3-PHASE
AC CURRENT

 
 

Throughout history academia have honored those pioneers and discoverers that have brought mankind out of darkness and into light. The list of famous physicists, scientists, engineers and inventors is long. Many of the units of electrical measurement quantity and expression come from the founding fathers who first postulated and discovered physical phenomena in electricity and magnetism. Volta, Ampere, Faraday, Hertz, Maxwell, Newton, Watt, Weber and Tesla, are among the names that have been synonymous with standard units of electrical and magnetic measure, since their respective times of discovery and contribution.

Tesla was the electrical engineer who invented the AC (alternating current) induction motor, which made the universal transmission and distribution of electricity possible.

In 1888 his discovery that a magnetic field could be made to rotate if two coils at right angles are supplied with AC current 90° out of phase made possible the invention of the AC induction motor. The major advantage of this motor being its brushless operation, which many at the time believed impossible.

One of Tesla's later experiments involved a ring with 3 coils, one for each phase of a 3-phase system, with a steel ball in the centre. By applying a 3-phase current to the coils on the ring (out of phase and physically separated from each other by 120°), a rotating magnetic field was created. The rotating magnetic field (primary field) would in turn induce a current in the steel ball. This current, with its own opposing magnetic field,  would act as an 'anchor' for the primary magnetic field, allowing it to 'pull' the ball as it rotated. This was the basis for the 3-phase induction motor, which is used in practically every form of industry today.

Tesla's experiment with the 3-phase induction motor is the inspiration behind the images at top of page. In place of the steel ball rotating with-in the ring, the copper ring rotates around the steel ball to represent the effect a magnetic field, created by a 3-phase alternating current, would have.

 
 
 
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