# How to Choose a Generator Set?

Sep. 27, 2021

In order to choose the right generator set for your needs, you must know the total power required by the equipment connected to it and the type of power supply (single-phase or three-phase). You also need to determine whether you need a mobile or stationary unit.

You also need to define the type of motor e.g. petrol engine (if you are looking for a small compact generator set), diesel engine (if you are looking for a large generator set) or gas or turbine engine (if this energy source is available and you want to be more economical and less polluting). Finally, you need to define whether voltage regulation is required. The system smoothes the output voltage to avoid damaging the electronic equipment that will be connected to the generator set.

## How much power should your generator set have?

To determine how much power your generator set needs, you must not only know the nominal power of the equipment that will be running at the same time, but also the peak power consumption, especially at start-up. For example, an electric motor may consume up to three times its nominal power at start-up.

The generator set must be able to supply the peak power consumed by all the devices that need to be started at the same time. For resistive equipment (lighting, TVs, small appliances, etc.), a safety factor of 30% must be added when determining the power of the generator set. For inductive equipment (i.e. electric motors), their nominal power must be multiplied by 3 to take into account peak consumption.

330kw 412.5kva Perkins Diesel Generator Set

For generator sets supplying three-phase power, the power is expressed in kilovolt-amperes (kVA): this is called apparent power. For power supplies supplying DC or single-phase power, the power is expressed in kilowatts: this is called active power.

The difference between kVA and kW comes from the phase shift between each phase. This phase shift is called cos φ (cosine phi). To obtain the active power of a generator set whose apparent power and cos φ are known, multiply these two values together, e.g. 1 kVA x 0.8 = 800 W (in general, the cos φ of a generator set is 0.8).

Generally generator set manufacturers indicate the continuous power and the maximum power corresponding to a continuous power of around 20% overload for a limited period of time.

## What type of motor should you choose for your genset?

Generator sets are equipped with an internal combustion engine. Depending on your needs and the type of fuel available, you can choose between petrol, diesel or gas engines.

Petrol generator sets are usually compact, quiet and versatile. Typically, these generator sets have a low power rating of up to 6 kW and provide single-phase current.

Diesel generator sets are more suitable for extended or even continuous use outdoors, for example on construction sites. They are more economical than petrol generator sets of the same power. These generator sets can be supplied with single-phase, three-phase or mixed currents.