Abstract: A natural commutation static frequency converter including a polyphase cycloconverter and its control circuit, a switching device enabling breaking of inputs of two Graetz bridges of at least one of monophase cycloconverters, as well as breaking of outputs of the bridges which are not connected to neutral point. The switching device results in insertion of a self-inductance between opened outputs of the Graetz bridges, and replacement of the control circuit of cycloconverter with a natural commutation rectifier-inverter control circuit, so as to form at least one natural commutation rectifier-inverter. The switching device further enables replacement of the outputs of the polyphase cycloconverter with the outputs of at least one rectifier-inverter so formed. The converter may be used to supply a synchronous motor.

Abstract: A device for transferring helium between rotating and non-rotating members includes first and second transfer reeds and a cylindrical sleeve. The cylindrical sleeve is provided between the first and second reeds and extends substantially throughout the region of axial overlap of the reeds. One of the reeds rotates with the rotating member while the other reed is fixed. Third and fourth coaxial transfer reeds may be provided for the transfer of gaseous helium. The third and fourth reeds concentrically surround the first and second reeds with one of the reeds rotating and the other reed being fixed. Cylindrical sleeve members are provided between adjacent reeds with the sleeve members all rotating with the rotating member. The sleeve members are connected to one another at opposite end of the intermediate sleeve member. Guide means may be provided to cancel a component of rotation of the gaseous helium. A bayonet fixing device releasably attaches the cylindrical sleeve to the rotating member.