Help calculating voltage drop through storm water 2

[etbrown4]

Our utility in Va, Dominion Power is locating 3 standard 12.5 or 7.5kv transforners in a residential area, that floods frequently to a depth up to 10' (really) , on a street near my home.

Neighbors are alarmed and want to know that if the transformer shorts, how much voltage might be present, say 100 ft away in the flood water on the road

I've looked into water conductivity and found that 1000 𝜇𝑆/𝑐𝑚 is close enough. I found a chart which converts this into resistance. It might be off but it looks like maybe 3 ohms. Wondering if any kind engineer or electrical whiz might help figure the voltage potential at 100 ft.

We have had swimmers killed recently around boat lifts with a nicked wire on a 120v cable, so this has to be 10x worse, one might think.
Thanks for any help.

 

[etbrown4]

In theory, the standard practice of utilities seems to be, to not place standard, non submersible 100kva transformers in the 100 year flood plain.

Dominion Va Power has nearly completed a 1.4 mile changeover from overhead to underground, with the last .4 mile 10' deep in the floodplain. They've placed the transformers and run the underground but not yet connected them.

Neighbors, once understanding what was going on, raised cain. Dominon swears it is their SOP to not use equipment rated for submersion in a flood plain, however I and others think their designer missed it, and they wont admit their error or the hazards.

So once caught (assuming that's the case) they have reluctantly agreed to relocate 5 of the transformers, and splice the underground at each location, in order to extend the wires to each new location.

They now appear to be listening closely to neighbors, and with the help of contributors here, now we know to demand splice kits rated for direct burial.

The entire situation, after consulting with an EE, appears to have been caused by their gross negligence, but thankfully a few sharp neighbors saw the risks they appeared to impose on us, and somehow the little people caused the Giant to stop. We appreciate all the help here as well.

Ps. We urged them to put the transformers back in the air, and they refused saying it's non standard. We urged for submersible transformers, again that's non standard or too expensive. They said, we'll get an engineer to stamp the plan, swearing it's safe. We said no.

We said your stamped plan won't make this safe. We're in a recreational area with swimmers, boaters, cars, and hikers. We said we'll accept the original plan with standard transformers if your engineer will agree to show up at the next 3' flood, in a bathing suit, and barefooted, and if he'll walk through 200' of potentially electrified water and place both hands on the top of a live 100kva transformer. There were no takers. So much for that engineer's plan or stamp.

Our belief is the only reasons Dominion yielded were A) we were ready to invite the TV media in, and B) they seemingly knew the plan was hazardous and C) apparently didn't want the embarrassment.

 

[wcaseyharman]

It seems to me that underground is so much safer, that almost regardless of what they put in is better than what you have.
It’s not uncommon to have overhead poles fall down, or conductor break, or cross arms rot, and have conductor fall to the ground. Unlike underground systems where the neutral is always close and therefore will almost always trip, overhead can arc for a while if the ground conditions are unfavorable. Insulators or cross arms can break leaving energized wire hanging at head level waiting for someone to walk (or boat) into it. You are so much more likely to kill someone with overhead versus underground. This doesn’t even consider the wildfire risk of overhead, which is considerable depending on where you live.
My utility has had people even saw into underground cable with a sawzall and survive because of the concentric neutral prevented them from being electrocuted.
Not to say you shouldn’t keep the utility company accountable to design things properly, but appreciate what you are getting over what you have.

 

[jghrist]

There are many choices for splicing 15 kV cables. All capable of being under water. Being above ground pretty much requires an enclosure and splices like elbow connectors that do not have be in-line. I would rule out hand taping.

 

[LionelHutz]

I haven't read a thread with as much ado about nothing as this one.

The high voltage side of cables and transformers is sealed and quite well protected from leaking voltage by design. It's just the way it is.

The low voltage side of a distribution system in a residential area usually goes into the ground or close to the ground in many, many places. Having a transformer that is sealed on the low voltage side doesn't protect anyone against all the other places it could be exposed to this flood water. At the transformer, any exposure to flood water would be inside a fully closed grounded metal box. Any current flow in the water would go to the box first before "leaking" out everywhere.

The deaths around docks you mentioned was probably caused by 120V. The same 120V that can be exposed to flood water at many locations that are not the transformers.

 

[Compositepro]

Reading this thread has brought images to my mind of a mob of angry villagers carrying torches up the mountain to storm the castle of the mad scientist.