High Voltage Wind Gen Brake Sw. [RE-wrenches]

[Matt Tritt]

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Hi Travis,

You're correct, of course, that the Bergey 10 does not self-destruct 
when free-wheeling. It does, however, make a hell of noise when so doing 
in high winds. Jakes definitely do require attention, but they are sure 
not the only variable-pitch machines on the market. Jake's pitch 
mechanism requires attention because of the design, others might not; 
funny what 80 years can do in influencing the way things are made. ;-)

Not every small turbine relies on a dump load for protection; The 
Kestrels, the Iskra, Eoltec, and now the Skystream do not. Kestrel, 
Iskra and Eoltec all use variable-pitch of a completely different design 
than does Jacobs, the Skystream uses dynamic speed limiting in a loop 
through the inverter and alternator (and has no mechanical backup 
protection). Iskra also has dynamic braking but does not go through an 
inverter to achieve it. (This is in addition to centrifugal controls). 
As you know, the Skystream has the inverter placed within the nacelle of 
the turbine, so the electrical "loop" is very short.

I disagree that mechanical self protection should be any less reliable 
than any other method; it's all in the way the system is designed and 
executed, not in the basic philosophy of mechanics (IMHO). Mechanical 
governors have been very successfully used for well over a hundred years 
on all kinds of devices, and even Jakes will take an eternity of hard 
weather if they are properly maintained. I personally prefer a good 
variable-pitch system over the other options.

Cheers,

Matt



Travis Creswell wrote:

>Hi Matt,
>
>A Bergey will not run away and go ka-blooey in the absence of a load.  It
>will be noticeably loader but it is designed to be able to run unloaded.  I
>think it's the only small turbine in the 1kW-10kW range that can do that.  I
>know because of inverter issues we've had several 10kW's run unloaded for
>months with no damage.
>
>I have little experience with variable pitch machines but it would only make
>sense that a turbine that doesn't rely on a mechanical system to protect
>itself would be more reliable.  Many a Jacobs dies an early life because
>maintenance is ignored.  I got a call recently about one whose complete
>rotor assembly had fallen to the ground!
>
>Of course a turbine that requires a dump load (every small turbine but
>Bergey) for over speed protection could go ka-blooey should a fuse open or
>any wires come loose.
>
>Best,
>Travis Creswell
>Ozark Energy Services
>
>
>-----Original Message-----
>From: Matt Tritt [mailto:solarone at charter.net] 
>
>
>
>Jeremy,
>
>As far as I know, there is no actual requirement for a brake switch. 
>However, one consequence of simply disconnecting any wind turbine with a 
>fixed-pitch rotor from a load , (like SWWP, Bergey, etc.) will be that 
>the machine can "run away", and sometimes even go ka-blooey. The only 
>thing that will cause these machines to yaw out of the wind is when the 
>wind speed is great enough for the yaw to commence, and not the actual 
>RPM of the machine. When the wind is below that threshold speed, there 
>is nothing to prevent the rotor from over-speeding except a connection 
>to some kind of load or short-circuit, but a direct short of the 
>windings will often not be able to stop the rotor in a high enough wind. 
>Machines that control their rotor speed by variable-pitch of the rotor 
>blades through mechanical means (centrifugal force) will only reach a 
>certain (non-destructive) speed, usually slightly higher than the rated 
>output of the alternator, regardless of the presence of a load. Because 
>of this, fusing the output of a variable-pitch turbine does not expose 
>the machine to potentially destructive forces should the fuse blow.
>
>A complicated answer to a simple question! ;-)
>
>Matt T
>
>
>
>
>  
>


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