How to solve for Va=Ea-(Ra+jXs)Ia 3

[Clyde38]

I need to solve for Va in an EXCEL spreadsheet. I'm not familiar with the functions required to do this. Any help is appreciated. I have looked at the posts about complex numbers, but I'm still lost.

Va=Ea-(Ra+jXs)Ia

Ea=35
Ra=.00065
Xs=.0562
Ia=77.7

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[magoo2]

If you write out the steps you use to calculate it by hand, the Excel piece will be a snap.

Have you tried solving it?

 

[DiscoP]

There are a number of complex number functions available in excel - you need to ensure the Analysis ToolPak is checked in your "Add ins". This is under the Tools menu

Type COMPLEX in the help, and it should detail all the functions available.

But for equations as simple as your example, it is probably easier to do it by hand !

 

[electricpete]

Hm, well there are a number of ways.

One is just use use the standard excel tools to do it, which I assume you could do based on your knowledge of complex arithmetic.

Another is excel analysis took-pak. A downside of that is that your spreadsheets aren't very portable (if you give them to someone without the took-pak installed, they won't be able to see it).

Yet another way is to build the tools for complex arithmetic from vba. Doug (ids) has done something similar to this, perhaps interfacing with Alglib. This treats complex numbers as two adjacent cells: left one with real value and right one with complex number. To enter a formula you need to select two adjacent cells, type the formula, and press ctn

Attached spreadsheet has all those routines in vba (see examples tab for their use) and your problem solved in the tab labeled Clyde.

I assumed Ea and I have the same angle (0), probably not the correct assumption, but good enough for illustration.

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[electricpete]

Sorry, I didn't see the prior responses before I responded... otherwise I wouldn't have repeated what they said.

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[Clyde38]

Thanks to you both.

magoo2 - I have not solved this. I'm am trying to incorporate some design work for an associate, but the help provided for complex numbers seems confusing to me. Maybe I'm the problem.

DiscoP - I do have the analysis ToolPak loaded. This is just the first of many equations that I will try to incorporate in the spreadsheet.

Would either of you mind posting an example spreadsheet for just this equation? I see functions for using text etc. in the group of complex functions and I'm not quite sure how this relates to task at hand.


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[Clyde38]

electricpete - Thanks for your post and spreadsheet.

magoo2 & DiscoP please ignore my request for a sample spreadsheet.
I did not see pete's post at the time I asked.

Thanks to all!


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[DiscoP]

Hi Clyde

I assumed you were going to do more complicated equations with it.

Attached is how you can do this using the Complex functions of excel.

I've included the answer with the magitude and angle too (which is what most electrical people really care about !)

The rectangular version of the answer uses 'i' for the imaginary part - you can get the answer displayed with a 'j' too if you want - see help for details.

 

[IDS]

Good to see the complex number functions being used. All the hard work is done by the Alglib routines (which are included in the file). My bit was just some interface routines to convert a two cell range into the Alglib comple data type.

More details at the link below:

http://newtonexcelbach.wordpress.com/2010/08/11/alglib-complex-number-functions/

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/

 

[DiscoP]

Oops - missed your last reply too !

The spreadsheet I made up uses a different method to electricpete - it may be of some use ??

 

[electricpete]

To enter a formula you need to select two adjacent cells, type the formula, and press ctn

Correction: That should have been ctrl-shift-enter.
This is of course standard syntax for entering array formulas.
There's more info at Doug's link.


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[magoo2]

You can also do the basic math

For (R + j X) * I

what is the real part, and what is the imaginary part?

All you're doing is added another real term to this result (Ea).

You should be able to check your result since this is a new member post and i suspect a student post.

 

[electricpete]

...since this is a new member post and i suspect a student post.

After joining Eng-Tips Forums on October 31, 2003, I've logged in 4,246 times. My last login was on Monday, January 30, 2012. I've started 36 threads, posted 350 replies, and written 2 FAQs

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[electricpete]

Before this thread passes away into oblivion, I just wanted to mention again that in general the angle between Ia and Ea for sync machine should be considered (in general we can arbitrarily pick one of the phase angles as zero = reference, but not both). To solve this, additional info would be needed such as machine real power or terminal power factor angle.

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[Clyde38]

magoo2 - No offense taken. My problem was not with the theory, my problem was understanding the crystal clear help from Microsoft Excel. Actually I'm somewhat embarrassed that I had trouble with these functions. For machine design help I think posting to Electric motors, generators & controls engineering Forum should have been appropriate. There are a lot of smart people there.

electricpete - Thanks again!



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[Clyde38]

I'm in good shape now thanks to all of your help. While I was researching this I came upon this site:

http://www.wisc-online.com/objects/ViewObject.aspx?ID=eng5603

Maybe it will help someone else. . .

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[magoo2]

My apologies, Clyde, if i came down too harsh on you. I thought from your original post you didn't understand how to work with complex numbers.

Before these complex functions were developed in Excel, I used to make worksheets with

products based on (a + j b) * (c + j d)

results would be in cells e and f

division based on (a + j b) / (c + j d)

again, results would be in cells e and f

Obviously, you have to multiply the equations to get the results, but once you've done so you can use the worksheet for many varieties of complex math problems.

It's just another way to skin a cat.

 

[yakpol]

By simple arithmetic equation Va=Ea-(Ra+jXs)Ia can be solved for Va:
Real Va = Ea-Ra*Ia
complex Va = Xs*Ia

Don't need to use analysis tool pak...

 

[electricpete]

Based on literal interpretation of op, yes. But as mentioned, Ea and Ia should not both be treated as scalars.

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[electricpete]

sorry, didn't mean to take over the thread. I'll butt out and let op speak for himself.

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