Dynamic vector diagrams in Excel

[Rudimard]

Hi everyone,

I was hoping that one of you guys can help me with an issue I've been having:

I want to create a dynamic vector diagram in Excel. What I want to do is geometrically add different phase currents in order to determine the current in the neutral wire (so basically determining currents in the neutral wire when unsymmetrical loads are connected to a Y system, see screenshot). Let me describe it on an example:

Let's say we have

Current L1: 7,5 A
Current L2: 12,5 A
Current L3: 15 A

Let's set the scaling in cm (or whatever excel uses to determine where something in the sheet is, I guess it would be X,Y coordinates - help!&#128517 with 1A/cm. It would be great if this was adjustable (so that if we have currents with 100A+ that the factor can be 100A/cm).

The way you add the currents is following:

First, you draw the current L1 with 90° (so straight upwards). Then, you draw the current L2 where the current L1 ends, with an offset of 60° (this offset is always the same). Then, you draw the current L3 where the current L2 ends, again with the 60° offset. After that, the starting point of the current L1 needs to be connected to the endpoint of the current L3. The length of this line should then be converter back to A, according to it's length.

I hope I was able to explain it well and that there is someone who can help me with this!

Thanks!

[MrShorty]

How much of this is Excel programming and how much is generic math/geometry/engineering? It looks to me like you are describing basic vector addition. Excel really doesn't have any built in functions for vector addition, but, if you understand the math/geometry well enough, we should be able to come up with formulas that will perform the addition.

Sometimes, I see people use complex numbers to perform the addition. There can be advantages to this. In this particular case, once you've expressed each current as a complex number, then the addition is a simple IMSUM() function. If needed, an IMSUB() function can get the neutral leg vector. Once you have the neutral vector expressed as a complex number, then the length of that vector is an IMABS() function. The main difficulty to using complex numbers for this is taking your r,theta expressions that you currently have and converting them to x+yi values (which is mostly a trig problem).

I obviously have only thought through this superficially. Is there a specific part of this that you need programming help with? Or do you need some help understanding the geometry/trigonometry/engineering side of the problem before getting to the programming side of it?

[Rudimard]

Hi MrShorty,

thanks for the quick reply - glad to know that you understand exactly what I mean.

Yes, I want to show my students how to add vectors without needing to calculate it with complex numbers. What I want to do is have a way (I'm not an excel expert, so I thought that VBA would be the only way to do it) where the vectors fetch coordinates/lengths and draw themselves in the worksheet - to automatically have the right answer and how it should look like. The calculation would be done in the backend, using different formulas.

Can you help me with this?

Thanks!

[MrShorty]

I'm sure we can help. It's been a long time since I've needed to do vector addition, so I don't recall all of the different strategies/algorithms for doing it. If you don't want to use complex numbers for this, what strategy would you like to use? Help us understand the algorithm/strategy you want to use for this vector addition, and we will help you program it into the spreadsheet.

Also, regarding VBA, it should not be required for this, but let us know if you prefer VBA over worksheet formulas and a little about why you prefer VBA. We should be able to help using either programming language for this.