Some diesel generator sets need to operate continuously for a long time either periodically or on a routine basis to serve as the primary power supply for electrical loads; such units are defined as prime power generator sets. A prime power generator set can function both as a regular operating unit and a standby unit.
Towns, islands, forest farms, mines, oilfields and industrial and mining enterprises far from the main power grid are equipped with diesel generators to supply power for local industrial production and residential living. These generator sets are required to run non-stop under normal circumstances.
Key facilities including national defense projects, communication hubs, radio stations and microwave relay stations shall be equipped with standby diesel generator sets. Under normal conditions, power for these facilities is supplied by the municipal public power grid. However, in the event of power outages caused by damage to the municipal grid due to natural disasters such as earthquakes and typhoons, wars or other human-induced factors, the pre-installed standby units shall start up rapidly and operate continuously for extended periods to guarantee uninterrupted power supply to the electrical loads of these critical projects. Such standby generator sets also fall under the category of prime power generator sets. Prime power units feature long continuous operating hours and highly variable load curves. The selection of unit capacity, quantity and type, as well as the operation and control modes, differ from those of emergency generator sets.
1. Determination of Prime Power Diesel Generator Set Capacity
The unit shall be selected based on its long-term continuous output power that can meet the total rated calculated load of the entire project. The capacity of standby generator sets shall be determined according to the criticality of electrical loads. The continuous output power of a diesel engine is generally 0.9 times its rated power.
2. Determination of the Number of Prime Power Diesel Generator Sets
Normally, no fewer than two prime power diesel generator sets shall be configured to ensure power supply continuity and accommodate fluctuations in the electrical load curve. With multiple units in place, the number of running generators can be adjusted in response to load variations, allowing diesel engines to operate under economical loads, thereby cutting fuel consumption and power generation costs. The optimal economical operating range for a diesel engine is 75% to 90% of its rated power.
To secure uninterrupted power supply, standby units shall be configured alongside the prime units. When an operating unit undergoes fault maintenance or shutdown inspection, the remaining generators shall still sustain continuous power delivery to critical electrical loads.
3. Determination of Rotational Speed for Prime Power Diesel Generator Sets
To reduce mechanical wear and extend unit service life, medium and low-speed prime power generator sets with a rated rotational speed of no more than 1000 r/min are recommended; medium and high-speed units may be adopted for standby units.
All units within the same power station shall be of identical model and capacity to facilitate the use of uniform spare parts and simplify maintenance and management. Projects with drastic load fluctuations may adopt units of the same series but different capacities.
The rated output voltage of the generator is specified the same as that of emergency generator sets, typically 400 V. High-voltage generator sets may be selected for individual projects featuring heavy power consumption and long power transmission distances.
4. Control of Prime Power Diesel Generator Sets
Prime power units shall generally be capable of parallel operation to simplify the main power distribution wiring. During alternating startup, shutdown and operation of units, paralleling, load transfer and unit switching can be implemented without power interruption.
Each unit shall be fitted with dedicated measurement and control devices, and its speed governing and excitation regulating devices shall meet the requirements for parallel operation.
Automated diesel generator sets are recommended for standby units supplying critical loads. Upon mains power failure, such units can start automatically and rapidly to restore power to critical loads.
Diesel engine operation generates intense noise inside the generator room, and automated units can be easily retrofitted for partitioned remote operation and automatic monitoring. During normal operation of the generator sets, operators do not need to enter the diesel engine room and can monitor and control the units entirely from the control room.
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Post time: Jun-17-2026