On Monday, May 28, 2012 04:12:48 AM Dave Caroline did opine: > I think most people looking at idler rotary converters dont actually > scope the phases > I only came across one site stating the obvious > > given the basic diagram of > > 120 ac to motor P1 and output phase L1 > neutral--nc > 120 ac to motor P3 and output phase L3 > Capacitor P1 to P2 and to output phase L2 > > will notice the 180 deg phase of the two 120 lines are connected > directly to L1 and L3 so that is at 180 degrees not the 120 it should > be. So L2 is some where in between L1,L3 but if it was 120 degrees from > L1 then it would be 60 from L3 > the voltage imbalance would be silly so it is adjusted to be 90 form > L1 and it just about works > > Now after that point there is a 3 phase transformer, one may think > that helps the > phasing but I am not so sure, a friend at a transformer company said > many years ago that there is no such thing as a three phase > transformer, > it is really 3 single phase transformers. > > Dave Caroline
True, they just wind 3 sets of coils on a 3 legged core. My suggested use was to convert the delta connected source with its 'wild leg' into a wye connected source that doesn't have the wild leg because the center of the wye is now connected to the neutral bus. However when it is wound on the 3 legged core, the other two legs represent a 1/2 level of magnetic coupling from one phase to the other 2, and vice versa. With the center of the secondary wye grounded, a rectifier load that effectively loads each leg to ground, should be a heck of a lot happier. Otherwise the generated leg, which is designed for a delta connected load, (notice the center of the wye in this idler motor is NOT connected to the local neutral or anything else, it must be free to float) can and often will measure over 200 volts to ground while the other 2 driven legs are only measuring in the 127 area for what we usually call 220 volt single phase. That is wrong in fact because 127+127=254 today. But vector addition in a true 3 phase system needs to be done such that the phase to phase voltages are doing to be in the ballpark of 220 volts. Back when we had a 117 volt a leg std voltage, that translated to a 208 volt 3 phase circuit, the loss from 234 to 208 being the result of the vector addition. I can't do it in my head, but any calculator with trig functions can do it as fast as you can enter the numbers. Cheers, Gene -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) My web page: <http://coyoteden.dyndns-free.com:85/gene> Don't believe everything you hear or anything you say. ------------------------------------------------------------------------------ Live Security Virtual Conference Exclusive live event will cover all the ways today's security and threat landscape has changed and how IT managers can respond. Discussions will include endpoint security, mobile security and the latest in malware threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
