Problem with a three phase circuit

Thread Starter

felastian123

Joined Oct 10, 2021
3
Hello, I have 2 questions, in the following circuit (is a balanced circuit) I know the value of the impedances, and the voltage of the source, on the left side I can transform the delta type impedance to a star type impedance, and then perform an impedance operation on parallel? (Z // Z) and my other question is, can I consider the line voltage as the phase voltage of the delta type source? Thank you very much and sorry for the bad English.
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MrAl

Joined Jun 17, 2014
8,555
Hello, I have 2 questions, in the following circuit (is a balanced circuit) I know the value of the impedances, and the voltage of the source, on the left side I can transform the delta type impedance to a star type impedance, and then perform an impedance operation on parallel? (Z // Z) and my other question is, can I consider the line voltage as the phase voltage of the delta type source? Thank you very much and sorry for the bad English.
View attachment 249945
Hello,

It is better to refer to the voltages as either line to line (LL) or line to neutral (LN).
This way line to line is always line to line, and line to neutral is line to neutral mainly when we have a wye type (you might call a star) but you can create a fictitious line to neutral for a delta too for a balanced load and for an unbalanced load although the unbalanced load case is a little different.

So for a wye setup the line to line voltages would be 208 volts and line to neutral 120 volts, and for the delta it would be just 208 line to line and no line to neutral voltage.

For three phase systems like this i always recommend using complex quantities to solve any network because i think that is the most general, and with that you can calculate the results for any system even wildly unbalanced, multiple loads (like yours), multiple grounds, etc. You name it you can do it.

If you need help with that i can help you get started. First, convert all three sources to their complex equivalents, and note that since they are connected in series you can leave out one of the sources (because the other two create that virtual source anyway) and go from there. It gets really simple and this can be used on any system not just some special networks.
 
Last edited:

MrAl

Joined Jun 17, 2014
8,555
Hello, I have 2 questions, in the following circuit (is a balanced circuit) I know the value of the impedances, and the voltage of the source, on the left side I can transform the delta type impedance to a star type impedance, and then perform an impedance operation on parallel? (Z // Z) and my other question is, can I consider the line voltage as the phase voltage of the delta type source? Thank you very much and sorry for the bad English.
View attachment 249945
To answer your question more directly, you can transform the source as you like but notice that if you transform the three 'delta' impedances into 'wye' impedances you end up with a delta source and just a wye load. Since the wye load is balanced you end up having a virtual ground at the junction off all the wye resistors. That should make it easier to solve as a balanced system.
 
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