Electric Generators
Posted under Industry, Power Source
Electric generators are all based on the fundamental concepts of electromagnetic induction developed by Michael Faraday in 1831. Faraday discovered that moving a conductor through a magnetic field induces an electromagnetic force (emf), or
voltage, across the wire.
A generator, very simply, is an arrangement of components designed to cause relative motion between a magnetic field and the conductors in which the emf is to be induced. Those conductors, out of which flows electric power, form what is called the armature.
Most large generators have the armature windings fixed in the stationary portion of the machine (called the stator), and the necessary relative motion is caused by rotating the magnetic field.
Voltage and current can be created by (a) moving a conductor through a magnetic field, or (b) moving the magnetic field past the conductors. The armature windings indicate current flow into the page with an “x” and current out of the page with a dot (the x is meant to resemble the feathers of an arrow moving away from you; the dot is the point of the arrow coming toward you).
The rotor in this case is just a 2-pole magnet (1 north pole and 1 south pole), which for now we can consider to be just an ordinary permanent magnet. The stator consists of iron, shaped somewhat like a C (backwards, in this case), with some copper wire (the armature) wrapped around the iron. The purpose of the iron in the stator is to provide a low reluctance path for the magnetic flux lines, channeling as much flux as possible through the copper armature windings.
As the permanent-magnet rotor turns, it causes magnetic flux within the iron stator to vary (approximately) sinusoidally. The windings around the stator therefore see a time-varying flux, which creates a voltage across their terminals.
As the rotor turns, magnetic flux passes through the stator and the armature windings, in one direction, then diminishes to zero, then increases in the other direction. Ideally, the flux ? would vary sinusoidally.
From Faraday’s law, whenever a winding links a time-varying amount of magnetic flux ?, there will be a voltage e (electromotive force) created across the winding:
