400 Hz

Chuck Guzis cclist at sydex.com
Wed May 5 10:29:45 CDT 2021

On 5/5/21 8:07 AM, Grant Taylor via cctalk wrote:
> I have found the Motor Generator thread to be fascinating and
> enlightening.  But it has made many a reference to the 400 Hz or other
> frequency much higher than mains line frequency.  Despite the comments
> about the frequency, I'm still confused as to why the higher than mains
> frequency was used.

Iron and filtering.  400Hz means far less iron needed in transformers
and variacs (CDC used a three-phase variac at the CPU cabinet for
adjustment of voltage).  Compare the sizes and it's obvious.

Filtering the ripple out of a 2400 Hz 92% DC rectified supply is
comparatively simple.  A 360Hz supply, less so.

In my salad days, I worked at a steel mill where a fair amount of
equipment ran from 25 Hz voltage.   The transformers were huge in
comparison to their 60 Hz cousins.


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