Understanding 3 phase sequencing

[ardhuru]

I'm working on a system that has to be polling the 3 mains phases, and to visualize the waveform, I created an Excel spreadsheet, where the 3 phases in sequence would be as denoted by the black, red and blue columns (using the US color convention), each 120 degrees out of phase.

Now, looking at the data, I would have expected the waveform to be 3 sign waves, in the sequence Black-Red-Blue, but they come out Black-Blue-Red. I found out another page that does something similiar at http://en.wikipedia.org/wiki/Image:T...e_voltages.png , and sure enough the sequence is Black-Red-Blue.

This has me perplexed. When I plot 3 waves, shouldnt they come out in sequence? (0 degrees-120-degrees-240 degrees)

I might be doing something entirely foolish here, and would greatly appreciate any help.

Regards,

Anand

[skimask]

Not exactly sure what you're trying to visualize here, but...
The graph is correct. You're expecting black-red-blue based on where they cross Zero. But, if you look, black crosses zero on the ascending, red crosses zero on the descending, blue on the ascending again.
You've got the formula's set up so that the last phase (blue) is actually leading the rest of them, and the middle phase (red) lags blue, leads red.
I think you want your formula's to be:
black = sin(a2) - leading all
red = sin(a2 - 120) - following black
blue = sin(a2 - 240) - following red

[ardhuru]

Oh, okay, that makes sense.

Just to make sure I understand this right; if I were to feed these Black-Red-Blue into pins 1,2,3 then the sequence of pins going high (or low) would be 1-2-3, and *not* 1-3-2, right?

Thanks for the prompt help.

Anand

[skimask]

Your answer is right there in your graph...but it really depends on where your referencing from.
If you're talking about the zero crossing point, it goes just like your graph...
1 going high - 0
3 going low - 60
2 going high - 120
1 going low - 180
3 going high - 240
2 going low - 300
1 going high - 0 (360)

wash-lather-rinse-repeat...