Skystream 3.7 braking at 60 RPM

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Re: Skystream 3.7 braking at 60 RPM

Postby gshteynberg » Sun Aug 09, 2015 11:09 pm

Hi Gordon,

I ll have to look up a few things to answer all the questions. But here are three screenshots of the ripple. Unfortunately it is not automatically tracked, I have to press show ripple to get it. The 1st screen shot is after it has braked, 2nd screen shot is when it is generating. As you can see the ripple varies quite a bit - not sure what the ripple means.


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Re: Skystream 3.7 braking at 60 RPM

Postby gshteynberg » Fri Aug 14, 2015 7:52 am

HI Gordon,

I've received a response (based on a data file I sent) from tech support. Perhaps you can help me understand it.

"The turbine appears to be experiencing repeated events coded as event “30” which decodes as “DC Offset Error”. This is the text that should/would show in the “last event” field of the Quick Diagnostics tab in Skyview if you happened to be watching the Skyview software at the time a shut down occurs. The only other event showing in the data log is one shut down for grid frequency but this appears to be an anomaly as it doesn’t look like grid frequency goes outside the allowable range (then again, grid frequency can vary rather suddenly and a one-second interval probably isn’t enough to catch the actual shut-down value).

The explanation of the DC Offset error from the engineer is as follows:

DC Offset refers to the AC Grid connection and the symmetry of the AC signal.
The AC signal is a sine wave – goes positive, then negative…. If it goes more one way then the other it has a DC offset by the amount it goes more one way then the other. It a bad thing from the utility perspective since it’s a waste of power. There is a limit Skystream has to detect (according to our certification) when putting out power and this is apparently exceeding that.

It could be a problem with the grid connection itself – a transformer feeding the Skystream could be going bad and causing it. Other household appliances wouldn’t have any symptoms of the problem because they don’t really have to care about it, the way Skystream does. Alternately, it could be measurement or other error on the inverter in the turbine, which would require a replacement."

The turbine is on a small island of St. John where the power company does not inspire confidence. So it very well may be the grid. Any ideas on how to figure this out? (A new inverter would cost $2k). Also, as a side note, the grid frequency DOES go beyond the allowable range -- but again we don't know whether it is the inverter or the grid, etc.

Any final thoughts would be much appreciated!

Thanks, Garriy
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Re: Skystream 3.7 braking at 60 RPM

Postby Gordon-Loomberah » Fri Aug 14, 2015 9:59 am

I think you'd need an oscilloscope to determine where any DC offset might be- not something anyone can do from a distance ;)

Have you ever had anything like rated output (2.4kW) from the wind turbine generator, or has it always been just a small output then it shuts down?

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