Vintage 275kV underground cable

[Lancs Lad]

Thank you, dodgy-dxer!

What are your thoughts about all this?

[Dave Moll]

Originally Posted by Lancs Lad

American households used to make do with a 100 amp supply, but now new houses all have 200 amp supplies.

We don't have anything like that in the UK. 100 amp is our maximum. And many of us don't even have that!

Surely our 100A supplies at (nominally) 230V are already roughly equivalent to the US 200A at 110V in terms of the power capacity.

[Jon_G4MDC]

And the buried underground cable they used to use / use today is...?
That is my interest here please.

I found the history from Auckland amazing. I have been to those places and I had no idea at all.

[G6Tanuki]

I wonder if there was ever a consideration for using SWER style HV distribution in the UK??

Would potentially save a lot of copper compared to the local setup of 132/33KV three phase overhead line distribution.

As to domestic supplies, I know plenty of local houses, both historic and new build, that have three phase 240V supply.

[Ed_Dinning]

SWER is not popular here for transmission as at transmission voltages high ground potentials can exist. It has been used in Australia (up to 132KV I believe) as it may only kill a few cattle. In recent times it has caused problems with bush fires if a wire falls onto low conductivity soils and the protective systems don't pick it up.
There is lots of interest in resonant earthing systems to detect this, but it can be difficult to set up so nuisance trips are not caused

Ed

[Roger Ramjet]

Interesting topic ...

In terms of the earth return current, would it [in theory] travel in a straight line and /or shortest distance between each end of the transmission line or am I maybe oversimplifying ?

Rog

[Wellington]

Originally Posted by Lancs Lad

This kind of thread is why I love UKVRRR.

Me too! I was curious about the 'DDB' oil that red16V referred to. It appears to be Dodecylbenzene. The Wikipedia page makes no mention of its electrical applications, though I found a few others that do, e.g. here, here and here.

Originally Posted by Lancs Lad

…but this new reliance on electricity as the answer to everything bothers me … Anyone else?

It would appear so. Interesting to note the Southampton connection - I wonder how much that has to do with Pirelli.

[Synchrodyne]

Originally Posted by Roger Ramjet

Interesting topic ...

In terms of the earth return current, would it [in theory] travel in a straight line and /or shortest distance between each end of the transmission line or am I maybe oversimplifying ?

Here is an excerpt from Lloyd Mandeno’s seminal paper on SWER (*), which I think answers your question:

>>>>>>>>>>

Impedance of an Earth Return Circuit:

The exact route whereby the return current traverses the earth between the two earth connections of a single wire circuit depends on the resistivity of the earth's crust in the locality. The higher the resistivity the deeper the penetration of the filaments of return current. Nevertheless mathematical investigation shows that for alternating current the return path will adhere roughly to the path of the overhead conductor and practically the whole of the current will be concentrated in the soil within a few hundred yards of the overhead line. For soil resistivities as high as are usually experienced the mean return path of the current works out at about 1500 feet below the earth's surface and the impedances are worked out accordingly.

>>>>>>>>>>


(*) “Rural Power Supply Especially in Back Country Areas”, by Lloyd Mandeno, NZIE Proc. Vol.33, 1947


Cheers,

[DrStrangelove]

Originally Posted by Roger Ramjet

Interesting topic ...

In terms of the earth return current, would it [in theory] travel in a straight line and /or shortest distance between each end of the transmission line or am I maybe oversimplifying ?

Rog

That brings back memories of field theory, equipotential lines and teledeltos paper accompanied by hours of tedium.

A simple example being:

https://academics.uccs.edu/rtirado/P..._2160_Lab3.pdf

With multiple sources I'll bet it gets a tad more complex than that.

[Jon_G4MDC]

Here is a picture I took on Friday of Town Hill near Winterbourne Abbas.
The farmer has gained a nice new access road that goes past his barns...

[sexton_mallard]

Originally Posted by Synchrodyne

Here is an excerpt from Lloyd Mandeno’s seminal paper on SWER (*), which I think answers your question:

>>>>>>>>>>

Impedance of an Earth Return Circuit:

The exact route whereby the return current traverses the earth between the two earth connections of a single wire circuit depends on the resistivity of the earth's crust in the locality. The higher the resistivity the deeper the penetration of the filaments of return current. Nevertheless mathematical investigation shows that for alternating current the return path will adhere roughly to the path of the overhead conductor and practically the whole of the current will be concentrated in the soil within a few hundred yards of the overhead line. For soil resistivities as high as are usually experienced the mean return path of the current works out at about 1500 feet below the earth's surface and the impedances are worked out accordingly.

