Transmission Line Sequence Impedance Calculation

[timm33333]

The document at the following link gives the calculations for the transmission line sequence impedance:

http://www.synchrogrid.com/upload/appnotes/Line Constants Calculations.pdf

This document uses a single circuit line (one 3-Phase circuit on 1 pole) with ground wire. We have a double circuit line (two 3-Phase circuits on 1 pole) with ground wire. As it is a short line, so the capacitance can be neglected.

For the double circuit line (two 3-Phase circuits on 1 pole) with ground wire, should we consider the effect of the mutual inductance of circuit 1 on circuit 2, or is it not needed? Thanks for help.

 

[davidbeach]

There's definitely coupling between the two; whether it makes enough difference or not depends on a number of factors, like how the lines relate to each other electrically.

 

[timm33333]

It looks that the coupling would exist between multi-conductor overhead lines for conductors of all circuits which are on the same pole. However when two double circuit lines (on 2 separate poles) run in close proximity to each other along the same route, the coupling between the lines (which are on separate adjacent poles) can be neglected for short lines.

Neglecting the ground wire will significantly simplify the calculations. As the transmission line in our case is short line (less than one mile), so can we neglect the ground wire when performing the sequence impedance calculations?