I know a low frequency transformer is not an efficient way to do it, that is why I only intend my prototype to drive into one so I can simulate the mains safely.

..........but the lineman will be DEAD...

I have a working off grid design

thank you for the comments made I wasnt expecting to be machine gunned down to suggest such an idea but I do see your points. However a number of people are still interested in this subject and therefore is a worthy discussion.

I already know about all the backfeeding problems, islanding etc. One of my good friends is also a linesman and he has shown me how they ground every cable to ensure no islanding can occur.

I do understand that giving anything more than a basic diagram to the average electronic DIYer could be a very dangerous thing to do.

I have a diesel generator with a 7.5kw induction motor with the famous C-2C wiring method already capable of grid connecting and have done several times for short time experiments and it works fantastically. But I want to use free, smell free wind power not vegetable oil!

I also have a single phase 240v 60kva stamford generator which I can use for my own OFF GRID / grid connection experiments when I get my electronics up and running.

I also have a 500w and a 1000w wind turbine both feeding a 48v bank of fork truck batteries. Hence the desire to feed in with my incoming supply to supplement my house loads instead of using a few ton of cells and an impractical inverter.

The approach I was going to take with the paralleling inverter was to have the control electronics fed via a transformer from the mains side of the breaker (APPROVED). The breaker would be powered from this transformer (through the circuitry) so IF the mains dropped or DC was present then the breaker would drop out. The inverter could only supply power as and when it detected EACH 0 crossing events on the incoming line AND if the voltage on the incoming line was in tolerance AND if the timing of the zero crossing events were in specification.

IF all of these requirements are not met then power will not be supplied to the DC contact breaker or the dc-dc converter or the h-bridge or the mains contact breaker. In the event of any of the requirements not being met the system would disconnect and not retry connection for a preset amount of time.

Please no more warnings and information about killing linesmen law suits and legal requirements unless they are about the circuit or the protection methods.

Thank you

Phil

 > Awaiting the next depth charge of warnings :-D

I aggree with what you said there. I think it is highly unlikely that an experimental grid tie inverter will have enough capacity to power an entire neighbour hood, so for this sake of this discussion, I aggree with you. But.

The question of backfeeding is one that most definately needs to be considered. I'll give two expamples why:

I live sorta in the forest, with only six houses nearby besides mine. We are all fed from one 50KW transformer, and when the fuse blows on that it is only us six that go down. So, now a hypothetical situation:
It is day time, everyone but me is at work, so in the other houses the only things on are a few friges, a computer or two, maybe a few lights. Max load there would probably be 10KW including my house, probably less than that. Now, smart me decides to connect my (hypothetical ;-)) 12KW deisel genny to my breaker panel, so I can power my whole house. But, I forget to trip the breaker going to the grid, and voila, my small island of 7 houses now has power. If a linesman touches those lines, it will hurt. Probably not kill, since it is only 120 or 240 volts, but still most certainly has the possibility to be deadly. Now I'd have to be a pretty big idiot to do this, but there are people who might. Also, lets say I build a genny from a huge induction motor and fed that straight to the grid to sell back current. If I put capacators on it, it will continue to generate power even when the grid dies. So, again, possibility of a dead linesman.

Now, my second situation is completely true (if you can believe the newspapers, that is, lol!). There is a sort of club/dancehall type place where people have wedding and parties in a remote costal location in my country called Pier 1. It is quite a large place, so their backup generator is probably around 20KW. One day, the power company had turned off electricity in their area to service the lines, so Pier 1's genny was on. But, due to bad installation, etc, it was feeding power to the lines, and the linesman who was servicing them was killed. Yup, killed. Dunno what happened as a result of this, like lawsuites etc, but the fact still remains that a guy DIED. That should be reason enough to be VERY CAREFUll with this sorta thing.

So, I say go to it with your small transformer design, if you know what you're doing. A small transformer with not be able to power even your whole house, let alone your grid, so there is no real danger there. Once you get to larger models though, you should make your own 'mini-grid' to test it with, by using a backup genny or something.

Not all the rules are there just to tease the people.

But: "You cannot connect hardware that's not approved..."

What's the legal details here? I'm a HAM and in The Netherlands, I can build anything I want and connect it to the grid to DRAW power. Backfeeding from a DIY inverter would be off-limits though, definitely not legal.

But, in USA, I assume it's legal too to draw current from the grid by homebuilt devices? Or does ANYTHING that connects to the grid need to be approved?

Since these are my opinons I'll end by merely agreeing to dis-agree.

When I was determining which GTI to get, I spent quite a bit of time reading the Outback Power Systems user forum (http://www.outbackpower.com/forum/index.php) and recall someone asking about exactly the configuration you described.  I just went looking and can't find it, but if I recall correctly the answer in the forum was along the lines that they are working on it.

1.  An inverter large enough to supply all your electrical needs.
2.  A smallish battery capable of carrying the invertor for at least a few minutes at full load.
3.  A grid tied battery charger
4.  Your RE power source to also charge the battery.

Idea # 3 appeals to me because it's such a nice understandable (straight forward mechanial) approach. I just wonder how to obtain the controller/regulator for the DC motor.  Probably easier to do when there is a battery bank inbetween, so that the DC motor can be fed more steadily. Still, the inverter is the way to go, having no moving parts seems to be the future.

I've tested the thing with a 12V motor from a fan to cool a car-radiator connected to a 12V/15A power supply and a 100W induction motor (1 phase, i don't see a capacitor for a phase shift...)

When I just turned on the AC motor, it drew about 0.5A (230V~ input). I put a kWh meter in between and it turned at a certain speed. (the DC motor was generating about 8V)
When I applied current to the DC motor (it drew around 8A (wich is close to the 100W from the AC motor)) I could see the kWh meter turn slower (less power used, still not turning backworths) but the amps that were flowing between the grid and the induction motor rose to around 0.7A or so.

Does annyone have an explanation why the amp-meter showed higher power being used and the kWh meter showed that less power was being used? Does it have something to do with the voltage being out of phase so that the meters can't detect it the same? (something with vectors and those things?)

I need to get my hands on a better and more powerfull DC motor, I also have another 100W indcution motor lying around that has got a capacitor for a phase shift but the axis is of a differint size and I don't have the righ parts to hook it to the DC motor.