On Fri, 20 Apr 2001 16:55:59 -0700 Eric Smith writes: > I posed the following two questions on sci.electronics, but got no > replies. > I'm posting them here because I know that there are people here who > have > used PICs for power measurement. > > > > 1: > > I've been trying to figure out how to measure the power consumption > on > a three-phase wye circuit, and I'm stumped. > > Things I can measure: > > Vx, Vy, Vz: voltage on each phase relative to neutral > Ix, Iy, Iz: current on each phase > In: current on neutral > > Wanted: equation giving power consumption as a function of these > variables > > For instance, with a normal single-phase device I measure the power > consumed by integrating Vx*Ix. This is simpler because there's only > a > single path for the current. In the three-phase case, there may be > varying > phase-to-phase loads as well as phase-to-neutral loads. > > My first thought was to integrate Vx*Ix + Vy*Iy + Vz*Iz. But this > doesn't > take into account any neutral current, and I'm not convinced that it > would > be right even for a three-phase delta circuit (no neutral). > I believe this is correct, even considering neutral current. What if you ran three separate neutrals back to the source and considered this just three single phase circuits. This would then be the correct formula (calculating instantaneous power, so you'd have to do a bunch of of samples per cycle then average them). I also believe your rectifier circuit is correct. It would be a three phase voltage doubler circuit. I'd put a capacitor between V+ and neutral, then another between V- and neutral. Otta work great! Harold > > > 2: > > I'm trying to figure out how to build a three-phase front end to a > bunch > of DC-DC converters (such as Vicor VI-200 series), and could use a > bit of > help. > > If I run three-phase delta power into a bridge rectifier as shown > below, > what is the relation between the phase-to-phase input voltage and > the output > minimum, maximum, and average voltages? Unlike a single-phase > bridge > rectifier, I know the minimum does not approach zero. > > The cases I am most interested in is 208V phase-to-phase (common in > the > USA). > > I've checked some of my electronics reference books, and they don't > seem > to cover this case. Web searches for three-phase rectifiers on > Google and > Altavista come up with all sorts of information on "controlled > rectifiers", > which replace three or six of the diodes with SCRs, apparently for > voltage > or power factor control. But I can't seem to find anything covering > the > simple "uncontrolled" case. > > > > Any help with either question will be much appreciated! > > Thanks, > Eric > > > > Crude ASCII art schematic of three-phase rectifier: > > > > phase X |\ | > -------+------| >|-------------+------------- V+ > | |/ | | > | | > | | > | | /| | > -------|< |------- | > | \| | | > | | > | | > | | > phase Y |\ | | | > -------+------| >|------u------+ > | |/ | | | > | | | > | | | > | | /| | | > -------|< |------+ | > | \| | | > | | > | | > | | > phase Z |\ | | | > -------+------| >|------u------+ > | |/ | | > | | > | | > | | /| | > -------|< |------+-------------------- V- > | \| > > -- > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > email listserv@mitvma.mit.edu with SET PICList DIGEST in the body > > ________________________________________________________________ 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