Complete process of a diesel generator set from startup to normal power delivery (tutorial for beginners, experienced workers can skip this)

I. Preparations Before Starting (Pre-steps, Before Ignition)

 

1. Check fuel, engine oil, and coolant levels; bleed the fuel line.

 

2. Turn on the start power and let the control system perform self-checks: battery voltage, water temperature and oil pressure sensors, speed sensor, voltage transformer, and protection module are all normal.

 

3. Open the no-load switch (do not connect the load), and power up the governor and AVR (Automatic Voltage Regulator) for standby.

 

4. Manual units: press the pre-oil pump to build engine oil pressure; automated units perform automatic pre-lubrication.

 

II. Ignition and Start Stage (Diesel Engine Ignition)

1. Control system outputs signal to connect starter motor power; the battery drives the motor to rotate the diesel engine crankshaft.

 

2. The crankshaft drives the camshaft; the high-pressure fuel pump begins pumping fuel, and diesel is delivered via high-pressure fuel lines to the injectors.

 

3. Pistons compress the air in the cylinder; compression ends with temperatures of 500–700°C, reaching diesel's self-ignition point.

 

4. High-pressure diesel is atomized by the injectors into the hot cylinder, where the diesel auto-ignites (diesel engines do not have spark plugs; ignition is compression-based, commonly called "start ignition" in the industry).

 

5. The cylinder generates power; the diesel engine runs on its own combustion, releasing the starter motor, which disengages from the flywheel.

 

6. At this point, the diesel engine is at low starting speed; oil pressure and water temperature have not yet reached standard levels.

 

III. Idle Warm-up Stage

 

1. The governor controls fuel injection to maintain low idle speed (typically 600–800 r/min).

 

2. Engine oil pressure gradually rises to the rated value, coolant temperature increases, and components heat evenly to prevent cold-engine wear.

 

3. The generator rotates slowly in sync with the crankshaft; the generator excitation winding receives a weak initial current from the AVR, inducing low residual voltage in the stator.

 

4. The control system monitors: if oil pressure is too low, water temperature too high, or overspeed occurs, the engine stops immediately for protection.

 

5. Warm-up time is 30s–3min (longer for cold engines); once oil pressure and water temperature are stable and meet standards, speed increase is allowed.

 

IV. Accelerating, Building Pressure, and Stabilizing Voltage Stage (Generator Reaches Rated Voltage)

 

1. The governor increases fuel supply, raising the diesel engine speed to rated speed:

- 50Hz industrial units: 1500 r/min (4-pole generators, mainstream in the domestic market)

- 60Hz units: 1800 r/min

 

2. Generator rotor synchronizes to rated speed:

AVR automatically increases excitation current, producing a strong magnetic field in the rotor; the stator winding cuts the magnetic lines of force, and induced voltage quickly rises.

 

3. Voltage rises to rated value (commonly three-phase 400V / single-phase 230V); AVR continuously fine-tunes excitation current to stabilize output voltage.

 

4. The control system collects voltage and frequency signals to confirm stable voltage (380/400V) and frequency (50Hz), entering ready status.

 

V. Closing the Switch to Output Electric Power (External Power Supply)

 

There are two operating conditions: single-unit independent operation and grid-connected operation:

 

1. Single-unit standby generator (common for residential areas/factories)

 

1. Confirm that voltage, frequency, and all protections have no alarms;

2. Manually/automatically close the output air switch (circuit breaker);

3. Three-phase AC is delivered to the load equipment through switches and cables, and the generator begins to output electric power externally;

4. Operate at light load initially, then gradually increase the load to avoid sudden load increases that may cause speed or voltage drops.

 

2. Grid-connected generator (parallel with utility power)

 

The following synchronization conditions must be met: equal voltage, same frequency, matched phase, and same phase sequence;

 

1. The synchronization device adjusts the generator's speed and voltage to match utility parameters;

2. Close the grid-connection switch at the synchronization moment, allowing the generator to supply power together with the grid;

3. Distribute active/reactive power according to the set allocations.

 

6. Normal Steady-State Power Generation Operation

 

1. Diesel Engine Side:

 

When the load increases → resistance rises → speed slightly decreases → the governor automatically increases fuel injection to restore 1500 r/min; when the load decreases, fuel supply is reduced to stabilize speed and frequency.

 

The cooling and lubrication systems continue to circulate, and the temperature-controlled fan automatically starts or stops according to water temperature.

 

2. Generator Electrical Side:

 

Load fluctuations cause output voltage changes, and the AVR adjusts the excitation current in real-time to ensure output voltage fluctuations remain within ±5%.

 

3. Control System Continuous Monitoring:

 

Oil pressure, water temperature, speed, voltage, current, power, overload, short circuit, leakage, etc. are continuously monitored, and any abnormalities trigger immediate alarms or breaker trip shutdown for protection.

 

Key Additional Common Mistakes

 

1. Diesel engines do not ignite with spark plugs; they rely on the high-temperature compression of air for compression ignition. The everyday phrase 'ignition start' is just a colloquial term.

 

2. A generator does not output rated power immediately upon starting: at low speed, there is only residual voltage, and it must reach rated speed and build excitation voltage before it can supply power.

 

3. The engine must be warmed up before supplying power; running at full load when cold will lower the voltage and increase engine wear.