Wire sizing

[fabricator]

OK, I'm building the seventeen footer, my wire drop in the tower will be approximately 90 feet long, my run to the control room will be close to 150 feet, I would like to use aluminum for the under ground run, and of course copper for the drop line, this is a 48 volt machine, advice on wire sizes would be greatly appreciated.

[wooferhound]

How much power do you think your wind turbine will make

 and

What voltage will your system run at  ? ? ?

[fabricator]

From what I have gathered from others who are flying these machines they see 5kw in high winds, I plan to limit mine to about 3kw.

[fabricator]

It makes 48 volts at 77 RPMs, I have no idea what voltage it will be at when making 3kw.

[cardamon]

Well I would say - and this may be splitting hairs for a rough voltage drop calc- If this is a battery charging system then you are looking at about 60 volts into the batts.  Your rectified voltage will be about 1.35 higher than your three phase, so voltage in the wire run will be 45 volts ac three phase.  3KW three phase is a line current of about 40 amps.  plug into http://www.nooutage.com/vdrop.htm.  2/0 al (#1 cu) gives 5% drop at full load, which it wont be at much of the time of course.  That is the theoretical answer, however others have said that without MPPT, voltage drop is not that important and in some situations more resistance can help depending on which voltage and speed your windmill is idealized for.  Perhaps others can chime in and explain that more...

[wpowokal]

Terminal volts at 3kw will be much the same as at 100w except for some increased voltage drop across the cable run.

The generated voltage will be much higher, and dependent on coil resistance and current, basically anyway for an air core alternator.

The difference between generated and terminal volts  x current is you stator heating in watts.

If I'm telling you something you know ignore me, I'm used to it.

allan

[ChrisOlson]

The difference between generated and terminal volts  x current is you stator heating in watts.

I guess I'd have to disagree with this.  Open voltage - load voltage / resistance of the stator coils and wire run in ohms = amps.

Generator shaft input power in watts - (amps x volts) = losses in watts.

Fabricator said he gets 48 volts @ 77 rpm.  That's 1.6 rpm/volt.  He wants to make 3 kW and said he doesn't know what the open voltage will be.  That's easy to figure out:

Volts + (amps x ohms) = required open voltage

At 3,000 watts you got 62.5 amps @ 48 volts.  I have to assume the resistance of the stator and wire run, but I'll use .8 ohms measured at the rectifiers:

48 + (62.5 x . = 98 volts

Fabricator's generator is making 1.6 rpm/volt so it needs to turn 157 rpm to make the open voltage to develop 3 kW, assuming that .8 ohm resistance in the coils and wire run.  If he uses blades that run at a 6 TSR loaded he should be at 157 rpm @ 16 mph wind speed.  Assuming the blades are 40% efficient (but I doubt it) there's only 2,358 watts of shaft power available.  So he's not going to make 3 kW at a 6 TSR.  He needs blades that run at a 5 TSR to get his 157 rpm, which is then going to happen at 19 mph wind speed.

In other words, at 1.6 rpm/volt the generator is wound a little tight for a good set of 17 foot blades.  You're going to have to open the air gap up a bit and let 'er spin so you get your 98 open volts at somewhere around 180-190 rpm (assuming the .8 ohms of resistance - once that's known you can figure the rest out).

--

Chris

[fabricator]

Wow! Ok Chris that looks like good numbers to me, but you have one thing wrong, I know just enough about this electronics stuff to be dangerous, so, given what you have there what does my drop need to be and what size aluminum wire do I need in the run to the pole barn?

[ghurd]

I agree.

Except some of the 17' machines are getting spurts past 100A.

AL #00 with 100A drops 10% in the 150' run, ignoring the 90' tower wire.

I find this chart handy,

http://www.windsun.com/Hardware/Wire_Table.htm

G-

[Roger Stafford]

 Hi fabricator

I would advise against useing aluminum. The NEC has outlawed it for the use in branch circuits in houses because it expans and contracts too much causeing loose connections. That causes the wire to heat and melt. You would see your wind gen self destruct. I seen this happen a lot of times in old houses where they used aluminum to feed air handlers with electric heators.

 If you go to Home depot or a electric supply store you can get a "UGLY'S" electical references book,(cost $10 or $12) it has all kinds of info that would be helpful and it will help with the wire size. It depends on kind of conduit and insulation type.

 I have a 17ft other power gen and I used #6 so cord down the 94ft tower and #4 THHN (copper)in pvc 240 ft to the batt. shed. and Chris is right on the money .08 ohms resistance.

