The reason that the waveform between two phases of a three phase connection is not distorted is that the sum of any two sine waves, of any amplitude and phase, but at the same frequency is always another sine wave at the same frequency. Bob Ammerman RAm Systems ----- Original Message ----- From: "Howard Winter" To: Sent: Monday, May 24, 2004 10:03 AM Subject: Re: [EE:] power factor change depending on voltage or phase? > Al, > > On Wed, 10 Mar 2004 07:11:19 -0800, al smith wrote: > > > I did some measurements, where I found peak current for 122VAC single phase > > to be 1.554A being pulled on the AC, and then did the same test using 212VAC > > (two legs of a 208 3 phase) and found the AC current draw to be 0.935A > > This has always perplexed me: surely if you're connecting across 2 of 3 phases (something we don't do in the > UK) then the voltages are at 120 degrees phase angle to each other, so you will be getting a distorted > waveform, not a sine wave? > > > Thus wattage is 189.6 for single phase, and 198W for the '3phase'. Pretty > > close in value, although I might expect them to be pretty much the same, > > since the same load was applied. So thats the first curious item. > > Unless you're using "True RMS" meters, I think the distortion I mention would mean that the readings would be > skewed. > > > Then, using the formula A=W/(V*pf*1.73) I get a pf of 0.58, much lower > > than I might expect. So is there a relationship of the pf related to > > voltage? I would tend to think not, as its the comparison of apparent vs > > real power, or the efficency of the supply. I wonder if running it using > > two of the 3 legs of a 3 phase power has anything to do with it? I do have > > a variac, so maybe I will run the same test, using a single phase 212VAC and > > see if there are any differences. > > I'd be interested to hear the results - and to see a 'scope trace of the waveform, so I can see if I was > right! :-) > > Incidentally, is power factor correction (PFC) a Good Thing for the user (ie. does the meter go round less for > a given power used) or for the supplier (the meter goes round more)? > > Cheers, > > Howard Winter > St.Albans, England > > -- > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > email listserv@mitvma.mit.edu with SET PICList DIGEST in the body > -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body