On Mon, 12 Mar 2001 09:44:23 +0100 Kent Johansen writes: Hi - The technology of small-scale putting power back on the net is well known. In Denmark, 10% of the energy is produced by windmills. They are simply phased to the power. Due to the magneto-electic coupling between the windmill generator and the coal/gas fueled ones the net result is that the windmill helps drive the generators, saving fuel in that end (in 3'rd grade terminology). We have about reached the limit of what we can do with this type of windmills now, since they will actually be able to raise the net frequency and at the same time lose their regulation. (They run at a fixed speed due to the net frequency). -----------------------HH Response------------------------------------------ Seems to me that the network frequency can always be brought down by backing down of the "big" plants (hydro, gas fired, etc.). Is this not the case? ------------------------------------------------------------------------- ------------ The usual trick is to first regulate the effective voltage up to match the net voltage (this stage can be rather coarse). Then you brake/regulate the generator until there is no significant voltage between the net and your generator (you are in phase). -------------------------------HH Response------------------------------------ If one were to use an induction motor as a generator (as has been discussed here), it seems that we only need to watch the speed of the windmill. If it's below sync frequency, we take it off line (as it is now a big fan). If it's equal to or greater than sync frequency, we put it on line. If it's right at sync frequency, it will ideally draw zero current. As it tries to go above sync frequency, it will pull the line along with it, putting power into the line. It seems like the neat thing about the induction generator is that it automatically syncs itself to the incoming AC and shuts itself down should the incoming AC disappear. I wonder if some mechanical maximum power tracking system could be put on the blades of the windmill. Maybe have springs that pull the trailing edge of the blade to perpindicular to the wind. As the wind increases, this edge of the blade gets pushed back, changing the pitch of the blade. ------------------------------------------------------------------------- ------------------- In the old days, this was done with a three bulbs (3-phase) connected between the phases of the generator and the phases of the net. You would regulate/brake until the lights were all out (they would blink at the difference frequency, it is very easy to phase). Then then you flip the switch. The net will then keep you in sync with the big guys. --------------------------------------------HH Response------------------------------ I remember seeing this in an old movie... Pretty neat! ------------------------------------------------------------------------- ----------------------- We have an old 10MW plant from 1912, that is still working http://www.elmus.dk it is running off 8 meters water level. They have occationally just flipped the switch out of phase and it goes BLOP! out in the turbine inlets. That is all that happens. The turbines of course goes fast forwards or backwards to match the phase. Three issues: 1) Would your electricity meter actually care, whether you put power backwards through it ? I think it ignores the sign, and you need a reversible one. ------------------------------------HH Response----------------------------------------------- Since these are watt-hour meters and not volt-amp-hour meters, I believe they do an instantaneous multiply of the voltage and current to get the power in watts. If the current is flowing "the other way", the meter goes the other way. This small scale cogeneration is regulated differently in different areas. Here in California, it is called "net energy billing" and is encouraged by the Public Utilities Code. Harold ------------------------------------------------------------------------- --------------------------------- 2) The power plant has certain standards for noise etc. that have to be met. You have to produce a lot of power to pay for the licence, most likely. 3) It might give the electricians working on the net a neato scare when they find that whatever is connected to your little gingerbread house is live when they disconnected it. Kent FCC Rules Online at http://hallikainen.com/FccRules Lighting control for theatre and television at http://www.dovesystems.com ________________________________________________________________ GET INTERNET ACCESS FROM JUNO! Juno offers FREE or PREMIUM Internet access for less! Join Juno today! For your FREE software, visit: http://dl.www.juno.com/get/tagj. -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu