Guide to Generator Set Power Selection

In modern society, the stability of power supply is crucial for the normal operation of various projects and facilities. Whether it is residential buildings, industrial production, or special-purpose sites, generator sets play an indispensable role. However, facing the wide variety of generator set products on the market, how can one choose a unit that meets needs while being economical and efficient? This article will provide a detailed analysis from multiple aspects, including generator set power selection, configuration points, and operation and maintenance, to help you make an informed decision.

When selecting a generator set, power selection is the crucial first step. The power of a generator set not only determines whether it can meet electricity demands, but also directly affects operating costs, service life, and overall efficiency.

Generator set power is usually divided into rated (continuous) power and standby power. Rated power refers to the power that the generator can continuously and stably output within 12 hours, while standby power refers to the maximum power allowed for one hour within the same 12-hour period. For example, a diesel generator with a rated power of 100 kW typically has a standby power of around 110 kW. This distinction in power is crucial for users when selecting a generator set, as different applications have different power requirements.

When selecting a generator set, attention must also be paid to power unit conversion. Generator power can be expressed in kVA or kW, where kVA is apparent power and kW is active power. The relationship between them is 1 kVA = 0.8 kW. Imported generator sets usually indicate power in kVA, while domestic electrical equipment generally uses kW. Therefore, when calculating power, if the unit is in kVA, it must be converted to kW according to the formula to ensure accurate power matching.

Determining generator set power is not simply adding up all appliance powers; it is also necessary to consider the starting method of the appliances. Common starting methods include direct start, variable frequency start (reduced voltage start), and star-delta start. For direct start, the current is about six times the working current, and instantaneous power can also reach six times the rated power; variable frequency start has a current of about three times, with instantaneous power about three times rated; star-delta start has a current of about five times, with instantaneous power about five times rated. Therefore, when selecting generator set power, in addition to considering the sum of all appliance powers, the starting power of each appliance must also be considered to ensure the generator can meet the demand for instantaneous high power.

The configuration of a generator set involves multiple aspects, including matching the diesel engine with the generator in terms of power, the number of units and backup setup, selection of generator speed, and determination of voltage level. These configuration points not only affect generator performance, but also directly relate to the reliability and economy of the entire power system.

Diesel engine power and generator power should not be configured to be exactly the same. The industry generally stipulates that diesel engine power ≥ generator power + 10%. If configured equally, it will reduce the service life of the unit, cause frequent maintenance, and increase operating costs. For example, if a diesel engine has a rated power of 100 kW, then the generator's rated power should be 110–120 kW, with standby power of 20–30%. At the same time, the power difference between the diesel engine and the generator should be within 10% to avoid high-load operation of the engine, which would affect its service life.

To ensure continuity of power supply and adapt to changes in electrical load curves, generator sets are generally configured with two or more units. Having multiple units allows the number of active generators to be adjusted according to load changes, enabling diesel engines to often operate at economic loads, reducing fuel consumption, and lowering power generation costs. In addition, primary units should also consider backup units. For example, in some important residential buildings or industrial production sites, backup units can quickly be brought online if the main unit fails, ensuring uninterrupted power supply.

Generator sets of different speeds are suitable for different applications. Generally, for residential use, high-speed units with 1000–1500 rpm are preferred, while low-speed units with 300–350 rpm are suitable for ship main engines. Therefore, when selecting a generator set, the appropriate speed should be determined according to the specific application scenario and requirements.

The determination of generator output voltage is the same as for emergency generator sets, generally 400 V. However, for projects with large electricity consumption or long transmission distances, high-voltage generator sets can be selected. Voltage level selection should comprehensively consider the voltage requirements of electrical equipment and transmission losses.

The following will provide detailed points on generator set operation and maintenance from aspects such as economic operating status, the importance of control panels, and power runtime limits, helping you better manage and maintain generator sets to ensure long-term stable operation.

The economic operating status of a generator set refers to operating between 75%–90% of rated power. Within this range, the generator has the lowest fuel consumption and highest efficiency. Long-term operation under economic load not only reduces generation costs but also extends generator service life. Therefore, during actual operation, long-term low-load or high-load operation should be avoided. For example, by reasonably setting start and stop conditions, the generator can adjust its operating status in time as load changes, keeping it within the economic operating range.

The control panel is a key component connecting the diesel engine and generator. It not only controls the start, stop, and operational status of the generator set but also enables automatic control and protection. A proper control panel ensures normal operation, enhancing safety and reliability. For example, control panels usually have various protection functions such as overload protection, short-circuit protection, and low oil pressure protection, capable of cutting off power promptly in case of abnormalities, preventing equipment damage. In addition, control panels can implement remote monitoring and automated control, allowing users to understand the generator's operational status in real time and carry out timely maintenance and adjustments.

In the generator set industry, definitions of rated power and standby power differ from current national standards (PRP, ESP). For example, rated power typically has an average load factor not exceeding 70% within 24 hours, while ESP limits operation to no more than 200 hours per year. Additionally, there are custom power types, such as continuous power (COP) and limited-time power (LTP) used in data centers and semiconductor manufacturing. For these different power definitions and runtime limits, users need to fully understand and comply with relevant regulations to ensure generator performance and lifespan. For instance, when selecting a generator set, the appropriate power type should be chosen based on actual application scenarios and runtime requirements, avoiding equipment damage or performance decline caused by exceeding runtime limits.

Through the previous theoretical discussion, we have gained a comprehensive understanding of generator set power selection, configuration points, and operation and maintenance. To better apply this knowledge, the following will analyze several practical cases, detailing generator selection, configuration, operation, and maintenance in different scenarios, helping users better understand actual applications.

Taking a mid-sized residential building with a total electrical load of 500 kW as an example, the first consideration in generator selection is rated and standby power. According to the principles above, two diesel generators with rated power of 250 kW and standby power of 275 kW each can be selected. In normal conditions, one unit meets the building's power demand while the other serves as backup. In case of emergencies or increased load, the standby unit can be quickly activated. Considering that appliances in residential buildings are mostly direct-start, starting power must also be considered in power calculations. Since residential load is relatively stable, high-speed units (1000–1500 rpm) can be chosen, ensuring a generator output voltage of 400 V to meet the voltage requirements of building equipment.

In industrial production, electrical loads are typically large and vary frequently. For example, a medium-sized factory with a total load of 1000 kW and some high-power equipment requiring direct start can select three diesel generators with rated power of 350 kW and standby power of 385 kW each. This allows flexible adjustment of active units according to production plans and load changes, keeping generators operating at economic loads. Since industrial equipment has high starting currents, the impact of starting methods on power selection must be carefully considered. For direct-start high-power motors, sufficient power margin should be reserved to meet instantaneous high-power demands. Additionally, due to the high continuity and stability requirements of industrial production, backup units are particularly important. Generator installation location and control methods should also be selected reasonably according to the factory's environment, equipment layout, and other factors.

Selecting the right generator set is a complex and important task, requiring comprehensive consideration of power selection, configuration points, and operation and maintenance. Through this detailed introduction, users can gain a deeper understanding of generator set selection. In practice, users should select generator power, configuration, and operation methods according to their specific needs and circumstances, ensuring stable and economical power supply. Users should also pay attention to industry trends and the application of new technologies to better meet future development requirements.