Unbalanced three-phase w. neutral. Finding currents

[EVriderDK]

Homework Statement

I have to find the currents in the three phases and the neutral.

I understand that it has got something to do with Kirchoffs law, but how on earth?

I can simulate it in multisim, and i get the right results for I_rms but i cannot figure out how to calculate.

N->L = 220V
L->L = 380V

Homework Equations

Here is the layout.

I found the I_L3 just by using I=U/R. I found it to be 2.5A

 

[rude man]

What are V1-1, V1-2 and V1-3 in complex notation? The rest is just cranking thru the KVL or KCL equations, whatever lights your bulb ... :-)

 

[EVriderDK]

I found out how to do it with vectors.

But i also want to learn how to do it with masks.
I have drawn a new one here:

http://www.studieportalen.dk/Forums/ShowFile.aspx?id=1225631

Is that better?

What do you mean by using KCL and KVL? I know it is Kichhoff current and voltage laws, but do I just have to do all the masks with respect to N?

 

[gneill]

A slightly rearranged schematic may make things more obvious:

You should be able to apply either mesh or node equations. Note that it might be worthwhile to recognize that you have the potentials at each end of the load resistors by inspection...

Va, Vb, Vc are the three-phase line voltages. Write them in complex form and then it's just plug 'n chug.

 

[rezeew]

Hello, I understand your confusion about how to calculate the currents in an unbalanced three-phase system. Kirchoff's law does apply here, specifically Kirchoff's current law, which states that the sum of all currents entering a node (or junction) must equal the sum of all currents leaving that node. In this case, the node would be the neutral point.

To calculate the currents in each phase, you can use the formula I=U/R, where I is the current, U is the voltage and R is the resistance. However, in a three-phase system, the resistance will vary depending on the phase angle and power factor. So, it is not as simple as just dividing the voltage by the resistance.

To accurately calculate the currents in each phase, you will need to use complex phasor analysis. This involves using complex numbers and vector diagrams to represent the phase angles and power factor. I recommend seeking guidance from a textbook or online resources on how to perform these calculations. Alternatively, you can use simulation software like Multisim to get the correct results.

I hope this helps clarify the process for you. Keep in mind that working with unbalanced three-phase systems can be complex and may require advanced mathematical techniques.