alt.energy.renewable

"Rich Grise" wrote in message
news: @ ...
> On Mon, 03 Sep 2007 18:22:38 +0000, philkryder wrote:
>> On Sep 3, 10:35 am, "Duane C. Johnson" wrote:
>>> Rich Grise wrote:
>>>
>>> > What does "unwinding" mean, exactly,
>>> > in this context?
>>>
>>> Windings breaking apart due to
>>> centrifugal force at high RPMs.
>>
>> interesting - are they wound on a different axis?
>> Why are they immune to "centrifugal force"
>
> I'd be guessing here. I'm with you on the "howcome they
> can't spin at higher RPM"? question, and I'm thinking
> that if you belted a generator high enough to charge at
> idle, then at cruising speed the generator would fly apart,
> or there's some other electrical issue that makes it
> unfeasible, which is the other possible meaning of "unwinding"
> in that post. To unwind a coil, you'd have to spin it on its
> own axis, which isn't the way any of the coils in a generator
> OR alternator are spinning, hence my confusion. And I've heard
> of integrators "winding up" in PID control loops, so that's
> confusor #3 or so. ;-)
>

Well, the term 'unwinding' isn't *completely* accurate. The coils of a DC
generator are laid in slots that run parallel to the shaft. At high speeds,
the wedges placed in the slots above the coil wire can fail and the
centrifugal force will fling the copper wires out of the slot. Where they
quickly hit the non-rotating part and get ripped to shreds. The result when
you look at it 'after the fact' is that many of the coils are ripped out of
the slots and chewed up badly. It *looks* as if it came 'unwound'

daestrom
(been there, seen that, rewound that :-)