Differences between three-phase, two-phase and single-phase system!

We know that the entire system of generation, transmission and distribution of electric energy in Brazil is immense and without these steps it would not be possible to reach us with electricity. Thanks to this whole system, in industrial, building and residential electrical installations, concessionaires can supply a three-phase, two-phase or single-phase network, but after all, what is the difference between them and where should each one be used?

With this in mind, the World of Electrical will explain the difference between single-phase, two-phase and three-phase systems and explain where each type of system is generally used, in addition to addressing the respective advantages of three-phase systems.

It is important to highlight that the values ​​of electrical power, phase and line voltage, in addition to their respective values ​​change according to the concessionaire, can also change these parameters depending on the location, such as within industries, where the need for voltage levels special.

Characteristics of three-phase systems.

Single-phase system

In a single-phase system, the network has two electrical conductors, one being a phase conductor and a neutral conductor, so that the electrical voltage of this system in electrical installations is 127V or 220V, which may vary according to the electric utility.

In electrical installations, the single-phase network is distributed through general-purpose outlets and is used to supply everyday equipment, such as notebooks, computers, cell phone chargers, lighting, electric shower and televisions. Generally, single-phase electrical installations consume an average of a maximum of 8KW (8000W).

Biphasic system

The two-phase system is characterized by the existence of three electrical conductors being delivered to the establishment, two-phase conductors and one neutral conductor, so that the phase and line voltage can vary between 127 / 220V or 220 / 380V, depending on the concessionaire power. Generally, electrical installations with a two-phase network consume on average a maximum of 25KW (25000 W).

Three-phase system

In the three-phase system, the electrical network has four conductors, three-phase conductors (R, S, T) and a neutral conductor. As in the biphasic system, the voltages of phase and line voltages can vary between 127 / 220V or 220 / 380V and in some situations the three-phase systems provide on average powers of up to 75KW (75000W), widely used in industry and commerce.

The three-phase transformer is powered by three phases, that is, they have three conductors entering the upper part of the transformer, but as we saw earlier, the supply is made to four conductors. With this we can observe that the neutral appears in the transformed, at the transformer input the closure is in a triangle and the closure at the transformer output is in star.

The electrical system is characterized by three single-phase waves that work together, with the phases lagging by 120 degrees. So the voltage is always very close to the maximum available voltage, due to this 120 degree displacement.

Three-phase system – 120 degree lagged sine waves.

Three-phase systems – Advantages

The distribution of electricity in most parts of the world is done by three-phase systems, this is because the three-phase system in fact offers several advantages when compared to the single-phase system, as we can see below:

  • The three-phase system requires a smaller amount of copper or aluminum to deliver the same power that a single-phase system would deliver, that is, conductors of smaller cross-section.
  • Three-phase generators are smaller and lighter than their single-phase equivalents because they use their windings more efficiently.
  • The three-phase motors are smaller than the equivalent single-phase motors, ie the same electrical power.
  • Due to the rotating field produced by the three phases, the three-phase electric motors start without the need for special devices, while the single-phase motors require an extra start winding.
  • Three-phase motors produce a constant torque and therefore are less subject to vibrations, which is not possible with single-phase motors;
  • In comparison to single-phase rectifiers, three-phase rectifiers have less ripples in the rectified voltage, that is, the ripple voltage is less (ripple).
  • The total power in a three-phase system is never zero, because in the single-phase system the electrical power is always canceled when the electric voltage or electric current passes through zero.
  • With the three-phase system it is the most efficient way to distribute electricity over long distances and allows large industrial equipment to operate more efficiently.

The following video presents the situations in which the use of a three-phase system is permitted in residential installations.