10 kw Wind Turbine

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A year ago, my contractor installed a 10 kw Wind Turbine (mfg'd in China),
two 6 kw Aurora inverters send AC power to the grid on a net metering agreement with BC Hydro.

One aurora inverter didn't work right away (even tho wired parallel), but after a month it "kicked in", and things were fine for about 10 months or so.

During a huge windstorm overnight two months ago I heard the turbine's blades spinning faster and louder than ever before. I sensed something was wrong because the turbine blades were not turning out of the wind (as they're supposed to do).
The next day, the turbine blades were not turning, the two 6 kw Aurora inverters were OFF, no power lights, no nothing.

Contractor came out, after checking the "controller box", he thought the "resistor block" was dead. Then he said "no, both inverters are fried".

Pictures can be seen at my Flickr site:
http://www.flickr.com/photos/southslope/sets/72157617702085418/

PowerOne in California, after 5 weeks, sent us one new inverter (the other was apparently "fixable" here). Contractor hooked it up yesterday, and after about 4 hours of wiring, declared that the new inverter didn't work! He phoned Power One and demanded a new one be put on Air Express, as I'm ready to send EVERYTHING back.

Nobody seems to have any idea WHY overvoltage entered the inverter(s). The wind turbine doesn't have a "memory", but from the sound it made that stormy night, it must've been HUGE voltage from big RPMs.

One important thing: The property has 138,000 transmission line running approx. 300 feet from the wind turbine. Turbine's tech cables were trenched underground, crossing underneath the transmission line into the shop where the controller box and inverters are located (including a heat dump).

My question (and the contractor's) is: during the storm could "pick-up" (induced voltage) from transmission line's 2 circuits, 3 phases each, have "momentarily frozen" the wind turbine's safety controls (via static? or ?) so that overvoltage to the inverters occurred?

B.C. Hydro won't tell me anything, but I need to know what happened so the contractor can prevent it occurring again. The inverters were still under warranty, as was the wind turbine, but nobody is saying anything!

I will ask my contractor to join in this conversation, because I have NO elec know-how (as though you hadn't guessed! ).

thank you for any ideas of what caused what, and how I can prevent this happening again.
 

mcclary's electrical

Senior Member
Location
VA
A year ago, my contractor installed a 10 kw Wind Turbine (mfg'd in China),
two 6 kw Aurora inverters send AC power to the grid on a net metering agreement with BC Hydro.

One aurora inverter didn't work right away (even tho wired parallel), but after a month it "kicked in", and things were fine for about 10 months or so.

During a huge windstorm overnight two months ago I heard the turbine's blades spinning faster and louder than ever before. I sensed something was wrong because the turbine blades were not turning out of the wind (as they're supposed to do).
The next day, the turbine blades were not turning, the two 6 kw Aurora inverters were OFF, no power lights, no nothing.

Contractor came out, after checking the "controller box", he thought the "resistor block" was dead. Then he said "no, both inverters are fried".

Pictures can be seen at my Flickr site:
http://www.flickr.com/photos/southslope/sets/72157617702085418/

PowerOne in California, after 5 weeks, sent us one new inverter (the other was apparently "fixable" here). Contractor hooked it up yesterday, and after about 4 hours of wiring, declared that the new inverter didn't work! He phoned Power One and demanded a new one be put on Air Express, as I'm ready to send EVERYTHING back.

Nobody seems to have any idea WHY overvoltage entered the inverter(s). The wind turbine doesn't have a "memory", but from the sound it made that stormy night, it must've been HUGE voltage from big RPMs.

One important thing: The property has 138,000 transmission line running approx. 300 feet from the wind turbine. Turbine's tech cables were trenched underground, crossing underneath the transmission line into the shop where the controller box and inverters are located (including a heat dump).

My question (and the contractor's) is: during the storm could "pick-up" (induced voltage) from transmission line's 2 circuits, 3 phases each, have "momentarily frozen" the wind turbine's safety controls (via static? or ?) so that overvoltage to the inverters occurred?

