Induction motor

The induction motor is the workhorse of industry — the motor in your fan, pump, washing machine, and most factory machines. It is brilliantly rugged because the rotor has no magnets, no brushes, no electrical connection at all: just bars of metal (a 'squirrel cage'). Three-phase AC in the stator creates a magnetic field that rotates around the inside of the motor like a invisible whirlpool, and this sweeping field induces currents in the rotor bars (hence 'induction'), which in turn create their own field that gets dragged along.

The trick is that the rotor must always lag a little behind the rotating field — if it ever caught up, the bars would stop cutting field lines and no current, no torque, would be induced. That lag is called slip. Because there are no contacts to wear out, an induction motor can run for decades; its only real downside is that, on a fixed mains supply, its speed is locked near the line frequency, which is why modern drives use a variable-frequency inverter to change its speed.