Generators, synchronous machines, dynamo

Electric generators turn mechanical rotation into electrical power, and the synchronous machine is the type that supplies most of the electricity carried by power grids. It is called synchronous because its rotor turns in exact step with the rotating magnetic field, so its output frequency is locked to the rotational speed and the number of magnetic poles. The rotor carries an electromagnet energised by direct current, and as it spins it induces alternating voltage in the stator windings.

A defining feature of the synchronous generator is independent control of its terminal voltage and reactive power through the field current supplied to the rotor. This allows operators to regulate grid voltage and share load between machines, which is why these generators dominate in steam, gas, hydro and large wind installations. Because the rotor must remain synchronised, such machines need careful control when connecting them to a live grid, a process called synchronisation.

Other generator types fill different roles. Induction generators, derived from squirrel-cage motors, are simpler but draw their magnetising power from the grid. Direct-current generators use a commutator to produce one-directional output. Three-phase arrangements are standard for power generation because they deliver steady, efficient power transmission and suit large rotating machines. Across all these designs the underlying physics is the same electromagnetic induction first described by Faraday, differing only in how the magnetic field and connections are arranged.

Frequently asked questions

Why is a synchronous generator called “synchronous”?: Its rotor rotates exactly in step with the stator's rotating magnetic field, so the output frequency is fixed by the speed and the number of poles.
What advantage do synchronous generators have over induction generators?: They can control their own voltage and reactive power through the rotor field current, allowing them to regulate the grid rather than depend on it.
Why is three-phase power used for generation?: Three-phase systems deliver steady, efficient power and are well suited to large rotating machines and long-distance transmission.

Motor and generators:
Brushless DC motors	Motor AC	Motor-Synchronous	Single phase AC motors
Generators: AC and DC	Motor DC	Robot	Stepper motor
Generator: asynchronous	Motor overview	Servomotor	Stepper motor drivers

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related topic: Motor-Synchronous

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