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Joined: Jul 2002
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Hi Scott and the regulars here. I have a question that I hope that you guys can help me answer. I have done these sorts of calcs a million times before, but owing to lack of practice in the last few years, I've forgotten how on earth they're done. OK, here we go: A given 3 phase Starconnected installation, has the following Phase currents:  R Phase= 30A
 Y Phase= 25A
 B Phase= 40A
Having this information, how then is the current likely to be carried by the Neutral calculated?. Thanks in advance, Mike Trump.




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Mike, just before my head exploded, I got 13.2 amperes, but I cheated and used Gerald Newton's www.electrician.com/electa1/electa4htm.htm (This assumes ONLY øn loads and an even 120° ‘spread.’)




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Oops, Sorry Bjarney, I'd forgotten that you guys call Phasors, Vectors!.




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Take the square root of the quantity R^2 + Y^2 + B^2 minus the quantity R(Y) + R(B) + B(Y). R^2 = R squared (900 + 625 + 1600)  (750 + 1200 + 1000) 3125  2950 175 Square rood of 175 = 13.2288
Don
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Phasors or Vectors... no problem. Isn't phasor a more accurate term in AC calculations?
Question for Trumpy... what is a tensor?




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Wow, question already answered by the time I got the notification! One question: Do the loads need to be pure Resistance LN, or will Reactive LN loads result in the balanced harmony also? Not trying to start any trouble, just want to be sure. Scott35
Scott " 35 " Thompson Just Say NO To Green Eggs And Ham!




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Tensors are used in some engineering calculations. I think the relationship between scalars, vectors and tensors is something like: Scalar: x This box weighs x ounces.  Vector: x, y I want this box x feet from that wall, y feet above the floor.  Tensor: a b c d I want to know how much stress ( tensiontensor, get it?) the hole for the box places on the wall. I don't remember how to calculate this, just that tensors were useful  Here is a proper description of tensors: http://www.physlink.com/Education/AskExperts/ae168.cfm You can even apply tensors to Ohms law: http://www.tf.unikiel.de/matwis/amat/semi_en/kap_2/basics/b2_1_3.html




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Thank you, CH. ‘A tensor may be defined at a …collection of isolated points of space (or spacetime), or it may be defined over a continuum of points.’Now, maybe that’s sort of like explaining n thdimensional systems. The simplest shadow of a 2dimensional plane is a 1dimensional line. The simplest shadow of a 3dimension cube is a 2dimension plane. [The simplest shadow of a 1dimension line is a “zerodimension” point.] Outside of the human realm, the simplest shadow of a 4dimensional “object” is a 3dimensional form called a tesseract—which we view in 3 dimesions to be (roughly) a set of nested cubes. We cannot perceive a 4dimension object—only its 3dimension shadow. Will someday be useful for polychoroniodic tetrasesquiphase zeptojoule power analysis..} http://pw1.netcom.com/~hjsmith/WireFrame4/tesseract.html (drag cusrsor through image) http://mathworld.wolfram.com ..search for ‘Magic Tesseract’ (drag cursor through java image) http://en.wikipedia.org/wiki/Tesseract Rest in peace, Doctor Sagan... [This message has been edited by Bjarney (edited 09052004).]




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Bjarney, A vector only gives, (as I understand it)a magnitude of a force by it's length, whereas a phasor also gives it's direction of movement.




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"A vector quantity is a quantity which is fully described by both magnitude and direction. On the other hand, a scalar quantity is a quantity which is fully described by its magnitude." From the physics classroom [This message has been edited by resqcapt19 (edited 09062004).]
Don(resqcapt19)



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