[ChrisOlson]

It would appear to me that a 100 amp AC service would be the bare minimum for a 5 kW machine on a 48 volt system and more than adequate for 3 kW.  In that case, according to my code book, assuming a 100 amp panel, you need #4 copper for the drop and #2 aluminum underground.  The wire table in my book says those sizes are good for 135 amp chassis wiring and 60 amp power transmission.  I don't know what's legal where you live.  But where I live that's what would be required, minimum, to meet code.

I don't think it would be prudent to size the wire for a 3 kW machine when the possibility exists that it can put out 5 kW if it doesn't furl right, or some other issue.  For 3 kW you could use #6 stranded generator cable for the drop and #4 aluminum underground.  If I was doing it I'd use #4 Type SO on the drop and #2 aluminum underground to reduce the losses in the wire run.  The cost of the bigger wire is not all that much, although Type SO or Type SOW cord is not cheap.

It's probably best to consult your electrician if you have doubts so you don't end up digging it up and redoing it if it doesn't meet code.

Chris

[dlenox]

Dale,

Biggest difference is if you are charging batteries or going to be using a charge controller.

If charging batteries the battery bank essentially 'clamps' the voltage, that is assuming that your inverter is providing a load or you have sufficient dump load.

If using charge controller then voltage will increase as rpm's increase.

I assume by your comments about this being a 48v machine that you will be charging batteries...

Dan Lenox

[dlenox]

Forgot to mention that if it does not furl properly (or is wind seeking) then the output from the turbine can easily get up to 5kw.

So if a nominal 48v bank is used, typically operating voltage is about 54v, so this would make the amps very close to 100a.  It would be nice to have at least a 50% leeway.

Of course the wire that you use between the turbine and the rectifier (assuming near battery bank) has an effect on how your turbine operates! Using a larger diameter cable will lower resistance and potentially run your turbine in a stall condition - IMHO not a bad thing as stall is easier to control...

Dan

[fabricator]

Thanks for all the good info guys, the light is beginning to dawn. I might be a little tight though, I have a 1" ID pipe sticking through my top cap, I'm thinking the OD of #4 copper cord might be pushing that, then I need to get an airline and a proximity sensor wire in there also, I see some rework in my near future.

[dlenox]

Dale,

I am using #8 for the 80' run from the turbine down to panel at the bottom of the tower.  From the bottom of tower I am using 100' of #8 to the inside of my garage. From garage to basement of house where I have rectifier I am using 150' of #2.

Hope this helps,

Dan Lenox

[dlenox]

Forgot to mention that at the top of the tower you should use a kellem grip to support and hold the wire bundle.  This will take a lot of the strain off the cables as well as reducing the possibility of developing a short from abrasion.

I am using a Hubbell #02206001, this is a double eye, double weave heavy duty cable support with a length of about 30" long. The cable which goes through it can be between .75" - .99" in diameter.  So anything similiar should work with your setup.

Here is a picture of it:

You will need to add something at the top of your yaw bearing to fix this grip onto.

Dan Lenox

[tecker]

Down wire that is not fine strand like SO cord gets to be a mess when it's twisted .The best way to handle an a long pull with heavy amperage demands on a buget is to run pipe

that's large like 1 1/2 pvc(pull  box in the middle) and Awg 10 thhn. Each will run 15 amps de rated for that pull and a roll is around 55 to 60 bucks per roll of 500 ft .Two rolls of that and a jet line  will cover 45 amps and you can get goin and if you see it's runnin warm pop for two more rolls .

[dlenox]

tecker,

yea I forgot to mention that the cable running down the tower is #8/3 SO.

the rest is THHN.

Dan

[fabricator]

Dan what are you using for a connector at the tower base for disconnecting and untwisting?

[fabricator]

Tecker, what is a jet line?

[DanB]

I think #4 Aluminum is probably appropriate.  The 17' machines as we've built them, tend to stall without a some resistance in the line.  It seems perhaps extreme, but in a few installations I've run #10 copper down the tower (80' or so) (because its flexible and we need some resistance anyhow) and then heavier stuff for the rest of the run.

My biggest worry about running thin wire in the line is letting the blades over speed.. that's what we want to avoid. Some voltage drop at 'peak output' in rare high winds is not going to hurt you otherwise.  

We put in a machine for my neighbor years ago (on a serious budget) - it's a 10' diameter 12V machine with a line that's over 400' long, and he's running that on the equiv. of 9 gauge wire.  In high winds his losses are dismal - in most winds they're quite small. His blades run quite fast but so far...(7 years) it's holding together and keeping his lights on!  That said... I would never do that over again but it's interesting to think about.

