1. Jul 27, 2014

### MissP.25_5

Hi,
how do I find the center and radius from these equations? The 2 equations represent 2 different circles, by the way. I need to draw 2 circles.

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2. Jul 27, 2014

### phinds

What have you tried so far? Those equations don't mean a thing to me, but you DO have to show some effort on your own before (or in addition to) asking for help.

3. Jul 27, 2014

### MissP.25_5

The equations are actually equations of power transmission and power reception circle diagram.
I am sorry for not having an attempt but I am stuck here.

4. Jul 27, 2014

### HallsofIvy

Staff Emeritus
I presume that the "$P_S+ jQ_S$" and "$P_R+ jQ_R$" on the left of those two equations are the complex variable "z" that is to be graphed.

An equation of the form "$z= Ae^{j\theta}$", with A a real number and $\theta$ from 0 to $2\pi$, is a circle with center at 0 and radius A. An equation of the form "itex]z= B+ A{j\theta}" is a circle with center at the complex number B and radius A.

Of course, as $\theta$ goes from 0 to $2\pi$, $\theta- \pi/2$ goes from $-\pi/2$ to $3\pi/2$ but the graph still covers the circle, just "starting" at a different point. The first circle has center at the point $j(0.81)E_R^2/X$ in the complex plane, which is $(0, 0.81E_R^2/X)$, and radius $0.9E_R^2/X$. The second has center at $(0, -0.81E_R^2/X)$ and the same radius.

5. Jul 27, 2014

### MissP.25_5

How do you get $(0, -0.81E_R^2/X)$ for the second circle? Shouldn't it be $(0,-E_R^2/X)$? I forgot to mention that $P_S$+$jQ_S$ are indeed a complex number in the form Z= X+iY because P is the real power while Q is the reactive power.

Last edited: Jul 27, 2014
6. Jul 28, 2014

### Staff: Mentor

You know that you *must* show your work in your posts of schoolwork questions here. Check your PMs.

7. Jul 28, 2014

### Staff: Mentor

Thread is closed. MissP.25_5 is on a temporary vacation from the PF.