Coiled electric wires have been developed for use in electromagnets that operate at high temperatures. Examples of such electromagnets could include the actuators in magnetic bearings in advanced gas turbines.
The primary distinction between these wires and previously commercially available high-temperature wires lies in the electrical insulation, which is intended to withstand operating temperatures in the range from 800 to 1,300 °F (≈430 to ≈700 °C). The com- mercially available wires feature tubular sheaths filled with insulating materials; while such insulation is effective, it is too bulky for electric-coil applications in which there are stringent limitations on the sizes of the coils and/or on the spacing between turns. The present wires feature improved insulation that is thinner, making it possible to fabricate coils that are smaller and more closely wound.
The starting wire material for a coil of this type can be either a nickel-clad, ceramic- insulated copper wire or a bare silver wire. The starting wire is either primarily wrapped with S-glass as an insulating material or else covered with another insulating material wrapped in Sglass prior to the winding process. A ceramic binding agent is applied as a slurry during the winding process to provide further insulating capability. The turns are pre-bent during winding to prevent damage to the insulation. The coil is then heated to convert the binder into ceramic.
In a test, coils of this type were mounted in a 12-pole magnetic bearing (see figure) and found to perform successfully at temperatures up to 1,200 °F (≈650 °C). Future development efforts will address the problems of increasing the thermal conductivity of the electrical-insulation materials to increase conduction of heat out of the coils, reducing the volumes of the coils, and fabrication of coils with various shapes (including square and other noncircular cross sections).
This work was done by Alan Palazzolo of Texas A&M University for Glenn Research Center.
Inquiries concerning rights for the commercial use of this invention should be addressed to
NASA Glenn Research Center
Commercial Technology Office
Attn: Steve Fedor
Mail Stop 4–8
21000 Brookpark Road
Refer to LEW-17164.