calculation for current in delta connected system.(unbalanced load)

Hi,
Can anyone adivse on the calculation and equation for current in the delta(unbalance).i had used kirchhoff's current rule and Equation( square root 3*Iab ) but still cannot get the answer.


Example
______A
/ / ____C/_ _ \B
_________|

If Iab= 105A
Ica= 33A
Ibc= 33A
after calculation, IA= 124.8A
IB= 124.8A
IC= 57.2A

 

[230842]

Current phase (angle) values are missing in your post. So there can be infinity valid results.
Kirchhoff ecuations are fully applicable provided that current phasors (complex quantities) are used to.
Julian

 

[electricpete]

I'm not sure if you used it in your calcs, but the sqrt(3) factor does not apply when you're using vector addition of unbalanced phase currents. (it arises when converting delta balanced currents).

If you have vector currents Iab, Ibc, Ica, then
Ia=Iab-Ica
Ib=Ibc-Iab
Ic=Ica-Ibc

Where Ia enters terminal A, Iab flows from A->B within the delta, etc.

 

Hi Guys,

For the current phase, where can i get the values? from measurment of current meter or by the manufacturer?
Can i use this equation to get the solution?


Ia square = (Iab+IcaCOS60)square + (IcaSIN60)square


Next, Can anyone adivse on what is a H -type tranformer?
Is there any Problem with step-down transformer is one of the coil changes colour(become darker than the other 2)


Pascal

 

[jbartos]

Suggestion to confused/blur (Visitor) Jul 3, 2002 marked ///\\Hi Guys,
For the current phase, where can i get the values?
///If you happen to know the delta circuit parameters, (C, L, R) you could calculated those.\\ from measurment of current meter
///You would need a Power Factor Meter.\\ or by the manufacturer?
///This would be recommended for any official purposes.\\Can i use this equation to get the solution?

Ia square = (Iab+IcaCOS60)square + (IcaSIN60)square
///Not in general, since COS60 may be COS70, or COS of any other angle.\\
Next, Can anyone adivse on what is a H -type tranformer?
///There is a Class H transformer. Visit

http://www.bartcolighting.com/Resources/3recessed.pdf

\\Is there any Problem with step-down transformer is one of the coil changes colour(become darker than the other 2)
///Yes, there just may be some, since the coil color change indicates some thermal problem.\\

 

[230842]

I´ll try to answer your questions.

1.- Current phases can be be obtained from some data values to be got from Manufacturer:
- Real (active)and reactive powers of every branch:
tan(phi) = Reactive/real = Q/P
- Voltage and Real Power of every branch:
cos(phi) = P/(V.I)
- Power factor of every branch
cos(phi) = PF

Phase angle can be then calculated assuming balanced voltages. So, assuming ABC to be a positive sequence, that is:
Phase(Vab)=0º; Phase(Vbc)=-120º; Phase(Vca)=+120º
Current phases become:
Phase(Iab)=0-(phi)ab; Phase(Ibc)=-120-(phi)bc; Phase(Vca)= +120-(phi)ca

2.- The equation is valid only when current phasors Iab and Ica are 120º phase shifted.

All preceeding information is not applicable in case of you are dealing with transformer windings. In that case it sould be preferable to directly meassure the line currentes Julian

 

Hi guys

Thanks for the informations.However i need just alittle bit more.

1.Do u have any more information on the H-type tranformer? 2.Is it the same as a core/shell type transformer?
or it has a better temperature tolerance than the other
type of transformer?
3.Just to confirm, too much current will cause the coil to change colour? yes or no.


Pascal