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Author Topic: Turbine generation in odd weather conditions  (Read 431 times)
heatherhopper
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« on: December 21, 2018, 12:03:28 PM »

A question for all turbine operators and/or meteorologists about the unusual weather we (and I imagine a few others) experienced last Saturday - we have only just had our phone/BB line re-strung (down due to the weather) so this is bit after the fact.

Short version of the weather conditions - very windy with bouts of freezing rain throughout the day.

Interestingly (perhaps annoyingly might be a better description as we should not be on battery power during a gale!) our turbine simply stopped generating for a couple of periods during the day and I would like to know the likely reason. Was it simply an equipment malfunction due to being iced-up or could this be related to layered air masses of different density?  This has happened a couple of times in the past for quite short periods in similar conditions but I have not been around to observe the circumstances so gave it little more thought. This time I was around but a bit pre-occupied with a heating system failure that took precedence so my observations were largely just in passing.

Put simply the turbine rotor speed reduced to that I would expect to see in 0-4 mph winds and the downstream inverters etc just shutdown - this despite the wind speed remaining well in excess of 20 mph and strong enough at ground level to require fighting against. The turbine head and blades did not appear to be any more iced-up than I have seen on many other (colder, icier, snowier etc) occasions. The general impression was that there was simply insufficient wind at 9m for cut-in although blowing a hoolie at the 4m weather station and at ground level. Normal operation resumed without any significant change in wind conditions. The neighbours observed some similar behaviour from their little Bergey.

Below are a couple of graphs - turbine output and weather station plot. The anenometer unfortuntely froze solid around 16.00. The wind was easing a bit through the afternoon but still worthy of up to 6kW peak.

My head says some icing-up issue in the head from the freezing rain but we do get very odd extremes of weather conditions here. Anyone experienced anything like this or know a little bit more about air density layering possibilities?





« Last Edit: December 23, 2018, 12:45:19 AM by heatherhopper » Logged

Off grid AC coupled, 6kW Proven, 2.8kW PV, SMA SI/SB/WB Inverters, 4x576ah Rolls batteries @ 24v, 25kW Biomass Boiler, Wood Stoves, Spring/Well water. Sorry planet - I did try.
marcus
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« Reply #1 on: December 21, 2018, 07:26:16 PM »

sounds like an intermittent shorted generator output to me - may or may not be weather related - unless the weather's affecting some kind of emergency turbine shutdown device?
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heatherhopper
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« Reply #2 on: December 23, 2018, 12:47:48 AM »

Yes Marcus my first thought was a short of some kind. Slip rings would seem the obvious area. When I first noticed the drop in generation the voltage at the inverters (which had reverted to waiting mode by this time) was around 230v so I assumed some power delivery down the tower. I suppose this may just have been reflecting the capacitor charge though. After that inverters had shutdown when I checked and subsequently restarted themselves quite happily (twice). I have never shorted the turbine so couldn't relate that effect to what I was observing.

The turbine does not have any electrical braking system. I have been wondering if the physical brake had somehow engaged, the rope does become solid in wet freezing conditions and clanks about inside the tower making quite a din. Although it doesn't require much force to apply the brake I'm not sure it would amass enough ice to activate it. It's only an adapted Astra (or some such) disc brake and I've never used it in anything but benign winds and have no intention of trying it in a gale.

The issue only manifests itself during the very unusual type of weather we had on the day and even then not every time, perhaps once every 12-18 months. So ,whatever the fault, it is certainly weather related.

I know it seems a bit fanciful that wind velocity could be so different over 5m but often our local weather is a bit surreal. As it was the whole system appeared to behave as though the wind had simply dropped to below cut-in speed.

I guess all I can do is check all the wiring next service.

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Off grid AC coupled, 6kW Proven, 2.8kW PV, SMA SI/SB/WB Inverters, 4x576ah Rolls batteries @ 24v, 25kW Biomass Boiler, Wood Stoves, Spring/Well water. Sorry planet - I did try.
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