Temporary Protective Grounds
Temporary Protective Grounds
(OP)
In sizing temporary protective grounds for distribution and sub-transmission voltages, I'm debating how to consider lightning. Would it be appropriate to estimate a current stroke and the associated voltage developed across the conductor/person? I'm leaning toward thinking that it is pointless to consider lightning however, as the Ldi/dt would be so high that no conductor could adequately reduce it.
If I'm mistaken though and you would consider voltage developed due to lightning, how do you determine inductance of the ground conductor? Inductance taken from data tables will always include self and mutual inductance, but as there is no second wire, there will be no mutual inductance. Is it appropriate to just consider the self inductance of the conductor?
If I'm mistaken though and you would consider voltage developed due to lightning, how do you determine inductance of the ground conductor? Inductance taken from data tables will always include self and mutual inductance, but as there is no second wire, there will be no mutual inductance. Is it appropriate to just consider the self inductance of the conductor?






RE: Temporary Protective Grounds
For purposes of understanding lightning behavior, it’s analysis and for specifying lightning protection devices, a common model of the lightning pulse has been specified by the Institute of Electrical and Electronics Engineers (IEEE). This model of the pulse is called the “The IEEE 8 / 20 Model” and is commonly used in specifying lightning protection devices. Figure 1 shows the current versus time graph of the pulse. It is generally thought
that this model is equal to or greater than 50% of lightning events. But, it should be remembered that the other half are more powerful than this
model predicts!
http://www.samlexamerica.com/support/documents/130...
In the class, I took at U of I, we used the 8/20 IEEE model. I don't know what the peak should be. The calcs are not too difficult and I posted examples below. In the class, we were modeling the lightning to determine what the grounding impedance would have to be so that you didn't have flashover when the lightning strike bounced off the ground and flashed over on the way back up, voltage doubling. You want your grounding wire to be as short as possible and for the connection to ground to be low impedance so that doesn't happen.
Example U of I lightning stuff
http://www.ece.uidaho.edu/ee/power/ECE524/Lectures...
http://www.ece.uidaho.edu/ee/power/ECE524/Lectures...
http://www.ece.uidaho.edu/ee/power/ECE524/
RE: Temporary Protective Grounds
RE: Temporary Protective Grounds
RE: Temporary Protective Grounds
On a related note, workers performing live line maintenance on transmission lines sometimes use arc gaps to control the flashover location in the event of an overvoltage on the conductor.