was a special conductor guide used in generator technology. The BBC engineer Ludwig Roebel was awarded a patent for these interwoven or drilled copper strips on 19th March 1912. The special feature of this conductor is the fact that every individual conductor within a specified length range is present in every layer of all the individual conductors. The individual conductors are insulated from one another, and therefore reduce the considerable eddy currents that cause losses. In induction furnace technology, advantage has been taken of this knowledge in the design and construction of air-cooled inductors of up to approx. 500 kW per inductor coil. This form of conductor cannot be used for crucible induction furnaces. Due to the dimensions of the channel, the iron core, the diameter of the coil, the number of windings, the length and the cooling air ducts necessary for the construction of inductors, the use of air-cooled inductors is necessarily restricted. From the physical and energy-technology point of view, their use can be highly recommended, since the losses are lower than with normal conductors formed in parallel and water-cooled hollow copper conductors. For comparison, the copper loss figures for the 3 most common conductor types at 500 kW nominal output are:
water-cooled hollow copper conductors approx. 90 kW
12-way flat individual conductors, undrilled approx. 75 kW
12-way flat individual conductors, drilled approx. 64 kW
However, since it is comparatively expensive to provide the relatively clean cool- ing air required, the water-cooled inductor has become the type more commonly used in practice. Air-cooled inductors are constructed with an output of up to approx. 150 kW and generally have 1-way flat conductors, or from approx. 120 kW also 2-way flat undrilled conductors.
