Grounding of Switching Station

See http://cr4.globalspec.com/thread/58500 you may recognise it

Did you definitely determine that the lower measured ground resistance vs. the calculated value was due to the bonded neutral? I have often seen CDEGS simulations not match actual measured values due to a variety of reasons, most of which relate to inaccurate soil resistivity data or inadequate modeling of the actual grid conductors in the ground. Also, more often the measured was higher than the calculated.

Having lower actual resistance is good, and the lower the ground potential rise (GPR) the better - it means that when a fault occurs, the current is diffusely distributed in the grid and earth, so that connected equipment does not have as much of an associated potential applied to it (V=IR. Lower R = lower V for the same I). This means lower step and touch potentials, so less danger of shock to personnel and overvoltage damage to sensitive equipment such as relays or communications.

I doubt that you will find much of the fault current will follow the bonded neutral wire. How much a #3 will overheat and whether it will be damaged depends on what percentage of the fault current it carries and how long it takes for your protective relays to trip for the fault and clear it.

Hi

Thanks for your reply. I went to site and found that the neutral coming from 25KV/120VAC transformer(from outside substation) is connected with substation grounding wire. I think it not normal practic. The neutral should not be grounded. The neutral point of pole mounted transformer is grounded which is ok. But the neutral line coming to 138kv switching station with 120vac phase line to operate only the relay for disconnected switch, connected with substation grounding system-is it normal practica? As per CEC code could you do such type of connection? My understanding the metal case of relay panel should be grounded with swithing station grounding system but not neutral conductor.