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There is a growing need for high voltage direct current (HVDC) power distribution systems in aircraft which provide low-loss distribution with low weight. Challenges associated with HVDC distribution systems include improving reliability and reducing the size and weight of key components such as electric load control units (ELCUs), or remote power controllers (RPCs) for load control and feeder protection, and primary bus switching contactors. The traditional electromechanical current interrupting devices suffer from poor reliability due to arcs generated during repeated closing and opening operations, and are generally slow in isolating a fault with potentially high let-through energy, which directly impacts system safety.

Traditionally aerospace applications have used 400hz 115/200VAC electrical power. While new commercial aircraft are now using variable frequency power – to eliminate the need for a hydromechanical constant speed drive or electronic frequency conversion, there are still may applications for 400Hz power – such as auxiliary power unit generators. For these applications either a 2 pole or 4-pole configuration generator could meet the requirement. For a given output frequency, such as 400 Hz, a 2 pole generator will spin twice as fast as a 4 pole generator does. Based on the generalized machine principles, it might be expected that a 4 pole generator be more or less 2 times as heavy as its 2 pole counterpart. During our trade studies it has been found that this is not necessarily the case. Many other factors like cooling schemes, rotor critical speed and mechanical stress considerations play an important role and can drive the design.