Kirk Wallace schrieb: > On Mon, 2011-03-14 at 22:55 +0100, Peter Blodow wrote: > >> Kirk, >> >> "Neutral" is not to be considered. You have two wires coming from the >> supplier. Adding a capacitor makes three of them. The two mains lines >> are 180 degrees apart by definition. The capacitor makes a third phase >> 90 degrees between them. Connect your motor, and it will be running, >> regardless of which line is grounded. >> >> Peter Blodow >> > > Sort of. Your description above I believe matches my diagram showing the > starting mode, or the middle picture: > http://www.wallacecompany.com/machine_shop/EMC2/three_phase_converter-1a.png > > In my original argument, I stated I thought L1 and L2 from the mains are > 180 degrees apart, because if you scope L1, you get a sine wave. If you > scope L2, you get a sine wave that is shifted 180 degrees from the L1 > sine wave. The problem is that the scope uses ground or neutral as the > reference for the L1 and L2 voltage. but the neutral is not used in the > circuit so the 180 degrees doesn't apply or add to the understanding of > how the circuit works. The only thing we know is that there is a single > 240 Volt sine wave when L1 is referenced to L2 or vis versa and this > single wave is connected across a single phase on the converter motor. > Once I drew this single phase wave on the A and B converter motor > terminals, everything else flowed from that. The only time 180 degrees > came to mind from developing this diagram was in considering the > unconnected C terminal relative to A and B. C looks like a transformer > center tap relative to A and B, so there should be a sine wave between > L1 (A) and and C that is 180 degrees from L2 (B) and C. To me so far, > this doesn't add anything to the understanding of the converter. > > You are considering a two phase system whichis actually a one phase system of, say, 230 volts per phase. In this case, everything is symmetrical, and each "wire" is 180 degrees apart form the other, regardless of which is grounded. One one them is defined as zero volts, so the other one will be 230 volts (therefore one phase). In a three phase system, three leads are carrying 230 volts per phase also, but considering the delta shape of the connection, beween them there will be a voltage of 230 volts times sqrt of three, approx. 400 volts. Imagine the whole thing as a regular triangle with three equal sides and the center grounded, it is easy to see that you can make three single 230 volts AC circuits referenced to ground or neutral (which will not be delivered by the power supplier in every instance, but defined locally by grounding the center tap of the power line transformer station). This is the basic great idea of three phase supply - transport 75% more energy by use of 50 % more wires, not counting the advantage of a direction of rotation information.
In summary, with a usual 230/400 volts three phase system, you can split this into three single phase, 230 volts systems (L1, L2, L3 or R, S, T) referenced to ground (N) or use it as a 400 volts rotary system for motion devices, regardless of ground. In case of unavailability of the two other phases, use a phase shift capacitor to create your own 230 volts rotary system (with power drawbacks), wire your motor in delta 230 volts and run your machines as good as they will run! Peter Blodow > My converter does have a pair of running capacitors and sometime I may > try to apply the start capacitor logic to these to try to figure out how > they work. My guess is that they store energy during the motor period > and release it during the generating period of each shaft rotation, but > I can't prove it, yet. > ------------------------------------------------------------------------------ Colocation vs. Managed Hosting A question and answer guide to determining the best fit for your organization - today and in the future. http://p.sf.net/sfu/internap-sfd2d _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
