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The US electrical system
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richard.cs:

--- Quote from: AlbertL on June 30, 2020, 09:49:04 pm ---So, here's a question: what would be the resulting voltage at the customer's premises (bottom of the drawing) in the case of an accidental short between the ungrounded side of the distribution transformer primary (7200V) and one end of the 240V secondary?

--- End quote ---

Just looking at the diagram I would say it depends on the saturation behaviour of the distribution transformer when it sees 7200 V on its secondary winding, and the impedance of the HV line and neutral at that point. Overall the secondary winding probably looks mostly like a short to the HV, and the shared neutral is probably pulled up to around half the HV line voltage. Clearly it should draw enough fault current to trip the HV, but until that happens I don't think I'd want to be touching any line, neutral or earth at any of the six consumers shown, including the ones on other transformers.

An impedance-earthed star point on the HV source would be much nicer.

james_s:
I've never heard of that happening although I suppose anything is possible.

Back in the 90s a high tension line fell on a 7200V line and resulted in a substantial overvoltage in my friend's neighborhood. It blew out a bunch of light bulbs and fried some of their electronics.
IanB:

--- Quote from: james_s on July 01, 2020, 08:30:32 pm ---I've never heard of that happening although I suppose anything is possible.

--- End quote ---

Apparently it can happen that the 7200 V line can fall onto the telephone or CATV line strung lower down the pole, and cause problems (occasionally fatal) in connected homes.
richard.cs:

--- Quote from: IanB on July 02, 2020, 02:06:33 am ---Apparently it can happen that the 7200 V line can fall onto the telephone or CATV line strung lower down the pole, and cause problems (occasionally fatal) in connected homes.

--- End quote ---

We don't share telephone etc. with HV poles here (UK), poles can have HV and LV or LV and signal stuff (but is possibly discouraged now?) but not HV and signals. Generally we have less overhead distribution in urban areas compared to what I have seen of the USA, and near-zero overhead HV in towns.

We have a lot of overhead LV and overhead telephone in older suburban areas, but all but the most rural newbuilds have all the cabling underground. Likely more to do with maintenance costs than safety, all the urban overhead LV was installed when labour was a lot cheaper.

Typical UK suburban area with overhead LV (note that line and several others is fed from a ground mounted transformer ~50m away via that PILC cable): https://goo.gl/maps/ruSgiQZ6PCM4PnNu9
A few hundred yards away it's been updated to aerial bundled cables: https://goo.gl/maps/Rxujc9uwFYUqKMDs5
Typical UK rural setup with a small pole mount transformer and HV and LV sharing that pole: https://goo.gl/maps/Ph3DQrHQmp7W6wMh7

TimFox:
In residential areas of Chicago, with alleys between rows of houses, there are usually poles along the alley that carry the overhead power line, pole transformers, telephone, and cable lines.  Typically, though, they are fed from underground cables.  Total underground distribution is typical in industrial parks in the suburbs.  If you want to see a sky extremely polluted with overhead wires, go to urban Japan.
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