B.C. Hydro won't tell me anything, but I need to know what happened so the contractor can prevent it occurring again. The inverters were still under warranty, as was the wind turbine, but nobody is saying anything!

I will ask my contractor to join in this conversation, because I have NO elec know-how (as though you hadn't guessed! ).

thank you for any ideas of what caused what, and how I can prevent this happening again.



I don't think it was induced voltage, I think the turbine oversped. It's need to be mechanically able to avoid this. It can be done a few ways, (turn from wind, braking, etc.)as well as sending excess power to a braking device, but you also were lacking some protection for the indvidual inverters, since wired in parallel, they need to be protected individually, and it sounds like theses are not. What if you inverters held the load? YOu could have burned the xfmr in the mill, so I think you a lacking some protection somewhere
 
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We do have surge protection, but I'll check with contractor to see if we have protection for each INDIVIDUAL inverter.

As you state, the wind turbine must turn out of the wind, and then brakes go on at "certain wind speeds", and that does happen.

Could something/anything have happened on the transmission line to "kick out" these sensors, even temporarily? i.e. Static discharges?

Thank you.
 
Good point, I'll ask the contractor.

But...what could happen on the transmission lines that cross my property that "momentarily deactivate" the wind turbine's sensors of wind speed to turn it out of the wind, and put the brakes on? Something did. Just want to know what it could have been. A lightning strike on the transmission line a mile away???
 

mcclary's electrical

Senior Member
Location
VA
Good point, I'll ask the contractor.

But...what could happen on the transmission lines that cross my property that "momentarily deactivate" the wind turbine's sensors of wind speed to turn it out of the wind, and put the brakes on? Something did. Just want to know what it could have been. A lightning strike on the transmission line a mile away???



So your turbine has all those features, but you say they failed to work?
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
Good point, I'll ask the contractor.

But...what could happen on the transmission lines that cross my property that "momentarily deactivate" the wind turbine's sensors of wind speed to turn it out of the wind, and put the brakes on? Something did. Just want to know what it could have been. A lightning strike on the transmission line a mile away???
Sorry, there is no plausible way for you to place blame on the transmission lines, this early in your troubleshooting.

Trying to use that as an excuse, seems to come from the camp of: "I don't want to take the responsibility so I will place the blame on something with a .000001% chance instead."

The odds are that the turbine protective systems failed to operate correctly.
 

mcclary's electrical

Senior Member
Location
VA
the failure rate for wind turbines seems to be fairly high, from the littly I have read.

I agree, there's alot of force there during a wind storm. If the "load" is removed electrically, as in the ops case an inverter failure, many times the turbine can overspeed so quickly the mechanical safety devices cannot stop it, and many times ends in catastrophic failure and self destruction of the mill
 

mcclary's electrical

Senior Member
Location
VA
To the op:

What do you mean by one inverter "kicked in" later on?

This should have been addressed as a conceern, because if later,,,,it
"kicked out" there would be a load shed that to go somewhere, that could have resulted in overspeed
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
100717-1857 EST

If it has not already been invented, then an overvoltage clamp might be a useful new product.

One very reliable way this could be made is with a Zener diode, resistor, and an SCR. Possibly put nearly a dead short on the generator. From this also trigger the mechanical brake. As soon as the SCR is triggered dynamic braking is in effect. This is just as soon as overvoltage is detected. Depending upon filtering maybe 1 millisecond. Probably also want a little filtering on the SCR gate input.

.
 

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
Sorry, there is no plausible way for you to place blame on the transmission lines, this early in your troubleshooting.

Trying to use that as an excuse, seems to come from the camp of: "I don't want to take the responsibility so I will place the blame on something with a .000001% chance instead."

The odds are that the turbine protective systems failed to operate correctly.
I couldn't agree more, except I think Jim is giving it a bit more of a chance than I would...

1) Voltages induce across very short distances, the amount of induction drops precipitously the farther you get from the source. That's why transformers are wound on the same iron core...

