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Generator School · 02

How does a generator actually work?

A generator is really three machines bolted together: an engine, an alternator, and a controller. They each do one job, and they all have to talk to each other for the unit to behave properly.

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1. The engine — converts fuel into rotation

A diesel or petrol engine takes liquid fuel, burns it inside its cylinders, and turns a crankshaft. For a 50 Hz Australian generator, the crankshaft has to spin at a precise 1500 RPM (for 4-pole alternators) or 3000 RPM (for 2-pole alternators) — every minute, every second, with zero drift. That's why a governor or ECU is fitted: it constantly adjusts fuel delivery to keep speed rock-steady even as the load changes.
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2. The alternator — converts rotation into electricity

Coupled to the engine is the alternator (genset technicians often call it the 'head'). Inside, a magnetised rotor spins past stator windings. The changing magnetic field induces a voltage in the stator wires — that's your output. An AVR (Automatic Voltage Regulator) keeps the magnetic field strength constant so the output voltage stays at 230 V (single-phase) or 400 V (three-phase) regardless of load.
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3. The controller — the brain

A Deep Sea Electronics (DSE) panel watches the engine and alternator non-stop. It starts the engine when the mains drops, stops it when the mains is back, monitors oil pressure, coolant temperature, battery voltage, fuel level, frequency, and load. If anything goes outside a safe range, the controller shuts the unit down before the engine hurts itself. Modern controllers can also be monitored remotely over GSM or Ethernet.
Quick answers

FAQs

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Frequency (Hz) = RPM × pole_pairs / 60. For 50 Hz with a 4-pole alternator: 50 × 60 / 2 = 1500 RPM. For 2-pole: 3000 RPM.

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