How Wind Turbines Generate Electricity

Introduction

• Wind turbines use generators to transform kinetic energy into electricity.
• Key physical phenomenon: Magnetic Induction.

Magnetic Induction

• Induction causes voltage when a conducting coil is in a changing magnetic field or when it moves within a magnetic field.
• Most wind turbines use the first approach: the mechanical force of the blades drives the rotor of the generator.

Synchronous Generators

• Basic setup: a synchronous generator with four magnetic poles.
• Permanent magnets cause magnetic flux or rotor coils are excited with a DC power source.

How It Works

• A coil wrapped around a rotor generates an alternating electromagnetic force (EMF) as the magnetic flux moves.
• Electrons in the material are disturbed, creating an alternating current (AC).
• Displacement of electrons during rotation creates a sine wave pattern, hence AC.

Three-Phase Current

• With three armature coils at 120-degree angles, a three-phase current is generated.
• Three-phase currents are primarily used for transporting electric power.
• Speed of the alternating magnetic flux defines the frequency of the current.
  • More poles and more RPM result in a higher frequency.

Connection to the Grid

• Armature coils connected to the grid's three-phase current (50 Hz) create a rotating magnetic field.
• The rotor’s magnetic field locks onto this rotating field.
  • Synchronous generator: rotor follows grid frequency.
  • Grid analogy: a steady moving heavy train - rotor can push but won’t go faster.

Rotor Speed

• Example: four-pole rotor connected to the grid turns at 1500 RPM.
  • Gearbox turbines use gearboxes to increase rotor shaft frequency.
  • Direct drive turbines use more poles.
  • Turbine system controls speed-up before connecting to the grid.

Variable Speed Generators

• Modern turbines often use variable speed generators like the doubly-fed induction generator.
• Use power converters to allow