# Thread: Help, finding points on circumference of circle(complex numbs-electrical engineering)

1. ## Help, finding points on circumference of circle(complex numbs-electrical engineering)

Hey there, hoping someone here can help me on an easy one here

basically I have a circle on a graph x/r (real and imaginay axis)

the circle is not centered

I have the which is 1.5ohm(units in use) (length) at a point of 76degrees

I am to find the reach at 5 more points on the circumference of the circle.

60,120,180,240,270 degrees.

Is this really as simple as the formula --> distance x cos(angle1 - new angle)
= 1.5 x cos(76-60)
= 1.44 ohm

I am shooting in the dark, so I cant assume this is right and go infront of my boss and do this wrong

Any help is appreciated.

Thanks,

2. ## Re: Help, finding points on circumference of circle(complex numbs-electrical engineer

Hey rumor84.

When you say it is not centered, do you mean its centre is not necessarily (0,0)? If this is the case, you will need some other piece of information.

Basically the relationship for a circle is (x-a)^2 + (y-b)^2 = r^2 for center (a,b). Two pieces of information (two points) should give you enough to figure out (a,b).

3. ## Re: Help, finding points on circumference of circle(complex numbs-electrical engineer

hey chiro,

yeah the centre is not necessarily (0,0)
/i see where you come from whith the formual, basically a right ange triangle, drawn on a circle and find you x,y points or a,b
but since this is a polar graph, i basically have a point that is 1.44units out (ohms) at an angle of 76.
maybe i need to convert from polar to rectangular then use the formula you posted?
you see 1.44 i would think be my r value in your equation or hypotneuse as typycally seen.

but how do i find more pints on this graph from here? im going through loops

4. ## Re: Help, finding points on circumference of circle(complex numbs-electrical engineer

Originally Posted by rumor84
hey chiro,

yeah the centre is not necessarily (0,0)
/i see where you come from whith the formual, basically a right ange triangle, drawn on a circle and find you x,y points or a,b
but since this is a polar graph, i basically have a point that is 1.44units out (ohms) at an angle of 76.
maybe i need to convert from polar to rectangular then use the formula you posted?
you see 1.44 i would think be my r value in your equation or hypotneuse as typycally seen.

but how do i find more pints on this graph from here? im going through loops
His point was that you aren't given enough information to determine the circle.

There are an infinite number of circles containing the point 1.5*{cos(76deg),sin(76deg)}.

You need at least one other piece of information before you can hope to proceed.

Are you trying to draw a transmission line impedance chart?

5. ## Re: Help, finding points on circumference of circle(complex numbs-electrical engineer

yes i am trying to draw a transmission line impedance chart, do you have experience in this?

6. ## Re: Help, finding points on circumference of circle(complex numbs-electrical engineer

Originally Posted by rumor84
/i see where you come from whith the formual, basically a right ange triangle, drawn on a circle and find you x,y points or a,b but since this is a polar graph, i basically have a point that is 1.44units out (ohms) at an angle of 76.
maybe i need to convert from polar to rectangular then use the formula you posted?
you see 1.44 i would think be my r value in your equation or hypotneuse as typycally seen.
but how do i find more pints on this graph from here? im going through loops
If you knew the lengths of each of those three vectors then we can find each of those three points.
Any three non-colinear points uniquely determine a circle.

7. ## Re: Help, finding points on circumference of circle(complex numbs-electrical engineer

Originally Posted by rumor84
yes i am trying to draw a transmission line impedance chart, do you have experience in this?
The bottom of your circle is at (0,0).

8. ## Re: Help, finding points on circumference of circle(complex numbs-electrical engineer

yeah, this is a MTA angle or RCA angle on a line distance relay used in high voltage transmission. the impedance is plotted by an engineer, and i have to test the relay, and i am trying to compute other points to test, because i am able to calculate the 3 phase voltage and current w/ respective angle to produce this impedance of 1.44 ohm at 76 deg. but only one point on any circle, once i change my formula, i get outside of that circle in the picture shown and this doesnt work, need 3 plus point on the circumference. its tough