SINGLE-PHASE AND THREE-PHASE GENSET

In previous articles we have seen different characteristics of generators, in today’s article we will try to explain the differences between a single-phase and three-phase generator, as well as the advantages and disadvantages of each of these options.

Once seen the advantages and disadvantages that give us these two options. We will see why we should decant depending on the use that we are going to give the generator.

Let’s start then.

SINGLE-PHASE AND THREE-PHASE SYSTEMS

Let us start with a little theory about the basic operation on single-phase and three-phase systems, before affecting the advantages and disadvantages of both systems.

Single-Phase Systems

A single-phase system is a system of production, distribution and consumption of electrical energy formed by a single alternating current or phase and therefore all the voltage varies in the same way.

The single-phase distribution of electricity is usually used when the loads are mainly lighting and heating, and for small electric motors. A single-phase supply connected to an AC electric motor will not produce a rotating magnetic field, so single-phase motors need additional circuits for startup and are unusual for power ratings above 10 kW.

The voltage and frequency of this current depends on the country or region, being 230 and 115 Volts the most common values for the voltage and 50 or 60 Hertz for the frequency.

Three-Phase Systems

A three-phase system is a system of production, distribution and consumption of electrical energy formed by three alternating single-phase currents of equal frequency and amplitude, which have a phase difference between them of 120 ° electrical, and are given in a determined order. Each of the single-phase currents forming the system is designated by the name of phase.

Voltage of the phases of a balanced three-phase system. Between each phase there is a phase shift of 120 °.

A three-phase system of voltages is said to be balanced when its currents are the same and symmetrically out of phase.

When any of the above conditions are not fulfilled (different currents or different gaps between them), the voltage system is unbalanced or more commonly called an unbalanced system. It receives the name of system of unbalanced loads, the set of different impedances that cause that the receiver circulate currents of different amplitudes or with differences of phase between them different to 120 °, although the tensions of the system or of the line are balanced or balanced.

There are two main types of three-phase connection; In triangle and star. Let’s take a closer look at these connection systems.

Star connection (generator or load)

If the generator or load phases are connected together by connecting the beginning of each phase to the end of the next one, the triangle configuration is obtained.

In a star configuration generator, the phase currents coincide with the corresponding line currents.

Triangle connection (generator or load)

If the generator or load phases are connected together by connecting the beginning of each phase to the end of the next one, the triangle configuration is obtained.

The phase and line voltages in the triangle configuration coincide, which is evident because each phase branch connects two lines to each other.

Advantages and disadvantages.

As discussed in the operation of three-phase and single-phase systems, discarding the mechanical part, the main difference of both systems is the number of phases.

  • One phase for single-phase generators.
  • Three phases for three-phase generators.

This implies certain advantages and disadvantages.

In a single-phase generator set having a single phase, the total power of the group applies to this single phase. This implies that a single equipment or machine could consume up to 100% of the total power of the generating set. In addition to having a single phase it is easy to control the load the generator is supporting to avoid overloading the equipment, thus avoiding possible problems or breakdowns.

In a three-phase generator set with three phases, the total power of the group is divided into three phases. This implies that a single equipment or machine could consume up to 1/3 of the total power of the generating set. If any connected equipment exceeds 1/3 of the power would cause serious problems to the generator. Therefore, it is important to carefully control the load on each phase, to avoid problems and breakdowns.

Taking into account the load to be borne by the single-phase or three-phase generator set is important to adjust the power of the generator when making a purchase, to avoid paying more power than we will need. It must be taken into account that a generator is more profitable in terms of efficiency / consumption, when it is working between 75% and 80% of its maximum power.

In the three-phase generators a new factor, the balance of charge of the phases, is added. This factor is important for the above reasons, that the 3 phases have a very similar volume of load to be able to reduce to the maximum the power of the group and to try that it always works to skim the maximum yield.

The three-phase system has an advantage over the single-phase system, as far as electrical installation is concerned, given that having three lower power phases as we saw above, a smaller section cable is needed to transport energy, lower power transformers, etc. ., All this has an economic impact on the reduction of the costs of the electrical installation.

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Focusing a little on the economic issue, as a rule, although there may be exceptions, a single-phase generator is usually a little more expensive than a three-phase of the same power.

Mainly because of the cost increase of the alternator. Given that to obtain the same power in the generator, it is necessary that the single-phase alternator is of greater power than the three-phase, having a development of power much smaller than its three-phase version, thus enhancing the generator set.

In addition to factors that have already been discussed previously, the components, especially safety are less powerful, and are more economical. Although these components have a smaller impact on the final price of the generator.

If we focus on maintenance issues, they are exactly the same, regardless of whether it is a three-phase or single-phase generator.

As far as failures are concerned, none of them has a higher failure rate, although as indicated above it is possible that some components may be cheaper to replace in a three-phase than a single-phase model.

Conclusions

Single-phase generators are mainly recommended for electrical installations with power loads of less than 10 kW, and as long as the connected equipment or machines are single-phase.

These single-phase generators are mainly used at the individual level, in country houses, or small installations.

For power above 10 kW or when it is desired to connect three-phase equipment it is advisable to purchase a three-phase generator.

It must be taken into account that the majority of machines and equipment of great power that they are offered in the current market, work with motors three-phase.

Three-phase generators are recommended in industry and facilities with high energy demands.

As a last observation we will indicate that the current three-phase generators usually already have a single-phase outlet, which can be very useful for certain occasions.

Looking for a three-phase or single-phase generator?

In Tecnics Groups Electrogenos S.L., we have a wide range of brands and powers, which we can adapt to three phase or single phase as manufacturers.

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