electromagnetic wires are embedded in the stator core slots to provide a rotating magnetic field for the motor to operate. There are two types of rotor core parts: one is a cast aluminum or copper rotor achieved by casting; the other is a wound rotor, that is, electromagnetic wires are embedded in the rotor core.
The slot shape of a wound rotor is subject to many design constraints due to factors such as the wire embedding process, electromagnetic wire type, and insulating material. For rotors made by casting, the slot shape can be personalized to the greatest extent possible according to performance requirements.
For rotors made by casting, cast aluminum rotors are the most widely used. The most widely used processes are high-pressure aluminum casting and centrifugal aluminum casting. Both aluminum casting methods have the characteristics of high processing efficiency. There is also a relatively rare low-pressure aluminum casting, which has a lower efficiency but is easier to meet the high efficiency requirements of motors.
However, no matter which aluminum casting method is used, the equipment, tooling, mold, process parameters, and the rotor end ring, wind blade, balance column diameter, etc. that match the slot shape all have an impact on the overall quality of aluminum casting; that is, on the one hand, we need to consider the correlation between the slot shape itself and the motor performance, and on the other hand, we also need to have a suitable process to ensure it.
The slot shape of a wound rotor is subject to many design constraints due to factors such as the wire embedding process, electromagnetic wire type, and insulating material. For rotors made by casting, the slot shape can be personalized to the greatest extent possible according to performance requirements.
For rotors made by casting, cast aluminum rotors are the most widely used. The most widely used processes are high-pressure aluminum casting and centrifugal aluminum casting. Both aluminum casting methods have the characteristics of high processing efficiency. There is also a relatively rare low-pressure aluminum casting, which has a lower efficiency but is easier to meet the high efficiency requirements of motors.
However, no matter which aluminum casting method is used, the equipment, tooling, mold, process parameters, and the rotor end ring, wind blade, balance column diameter, etc. that match the slot shape all have an impact on the overall quality of aluminum casting; that is, on the one hand, we need to consider the correlation between the slot shape itself and the motor performance, and on the other hand, we also need to have a suitable process to ensure it.
Application of skin effect in motor starting performance control
When there is alternating current or alternating electromagnetic field in the conductor, the current distribution inside the conductor is uneven, and the current is concentrated in the "skin" part of the conductor, that is, the current is concentrated in the thin layer on the surface of the conductor. The closer to the surface of the conductor, the greater the current density, and the actual current inside the conductor is smaller. As a result, the resistance of the conductor increases, and its power loss also increases. This phenomenon is called skin effect. Through the design of the cast aluminum rotor slot of the motor product, the skin effect is used to improve the starting performance of the motor.
The effect of an alternating current in a conductor increasing the current density as it approaches the surface of the conductor. A constant current is distributed evenly across the cross-section of a straight conductor. For alternating current, a self-induced electromotive force appears in the conductor to resist the passage of current. The magnitude of this electromotive force is proportional to the magnetic flux cut by the conductor per unit time. Taking a conductor with a circular cross-section as an example, the closer it is to the center of the conductor, the greater the self-induced electromotive force generated by the external magnetic field lines; the closer it is to the surface, it is not affected by the growth and decline of its internal magnetic field lines, so the self-induced electromotive force is smaller. This results in a higher current density near the conductor surface. Since the self-induced electromotive force increases with the increase of frequency, the skin effect also becomes more significant with the increase of frequency. The skin effect reduces the effective cross-sectional area of a conductor when current passes through it, thereby increasing its effective resistance.
The effect of an alternating current in a conductor increasing the current density as it approaches the surface of the conductor. A constant current is distributed evenly across the cross-section of a straight conductor. For alternating current, a self-induced electromotive force appears in the conductor to resist the passage of current. The magnitude of this electromotive force is proportional to the magnetic flux cut by the conductor per unit time. Taking a conductor with a circular cross-section as an example, the closer it is to the center of the conductor, the greater the self-induced electromotive force generated by the external magnetic field lines; the closer it is to the surface, it is not affected by the growth and decline of its internal magnetic field lines, so the self-induced electromotive force is smaller. This results in a higher current density near the conductor surface. Since the self-induced electromotive force increases with the increase of frequency, the skin effect also becomes more significant with the increase of frequency. The skin effect reduces the effective cross-sectional area of a conductor when current passes through it, thereby increasing its effective resistance.
Other applications of the skin effect
In high-frequency circuits, hollow copper wires can be used instead of solid copper wires to save copper materials. The central part of the overhead transmission line is replaced with steel wire with high tensile strength. Although its resistivity is larger, it does not affect the transmission performance and can increase the tensile strength of the transmission line. The skin effect can also be used to quench the metal surface, making the surface of some steel parts hard and wear-resistant, but having a certain degree of flexibility inside to prevent the steel parts from brittle.
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