Crushed rock in Substation (Wet or Dry)

[cuky2000]

What is the best engineering practice selecting resistivity of crushed rock in HV substation?

There are published values for dry and wet conditions with significant differences. Appear to me that a wet condition is a realistic scenario that should be considered for the design.

Thanks

 

[jnunner]

I use the resistivity of the crushed rock when it is wet. If you refer to IEEE 80, you will find that the lower wet resistivity provides less insulation, and the station will have lower safe limits for step & touch voltages.

 

[dpc]

Since the purpose of the crushed rock is to increase resistance to earth, I would think that the wet value would have to be used for calculating resulting step potentials.

But for specifying the rock itself, it may be that the dry value is used.