Three-phase capacitor formed by two cylinders where each of the cylinders comprises an outer part which corresponds to a capacitor (1) and (2) while the inner part of each cylinder corresponds to a capacitor (3) and (3') and which are connected in delta with phases (A), (B) and (C), where each capacitor is separated from the adjacent of each cylinder by means of an insulating material which allows the movement of the inner part with respect to the outer one of each cylinder in case of overpressure, which causes the breakage of the connections made in a particular manner, the breakage of the conductive coating layer (7) which connects armatures (3.1) and (1.2); the breakage of the conductive coating layer (8) which connected armatures (2.2) and (3'.2), the breakage of the connection of connection cable (6) with phase (C), serving as an effective means of protection against internal overpressures.