A friend of mine was working on something and that something was originally set up for 400Hz, which should immediately tell you what it was for.
Someone decided to put 60Hz line on the incoming power and turn the lights on. All of those 400Hz units popped and made a helluva smell.
One of the engineers, a gentleman from somewhere other than the USA, wanted to know what happened. Friend said that one of the engineers put 60 on a 400 input.
Gentleman goes "Ha ha. Eddy current, very bad."
Without cheating by web search, 400Hz is used in aerospace and railway applications, right?
Mostly Military because 400Hz allows you to use smaller cores in transformers and things, but it shows up in other weight-critical applications.
Huh, I thought it was somewhat common in railway too. Pretty sure we made some parts for that application but it's been a while, I might be misremebering. I'll ask my co-worker, could be for auxiliary equipment.
Yeah, higher frequency, smaller cores. We know the drill from SMPS. It felt quite weird when the wall warts' weights changed from a pound to three ounces at higher output wattage.