An electrical substation, transformer substation or transforming electrical substation (abbreviated ST or SET) is a facility intended to establish the voltage levels "Voltage (electricity)") suitable for the transmission and distribution of electrical energy. Its main equipment is the transformer. It is normally divided into sections, usually three main ones (metering, pitch blades and switch), and the others are derivatives. Branch sections normally carry switches of various types to the transformers.

As a general rule, we can speak of "boosting" electrical substations, located in the vicinity of the electrical power generating plants, whose function is to raise the voltage level, up to 132, 220 or even 400 kV, before delivering the energy to the transmission network; and "step-down" electrical substations, which reduce the voltage level to values ​​that usually range between 10 and 66 kV and deliver the energy to the distribution network. Subsequently, the transformation centers reduce the voltage levels to commercial values ​​(low voltage) suitable for domestic and industrial consumption, typically 400 V.

There are two technical reasons that explain why the transportation and distribution of electrical energy is carried out at high voltages, and consequently, why electrical substations are necessary:

Therefore, the higher the voltage value, the lower the intensity must be to transmit the same power and, consequently, the lower the losses due to the Joule effect.

In addition to transformers, electrical substations are equipped with switching elements (switches, disconnectors, etc.) and protection (fuses, automatic switches, etc.) that play a fundamental role in the maintenance and operation processes of distribution and transportation networks.

One of the most common maneuvers carried out in an electrical substation, and at the same time one of the most dangerous, is the opening and closing of switches, because the inductive nature of the circuits rejects the cut in the circulation of electric current that occurs when opening a switch. Even electric arcs can appear, which release a large amount of energy and can be dangerous for people and facilities. Therefore, special personal protective equipment made of dielectric materials that provide sufficient insulation for the operating voltage must be used.