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#129159 08/31/04 02:14 AM
Joined: Jul 2002
Posts: 8,407
Trumpy Offline OP
Member
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 Star-connected 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. [Linked Image]

#129160 08/31/04 03:08 PM
Joined: Apr 2002
Posts: 2,527
B
Moderator
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 ø-n loads and an even 120° ‘spread.’)

#129161 08/31/04 07:55 PM
Joined: Jul 2002
Posts: 8,407
Trumpy Offline OP
Member
Oops,
Sorry Bjarney, I'd forgotten that you guys call Phasors, Vectors!. [Linked Image]

#129162 09/01/04 01:38 PM
Joined: Nov 2000
Posts: 2,148
R
Member
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


Don(resqcapt19)
#129163 09/01/04 11:38 PM
Joined: Apr 2002
Posts: 2,527
B
Moderator
Phasors or Vectors... no problem. Isn't phasor a more accurate term in AC calculations?

Question for Trumpy... what is a tensor?

#129164 09/02/04 02:15 AM
Joined: Oct 2000
Posts: 2,721
Broom Pusher and
Member
Wow, question already answered by the time I got the notification! [Linked Image]

One question: Do the loads need to be pure Resistance L-N, or will Reactive L-N 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!
#129165 09/05/04 10:03 AM
Joined: Sep 2002
Posts: 1,498
C
C-H Offline
Member
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 (tension-tensor, get it?) the hole for the box places on the wall. I don't remember how to calculate this, just that tensors were useful [Linked Image]

-----------

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.uni-kiel.de/matwis/amat/semi_en/kap_2/basics/b2_1_3.html

#129166 09/05/04 02:35 PM
Joined: Apr 2002
Posts: 2,527
B
Moderator
 
Thank you, C-H.

‘A tensor may be defined at a …collection of isolated points of space (or space-time), or it may be defined over a continuum of points.’

Now, maybe that’s sort of like explaining nth-dimensional systems. The simplest shadow of a 2-dimensional plane is a 1-dimensional line. The simplest shadow of a 3-dimension cube is a 2-dimension plane. [The simplest shadow of a 1-dimension line is a “zero-dimension” point.]

Outside of the human realm, the simplest shadow of a 4-dimensional “object” is a 3-dimensional form called a tesseract—which we view in 3 dimesions to be (roughly) a set of nested cubes. We cannot perceive a 4-dimension object—only its 3-dimension shadow.

[Linked Image from 6l6.net]

Will someday be useful for polychoroniodic tetrasesquiphase zeptojoule power analysis..}

[Linked Image from 6l6.net]
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 09-05-2004).]

#129167 09/06/04 07:57 AM
Joined: Jul 2002
Posts: 8,407
Trumpy Offline OP
Member
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.

#129168 09/06/04 01:27 PM
Joined: Nov 2000
Posts: 2,148
R
Member
"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 09-06-2004).]


Don(resqcapt19)
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