Walk into any major power plant — steam, gas, hydro, or nuclear — and the generator you'll most likely find is the synchronous type. Its name carries the secret of its dominance: its speed and frequency are tied to the grid with strict precision, and that very discipline is its strength.
Why "Synchronous"?
The synchronous generator is the most common type in power plants. It is called synchronous because its speed and frequency are tied to the grid and must be controlled precisely: it rotates at a fixed, defined speed dictated by the grid frequency and its number of poles — no faster, no slower. Try the synchronous speed calculator to relate frequency, number of poles, and speed.
How Does It Work?
- The rotor carries a magnetic field controlled via the excitation current — a direct current that feeds the rotor windings.
- The speed is regulated by the turbine or prime mover through speed governors.
- With these two control handles, the operator manages the generator: excitation regulates the voltage, and the turbine regulates the power and frequency.
Its Golden Advantage: Real and Reactive Power Together
One of its key advantages is that it can produce both real power and reactive power, which is extremely important for grids: real power feeds the loads, while reactive power supports the grid voltage and meets the needs of inductive loads. The synchronous generator does not just feed the grid — it also participates in regulating its voltage through excitation control.
A Brief Comparison with Its Relatives
| Synchronous | Induction | |
|---|---|---|
| Field in the rotor | Controlled via excitation current | No controlled field — mutual induction |
| Reactive power | Produces and controls it | Consumes it and needs compensation |
| Voltage and frequency control | Full and precise | Limited |
| Usage | Power plants — the standard | Some older wind applications |
Sample answer: For three reasons: its speed and frequency are precisely matched to the grid (the basic condition for connection), it controls its voltage via the excitation current that feeds the field on its rotor, and most importantly, it produces both real and reactive power together — feeding the loads while supporting the grid voltage at the same time. The operator has two control handles: the turbine for real power and frequency, and excitation for voltage and reactive power — and this full control is exactly what grid management requires.
Confusing the roles of the two control handles: increasing excitation does not raise real power but rather voltage/reactive power, while increasing the turbine's fuel input is what raises real power. Mixing these up in an answer reveals a superficial understanding of the synchronous generator.
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