Multiple section lines 1

[jacksonville]

hi there.

i need to simplify/reduce a multiple sectioned line into a single equivalent line. How do i simplify/reduce these lines as to represent it as a single line with equivalent impedance? Also to bear in mind that i need 'eqivalent' zero and positive sequence impedances of this equivalent line. Is there a way to find the equivalents of the sequence components as well?

Can the equivalent parameters that i require be calculated? if so,how?

please assist.

thank you.

 

[magoo2]

If I have 10 resistors in series, what is the equivalent resistance? If you can answer this, then you've answered your question.

 

[jacksonville]

Does this also hold for the sequence impedances? What if the sectioned line has different types/configurations?

 

[magoo2]

Yes, it does hold for the sequence impedances.

What type of line are you dealing with - transmission or distribution? Also, what length and voltage?

 

[jacksonville]

Its a massive detailed network dealing with transmission and distribution. Voltages range from 400kV to 11kV. Lengths of lines can be from a few meters to a few kms.

 

[magoo2]

The common impedance representation for transmission and distribution lines is a series R + j X in both the positive and zero sequence quantities. For 11 kV distribution, this is fine. For 400 kV transmission, sometimes a pi or L-shaped impedance is used in which the shunt branch is the capacitance for both sequence impedances.

If you're just doing fault studies, then the series R + j X is fine for both transmission and distribution lines. If you have any significant amounts of underground cable, then its capacitance should be included.

 

[jghrist]

If you have a massive detailed network of transmission and distribution, the best way to represent it as a single line is to analyze the system with fault analysis software. Most software will have an option to show positive- and zero-sequence Thevenin equivalent impedances at faulted buses.

 

[jacksonville]

i can access the sequence impedances with the software i am using, i just needed to know if the sequence componenent could be combined in series as well.

If i came accross a T junction of a sectioned line, im assuming i should find the parallel equivalent impedance?

 

[magoo2]

If i came accross a T junction of a sectioned line, im assuming i should find the parallel equivalent impedance?

If I understand what you're saying, if you have a T junction, where one branch goes off in one direction and the other in a different one, then you would not parallel them. You would maintain the series impedance of each separate path. Like:

X Y
- - - - - - - - - - -
|
| Z
- - - - - -

If you're interested in the fault at the right of section Y, then you would add the series impedance of X and Y.

Likewise, if you're interested in the fault at the end of Z, you'd combine the impedance of X and Z.

As I've drawn it, you would not parallel the impedance of Y and Y unless they came together at the ends.

 

[jghrist]

i can access the sequence impedances with the software i am using, i just needed to know if the sequence componenent could be combined in series as well.

In general, you can combine sequence components like any other network elements. Keep in mind that in some cases, like delta windings of transformers, there will be open points in the zero-sequence equivalent circuits.