High voltage DC?

[sbotsford]

Most of the units I've seen described here are either 12 or 24 v. 

My ideal location is about 400 meters from the house.  I'd like to put up a 7 KW unit, and sell the surplus to the grid.  (We have net metering coming in now.)  7.2 (makes for round numbers) KW at 12v is 600 amps.  Pretty hefty wire.  At 120v it's 60A.  Still chunky.  At 1200v it's 6A.  That's reasonably affordable.  Ok.  It won't be done with wire from Home Depot.

1.  Is it reasonable to wind a generator to produce that kind of voltage?

2.  Where to you find  0-1200v DC to 240v ac grid inverters?

[joestue]

Go with a +/-580 volt system, which will keep the voltage within the 600 volt limit so you can use standard wire.
I'd go with UF 14 awg wire and just bury it, ground the center line of course.

you can then buck that 1200v down to a more reasonable 400 and feed that to the grid tie inverter...
Or you can just go with a +/- 400 volt system and buy two grid-tie inverters, this is certainly the easiest.

to get the dc from the turbine, use a 12 pulse transformer, disconnecting the delta coils on the ac side if start up is a problem.
or use two generators run in series,
or boost whatever voltage the generator makes to 1200 vdc.
the latter is how i'd do it, because it lets you easily control how much power you take from the turbine with no additional expenditure.

the cheapest and fastest way to do this is run a +/-400 volt line with two inverters, wind the generator with two separate wye coils, each to produce about 400 volts max, then rectify and run them in series.

yes, it is reasonable to wind a 7Kw generator for 600vac, that's about 8 amps per phase into a standard 3 phase diode block.

[dnix71]

1200v DC is insanely high except for power company types. You would need IGBT's for switches.
http://www.dynexsemi.com/products/igbt/index.htm   1200 vdc isn't touch it and die, it's more like get too close and will jump over and kill you.

Go three phase 208 ac from the mill. At 7.2KW you have enough power to run a commercial pizza oven.

http://www.dvorsons.com/Holman/Ovens/Miniveyor.html

[12AX7]

Hi!

1200 DC is fine!   that is..  if your talking about the Plate voltage in a high power transmitter.
Other wise,  I'd not want to be near it!

ax7

[bob g]

in my opinion anything over about 400volts is going to be a problem
insulation issues abound the higher you go,

its hard to wind coils that are free of abrasions or nicks as it is, and iirc H class wire is good for what
600volts?

no way i would want to build any power generation equipment at anywhere near those levels, its bad enough
to do so and have it all contained in a metal box, let alone running some long distance buried wire, and all the places
where human or animal contact is possible.

my vote is stay down below 400volts, and even then i am not at all comfortable there.

and i frequently work with 440-480vac three phase systems.  they are all AC and they are all in our of the weather
and usually dry.

no way am i going anywhere near a tower with a high voltage down feed, let alone climb the thing.

one thing for sure, during a high wind and heavy load, a stator fire would be spectacular at 1200 volts i would think

bob g

[jamromhem]

as with the concerns with the others who have posted... I would take a very close look at the local laws of dealing with those voltages...  I could only imagine the restrictions of dealing with those levels..  IE certifications, licences, insurance....    The risk may not be worth the gain of a system that pushes that power..

*random kid has to pee walking through a feild and decides to hide next to your building to do so and happens to pee on the line that the small rat toast was previously chewing on*

your costs for precautionary measures, insurance liability (if you would be able to even get home owners insurance to protect your liability with a death trap on the property)

a couple lower voltage systems in the long run would most likely be much cheaper than one high voltage system like that with the heavier equipment all around..  and I might venture to say you would legally need a license in many locations to even get within 50ft of your own equipment. 

I could be wrong, but my post is less on the capability than a probably less costly method (that will probably see a higher return with the purpose of selling to the grid.)

[Ungrounded Lightning Rod]

If you absolutely MUST run it at a high voltage, generate it at no more than 120ish V, get a couple "Pole Pig" transformers to shift it up and back down, and run it like a utility power line on elevated poles.  Don't forget the surge arresters for lightning protection, and follow all the rules like you were a power company.

The reason most DC systems don't go over 48V nominal is that the code rules change at 50V.

[Rob Beckers]

Hi sbotsford,

You mention that you have grid power, what you have not told us is if your system is battery based (with an inverter), and you're looking to charge batteries with that 7kW wind turbine. Alternatively, you don't have any inverter yet, and are looking for net-metering, so all you need is a grid-tie inverter for the wind turbine.

In the latter case, I would suggest either a Power-One Aurora wind inverter (they can safely be programmed up to 6.2kW of output power), or an SMA Windyboy. Keep in mind that both need to be programmed with MPPT information for your specific wind turbine to work properly. They do *not* work out of the box. Both have an absolute maximum voltage of 600V DC, and I make good money selling Aurora inverters to people that blow them up by going overvoltage. That is the one guaranteed way to let the magic smoke out, and warranty does not cover it. In other words, you have to make sure your turbine can not produce more than 600V DC (there are several ways to do this).

