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Choosing The Right Generator Set

Feb. 18, 2022

Correct sizing of generators is a key factor to avoid efficiency and durability losses. When performing an analysis focused on power ratings, this analysis can focus on two scenarios: selecting an undersized or oversized generator.


If undersized: From the end user's point of view, the main problem will be underpowering and the generator set will be required to deliver power outside of its design, which can lead to a drop in voltage and a drop in engine speed, which in turn can lead to a drop in frequency and overheating of the alternator, as the alternator output current far exceeds its size and can affect the coating of the isolator. 

From an electrical point of view. From a mechanical point of view, it leads to an increase in the operating temperature of the engine, as well as to an increase in wear and vibration of the internal components; it must be remembered that the optimum operating point of the engine is between approximately 70% and 80%.

1000kw 1250kva Cummins Diesel Generator Set

 1000kw 1250kva Cummins Diesel Generator Set

If it is oversized: In order to understand the problem of oversizing, we must resort to a comparison where the engine of a generator set works under the same conditions as a car that climbs a hill. If we oversize the engine of the generator, it will also work outside the 70 to 80% range we indicated above, which is the optimal function point we indicated above. 

In this case, the main problem is mechanical, which can lead to an array of other problems, from operating out of range and below the optimal load threshold, the operating temperature will drop, which can lead to poor combustion, which affects induction, as well as anti-pollution systems such as filters and valves that produce smoke in the exhaust, ejecting suspended and unburned particles.

400kw 500kva Perkins Diesel Generator Set

 400kw 500kva Perkins Diesel Generator Set

What is the key to making the proper decision?

Finding the right measurement

The initial and most basic step is to define which equipment will be connected to the generator and to know the power rating required for the project. In other words, know the total power of all electrical equipment that will need to be powered by the generator set, applying simultaneous rates whenever possible and always responding to the customer's requirements and needs.


However, a simple mathematical operation will not give us enough information. There are many other factors to consider, as they affect the results of the calculation. They relate to technical aspects as well as to usage and environmental aspects.

550kw 687.5kva Deutz Diesel Generator Set

 550kw 687.5kva Deutz Diesel Generator Set

There is a need for more thorough control of the larger loads in the installation; electric motors, discharge lamps or lighting from LEDs are all difficult electrical loads to power because they involve transition processes that can lead to sustained momentary peak consumption that poorly designed equipment will not be able to sustain.


Sizing the generator set

In order to size the generator set and decide on its configuration, the team of engineers will base it on an electrical, mechanical or civil engineering project. This will define


The necessary power rating and load type required to meet current and future demand

Elements that the equipment needs to have (manual or automatic start, parallel operation with other equipment or public power, soundproofing, auxiliary fuel storage, heaters, etc.)

Legal standards that must be observed (electricity, noise, gas and particle emissions, transport norms for mobile generators)

Location of the equipment installation (under the roof, outdoors, altitude, dusty environment, etc.)

200kw 250kva Volvo Diesel Generator Set

200kw 250kva Volvo Diesel Generator Set

Applications and frequency of use

Some applications may require a safety margin regarding the rated power, providing continuous power to maintain a constant electrical load without interruption (COP generators) or using variable power (PRP-STP generators) to do the same thing is different) or to respond to emergency or standby situations (ESP generators). Therefore, it is necessary to properly define the energy requirements of the generator in order to provide a solution that fits your needs.


Environmental conditions

The location of the generator set is the decisive factor. starlight Electricity Equipments can provide solutions for


Salt water environments.

Marine generators.

Mining and dusty environments (IP 45).

Nuclear areas.

Vibration-proof electrical panels.

Extreme temperatures (-32°c to +50°c).

Mobile generators ruggedized for military use.

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Mounting Height

This factor may come as a surprise, but if it is not taken into account, it can completely derail engineering efforts. Engines require oxygen to operate and the oxygen concentration decreases as the height of the generator set location increases. This can result in a low oxygen content in the mixture in the combustion chamber and, if the engine has atmospheric inhalation, reduce the engine's power output by as much as 10% over the first 1000 meters of altitude. However, in the case of turbine engines, there is no loss of energy output at this level.


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