# Thread: Time current Curves - Coordination Study

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## Time current Curves - Coordination Study

I would like to learn the coordination study. As a starting point, I have decided to do the below exercise

I have a time current curves of upstream and downstream breakers in PDF. How can I do the co-ordination study manually. By manually, I mean I don't have any software with me.

How should I approach?

Thank you!

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Originally Posted by Charz
I would like to learn the coordination study. As a starting point, I have decided to do the below exercise

I have a time current curves of upstream and downstream breakers in PDF. How can I do the co-ordination study manually. By manually, I mean I don't have any software with me.

How should I approach?

Thank you!
determine the range of opening time for both breakers for all conceivable currents. compare them to see the amount of overlap. ideally there should be none, but non-adjustable thermal magnetic breakers have sloppy curves with wide variance in open time. depending on how critical the upstream breaker is, some overlap is acceptable.

this is a more complex way of saying, you overlay one TCC over the other and adjust any available settings so that the trip curves do not interact.

3. As mentioned, you overlay one on the other. I use Bluebeam for PDFs which allow me to do this if you don't have software. We use SKM for example

Consider that the TCC is based on a multiplier of 1

For example, if the QO breaker handle rating above was 20A, the 1 is the X axis represents 20A. You shift each in the same way.

If the voltage for that breaker is different than the next, you shift the next by the ratio of the voltages.

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Originally Posted by ron
As mentioned, you overlay one on the other. I use Bluebeam for PDFs which allow me to do this if you don't have software. We use SKM for example

Consider that the TCC is based on a multiplier of 1

For example, if the QO breaker handle rating above was 20A, the 1 is the X axis represents 20A. You shift each in the same way.

If the voltage for that breaker is different than the next, you shift the next by the ratio of the voltages.
I have bluebeam PDF. If I need to shift the curves left/right or Up/down and check, I dont think it can be done in bluebeam PDF.

What can be done to shift the curves?

5. Originally Posted by Charz
I have bluebeam PDF. If I need to shift the curves left/right or Up/down and check, I dont think it can be done in bluebeam PDF.

What can be done to shift the curves?
When you overlay the pages, you need to use the offset X to move them left / right. It only moves the entire image/curve, not individual LSIG segments.

In the old days I've also redrawn the 2nd TCC and then pasted that on the 1st TCC and moved it around.

It is definitely the poor mans way to do it.

Consider back in the day, we used to have all the TCCs on translucent vellum paper and lay them on top of each other on a light table and draw the overlaid logarithmic graph with them shifted around below.

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Originally Posted by ron
When you overlay the pages, you need to use the offset X to move them left / right. It only moves the entire image/curve, not individual LSIG segments.

In the old days I've also redrawn the 2nd TCC and then pasted that on the 1st TCC and moved it around.

It is definitely the poor mans way to do it.

Consider back in the day, we used to have all the TCCs on translucent vellum paper and lay them on top of each other on a light table and draw the overlaid logarithmic graph with them shifted around below.
You could trace each curve, convert the segments into a group, and put each group in the Toolbox for later use. You can re-size the curves using the "Scale" function in the "Properties" box.

7. Originally Posted by ron
...

Consider back in the day, we used to have all the TCCs on translucent vellum paper and lay them on top of each other on a light table and draw the overlaid logarithmic graph with them shifted around below.
That was how I learned it!
Later (but still prior to the age of PCs) we were able to photocopy onto clear plastic sheets used for overhead projectors which made it even easier.

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Thanks All!

Now I have the curves in PDF of an ETU of GE (Entelliguard Trip unit). It has LSIG function in it. I do not know the equations used to draw the curve. I would like to plot the curve in excel.

1) Is there any way I could derive the equation from the curve?
2) Should I consult the manufacturer to get the equation? Will they provide a digitized curves which I can use it with some free softwares?

9. Originally Posted by Charz
Thanks All!

Now I have the curves in PDF of an ETU of GE (Entelliguard Trip unit). It has LSIG function in it. I do not know the equations used to draw the curve. I would like to plot the curve in excel.

1) Is there any way I could derive the equation from the curve?
2) Should I consult the manufacturer to get the equation? Will they provide a digitized curves which I can use it with some free softwares?
With enough brain power, you could likely derive the formula for any curve, which I think is related to a Fourier series approximation.

The manufacturer will NOT give you the formula because it is not something they have derived. They provide the curves on their website and the software companies digitize them to work with their database. I'm not familiar with free TCC software

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Originally Posted by Charz
Thanks All!

Now I have the curves in PDF of an ETU of GE (Entelliguard Trip unit). It has LSIG function in it. I do not know the equations used to draw the curve. I would like to plot the curve in excel.

1) Is there any way I could derive the equation from the curve?
2) Should I consult the manufacturer to get the equation? Will they provide a digitized curves which I can use it with some free softwares?
Charz
I use a program called "GetData" for taking a TCC and importing into Excel. What I am importing is JUST the MAX (upper edge) trip side of the curve for use in Arc Flash calculations. There are some FREE programs available, but for me they did not work very well or maybe just not smart enough to figure them out.
Again, this only yields side of the curve. I suppose you could figure out a method to import the upper AND lower boundaries and attach them together somehow.
You are working with ETU's so you could be looking at generating an lot of graphs.

Try "Youtube" Excel-importing graphs", you will learn quite a bit about Excel.

Please note that "Siemens" offers free a program for engineers (and I would assume ECs also) for viewing ALL of their TCCs. You can make adjustments on ALL the settings and OVERLAY as many as you fit on your screen. VERY easy to work with.