Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

3pahse

Status
Not open for further replies.

Electronman

New Member
somebody told me that if we do so for 2 of phases then we lose the fuse, but if do so for 3 phases then they will cancel eachothers?
 

dknguyen

Well-Known Member
Most Helpful Member
I can see where he's coming from. Intuitively it seems wrong...but after looking at the graph it seems to me that it could be true. Every time one wave peaks, the other two waves each have a magnitude that is half as large, and half the magnitude. So for every peak, the other two waves have a sum that is the same magnitude as the peaking wave, except it's opposite polarity so they would cancel. And every time a wave crosses zero, the other two waves have polarities that are of equal magnitude and opposite polarities so the sum of all three would be zero.

EDIT: I graphed it out in MATLAB and it appears that

0 ≡ Asin(ωt) + Asin(ωt-2/3*pi) + Asin (ωt - 4/3*pi)

so the cancellation seems to hold true for all areas of the curve, not just the peaks and zero crossings. But 0V at a single node does not mean no current flow. After all, a common short is some +V connected to 0V.
 

Attachments

  • 3 Phase.jpg
    3 Phase.jpg
    55.2 KB · Views: 71
Last edited:

dougy83

Well-Known Member
That is rediculous dk.

Your equation shows that there will be zero volts at the connection point of the 3 phases. However, there is also up to 440V (or whatever it is) at the source of any of the 3 phases, which will be pumping a heap of current through the cable to force the connection to 0V.

It's like saying that connecting a -12V supply to a +12V supply will be a good idea because 0 = -12 + +12.
 
Last edited:

crutschow

Well-Known Member
Most Helpful Member
somebody told me that if we do so for 2 of phases then we lose the fuse, but if do so for 3 phases then they will cancel eachothers?
Don't let "somebody" anywhere near electricity.
 

dknguyen

Well-Known Member
Most Helpful Member
Ah, yeah. Good point. 0V at a single node doesn't mean no current flow.

(psst, it's spelled ridiculous).
 
Last edited:

Menticol

Active Member
I think I've found the cause of "Mr. Somebody's" mental fart

(Sesame Street Theme starts playing)
Yes, every phase (R,T,S) goes into the center of the star, But look, there is a load in between!
(Sesame Street Theme stops playing)
 

Attachments

  • 685px-AC_star_connection.svg.png
    685px-AC_star_connection.svg.png
    12.7 KB · Views: 70
  • Asynchronous-Motor.jpg
    Asynchronous-Motor.jpg
    15.4 KB · Views: 70
Last edited:
Status
Not open for further replies.

EE World Online Articles

Loading
Top