2) Induction takes place when conductors are parallel to the source, and the way to avoid that (even if they were close enough) is to have them cross perpendicular to the source. From that great photo stream you made (thanks for that by the way), I see no problems with what was done (other than maybe the trench depth seems a little shallow for my tastes) and I see no way that would or could create a problem.

I'm curious as to why you have two inverters on one generator. Is one a back-up? Regardless, it's imperative that the safety speed controls work. Not only because of the likelihood of damaging the inverter(s) and/or the generator from high voltage, but also because of the possibility of the turbine itself running away and coming to pieces, killing anyone in the way! Video of what can go wrong!

What you are looking at in those pictures is the result of an over voltage failure, but not the cause. The resistors burning out would not be the start of the problem because they are used to dump power when the voltage exceeds the capacity, but if the over voltage continues, you have to be able to shut down completely. An induction generator needs to be connected to the grid both to generate and to help regulate speed, but the speed regulation is minimal. A runaway is possible in high winds and the safety systems must function to stop the turbine, usually with pitch control and brakes. You must insist on a serious study of the safety systems and a failure analysis by a qualified independent engineer.
 
I'm very grateful

I'm very grateful

...for all the replies.

Have emailed the topic link to my contractor, but haven't heard from him yet.

While I lack everyone's technical jargon, will mention that YES the turbine's blades do turn out of the wind (at a set voltage or rpm, not sure which). If winds continue to increase or don't abate, brakes automatically go on. The contractor has been fine-tuning the software from the manufacturer.

And it's not that I'm looking to place blame on Hydro (without doing further investigation), it's simply that the storm happened May 19th, exactly two months ago, and nothing's been fixed yet. The hydro guys have told me a "static charge" on the transmission lines could produce a lot of heat in the nearby turbine, possibly affecting the software's ability to respond to increasing winds? The big delay seems to be Power One (California inverter company).

It took a month just to get "permission" (and a number) to return the inverter. The California "tech guy" told my contractor he would send parts to repair the other inverter here...to the tune of $600 to $800 (!!!!???? it's only 12 months old).
Two weeks ago, after many more phone calls to California, they still hadn't figured out why the inverter they received back is broken; its internal log showed NO overvoltage as the last entry...(but I forgot what the numbers were).
So I told my contractor he must demand a NEW inverter be sent. He did that, and when the replacement inverter was received last Wednesday, and after the contractor spent 4 hours downloading the program into it, and then rewiring it into our Shop (along with the first inverter that he had repaired himself), IT DIDN'T WORK. He said it too had an internal fault and it needed to be un-wired and repacked and shipped back to California. Needless to say, I went ballistic! I demanded that he call Power One and tell them to get a NEW inverter (not repaired) onto a plane TODAY. Power One apologized and said we had missed the courier pick-up for that day!

To address other comments:
Why there are 2 inverters on one generator...turbine is a 10 kw, each Aurora inverter is 6kw.

I've been looking for an independent failure analysis person, presume he needs wnd turbine experience. Found one who told me he was "not an engineer YET, but close". But he didn't phone back.

I felt it important to get as much info together (for when I do find someone qualified) i.e. B.C. Hydro internal log-book for transmission line, etc. etc. through a Freedom of Information request.

Apart from renaming Power One, "Power None" for their horrible customer service and unacceptable delays, I have no idea where to go with this.

Thanks for sharing my concern, folks.
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
100719-1949 EST

Buchanan1:

I have to assume that you have a DC generator in the windmill. This could be a commutator type or alternator with diode rectification. The later would be more reliable if quality components were used. In either case the output voltage is proportional to speed.

There should be a reliable method to prevent overspeed and therefore overvoltage. This needs to be evaluated. The least possible number of components and most reliable should be in this function. Probably means no microprocessor in this system and it should be at the windmill.

