slip rings [RE-wrenches]

[hugh piggott]

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At 8:45 am +1200 12/7/01, Carl Emerson wrote:
>
>
>I would like to know if the AWP sites on the falklands have had cable
>snapping problems.

There are no AWP machines in operation in the Falklands, yet.  Cables 
should have ample slack, so 'snapping' is not a danger.

>We tend to use 200 volt three phase machines here with quite light cable,
>usually 3 x 2.5mm2 again to cut costs on long cable runs. With such light
>cable the machine would certainly need some cable support to prevent
>damage.

Cable support at the ends is essential.  However, lighter 
high-voltage cabling makes it easier to design for twist because it 
can accommodate a lot more twists in a short length of cable.  My own 
AWP36 is a high voltage one and the cable twist is all contained in 
about 6 feet of topmast.  I have not counted the turns, but it has 
not been taken down for about two years.  The wire does not look any 
shorter or particularly twisted up.  I would expect about ten 
cumulative twist revolutions per year.

>
>Regarding Michael's comment on lost watts, the high tensile steel tends to
>act as a spring and will flick the machine back a turn when it reaches the
>limit. The proportion of time that this will happen is minor as the
>rotation tends to average out most of the time.

That very springiness will bias the yaw furling mechanism, so it 
furls more (or less) than the optimum.  If it's enough to untwist it, 
then it's enough to cause problems with over-speed or under 
production.
-- 
Hugh

http://www.ScoraigWind.co.uk

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