Even with overvoltage protection I would not get anywhere near 600V DC for normal operation, you need a buffer to protect the inverter in case things go wrong. A good voltage to shoot for is 400V DC, maybe 450V (as a maximum). At 400V DC you're looking at 15.5A for 6.2kW. For 2% losses at 400 meters that works out to 0.52 Ohm total, or 0.26 Ohm for each leg. That means 1 AWG aluminum wire (nobody uses copper for those distances, just too expensive). about a thousand dollars will do that, for underground service entrance rated wire  that can be dropped directly into the ground. Less if you're willing to go for somewhat higher peak losses, which has almost no effect on total energy production for a wind turbine since so little time is spent at peak power.

On the total cost of a 6 or 7kW wind turbine, inverter, tower and everything else, the cable cost is a small portion when going with the voltages above (400V DC or so). No point in shooting for 1kV or more, there's very little to be saved and you can't get inverters for it. Nothing off-the-shelve that's UL/CSA listed in any case.

By the way, I used DC voltage above, putting the rectifier near the turbine. You can also go with 3-phase AC voltage over the wires, for 400V DC that works out to about 300V AC phase-to-phase. It will cost just about the same in cable though (3-phase current will be less, you can probably go a gauge smaller, but now need 3 conductors instead of 2).

-RoB-

[taylorp035]

I fused some  Anderson Powerpole connectors the other day at about 100v dc.  Working with 1200v would be insane and very dangerous for something that could use a much lower voltage.

(my thoughts)...
At 7kw, it would be 70v and 100 amps or 140v and 50 amps.  400 meters is a long way, and the voltage drop would be too high.  Probably some type of transformer to get to 400v at 17.5 amps.  (6 gauge wire) 0.516 ohms * 17.5 A = 9 volts or about 2% loss.  Then include the transformer loss (?%)...

[Rob Beckers]

I fused some  Anderson Powerpole connectors the other day at about 100v dc.  Working with 1200v would be insane and very dangerous for something that could use a much lower voltage.

(my thoughts)...
At 7kw, it would be 70v and 100 amps or 140v and 50 amps.  400 meters is a long way, and the voltage drop would be too high.  Probably some type of transformer to get to 400v at 17.5 amps.  (6 gauge wire) 0.516 ohms * 17.5 A = 9 volts or about 2% loss.  Then include the transformer loss (?%)...

6 AWG copper is 0.51 Ohm for each leg of the 1300+ feet (400m) we're talking about. Which works out to I^2 * R = 17.5^2 * 0.51 = 156 Watt per leg, or 2 * 156 = 312 Watt in total losses at 17.5A (both the positive and negative DC lead are carrying that current, both have losses) . That's 4.5% of 7kW. That's not a bad loss-percentage to shoot for, for a wind turbine (as stated before, the amount of time spent at peak power is so little for 99.9% of sites that your actual energy loss is far less than 4%). Copper is expensive, the equivalent gauge (for resistance) in aluminum is 4 AWG, and it would be far cheaper for 400 meters.

It is possible to work safely with 1200V, and it's possible to work safely with 400V. Both are about as deadly when handled badly (400V DC is an entirely different beast from 400V AC, and far more deadly). I have no trouble with either one, and don't consider it 'insane', except that over 600 Volt you need different wires, different switches etc, making it more expensive. For either the same goes; unless you know what you're doing don't mess with it! Those voltages and currents are deadly!

-RoB-

[T2]

It is possible to work safely with 1200V, and it's possible to work safely with 400V. Both are about as deadly when handled badly (400V DC is an entirely different beast from 400V AC, and far more deadly). I have no trouble with either one, and don't consider it 'insane', except that over 600 Volt you need different wires, different switches etc, making it more expensive. For either the same goes; unless you know what you're doing don't mess with it! Those voltages and currents are deadly!

-RoB-

I agree, I work with DC voltages many times these every day. I think the over doing the scare factor may make warnings get ignored. Most people should not go any where near anything over 600 VDC standard wire will arc through and nothing good will come of it. All the equipment I deal with keeps the "low voltage" DC buss at 525VDC max when standard wiring is used. That should really be a good rule with any standard wiring. I have all my AE stuff running under 100VDC before the inverters even though I have plenty of stuff around that is rated up to 80kv DC.

[RP]

I have plenty of stuff around that is rated up to 80kv DC.

Are you a time-machine repair man or something?   

[12AX7]

I have plenty of stuff around that is rated up to 80kv DC.

Are you a time-machine repair man or something?   

I was wondering the exact same thing!

80KV DC?  gotta ask...   at what amperage?

[T2]

only up to 1.2 AMPs but the cables are all good for 25-30, if it helps any most have a positive and negative supply center grounded with each side able to run up to 80 kv. I think I was time traveling or something when I caught a 50 kv discharge off a cable once.. that hurt bad.