I seriously doubt the power lines had anything to do with the problem. However, high voltage transients on your service entrance lines could cause problems with the inverters. There should be healthy (meaning big, etc) transient limiters at both the input and output sides of the inverters.

In the early days of electronic regulated power supplies for expensive semiconductor circuits the SCR method I mentioned above was used and called a crowbar transient limiter. It had a very sharp threshold point.

.
 

Electric-Light

Senior Member
Many induction motors use centrifugal switch to deactivate the starting winding.
Couldn't a turbine have a centrifugal switch that activates a latching relay which clamps down the output with heaters or something?

Elevators use a rotor that is attached to a centrifugal clutch and where there is an over speed, the clutch engages yanking on the brake cable which kills the power to traction motor and bring the elevator to a stop. It must be reset by a service tech later.
 
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Besoeker

Senior Member
Location
UK
100719-1949 EST

Buchanan1:

I have to assume that you have a DC generator in the windmill.
Not necessarily.
Some, maybe most, wind turbines use AC machines and an inverter to match the variable frequency of the generator to the fixed frequency of the grid.
 

Besoeker

Senior Member
Location
UK
...
To address other comments:
Why there are 2 inverters on one generator...turbine is a 10 kw, each Aurora inverter is 6kw.
Why not use just one 10kW inverter?
At such low power levels, I don't see the justification for paralleling two smaller units. I think it adds a degree of complexity that would be better avoided.
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
100720-0604 EST

Besoeker:

The point of my post was that whether the generator in the windmill is AC (alternator) or DC (mechanical commutator) it will be DC at the input side of the inverter. It really doesn't matter whether the diodes (rectifiers) are at the windmill itself or at the inverter.

The process is AC (even in the DC commutated generator) converted to DC and then back to AC at 60 Hz.

Even without the AC DC distinction the output voltage is propotional to speed.

.
 

Besoeker

Senior Member
Location
UK
100720-0604 EST

Besoeker:

The point of my post was that whether the generator in the windmill is AC (alternator) or DC (mechanical commutator) it will be DC at the input side of the inverter. It really doesn't matter whether the diodes (rectifiers) are at the windmill itself or at the inverter.
I agree. I should have read the whole of your post.


Even without the AC DC distinction the output voltage is propotional to speed.
That would be true if there was no control of the excitation.
Think about a vehicle alternator. It can charge the battery at idle speeds (<1000rpm) and not be overloaded at 6000 rpm.
 

Jraef

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Staff member
Location
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Occupation
Electrical Engineer
100720-0604 EST

Besoeker:

The point of my post was that whether the generator in the windmill is AC (alternator) or DC (mechanical commutator) it will be DC at the input side of the inverter. It really doesn't matter whether the diodes (rectifiers) are at the windmill itself or at the inverter.

The process is AC (even in the DC commutated generator) converted to DC and then back to AC at 60 Hz.

Even without the AC DC distinction the output voltage is propotional to speed.

.
If you look at his photo of the generator itself, it is 240VAC, Y wound. The inverter(s) would be to regulate frequency into the grid under widely variable wind speeds. Could have been done without the inverters of course because it's an induction generator, but then you need more complex speed regulation. It's a trade off driven by economics of an installation. The "input" into the inverter is actually AC, converted to DC, then back to AC. But it would probably be an active front-end converter, hence the term "transformerless" used in the description. That means it monitors the AC coming from the generator and optimizes the active front-end converter firing pattern to provide the maximum energy input to the DC bus.

That said, I agree with the comment on the parallel inverters; unnecessarily complex when a single 10kW inverter would have done better. If one of those inverters dies, the other one would be toast relatively quickly unless the protection kicks in immediately. Looks to me as though the only reason they did it is because the company they distribute doesn't make a 10kW inverter. System design by distribution contract; never a good plan.
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
100720-1254 EST

How are most small wind alternators built -- PM or wound rotor?

My assumption would be PM (permanent magnet) to extract as much energy as possible and let the inverter work with the dynamic range of voltage from different speeds.

.
 
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