300 V point calculation

[NAZ55]

Does anyone here knows how to do a 300 V point calculation?

I am looking at a fault of 18KA for 0.5sec with a GPR of about 15kV and a grid impedance of .7 Ohms

Any excel calculators will be helpful!

Thanks in Advance

 

[rcw retired EE]

I don't understand the "300V point" terminology.

Are you trying to calculate the "zone of influence" of a substation during a fault for telecommunications?

Look at IEEE Standard 367, equation 32. The equation is more complicatd than I have time to type out here.

Read the warnings aobut the assumptions made to get that simplified equation.

 

[jghrist]

I use CDEGS by SES to produce a voltage profile and make 300 volts one of the profile lines. With a full blown grounding analysis program, you can model all of the grounding electrodes including the utility ground rod at the transformer. You can also model underground pipes if you know where they are; these will influence the voltage profile even if they are not connected to the grounding electrode system.

 

[NAZ55]

rcwilson, thanks for your response. I will check out the standard tomorrow morning.

jghrist, we do have CDEGS, but I guess I am not familiar with full functionality of the program. Could you please explain a little bit more as to how should I go about making 300 V one of the profile lines?

I am trying to figure out how telecommunications personnel calculate 300 Volt point from the data I shared above, which by the way is extracted from CDEGS MALZ report.

I am guessing 300 Volt point is a point certain distance away from the grid where GPR falls down to 300V.

 

[jghrist]

zazmat,

From the MALT Examine Computations screen, choose Scalar Potentials, Contour 2D view, then menu Settings, then Setup. This brings up a dialog box that allows you to put in user-defined contour plot levels. If you define a single level at 300 volts, this will show the locus of 300 volt points. You have to have calculated voltages over a large enough area to get the surface voltage down to 300 volts.

The 300 volt point is where the surface voltage decreases from the GPR to 300 volts. That means that the voltage between the earth at this point and a communications line grounded at remote earth will be 300 volts.

 

[jnunner]

SES has published several articles on ZOI. Particularly interesting is "Zone of Influence around Electrical Installations Subjected to Ground Faults" which compares simulated methods to IEEE 367-1996 for determining ZOI. As a CDEGS user you should be able to request this document from SES.

 

[NAZ55]

Thank you guys!
I really appreciate all the responses.
You are no doubt experts in your fields.

Thanks to rcwilson, I now know exactly what ZOI is and how to calculate it using IEEE 367.

Thanks to jghrist, I now know how to calculate a 300V point in CDEGS

and last but not least, thanks to junner, I will soon have a valuable article on this topic from SES in my Grounding collection.