Ground Potential Rise > Surface Voltage Potential - possible?
Ground Potential Rise > Surface Voltage Potential - possible?
(OP)
Hi all,
Is it possible to have a surface voltage potential (surface voltage profile) which exceeds the grid potential (GPR)?
Refer to Figure B.8 of IEEE (image attached). Is this what it is showing us?
Thanks to all.
JP
Is it possible to have a surface voltage potential (surface voltage profile) which exceeds the grid potential (GPR)?
Refer to Figure B.8 of IEEE (image attached). Is this what it is showing us?
Thanks to all.
JP






RE: Ground Potential Rise > Surface Voltage Potential - possible?
RE: Ground Potential Rise > Surface Voltage Potential - possible?
RE: Ground Potential Rise > Surface Voltage Potential - possible?
RE: Ground Potential Rise > Surface Voltage Potential - possible?
This may seem like a silly question but I have done some modelling which shows surface potential greater than GPR.
RE: Ground Potential Rise > Surface Voltage Potential - possible?
RE: Ground Potential Rise > Surface Voltage Potential - possible?
Alan
"The engineer's first problem in any design situation is to discover what the problem really is." Unk.
RE: Ground Potential Rise > Surface Voltage Potential - possible?
Can anybody explain it?
RE: Ground Potential Rise > Surface Voltage Potential - possible?
We don't all enjoy the luxury of access to IEEE documents.
Is this homework?
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Ground Potential Rise > Surface Voltage Potential - possible?
Maybe some round off error in the program? Doesn't really matter since the areas of concern are not at the wire locations, but in between where the difference is greatest.
RE: Ground Potential Rise > Surface Voltage Potential - possible?
Are you sure that your model is showing surface potential? The IEEE std 80 definition of GPR is "The maximum electrical potential that a substation grounding grid may attain relative to a distant grounding point assumed to be at the potential of remote earth." If the fault is to an object connected to the ground grid, then the maximum grounding grid potential will higher than any point in the soil at a distance from the grid (even directly above it). The voltage difference between the grid conductor and any point in the soil is caused by the fault current flowing through the soil resistance. This will always be a voltage drop, not a voltage rise. If your modelling shows differently, it is wrong.
RE: Ground Potential Rise > Surface Voltage Potential - possible?
was modeled as shown in Figure B.7.
The computer output included the grid resistance, a surface voltage profile, the step voltage, and the corner
mesh voltage."
RE: Ground Potential Rise > Surface Voltage Potential - possible?
Jpatrick,
Read this thread:
http://www.eng-tips.com/viewthread.cfm?qid=167438
Jghrist replies about grounding are one of the best posts on this website.
RE: Ground Potential Rise > Surface Voltage Potential - possible?
Conclusions:
1. It is theoretically not possible to have a surface potential which exceeds the GPR. Practically, through modelling inaccuracies, it is.
2. Figure B.8 in IEEE80 shows an error with the EPRI program. It was caused by inaccurate current ditribution representation (particularly at the connection nodes) due to a lack of segmentation (division) of the conductors.
RE: Ground Potential Rise > Surface Voltage Potential - possible?
I concur with the comment associated with fig 8.
However; we should be aware that there are special conditions were induced voltages in metallic return conductors such as shield wires, telephone cables, pipelines, fences, etc. transfering voltages that produce touch potentials larger than the GPR.
For additional details in this subject check the IEEE Std 80.
RE: Ground Potential Rise > Surface Voltage Potential - possible?
I'm curious how the touch potential could exceed GPR. This would require that you were touching (or standing on) something that was at lower potential than remote earth while touching something connected to the ground grid, which is at GPR potential with relation to remote earth.
RE: Ground Potential Rise > Surface Voltage Potential - possible?
Page 1: Excerpt from the IEEE Std 80 describing cases for touch potential exceeding GPR.
Page 2: Alternate calc for Example of IEEE Std 80- for Figure B.7 confirming that Vtouch < GPR.
Page 3: Fig B.7 edited with remarks.
I hope this could help clarifying this post.