Transmission Line Constants Calculations

[timm33333]

I have question about the calculations of transmission line constants (sequence impedance, phase impedance, inductance) for a short overhead line (with optical ground wire.) These constants are required for relay settings.

Software like Aspen and Cape are available for these calculations; however I want to do the hand calculations. Is there some IEEE standard or other document which describes the procedure (with solved example) for hand calculations of the transmission line constants. Thanks for help!

 

[HamburgerHelper]

Sarma and Grainger have sections on this. Most college power analysis text do.

Here are some calcs.

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

ATP-EMPT is free and has a moduel to calculate all the constants if you want to check your work.

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If you can't explain it to a six year old, you don't understand it yourself.

 

[timm33333]

Thanks for information. A few questions:

- Will the line constant calculations be the same for both wood-poles and steel-lattice-towers?
- Should the length of the transmission line be taken from breaker to breaker, or from first tower to last tower?
- If the phase sequence is different at the sending and receiving ends: for example, if the phase sequence at the sending end is ABC and at the receiving end is CBA, will it make any difference in the line constant calculations?

Thanks for help.

 

[davidbeach]

Structure type does not enter the calculations.

Breaker to breaker.

If you're trying to calculate individual phase impedances the actual phase arrangement matters. If you're calculating sequence impedances then no, it doesn't matter.

 

[timm33333]

Thanks. As it is short line so capacitance can be ignored. So if we take breaker to breaker, then should we calculate the sequence impedance of the gas insulated bus from breaker to gantry, and add it to the sequence impedance of the overhead line?

 

[timm33333]

I meant to say that the transmission line is a combination of “overhead line” and “gas insulated line (GIL)”. So the sequence-impedance of the “overhead part” and the “gas insulated line(GIL) part” has to be calculated separately and then added together to find the total sequence-impedance of the transmission line.

Documents are available for the calculation of sequence-impedance of the overhead line. Is there some document/standard available which shows the calculations of sequence-impedance of the gas insulated line (GIL)?