GROUNDING: Weight Factor f/Children Allowable Step & Touch Potentials

[cuky2000]

Hello all,

If any one would like to share a link or reference regarding the k factor for the allowable step and touch potential as a fuction of the body weight, please let me know.

BACKGROUND:
The IEEE Std 80 had been stablished the following k values:
k = 0.157 for body weight of 70kg
k = 0.116 for body weight of 50kg

I am in search articles associated with k values for children from 30 to 10 kg. The other unknown for me is the effect on step and touch potential for lower step length in children compared with typical adult of approximatelly 3ft(1m).

We are performing a grounding analysis in a metro area substation. To increase the challenge, the adjacent property is a public park with a playground closer to the substation masonry fence.

Thanks for any help in this matter.

 

[eamonkerrigan]

cuky2000

You should look into IEC body resistance calculations. The difference is the body resistance is calculated according to stress voltage versus body resistance curves published in IEC Report 479-1. hope this helps.

 

[waross]

It's good to see you back cuky2000. I have always enjoyed your graphics.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[jghrist]

The shorter step length will reduce step-voltages because there will be less voltage for the same voltage gradient.

One thing to look for in parks adjacent to substations is transferred voltages. A water fountain supplied by a transformer with a neutral bonded to the nearby substation grid may reach close to full GPR in case of a high side fault in the substation. This could make for high step- and touch-voltages at the fountain.

 

[cuky2000]

Waross, it is nice to say hello to all e-friend again. I wish to have more time to share with all of you.

Regarding public safety near the HV substation, it is unclear to me if the IEEE Std 80, IEC and any other major standard address safety issues beyond the substation property line, perimeter fence or external wall particularly in metropolitan areas.
[sub]Grounding became a major issue in existing substations since many of them are old, the SC level exceed the original design, more chance of failure due to reliability degradation, locations are not longer in isolated places, corrosion, vandalism and cable theft are on the rise, etc. This appears getting worst.[/sub]

One of the engineering concerns is associated public safety are as follow:

* Adult pedestrians standing outside crushed rock in a low resistivity surfaces such as native soil or concrete. [small](Please see graph with touch potential exceeded. A common practice is to ignore that particularly for areas beyond the property line)[/small]

* Jghrist, I am agree with you that step length will reduce step-voltages. Unfortunately the step length and the children foot model are not established yet. [small]The table enclosed shows that children body resistance under wet conditions is 1.25 to 1.55 time the resistance of an adult for 95% of the population. [/small]

Any comments/concerns?
Thanks

 

[cuky2000]

Please see the enclosed file