[aprssig] TAPR Dayton Solar Talk

Steve Noskowicz noskosteve at yahoo.com
Mon May 23 00:59:37 EDT 2011

Background to understand:

These 'line-tie' inverters are clearly not free running AC inverters as commonly envisioned.  Thay can't be.  They must have a very stiff (low impedance) grid to connect to and they phase lock to it in order to feed power back into the grid.  The voltage is controlled by the low impedance grid and the line-tie electronics injects current into the line in the proper phase.  The actually don't need to be (and aren't) a constant voltage type thingy (technical term). The phase of the currnet *must* be precisely controlled and locked to the grid in order to do this.  No low impedance grid supplying voltage, no phase lock reference, no power back-feed.    No tickey, no washy.  

The electronics certainly have everything there, or could, to be configured to generate in a free run mode (if so allowed), but to feed power into the grid, phase lock to the source voltage is a necessity.  All the big boys have to do this.

Now, A fueled, stand-alone *generator* is another story.  It does generate a free running, AC voltage source type output and you better disconnect if you don't want to electrocute that lineman reparing the downed line.  It's happened before...

Hope that helps understand it.

P.S.  Electromechanical Steam, coal, etc fired power-plant generators, we are told, can maintain this lock-up automatically as long as you get them in phase before connecting them.  They put a light bulb between the grid and local generator hot lines.  Then they tweek the phase (frequency) of the local generator until the bulb goes out, then quickly close the switch.  The low impedance grid pulls the generator along and as you feed the local generator more fuel, it pushes power into the grid while maintaining phase lock because, well, that's the way it works.  I undersrtand it, but too many words and too late...it has to do with slip sort of things.
If you understand induction motors, just put mechanical power into it and the slip direction reverses and back feeds power.  Google "induction generator" to get an idea.
A friend of mine wanted to take a common ceiling fan outside and make a wind generator out of it.  OK in theory, but better if U have one designed for generating, I'm sure.

 73, Steve, K9DCI   USN (Vet) MOT (Ret) Ham (Yet)

I served during the cold war, so you can continue to be served a cold one.

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--- Glenn Little WB4UIV wrote:

> There would have to be some
> automatic, fail safe, means to disconnect your grid tie from
> the grid during a distribution failure.
> Without this you would energize a section of line that the
> line workers are expecting to be dead.
> 73 Glenn WB4UIV

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