3 phase feeder

junkhound

Senior Member
Stand alone 500W microhydro installation.

crossflow turbine and custom generator (300V/500 Hz nominal rewound delco alternator) at stream, 900 feet away

1. assume NEC does not apply, consider system as an experiment. No untrained persons involved.

2. what is best feeder configuration, given what is available (have a lot of UF) is 12-2 wg UF - consider both safety, economy, and line loss.
a. send the 3 phase ungrounded delta (using the ground as a phase conductor) as wild frequency to the cabin, rectify there with buck/boost to feed 400V dc link of 120Vac inverter (and 14V dc)
or,
b. rectify at the generator and send variable dc to the cabin to feed similar electronics, either with ground (as ground) or bare UF conductor in parallel with one of the conductors.
or,
c. other suggestions?
 

topgone

Senior Member
The usual arrangements I saw used on microhydro generators is to rectify the generator output into DC and invert the DC into the normal frequency prior to transmitting over to the intended loads!
 

GoldDigger

Moderator
Staff member
Run the longest conductors at the highest voltage possible to minimize voltage drop and conductor cost.
Complicated by the voltage drop advantage that three phase gives you.
 

electrofelon

Senior Member
Stand alone 500W microhydro installation.

crossflow turbine and custom generator (300V/500 Hz nominal rewound delco alternator) at stream, 900 feet away

1. assume NEC does not apply, consider system as an experiment. No untrained persons involved.

2. what is best feeder configuration, given what is available (have a lot of UF) is 12-2 wg UF - consider both safety, economy, and line loss.
a. send the 3 phase ungrounded delta (using the ground as a phase conductor) as wild frequency to the cabin, rectify there with buck/boost to feed 400V dc link of 120Vac inverter (and 14V dc)
or,
b. rectify at the generator and send variable dc to the cabin to feed similar electronics, either with ground (as ground) or bare UF conductor in parallel with one of the conductors.
or,
c. other suggestions?
I have some first hand experience with a very similar setup. I have a 1kw wind turbine with a 1400 foot wire run. The output is three phase 240-300 volts. I sent the three phase down on 2+ ground UF using the EGC for one of the phases. The UF was just layed on the ground. I meant to sleeve it or bury it in a shallow trench but never got around to it. I had frequent problems with rodents chewing on it and it would cause it to short out and stall the turbine. This was particularly fun in winter with two feet of snow trying to find the bad spot. Needless to say, sleeve it in PVC. At the house, it was transformered down to ~12V, then rectified. Rectifying at the tower wasnt an option because of course I had to transform it first and I would lose my high voltage. For you, as I'm sure you have calculated, #14 would easily be all you need and a spool of that wouldnt cost much. I remember that that would have been fine for my setup but I used 10 because I had most of it. I would think you would want to feed batteries and not feed an inverter directly as that is generally quite problematic. Sounds fun.
 

JFletcher

Senior Member
Since you have a lot of 12-2 UF, I'd run parallel sets (2 or 3) for several reasons:

1) you have it
2) reliability ; if you get a damaged conductor, you can switch to another and keep going w/o having to find the break right away
3) paralleled conductors cuts voltage drop (yes i know its a nec violation to parallel 12 ga wire)

I would still trench it for safety and protection. Do all rectifying and transforming at load end. 3 runs of 12/2 gives the option of a second 3ph generator, and not having to use the bare ground wires as CCC.

eta: didnt realize 1k' rolls of 12/2 UF are pushing $250. Still would do 2 runs for reliability reasons and not using the ground as a CCC. You could also go with one run of 12 or 14/3 and rpvc conduit. Id rather pay the extra upfront for conduit than have to retrench any/all of 900' for upgrades or repairs.
 

iwire

Moderator
Staff member
If you can’t “think outside the box” then R&D is dead.
:roll:

If you can't figure out how to do things safely you have no business designing anything.



The machine being produced would be outside the NEC, the cables bring power to it would be under the NEC along with OSHA.
 

iwire

Moderator
Staff member
I'm sure junk hound is a big boy and has his reasons for not needing nec compliance. :roll:
If he is doing this at his house for himself, more power to him. The NEC does not apply at my home either. :D


If this is on public land, some other persons land or at a business things change.
 

junkhound

Senior Member
For clarification, this is on my own land and to own cabin. No poco connections.

I liked the previous rodent damage comment, that might be a concern. Or elk and deer trampling over exposed UF. I need to leave the hood of a 4x4 I leave at the cabin always open otherwise the squirrels chew thru all the wire and generally make a mess in just a few months. I might just decide to string the UF up thru fir branches ? Everything is a few months away, will enlist grandkids to help drag 200 ft of 4" PVC thru the woods for the penstock.

Overall, eng. student grandkids education project (avoidance of NEC notwithstanding) in power electronics, generation, and fluid dynamics.
GKs learning welding and lathe operation also. Turbine weldments shown in picture, grandsons learning to weld also. Old 2.8L chevy flywheel will drive pinion on 4000+ rpm generator.

View attachment 15085
 
I work alternative energy although hydro is very experimental because the volume of production is so low.

My ideal configuration for this system would be to install a unitized, potted 3 phase bridge rectifier at the generator to bring it down to 2 conductors and also to keep current flowing on the wires consistently. Remember that in AC the current is always crossing through zero and back again so that is lost current time on the wire. Run high voltage DC to where you need it and then use a Maximum Power Point Tracking charge controller into batteries. (Are you running batteries?)

However, I don't know of a charge controller that works on that high of voltage but we would like to keep the voltage high.

I guess the next best thing would be to run the 3 phases back to the house at high voltage, step down to 100 volts plus or minus, rectify and feed the charge controller that way.
 

electrofelon

Senior Member
I might just decide to string the UF up thru fir branches]
I considered doing that, I think that would keep the UF reasonably safe except for the occasional fall in limb.

This is the cats meow for trenching on such situations: the brown bed edger. Makes a slot up to 7 inches deep just big enough to stuff 3/4 pvc in, carbide tipped rotor will grind thru roots and small rocks, super low impact, push the tailings back on with your foot. We used it at a fancy hotel for a landscape/tree lighting job where digging with traditional methods and to code depth was absolutely not an option.
 

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Tony S

Senior Member
:roll:

If you can't figure out how to do things safely you have no business designing anything.

In that case I’d better send out blanket e-mail to stop the world wide production of spun iron pipes. Nearly all manufacturers use one of my duct tape and bits of string “out of the box” ideas. The first trial was a total bodge, it sort of worked so more trials were carried out. Once proved all the refinements were added.

You have to prove a theory before you get any major backing.
 

junkhound

Senior Member
(Are you running batteries?)

.
Would only have 1 12 V battery when actually there, otherwise wild frequency, voltage from zero to about 300V. Stream flow is very seasonal, trickle in early September to over 2 cfs during winter thaw/spring rain, so power will also vary.

I can design ground up power converters so was thinking to take the wild 3 phase to the cabin and do power electronics magic with it there - e.G. Vienna bridge type buck/boost rectification, or similar, etc..

Likely only use regulated power a few days at a time during the year, otherwise will simply have a simple resistor bank at the cabin on on/off thermostat to keep inside condensation/mold down.

If I ever became a widower and hermit and lived at the cabin, then might look into building PPT. That would really be wild frequency/voltage, as turbine rpm at ppt would be directly related to the flow.
 
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