Metadyne

A metadyne is a direct current electrical machine with two pairs of brushes. It can be used as an amplifier or rotary transformer. It is similar to a third brush dynamo but has additional regulator or "variator" windings. It is also similar to an amplidyne except that the latter has a compensating winding which fully counteracts the effect of the flux produced by the load current. The technical description is "a cross-field direct current machine designed to utilize armature reaction". A metadyne can convert a constant-voltage input into a constant-current, variable-voltage output.

The word metadyne is derived from the Greek words for conversion of power. While the name is believed to have been coined by Joseph Maximus Pestarini in a paper which he submitted to the Montefiore International Contest at Liège, Belgium in 1928, the type of machine which it described had been known since the 1880s. The first known British patent for a direct-current, cross-field generator was obtained by A. I. Gravier of Paris in 1882, and two further patents were obtained by E. Rosenberg in 1904 and 1907. Rosenberg later became the chief electrical engineer for Metropolitan-Vickers, and his machine produced a cross field by applying a short-circuit to an additional set of brushes. M. Osnos looked at the practical arrangements for several such machines in 1907, and in the same year, Felton and Guilleaume obtained a British patent, number 26,607, which described auxiliary windings, armature windings and multiple commutators, although all in fairly general terms. He also indicated that they could be used to transform a constant voltage into a constant current. Other patents were obtained prior to 1910 by Mather & Platt, Brown Boverei and Bruce Peebles.

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