The stator only requires the use of back iron acting primarily as a shield to keep magnetic flux inside the machine. This will reduce the overall hull length by up to three times the length savings in the drivetrain, depending on hull balance and overall trimming of the mass of the boat. More Winding Slots Removing iron teeth dispenses with the need for winding slots. That yields several advantages. Less iron equates to less synchronous and subtransient reactance as well, enhancing a machine's transient stability.
Power density improves after the iron comes out since more space can be set aside for windings.
The smaller machine, approximately 90 x 65 inches full scale, owes its svelte figure to iron tooth loss and higher flux density. Probably not as noiseless as a homopolar machine with its constant current and magnetic field that remains uniform throughout the air gap. It is possible, however, that ac machines could make use of the so-called quiet technology that has been developed for permanent magnet motors, Gamble said. And air core machines could use helically wound, monolithic armatures with their fewer parts and bonded components to reduce noise further, he said. As for speed control, superconducting ac machines could be driven by pulse-width modulated converters using the latest insulated gate bipolar transistor, or IGBT, technology, just like ordinary motors, Gamble said.