WHAT IS THE DIFFERENCE BETWEEN THEM?
One of the most important parts of a generator sets is its electric generator, a machine that is responsible for transforming primary mechanical energy into electrical energy, usually in the form of alternating current. It is also the part that will define whether a generator set is three-phase or single-phase, regardless of the type of fuel and engine.
Electric generation is based on Faraday’s law, which defines the generation of an electromotive force in a conductor moving in a magnetic field. In a single-phase system, there is a single magnetic field that will move due to the rotation produced by the combustion engine. The magnetic field will be created by a magnetic element (or magnet) or by an electromagnet that must be powered by an external auxiliary source.
However, in a three-phase system, generation is produced by three magnetic fields at 120° angles that create the three poles of the three-phase system. Due to the arrival and cheapening of power electronics during the last years, we can find single-phase inverter generator sets on the market. Actually, these are three-phase generators to which an electronic converter has been added at the power output aiming to transform the three phases of the generator into a single-phase system with the help of electronics. In this way it provides the advantages of three-phase generators and the versatility of an electronic converter.
Single-phase networks are typical for domestic use and for small tertiary installations and services. Why? Because the transport of electrical energy in alternating current is more efficient when it is three-phase, in addition to the fact that basic electrical machines give better results in three-phase systems. This is why most administrations and electricity companies do not allow single-phase supplies above 10 KVA.
For this reason, single-phase machines (including generator sets) normally do not exceed this power, although it depends on the country since there are many where single-phase power is higher, sometimes reaching 50 or 80kVA.
In these cases, it is usual to use three-phase alternators that are reconnected so that they can work in single phase, although this means having considerable losses (40% or even more) depending on the model and the alternator manufacturer.
It is also frequent to use three phase alternators reconnected in single phase due to several reasons (lead times, stock, etc.). Apart from the fact that it is possible to reconnect the alternator to three phase (when for some reason there are changes in the three-phase installation), the alternator is still just as valid. Moreover, if the engine power is higher, it can offer the original three phase power of the alternative.
Diesel, gas, or petrol engines
Since they are frequent in small power rates, single-phase generator sets are less robust and have a simpler operation than three-phase ones. With these characteristics, there are machines that can work for some hours and in a non-continuous way, an aspect that is also common to the engines that move single-phase generators.
In these cases, in addition to diesel and gas systems, it is possible to find petrol engines in this small power range.
In general, single-phase diesel generators are designed for:
- Minor uses in locations where an electrical network is not available.
- Homes and businesses that need a backup system to provide energy in the event of a mains failure, normally for few hours as the blackout is not supposed to last long due to the existence of a robust electrical network.
- In special cases, it is possible to find robust single-phase generators prepared for an intensive use.
The possibilities of inverter
For intensive use and special cases, a new product with great advantages has been developed in the last years: the so-called single-phase inverter. These are robust three-phase generator sets to which an electronic converter has been added, capable of converting the three-phase power supply into a quality single-phase one.
This process can usually be done efficiently and backed up by more compact and high quality three-phase gensets. In addition, the power electronics can incorporate several controllability advantages, making it a compact and cost-saving element.
THREE-PHASE GENERATOR SETS
Three-phase generator sets are, doubtless to say, the greatest reference in this type of machines. They can be found in almost any power range and their intensive use and proven efficiency make them more compact, more robust and more efficient than single-phase generator sets.
These advantages mainly stem from the electrical machine (the generator) but also affect the engines in many relevant aspects.
A three-phase generator is normally more compact than a single-phase generator as it can benefit from current effects and zero magnetic flux, which means that, to move the same power, less iron and copper are needed in electrical machines. This makes them more efficient, both in the generation and transportation of electrical energy. On the other hand, due to the construction of the magnetic circuits themselves, three-phase generators tend to be more efficient.
Another effect, perhaps less well known, is that whereas the single-phase motor has one pair of poles, the three-phase motor has three. This makes the torque absorbed by the three-phase generator “rounder” and therefore, the mechanical transmission system, bearings and other parts not only suffer less wear, but are also more balanced. Frictional heating is also lower in a three-phase machine, which increases durability and reduces maintenance work. These effects are most notable the larger the electrical machine is.
The three-phase machine in a generator set is robust and reliable, and it has been amply tested in all kinds of situations and for a long time with great results (at an engineering level, there exist more knowledge and experience on the three-phase machine, and also the technical background between the different types of three-phase machines is greater). For this reason, they are an almost essential part of any complex project: a hospital, a military installation, a computer farm, etc.).
WHERE TO USE THEM?
A single-phase generator set is normally used in LV installations, where intensive use is not required. This makes possible to have electrical power in locations where the grid is not available so that small power tools (or similar uses) can be used.
It can also work as a backup power supply system for a few hours, as long as it is for domestic use or small business usually powered by a robust electrical network. This will allow the installation to continue working in the event of a short breakdown or disconnection.
However, three-phase generator sets are ideal when it comes to supply several big single-phase and three phase loads as they are generally more reliable, robust and efficient due to their technology and the great knowledge we have of them.
Three-phase gensets are used every day in the most hostile environments and conditions, from working as backup power for computer systems to military or naval applications. This type of generators feed critical and emergency loads in the five continents, all over the world.
However, the current trend is to replace a single-phase genset with a three-phase one plus an inverter electronic converter that transforms the three-phase electrical power source into a single-phase one. It is possible that in the medium term, single-phase generators will end up disappearing, being replaced by this equipment, which is cheaper and more reliable despite being somewhat more complex as it adds electronic stages to the device.
In short, each generator set, whether single-phase or three-phase, has its field of application, which depend on the technological capabilities of each system and the advantages and disadvantages of each technology.
Nowadays, single-phase technologies are associated with small domestic power rates, but things are changing and the use of three-phase systems even for domestic use is growing at an international level.
In any case, single-phase is an attractive, economical, and easy-to-use system for domestic use or certain applications.
We can help you
When installing a generator set it is essential to know its application, the place where the equipment will operate, the environmental conditions, its limitations of use, the current regulations… These are just some of the reasons why it is so necessary to have the support from professionals who offer you the best energy solution.
At Genesal Energy we have more than 27 years of experience in the sector. Our deep knowledge of the market needs, and our investment in R+D+I allow us to design, manufacture and maintain reliable, efficient and safe generator sets. This is our main strength, and our work both at a national level and worldwide endorses us. Our technicians and engineers analyze, study and seek the best solution, always adapted to the real needs of each case.
And although we design, manufacture and install generator sets, our work does not end there. We also participate very actively in the maintenance of the generator set as we have a large stock of approved spare parts ready to assist our generators at any time so that the equipment is ready to start in any situation.
Genesal Energy is always ready to provide the most efficient solution. A bespoke generator set adapted to each client.You can find us at email@example.com.