Corrente continua e alternata, monofase e trifase

When discussing electrical systems, we often hear terms like "single-phase" or "three-phase" current. But what exactly are they? Alternating current, usually referred to as AC, is a type of current in which voltage and current fluctuate constantly over time. While in direct current (DC), the flow of electrons moves consistently in the same direction without ever changing direction, with constant voltage and current over time, things are very different with alternating current. Well, a single-phase system is simply the simplest of the systems used for the distribution and use of alternating current. A three-phase system is a system composed of three circuits used to produce, transmit, distribute, and use alternating current. So, let's understand how alternating current is structured and see how they differ and when to choose one over the other. In alternating currents, the flow of electrons continuously reverses direction over time, causing true oscillations. These oscillations follow a sinusoidal pattern, with a frequency typically of 50 or 60 Hz. Current intensity and voltage also fluctuate over time, between a minimum and a maximum value, always with a frequency of 50 or 60 Hz. These characteristics of alternating current derive directly from the structure and operating principle of the generators that produce it. In home electrical systems, single-phase alternating current circulates with a voltage that oscillates between +230 V and -230 V, at a frequency of 50 Hz. This is the national standard, but many others exist. In any case, the vast majority of our appliances operate on direct current, which is why they are equipped with special transformers or AC-DC adapters. This is because alternating current offers significant advantages in terms of its generation and transmission over long distances. An alternator is much simpler and more efficient than a dynamo, while high-voltage AC power transmission works better than DC. Less energy is dissipated along the way and is easier to convert from one voltage to another, which is crucial in transmission and distribution. Alternating current is produced using the principle of electromagnetic induction, exploiting time-varying electric and magnetic fields. In turn, alternating current flowing through a circuit can also generate electric and magnetic fields in the surrounding space. These fields will also vary over time and have the same frequency as the mains voltage (50 Hz). In the case of direct current, the direction of electron flow, intensity, and voltage remain constant, generating static fields. In the case of alternating current, the direction, intensity, and voltage fluctuate over time, so the fields generated will also have variable direction, direction, and intensity over time. Let's now look at the difference between single-phase and three-phase alternating current. A single-phase system essentially consists of two wires: one with zero potential, called the neutral, and one with a variable potential. In Italy, the phase voltage varies with a sinusoidal pattern and constant frequency. The voltage between phase and neutral is 230 volts. The voltage is therefore not constant but oscillates between a minimum and a maximum, with moments between them when the value is actually zero. In single-phase systems, the function of the neutral is to allow the phase current to return. The current flowing in the neutral is equal to the current flowing in the phase. The structure of a three-phase system is much more complex. First of all, today all alternating current electricity is generated as three-phase current, and it is in this form that it is transported over long distances, distributed, and used, for example, in the industrial sector. I close with a quote from Guglielmo Marconi: "Electricity has given us light to see, sound to hear, and communication to connect." We thank Dr. Luigi Rescigno for his scientific support. Summary 0:00:00 - Introduction 0:01:09 - Single-phase and three-phase alternating electric current 0:07:28 - Conclusions ____________ For quote requests, please write to: [email protected]