Ultimately getting the resistance of the stator + the line right is the key I think so the blades are at their best speed.  Odds are the stator is wound with much thinner wire than the line.

[KarlJ]

Equally important are the connections, anything over 20A needs to be a soldered or mechanical bolted connection or the resistance will cause heat and melt things.

EG dumpload relays.

I destroyed a 40A relay with just 20A using spade terminals, they got hot and melted the relay housing causing it to fail within minutes.

I just finished mine and I have run 16mm2 (about 5AWG) 240' for a 10'mill 1.2KW.

plus the drop wires which are 6x 3.5mm2. (and only 24')

I rectified at the mill as it does save on cable costs.  Expect that at 3-5KW the thing will be running at best part of 60V and 50-80A

My observation is bigger is better but within the budget will work fine, "normal"

6AWG cable will handle the 50A no problems but the losses at 80A will be significant.

The question is can you handle the power if it does get up there? (to 5KW)

As agricultural as this sounds, if you are dissipating 25% in the line at 5KW ie 1000W being lost -are you able to use this power at the other end or will you be dumping it anyway?

If you would be dumping it then I would go 4AWG and if i wanted to use it then I'd be going 2AWG (copper)

I also like the idea of using smaller cables and if they get warm just pull through some more, in practise this is basically impossible on a 150' run as you just cant putt them through, it was tough enough threading my 5AWG pair through 1" conduit just 18' long

[dlenox]

I am using a 75amp 3prong plug/receptacle, so far it's been extremely reliable and handled short bursts of 90amps.

I have a smaller receptacle (not attached so I can hold in my hand) that has all 3 phases shorted, so when remove from being inline into system I quickly switch it an put on the shorted receptacle.  Then I can unwind the cables, remove the shorted receptacle and plug it back into the inline receptacle.

Just in case I always wait till it is a very calm day, cause if you drop the hand held recptacle you have to move fast before the turbine speed ramps up!!!

That condition would follow with your signature pretty well...

Dan Lenox

[fabricator]

I intend to bury at least 2"pvc along with two 1" pvc conduits because I will be pulling 220/110 out to the mill so I have power out there for my winch and an outlet for my welder and power tools, and it will be a dead straight run all the way to my pole barn, so I will always be able to change/update things, budget here is not a problem, doing it right is my driving force, I will have the air brake to keep things stopped while untangling, if I reverse the quick connects there so the female is on the drop it will hold pressure on the brake while it is disconnected.

I also need to run three 16 gauge wires tot he mill for the proximity sensor for the brake, so there will be the large drop the 16 gauge wires and an air line running up the tower, and possibly a wire for a camera of some kind, it would be a shame to waste the view of the neighborhood from 85 feet.

[TomW]

it was tough enough threading my 5AWG pair through 1" conduit just 18' long

Why they invented the electricians fish tape. Pushing cable is much like pushing chain. It is a whole lot easier to pull it.

Anyway, a shop vac a string and a ball of fluff can get a small string through a conduit them pull a heavier line then pull your cables. More folks have string and vacs than fish tapes so there is another way.

Pushing cable through conduit is a lot of hassle.

I like to leave a loose line pulled through my conduit in case I need to redo it.

Do not use too many elbows, either as pulling around corners is much tougher than a straight pull.

Just a couple thoughts.

Tom

[Timeless Turbines]

     Fabricator

I am an electrican and would like to correct some things I have read here but I do not have the time right know as I am at work, you can email me and I will give you my phone #. lholmes@emich.edu. I ran 2-2" conduits to my tower, plus two 1" What state do you live in.

[fabricator]

Email sent.

[RP]

Not to mention the view of the turbine as well.

Here's an idea I had a couple years ago:

http://www.fieldlines.com/story/2007/1/1/201948/8323

[tecker]

Jet line Poly line that's used as a pull string you can add more conductors later . Aluminum has a corrosion problem and is stiff to pull .  

[tecker]

One other issue with using a pull string with multiple conductors is the pull sting needs to go in with the first pull IE pull out the conductors pre cut and then add the pull in with that for ease in making the pull go with a 1/4 poly rope It will be less likely to bind in the pipe . If you use a pull box half way you should be able to work the pull easier and have another entry point for future .  

[fabricator]

I don't think I'm gonna need a halfway box, I only have 125 feet to pull.

[tecker]

That's a reasonable pull. Put a string in when you lay the pipe. Not trying to be bitchy

[cardamon]

"The NEC has outlawed it for the use in branch circuits in houses because it expans and contracts too much causeing loose connections"

That is not true, you can use aluminum. We often use SER for ranges and such.  A properly made Al connection is not an issue.