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From DC to AC: How do different forms of field coils affect motor operation?
In the history of motor development, the design and application of field coils have a crucial impact on the performance and reliability of the motor. The field coil, as a core component in an electromagnetic machine, is mainly used to generate a magnetic field to drive the operation of various motors. With the advancement of technology and the need for efficiency, the structure and purpose of field coils have gradually changed.
Field coils are mainly made of wound wires, and generate magnetic fields by flowing current. This magnetic field is wrapped around the core in a rotating machine, directing the flow of magnetic field lines.
Fixed and rotating magnetic fields
Conventional DC field coils usually generate a static magnetic field, while most three-phase AC field coils are used to generate a rotating magnetic field, which is essential for the operation of the electric motor. The design of a single-phase AC motor may adopt a static or rotating field coil wrapped around the motor, and the design varies depending on the application.
Stator and rotor
Many rotating electrical machines require sliding contacts to transfer current to the rotor, which usually involves more complex structures such as commutators or slip rings. These contact points are often the most challenging part of the machine and can limit the maximum current carrying capacity of the machine. Therefore, when a machine requires two sets of windings, the winding with lower current is usually placed on the rotor and the winding with higher current is placed on the stator.
Bipolar and multipolar magnetic fields
During the early development history of generators, the stator field evolved from a bipolar field to a multi-pole design. Bipolar generators were commonly used before 1890, but were gradually replaced with the introduction of multi-pole field magnets. This change allows the generator to increase its output voltage without increasing its speed, because more poles allow the magnetic field lines to pass more efficiently.
The design of the multi-pole generator not only simplifies the structure, but also improves the strength and efficiency of the magnetic force and minimizes the leakage of the electromagnetic field.
Winding Materials
The winding material of the field coil is usually insulated copper wire, which is undoubtedly because of its low resistance, which can reduce the power consumption and heat dissipation of the coil. However, as copper prices rise, the use of aluminum windings is increasing. Although silver is the best material, it is only used in special circumstances due to its high cost. Historically, during World War II, the Manhattan Project borrowed heavily from the U.S. Treasury's silver to create efficient low-resistance field coils.
ConclusionThe evolution of field coils from DC to AC not only improved the stability and efficiency of the motor, but also promoted the use of new materials and design innovations in the process. All of this change stems from the pursuit of more efficient, reliable and economical electromagnetic machines. However, with the advancement of technology and changes in demand, where will the future field coil design develop?
