A more accurate approach to machine induction motor rotors to become synchronous

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "RMC by way of Terry Fritz <teslalist-at-qwest-dot-net>" <RMC-at-richardcraven.plus-dot-com>

Various rules-of-thumb have been written, regarding the amount of rotor
material to be machined off to make flats to enable synchronous operation.
This has usually been in the form of "remove a 1 inch depth of material" or
" make the flats 2 inches across" etc. etc.

These rules don't take into account the rotor size in the first place,
whereas a 1939 text by Veinott, published by McGraw-Hill, discusses the
method a little more precisely.

Chapter 15, titled "Synchronous Motors", describes the process of
calculating the size of the flats thus:

"... it is recommended that the easiest way [to make a non-synchronous motor
become synchronous] will probably be to mill flats on the rotor surface,
equally spaced, there being as many flats as there are poles. The total area
of these flats should be approximately 40 per cent of the total cylindrical
area of the rotor before the flats are milled ... The motor should be able
to carry roughly about one-third its nameplate rating".

So, if people want to get their rotors to lock up *and* avoid removing more
material than necessary (torque suffers as a result), this is the approach
to use rather than just assuming a set depth independent of rotor size.


Cheers

RMC, England