strange defect with Windspot turbine

[Cor van Houtum]

hi guys,

last week we had a major storm in the netherlands , biggest in 25 years
we have installed 4 windspot turbines in the netherlands
Because of the variable pitch system on the windspots we did not put them on brakes or out of the wind,
the storm reached 150 Kmh windspeed.
Our turbines went up to produce the maximum power and did not fail.

BUT one of our customers has put the turbine on brake before the storm
The brake is done by a short circuit swich on the 3 phase of the generator
this is not original implemented in the controller but put as a extra stop button on the installation.

the turbine could not spin up due to this stop circuit

guess what happened
all three blades cames off , as they simply broken on the setting.

it seems that it is better to let it run , then to put it on stop
Could be , could be not,
let me know your ideas.
one thing is for sure that the automatic pitch controll could not work because this is a centrifugal controller and in stand mode does nothing.

kind regards

Cor

[Peter Klaassen]

Hi Cor,
I am in the process of putting up a 3.5 kW windspot and I wondered about doing this if the forecast was for strong winds. I won't be braking the turbine after seeing this result. Thanks for the warning!
I still have to get the tower together so it won't be up for while yet.
Pete

[Rob Beckers]

Cor, are you sure that turbine didn't speed up? Shorting out the alternator to keep a turbine stopped works well on some, not so well on others. There may well be a speed where the wind forces overcome the braking forces of the alternator, and it runs away regardless of the shorted alternator. It would burn up the alternator windows if that happened though, so you can check.

It seems unlikely to me that blades would get damaged by a mere 150 km/h when they are not moving (this is in effect the ultimate case of 'stalled bladed'). I would consider that a design defect. I'll grant you though that the loads are different when the blades are not moving vs. when they are rotating. In the latter case there will be large centrifugal forces loading the blades in tension, so the bending moment generated by the wind could be less of a problem. When the blades are not moving there is just that bending moment. Still, it is crazy that they'd break off at 150 km/h...

-RoB-

[Cor van Houtum]

Today we got the new blades from the windspot
Perfect service , and under warranty

We sent the old ones back , they want to know at the factory what happened
and investigate the blades
keep you posted

Cor

[Steven Fahey]

Hello Cor,
Have you been informed about the blade failure yet?
It piques my curiosity, and mechanical failures are an interest of mine.

I have studied the photo and the first question I must pose is about the bolts: they appear to be bent. Did you observe this when you examined the damaged blade grip yourself? Further along that subject, how much clearance does the bolt have in its hole? Do you believe that these bolts were installed into the grip with this bend or angle originally, or do you believe it is a consequence of the failure? Do the other grips have the same failure through the bolt hole reinforcing cylinders?

It is most curious that the cylinders that reinforce the bolt holes are cracked through. It is nearly impossible for core foam to be strong enough to frature the cylinders, therefore I believe these cylinders were cracked before the foam. Possible starting point of the failure.

These two observations combine in a way that lead me to believe that the failure mechanism started with mis-aligned blade grips when the bolts were installed. Due to the misalignment, the bolts were forced diagonally through the holes. Perhaps the bolt holes were re-drilled to a larger opening to accommodate. Once the bolts were inserted, they were tightened and torqued. Even if they were not over-torqued, the crooked angle of the bolts caused a compression on the reinforcing cylinders in the blade which was oblique to their end surfaces. This allowed the cylinders to crack, and upon movement of the pieces of cracked bolt cylinder, the crack propagated through the foam core of the blades. Once the core was undermined, at the edge of the blade grip, then the skin of the blade could buckle at the edge of the grip, too. Complete failure follows quickly after that step.

To confirm or disprove this theory, examine the bolts for signs of bending, either through the length of the bolt or a bend head. Also look at the bolt's surface for grooves made by the blade grip holes. In the holes in the blade grip, look for signs of the holes being re-drilled, or whether the bolt has borne down against the hole in a way that made it oval. Lastly, study the cracked cylinders that were supposed to support the bolt, and try to determine of they were seated flatly against the blade grips, or if a depressed crescent was made by overpressure on its end.

If you can, try to examine the blade installation on a surviving Windspot turbine, and if you are premitted, remove a bolt to examine the hole alignments. Then re-install the bolt at only the RECOMMENDED torque. Look at the protrusion of bolt threads out of the nut, and compare with the number of bolt threads showing out of the other nuts in the grip, and with the photo of the bolt threads that you have just shared here. It is not an accurate measurement, but often a good starting point for determining if a group of bolts has been over-torqued or not.

[Peter Klaassen]

Hi Cor,
Have you heard any news about Windspot lately? On the internet there was something about bankruptcy protection. I am about to put my 3.5 kW up in the air finally. I had some questions about the wiring and maintenance but no response from windspot.
Pete Klaassen

[Cor van Houtum]

Hello Peter,
as far as we know everything is allright with sonkyo
in two weeks we have a exhibition in the Netherlands and they come to join us on the stand

but can I help you maybe

Cor

[Peter Klaassen]

Thanks for your offer Cor. I have used my multi meter to check the wiring continuity at the slip rings. There looks to be a connection between all three rings. Should this be the case? I have the brake switch on so I can see two being connected. This is supposed to be the electric brake, but I can still rotate the blades slowly without apparent resistance. Do you think there might be a problem in the generator? Do you have a routine to follow for checking the Windspot prior to using it?
Thanks for your advice!
Pete

[Cor van Houtum]

The windspot is not need to be connected to anything
so just put it on a pole
connect 3 cables to the turbine and let it spin

measure the AC output on the 3 output cables
should be about the same on whatever 2 cables you measure

if this is true then the generator is working fine

what you did noy say yet is what the problem is ?

Cor

[Cor van Houtum]

The windspot as we have them here are not standard with a brake switch
the controller also has no connection to do this

if you want a brake switch conected then use a 3 pole switch on both sites of the switch
so 3 poles in the switch and 3 poles out the switch

the 3 outgoing poles connect together (short circuit)
the 3 incoming poles connect to the same input terminals where also the generator is connected

cor

[Cor van Houtum]

hereby the manual

to connect the dumpload use B1 and B2

there are double connections present
there could be 2 dumploads connected thats why

SO DO NOT CONNECT THE DUMPLOAD 2 WIRES TO B1 only
use 1 cable on B1 and the other on B2