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The mystery of the rotating magnetic field: Who discovered this amazing phenomenon?
A rotating magnetic field (RMF) is a magnetic field generated by a system of symmetrically placed coils that are powered by multiphase current. The rotating magnetic field can be generated by a multiphase (two or more) current or, in the case of a single-phase current, by two coils designed with a phase difference. This phenomenon has a wide range of applications, especially in the field of electrical machinery, such as induction motors, generators and induction regulators.
In 1824, French physicist François Arago first proposed the existence of a rotating magnetic field in an experiment using a rotating copper disk and a needle, which he called "Arago's rotation".
The history of rotating magnetic fields dates back to the 19th century, when several scientists studied the phenomenon. British experimenters Charles Babbage and John Herschel discovered that they could cause Arago's copper plate to spin simply by spinning a horseshoe magnet beneath it. Later, British scientist Michael Faraday attributed this phenomenon to electromagnetic induction.
In 1879, British physicist Walter Bailey demonstrated a primitive induction motor by replacing the horseshoe magnet with four electromagnets and manually switching a switch. This innovation laid the foundation for subsequent research on rotating magnetic fields.
The concept of a rotating magnetic field in an AC motor was explored extensively in the 1780s by Italian physicist and electrical engineer Galileo Ferraris and Serbian-American inventor Nikola Tesla. Ferraris built a teaching demonstration model in 1885, although he did not publicly describe the principle until 1888. Tesla built a successful prototype in 1887 and was granted a U.S. patent in 1888.
Based on Ferraris' rotating magnetic field principle, Friedrich August Hazelwand developed the first AC three-phase generator in 1887. Later, Mikhail Dolivo-Dobrovolsky developed the first three-phase power source using the Hazelwand generator, and in 1891, he built the world's first three-phase power plant in Frankfurt, Germany. factory.
How a rotating magnetic field works
Rotating magnetic fields are the key principle behind the operation of induction machines. An induction motor consists of a stator and a rotor. In the stator, the fixed coils are arranged in a specific way so that the magnetic field generated by the two-phase current rotates at an angular velocity determined by the AC frequency. The rotor consists of coils wrapped along slots, which are short-circuited and into which current is induced by the changing magnetic flux produced by the stator.
Although only two coils driven 90 degrees out of phase are needed to produce a symmetrical rotating magnetic field, in practice three sets of coils are almost always used to accommodate a symmetrical three-phase AC sinusoidal current system. The phase difference between these three sets of coils is 120 degrees. In this case, the magnetic field is treated as a linear function, and three sine waves with a phase difference of 120 degrees are applied to form a rotating vector with a constant magnitude.For the rotor, the initially generated magnetic flux will react to the magnetic poles of the stator, causing the rotor to rotate in a certain direction.
In this rotating magnetic field, the rotor will continue to maintain a constant magnetic field and will move synchronously with the magnetic field of the stator. When a permanent magnet is placed in this magnetic field, it maintains alignment with the external field. This effect was used early on in AC motors.
Modern applications and development
The applications of rotating magnetic fields are now not limited to electric motors. Today's induction motors often have short-circuited rotors instead of magnets, which allows the rotor to follow the rotating magnetic field of a multi-winding stator. The short-circuited coils on the rotor of this type of motor create eddy currents in the rotating magnetic field of the stator, which in turn generate a Lorentz force to propel the rotor. This revolutionary design makes modern rotating magnetic field motors more efficient and reliable.
Although the principles of rotating magnetic fields are timeless and the technology continues to advance, the discoverers and their contributions to this field are still fraught with discussion and controversy. When we look back on this history full of innovation and hard work, can we clearly define who was the first discoverer to reveal the mystery of the rotating magnetic field?
