High power density technologies for large generators and motors for marine applications with focus on electrical insulation challenges
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High power density generators and motors are envisaged in modern all-electric ships where electrical power for both propulsion and service loads is provided through a common electrical platform known as an integrated power system. Three recent high-power density technologies for generators and motors proposed for marine applications are reviewed, and the author focuses on their electrical insulation challenges. These technologies are high-frequency (high-speed) generators (200400 Hz), superconducting generators, and novel insulation materials and systems. For high-speed generators, high loss in magnetic materials may shorten its insulation life. Thus, these generators should be designed to be cooled by water instead of air. For superconducting generators, the most significant concern is the integrity of the insulation system over the large thermal excursion whenever the system is cycled between room temperature and operating temperature. In novel insulation materials and systems section: (i) using mica paper tapes containing boron nitride filler in the binding resin of the glass backing insulation, developed by Toshiba and Von Roll, resulted in a 15% increase in the MVA of generators for the same slot dimensions and operating temperatures, (ii) GE developed an enhanced polyethylene glycol terephthalate-mica tape having superior voltage-endurance characteristics, (iii) Isovolta has introduced a mica paper tape using a flat glass fibre backing material, called Powerfab, rather than the more common woven structure, leading to a 15% reduced mica tape, and (iv) adding novel nanocomposites as fillers to ground wall insulation, introduced by Siemens, is a promising technique towards more high power density designs. Furthermore, accelerated aging of insulation systems especially those in electrical rotating machines exposed to voltage pluses with high slew rates up to hundreds of kV/mu s and high-repetition rates ranging from hundreds of kHz to MHz is discussed. These voltage pulses are generated by wide bandgap-based converters envisaged in the medium voltage DC architecture for future U.S. naval ships.