Diesel generator sets are rated differently depending on regional standards. In China, generator sets are typically labeled with prime power, while internationally, standby power (maximum power) is more commonly used. Understanding these definitions is essential for selecting the correct generator and ensuring safe operation.
Prime power refers to the maximum power a diesel generator can deliver continuously over a 24-hour period under variable load conditions. It is the standard rating used in China and represents the normal operating capacity of the generator.
Standby power is the maximum output a generator can provide for a limited time. Typically, a generator can operate at 110% of its prime power for 1 hour within every 12-hour period.
For example, a 400 kW prime power generator can temporarily operate at 440 kW for one hour within 12 hours. However, running a generator continuously at standby power will overload the unit, reduce its service life, and increase the risk of failure.
Apparent Power (kVA): Used to express the total capacity of electrical equipment such as transformers and UPS systems.
Active Power (kW): The usable output power of a generator, typically calculated as 0.8 times the apparent power due to the standard power factor.
Rated Power: The power level at which a diesel generator can operate continuously for up to 12 hours.
Maximum Power: Approximately 1.1 times the rated power, but only allowed for 1 hour within a 12-hour period.
Economic Power: Typically 50% to 75% of rated power, which is the most efficient operating range with the lowest fuel consumption and minimal wear.
The following are key electrical specifications for a 1000kW diesel generator set (prime power) with 1100kW standby power:
1) Rated voltage: 400/230V (load voltage 380/220V)
2) Rated frequency: 50Hz
3) Rated power factor: 0.8 (lagging)
4) Wiring method: Three-phase, four-wire system
Voltage regulation:
Steady state: ≤ ±1%
Transient state: +20% to -15%
Frequency regulation:
Steady state: ≤ 3% (adjustable between 0–5%)
Transient state: +10% to -7%
Rated speed: 1500 r/min
Recovery time: ≤ 6 seconds
Voltage fluctuation rate: ≤ 0.5%
Frequency fluctuation rate: ≤ 0.5%
Load change response:
Voltage stabilization time: ≤ 3 seconds
Frequency stabilization time: ≤ 5 seconds
Waveform distortion rate: ≤ 5%
Electromagnetic interference suppression complies with GB2820 and VDE0875-N standards.
The diesel engine must be compatible with BS2869 A1 or A2 fuel standards and use light diesel fuel. It should be water-cooled, four-stroke, direct injection, and either naturally aspirated or turbocharged.
The engine must comply with BS5514 standards, ensuring continuous operation at rated capacity for power generation.
The rated engine speed is 1500 r/min, and the rotation direction should be counterclockwise.
The generator set should be equipped with an electronic speed governor and stabilization system, as well as an overspeed protection mechanism that cuts off fuel supply when speed exceeds 15% of the rated value.
The cooling system should use a forced closed-loop water circulation design to ensure efficient heat dissipation.
The engine must be equipped with a manual shutdown lever for emergency stopping.
The engine water jacket should include an electric heater controlled by a thermostat. The system should maintain the coolant temperature at approximately 20°C (or as recommended by the manufacturer) to ensure reliable starting.
When the generator is running, the heater should automatically shut off. A manual control switch should also be provided on the control panel for operator convenience.
Understanding the differences between prime power and standby power, along with key generator specifications and technical requirements, is essential for selecting and operating diesel generator sets efficiently. Proper usage within rated limits ensures optimal performance, fuel efficiency, and extended service life.
