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June 22, 1998
Paul Gipe

Lowering the BWC 850 with a Griphoist


June 22, 1998

by Paul Gipe

My thanks to everyone on the awea-wind-home list for your help raising the BWC 850. Sunday 21 June, Nancy and I lowered the turbine with the griphoist. (Because we will be traveling for the next five months I didn't want the turbine to run unattended and thought it best to lower the turbine and store it in a safe place.)

To date we've raised and lowered the tower twice. Each time we are becoming more proficient. The lowering went smoothly and as I develop a sense of how the tower behaves I adjust the guy cables less frequently.

 

Bugs and Dust

Though the turbine only operated for two weeks it was amazing to see the number of bugs splattered on the leading edge as well as a thin but dense layer of dust along the leading edge from the hub to the tip. Tehachapi is in a semi-arid to arid environment and the winds are strong (the site abuts on of the largest wind farms in the world). Though there are no "dirt" roads nearby (our road is a "track") there must be a lot of dust in the air that we residents can't see.

 

Tower Height

I was concerned that the 64-foot tower wouldn't clear nearby obstructions since I've been such a stickler about tower height in my books. But I didn't want to work with a taller tower either until I gained some experience with the NRG tower system.

After installing it I can conclude that the 64-foot height was sufficient and gives us about 20-30 feet clearance above some nearby willows (the only trees on this windswept grassland). It also gave us sufficient clearance from the hilltops overlooking the site.

 

Turbine Thrust

One day on our way to Los Angeles we visited the site to check on the turbine. There's often a reason to check things and sure enough one of the wire rope clips had slipped and the tower was no longer vertical. A stiff wind was blowing and the tower was pulling against the top cable that had slipped.

In the NRG system, the guy cables are tightened by hand. Let's just say that I wouldn't want to try this with a BWC 1500 in a strong wind. Nor would you ever want to make the mistake of not using the friction over the surface of the guy anchor to help hold the cable after loosening the wire rope clips. While it was never in danger of getting away from me, I was immediately conscious that I had to really lean into (or away from the tower in this case) tensioning the cable and not make any mistakes. As it was the thrust on the turbine wind was too great for me to get the tower top back to vertical. I got it to where I was comfortable with it and then we left. The tower survived and we lowered it a few days later.

 


Note: When this was written I was not aware of a method for tensioning the guy cables without loosening all cable grips at one time. My advice today is never loosen all the grips on a windward guy cable unless there is no wind and you know exactly what you're doing.


Operating the Griphoist

Lowering the tower was uneventful. Because we've become more confident with the tower system, I made far fewer guy cable adjustments than I did when we raised the tower the first time. The down side is that there were fewer breaks from operating the griphoist lever. The cable moves only a few inches each stroke of the lever. So, to lower the tower you need to operate the lever quite a few times. As an office type, I am not use to all that activity and today I am sore. Other than that everything worked as planned.


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