Resonant-Grounded Line: Zero-Sequence Current - Resonant Point at middle of line? (Shorebrook Problem 71)

Hi guys,

On Shorebrook PE Power Exam question 71, it briefly mentions that on a resonant-grounded system, the resonant point is located at the middle of the transmission line, regardless of where the ground fault is located at. What is the explanation behind this? Is there more literature regarding resonant-grounded system and the resonant point?

This is not something that I have encountered in other sequence components or grounding materials or practice PE exams other than Shorebrook. So I'm just trying to understand this better.

Thanks for any input on this!

If you have Protective Relaying by Blackburn, check out section 7.5.1 Resonant Grounding.

Here is a paper by SEL that also covers Resonant Grounding on page 7. 

Here is a link to a webpage that covers it as well.

So after reading all those, why do you think the resonant point is at the middle of the transmission line (or why is zero sequence fault current 0 at the middle of the line)?

Chattaneer PE said:

If you have Protective Relaying by Blackburn, check out section 7.5.1 Resonant Grounding.

Here is a paper by SEL that also covers Resonant Grounding on page 7. 

Here is a link to a webpage that covers it as well.

So after reading all those, why do you think the resonant point is at the middle of the transmission line (or why is zero sequence fault current 0 at the middle of the line)?

Click to expand...

Chattaneer, thanks for these links and references.

They were long reads, and admittedly some of it flew over my head. I couldn't find a definite answer for why the resonant ground is in the middle, but my best guess is because of the fact that the Petersen coil's inductive reactance is equal and opposite to the transmission line's capacitive reactance to ground. This also makes the Petersen coil current IL equal and opposite to the fault current IF.