Three Phase Grid Tie

[Tbailey4]

Hi, I am working with a school in a diesel dependent Village in Alaska.  They have a Bergey XL1 on a 32meter tower and a Xantrex xw 4000 watt inverter, 4 golf cart batteries.  The batteries are not necessary because the grid is reliable.

I was told since the school has three phase power the Inverter was only hooked up to feed two outlets in the laundry room of the gym, and is not tied to the grid.  Consequently the power is not used.

The site does not appear to have that good of a wind regime, I would guess class 2 or 3, but the grid power is $.60/kwh.

The science teacher got some funding to monitor power production with a ted or onset, but since no power is used the information will not be that interesting for the kids.  We are going to use the tower to monitor the wind resource, but it would be nice to set up the whole system more effectively.

Could the inverter just be hooked to one phase of the three phase service? 
Should they sell the inverter and find one better suited to three phase, or would that be three inverters?
Is there a Phase converter they could use?

I kind of have a sense they should sell the whole system and buy solar panels, but the system exists in the community, and it would be nice to get it working better. 
Thanks for your input,
Todd

[DamonHD]

I suspect that hooking up to feed just one phase, eg unbalanced, would not be popular with whatever entity handles the electricity distribution (poles and wires).

Rgds

Damon

[joestue]

4KW is a trivial amount of power so they would likely care less if you're back feeding the grid single phase or not.

but at 60 cents/kwh.. eh, you guys running diesel generators up there?

[dnix71]

That close to the pole there is very little sun for 1/2 the year. The cold helps boost panel output some, but the Bergey should stay as long as it works. As others have noted here diesel will run in weather cold enough to store propane in an open container.

In a harsh environment a long way from nowhere, it's nice to have more than one way to make power.

The inverter may have been installed to make 240 split phase for an electric dryer in the laundry room. You can't make 208 3-phase into 240 split phase any other way except with a center tapped boost transformer.

[Bruce S]

To make it a little more interesting to the students, find something that the power can be used for.
Since it's already being converted to AC, you could have the school's maintenance person(s) wire one outlet to a separate outlet that goes to the science classroom, and possibly use that outlet to grow herbs during the school year?
That along with monitoring equipment such as an anemometer, logging equipment for the incoming energy as well as energy used will go a long way is keeping people interested. Plus having basil in the deepest part of winter is pretty nice . Next could be a little fish farm, that uses the battery power for the pumps, that provide aeration, and one that pumps the fish droppings to the plants as food, etc.
Can't hurt the use the monitoring equipment to find out how well the mill is doing too.
Having a mill up nice and high is a good thing, how's the terrain around it?
   

[OperaHouse]

I would have to expect that heat is always an option in Alaska.  I use excess PV power to heat hot water. A 2KW water heater used as a water pre heater into the existing system would be an easy fit.   4KW of resistance heating distributed into a couple rooms would not overpower the controls of existing heating system.   The real educational part of the system would be an Ardunio UNO as a controller to direct the power where it could be used most effectivly.  A couple sensors, controller and a few solid state relays would come in under $100.  The programming would be hands on for the students and allow them to test strategies for most effective use of the power. 

[thirteen]

Making a duel system would be interesting for most everyone. adding some bicycle peddling to add power maybe worth looking into for things to do out in the sticks. Make your system usable for power outages might be worth looking in to. A hydro phonics system might be interesting to run. Off your system. 13

[SparWeb]

Not sure how the turbine got paid for without a proper hook-up being part of the project.

Somewhere on e-bay you may be able to track down a single-phase-to-three-phase transformer.  Finding one with a 5kVA or greater rating and also wound to match up the voltages you need in on primary and out on secondary will make for a pretty specific search...  I gave e-bay a shake and didn't find one after a couple of minutes, but of course if you're more dedicated you may be able to track it down.  Expect it to cost ~500 dollars.  You may also pick that stuff up from government surplus sales - if they happen in AK, that is.

I realize it's not a cheap solution, but it costs way less than buying one new.

[SparWeb]

Close...

http://www.ebay.com/itm/Temco-Transformer-Buck-Booster-Series-4192-208-240Volts-/300985155512?pt=BI_Circuit_Breakers_Transformers&hash=item46141cffb8

But not quite.

[joestue]

if all you need is to convert 240 to 208 you only need a 32 volt transformer rated at 1/8th the kva required for the buck/boost.

there is a way to convert three phase to two phase but there's no such thing as a single phase to three phase transformer.

[dnix71]

joestue There is indeed a single/split to three phase converter. They are power hogs. A printer I used to visit had one in his loft. It looked like a big motor. He had a large Hamada sheet fed press that required 208 3-phase, but FPL wanted $20k to add transformers and run wires across the street where the nearest 3-phase was. He bought the converter and tapped two 100 amp service panels to feed it. He tapped his neighbors bay panel in exchange for paying the whole electric bill each month.

The converter pulled about 150 amps at 240v so he had to turn off the a/c when he bumped the press to set up a job. The converter was only run when needed. He had to wait for it to spool up before using it.

What made all that worthwhile was he printed full color sales brochures for million dollar homes for sale on the island of Palm Beach with that Hamada.

[joestue]

well yeah, i wouldn't say they are power hogs though.. a nice quiet three phase 8 pole induction motor and a few run capacitors gets you a converter, depending on the loading and all that it won't be a perfect 120 degree phase shift.
note that i said single phase to three phase transformer.

[dnix71]

This rotary should do it.
http://www.ebay.com/itm/Rotary-Phase-Converter-AR5-5-HP-1-to-3-Three-PH-Heavy-Duty-HD-CNC-American-Made/281095520874
Includes the motor.

[fabricator]

I have a ten horse rotary phase converter it is mounted in the attic above my shop because it is so noisy, a high pitched whine, my friend has a 15 hp rotary to run an irrigation pump, you can carry on a conversation standing right next to it it's so quiet, wish mine was that quiet.

[Tbailey4]

Thanks for the input,
I do think it is an important part of the project that it is tied to the grid, in that the problem of power generation is something faced by the whole community.
I think we have the funding for a rotary phase converter, but would it be a parasitic load, ie in a class 2 wind zone and a 1kw bergey would this thing be spinning all the time or just when there was extra power. 
I am not sure how big the service is to the school, but it is a, modern school with around 80 students, if it were just hooked to one phase of the service, would it actually make a difference in the power consumed by the school (not wanting to get to the question of, on a diesel based micro-grid does distributed energy negatively affect costumers without distributed energy systems)  or would it just appear as heat in the transformer?
Thanks
Todd

[dnix71]

I would leave what works intact and buy solar to go with it. The teacher could add monitoring equipment to the solar and wind and let the students see exactly where they would be if the diesel grid failed (up a frozen creek without a paddle). The value of a good diesel mechanic would immediately become obvious. The sooner these young people see the precarious position our oil dependent society is in the better.

You might see if it is possible to just run lights at night on what the Bergey and solar make and store in the batteries.

[Mary B]

Connected to one phase will offset some of the schools use. Might want to work with the power people to see if one phase is unbalanced and drawing more and put it there to offset that.

[SparWeb]

... but there's no such thing as a single phase to three phase transformer.

Explains why I was having trouble searching for one...   

[OperaHouse]

Every three phase system is unbalanced.  80 students is pretty small but likely 4KW will be easily lost. By its very nature every three phase motor in the system will try to rebalance the phases.  No need to buy a rotary converter, the generator will do that for you.  This is a teaching moment.  Some do gooder has spent a lot of money and just taught a generation that RE doesn't work.