Transformer with a turn ratio variable while in operation which has at least two wires (20,22) wound together on the same core, exactly interleaved and insulated with respect to each other, and on them there is formed a collector free from insulation, on which a contact metal brush (24) slides, that at every moment, during its movement, touches every wire (20,22) of the winding at the most at only one point. The ends of the wires (20,22) are connected to each other, possibly through impedances and the end inductances counteract the internal circulation current due to the turn short-circuit. At least one turn of at least one wire (20,22) of the winding is only partially linked with the total flux of the magnetic core of the transformer. By means of the use of at least another parted flux turn, the balancing of the voltage differences at the ends of the numerous wires is assured anyway, and the arrangement is such that each wire of the collector has the same voltage difference with respect to each of the two contiguous wires.

An electrical device having a commutating surface formed of segments of electrical conductors upon which a contact brush is movable while in electrical engagement therewith. Means are provided to "step" the brush between segments, so that when at rest, the brush contacts no more than one segment, thus reducing short-circuiting currents and overheating.

L'invention concerne une inductance formée à partir d'une ligne dissymétrique. Cette inductance comprend un conducteur-plan (31), de préférence cylindrique, un conducteur linéaire (34) s'étendant le long et à proximité du conducteur-plan (31) et ayant une extrémité court-circuitée avec le conducteur-plan (31). Des moyens de maintien (36) permettent de maintenir le conducteur linéaire (34) dans une position déterminée par rapport au conducteur-plan (31).

Application notamment à la fabrication d'inductances de puissance pour ondes courtes.

A variable transformer comprising an annular core with a winding which at the end surface of the core is provided with a circular contact path to be connected with a current brush mounted on a rotor (7). The current brush consists of a contact roller journalled on a shaft pin (11) which from the rotor (7) is directed obliquely downwardly towards the end sur­face of the core and inwardly towards the axis thereof. The contact roller includes a double-curved contact path (17) for punctiform contact with the contact path (18) of the winding. The reactive pressure provided by said contact urges the contact roller upwardly along the shaft pin (11) which were secured to the rotor (7) is provided with a contact plate (14) that is in heat-­conducting communication with the rotor (7). The con­tact plate (14) includes a plane circular surface (15) against which a correspondingly plane, circular surface (16) of the contact roller about the bore (12) thereof abuts. The contact roller is delimited by a conical surface the generatrix of which extends from the peri­phery of the circular surface (15ʹ) to the outer peri­phery of the contact path (17) of the roller. The rotor (7) is bowl-shaped and its top surface shape corres­ponds to the internal surface of the upper part of a housing for encasing the transformer.

An electrical device having a commutating surface formed of segments of electrical conductors upon which a contact brush is movable while in electrical engagement therewith. Means are provided to "step" the brush between segments, so that when at rest, the brush contacts no more than one segment, thus reducing short-circuiting currents and overheating.

Le conducteur en forme d'hélice (2) constituant l'inductance est un ruban (1) imprimé obtenu par l'utilisation des techniques de circuits imprimés. L'inductance est rendu ajustable à l'aide d'une bague curseur (5) comportant des couronnes à multicontacts (6, 7). Cette bague est entraînée d'une manière équilibrée le long de l'inductance de façon à obtenir son positionnement rapide.

Application en particulier dans les émetteurs de moyenne puissance.