Supply Well Pumps Grounding

[rezaa]

What do you suggest to design for grounding of Supply Well Pumps that are located outside of current safety fence of a station?
1) Use Isolated Transformer?
2) Design a ground math (Seems to take care of potential rise for the small area around the supply Well Pumps)
3) Extend the available ground grid math to cover the Supply Well Pumps area? (Needs more study)

What are other options and what do you think of the above options?

 

[rbulsara]

what size? what voltage? how many?

I would think , in addition to the equipment grounding conductor run with the supply conductors, a ground ring (bare copper conductor buried 24 inches below grade) around the base of the pump(s) and connected to two or more ground rods should suffice.

Ground mat may be considered if the terrain is rocky..


I do not understand how a isolation transformer helps grounding.

What is and how far is the existing ground mat you mentioned? That seems to be a good choice.

 

[rezaa]

It seems use of Isolation Transformer is an expensive option. Isolation Transformer with a good isolation lets say 10 kV avoid fault current travel through the armor power cable that is used to supply those four supply well pumps (4*50 HP. Those pumps are 3 to 4 meters apart from each other and are 30 to 40 meters far from the station ground grid math. The level of fault voltage during summer is 3000 V and wintertime is 5000V.

 

[jghrist]

A local ground mat should be adequate to reduce touch potentials to safe levels. Anything metallically connected to the station ground mat (local grounding, grounded equipment, etc.) will be raised to nearly the same voltage as the station ground mat. Perimeter wires (one meter away) around the pumps and around any fences will probably reduce touch potentials adequately by raising the surface voltage close to that of the equipment. The local mat can be analyzed as you would a station ground mat. You might need to check step potentials.

 

[mc5w]

Your well casings are very likely metal and to meet National Electrical Code requirements for something that the public can touch and for something that is NOT a utility substation item you would need to bond the well casing to each other and to the pumps and to a rather hefty ground wire coming off of the substation mat. Well casings make for excellent grounding electrodes especially in dry climates and they might even provide a better ground that your station mat - in this case a pair of 500 KCM grounding cables from the substation mat to the well group would be a bare minimum.

You will not really be able to isolate the well casings and pumps from the substation mat using plastic pipe and an isolation transformer. There are recorded instances of electricity flowing through the inside of drian pipes that have mostly air inside.

As jghrist suggested, run a ground mat or ring around each well to reduce step potential.

Mike Cole, mc5w@earthlink.net

 

[rezaa]

The purpose of our Grounding is to diminish the electrical fault can travel through supply cable(Power Cable Armor 600 V Tek cable) to well pumps.

 

[rezaa]

The soil resisitivity of the region is not high. I do not think the electricity flowing through plastic pipe rather than soil.

 

[mc5w]

If your soil resistivity is not high then metal well casings would make for an even better grounding electrode for your substation mat. They would also provide a backup ground during a drought. Using a bunch of 500 KCM copper grounding cables immediately adjacent to your power cables will keep most of the ground fault current out of your power cables.

A drought can also be a very bad time period for lightning damage from clear weather lightning. During the summer of 1987 an Akron, Ohio area roofing supply dealer sent out one of their conveyor trucks to a house in Hartville, Ohio to put roofing supplies up on the roof. The truck operators parked the truck a somewhat safe distance from an Ohio Edison 40Y69 KV transmission line and put the conveyor of the truck up on the roof. While they were sending supplies up the conveyor clear weather lightning jumped off of the 69 KV line, went down the mast for the conveyor, and incinerated all 4 rear tires. Nobody was hurt but the burning tires made for a very bad mess.

How you get clear weather lightning is that if the winds at 2 adjacent altitudes are moving in 2 different directions you get a horizontal Van de Graff generator.

Mike Cole, mc5w@earthlink.net

 

[rezaa]

The transferred voltages(cause the touch voltage) by 600 V power cables at well water supply pump locations are around 350 V more than allowable touch voltages 117 V. The local surface soil is of order 103 ohm-m and a lower resistivity layer under that (12 ohm-m). The maximum GPR at station is around 2600 V during the fault. It seems the only solution is to design a local ring grounding around those well water supply pump locations. Any comments on how to design the ring grounding and the procedures?

 

[mc5w]

A touch voltage of 117 volts is rather nasty. I would try for something lower such as 24 volts indicating the you need a ground mat around the wells.

I one time had to barehand 24 volts AC in rain while troubleshooting some commercial air conditioners. Barehanding 24 volts in the rain has a bit of a sting to it.