400Hz Frequency Converters:
The need for a 400Hz frequency converter is based on the power used by aircraft. This means power is needed on the ground, to keep from using the engines on the ground. The 400Hz power was developed by the Edison Company for aircraft requirements. From 1945 - 1970 the only way to get 400Hz power was from a motor generator system. The maximum speed of a 400Hz induction motor is 24,000 RPM, about seven times faster than is possible with a 60Hz motor. This higher speed and the use of higher quality wire makes it possible to produce 400Hz motors with 10 times the power for the same weight and footprint. Today there are both Static (Solid-State) and Rotary (M-G) solutions for 400Hz requirements.
Who uses 400Hz electrical systems:
400Hz is a type of frequency within Alternating Current (AC) electrical power, which has become the standard for weapon systems, aerospace, and aircraft industries across the world. It has become the standard of the aircraft and aerospace industry because of its lightweight, reliability, and high power capability. In an airplane, the 400Hz power created by the alternators on each engine power the overhead lights, air conditioning, etc. Almost everything on an aircraft that is utilizing Alternating Current (AC) is designed for 400Hz.
With all this said, it is important for Airports, Hangars, and ships that carry aircraft to have access to a 400Hz frequency converter as this is not a standard power. What makes sense for ships that carry aircraft, like an aircraft carrier is that weapons systems also require the same 400Hz power and as such will need a 400Hz frequency converter or primary power. As an example, a land based airport that has 50Hz or 60Hz absolutely need a 400Hz rotary or static converter. This is the same for ships as their typical power is 440V at another frequency, so in this case, they need the converter to change voltage and frequency.