>>>>>>>>>>


(*) “Rural Power Supply Especially in Back Country Areas”, by Lloyd Mandeno, NZIE Proc. Vol.33, 1947


Cheers,

Totally fascinating. i wonder if anyone has tried to 'harvest' this return path of current. Probably as easy as harvesting the dissolved gold in seawater.

[Jon_G4MDC]

As some used to harvest the RF from Brookmans Park for house lighting.
Very off topic here but there could be another one about such stories.

The Droitwich singing gate was already mentioned in another thread.

For me, seeing the transition gantry from the last pylon and the great big tower insulators for the underground cable entry made the trip very well worthwhile.

No-one has added any more about what the underground cable actually is. I would very much like to know.

[broadgage]

Originally Posted by Dave Moll

Surely our 100A supplies at (nominally) 230V are already roughly equivalent to the US 200A at 110V in terms of the power capacity.

No, not really. USA residential supplies are generally single phase, 3 wire, with 120 volts between either live pole and the earthed neutral, and 240 volts between the two live wires.
Domestic lighting and general purpose small power circuits are 120 volts, distributed equally between the two live wires.
Heavier loads such as cookers, water heaters, clothes dryers and central air conditioning are on 240 volt circuits.
So a 200 amp supply has a capacity of 48 kw.

Blocks of flats generally have a 3 phase 4 wire supply with 120 volts between any phase and neutral, and 208 volts between phases.
Each dwelling has any two phases and the neutral for smaller homes, or all three phases and neutral for larger homes.
The drawback of this system is that very few appliances are made for 208 volts, it is usual to utilise 240 volt loads and accept reduced performance.

[Roger Ramjet]

Originally Posted by broadgage

Bo, not really. USA residential supplies are generally single phase, 3 wire, with 120 volts between either live pole and the earthed neutral, and 240 volts between the two live wires.
Domestic lighting and general purpose small power circuits are 120 volts, distributed equally between the two live wires.
Heavier loads such as cookers, water heaters, clothes dryers and central air conditioning are on 240 volt circuits.
So a 200 amp supply has a capacity of 48 kw.

Blocks of flats generally have a 3 phase 4 wire supply with 120 volts between any phase and neutral, and 208 volts between phases.
Each dwelling has any two phases and the neutral for smaller homes, or all three phases and neutral for larger homes.
The drawback of this system is that very few appliances are made for 208 volts, it is usual to utilise 240 volt loads and accept reduced performance.

Very interesting broadgage, clearly the American's appear to have a mixed local distribution network. What puzzles me is where houses or flats are on the same distribution cable, how can two different line voltages of 240 & 208 volts exist .....so are they connected to different supply transformers in the substation.

Rog

[dave walsh]

Some of the concerns about the distribution, delivery and usage of the UK electrical supply [as expressed by Lancs Lad, among others] in posts 36* 37 * and 39* are touched on in a recent BBC1 series confusingly titled "Heat Pumps What They Really Mean For You". In a perhaps over chirpy manner, it actually covers a much wider group of topics related to the generation and delivery of power including fossil fuels, hydrogen, and at the end [from 50 mins in] the 20 miles of cabling being laid deep under London. It's rated at a mere 40k volts [not 275k] and installed in concrete tunnels. [Nothing about predictable wave power sources so far!]

That takes us back to the beginning of this thread, I think and the question of why cabling underground costs more because it requires attention to both overheating issues and access for maintenance. I think it's well worth looking at the whole program, after the Heat Pumps [not much of an advert there] despite the patchy presentation but then it's not aimed at Engineers. Part one was on Tuesday 1/8/23 and repeated BBC2 Sun 5/8. Available for a year!

A companion series "Electric Cars: What They Really Mean For You" P1 BBC1 was shown on Tuesday 25/8/23 [R] Sunday 30/7/23 BBC2.

Even with the Radio Times I found it difficult sorting out these dates and times as the I-Player [or eqivalent] doesn't seem to list the dates of transmission anymore. An annoying and unnecessary change in my view

Dave W

[chaz007]

Originally Posted by Lancs Lad

It worries me about when everybody has an electric car that they need to charge up every night, and induction hobs that seem so fashionable these days. Not to mention everything else!

The average UK house is going to need a far higher amperage supply than they have at present.

American households used to make do with a 100 amp supply, but now new houses all have 200 amp supplies.

We don't have anything like that in the UK. 100 amp is our maximum. And many of us don't even have that!

Lots of older properties only have 60 or 80 amp cut-out fuses. Try plugging your new Tesla in while someone is having a shower and see what happens!

And it's only going to increase as petrol/diesel cars disappear from the roads.

Where is all this extra electricity going to come from?

I'm fairly sure our power grid, at present, won't be able so supply it.

We'll probably see the cables between pylons glowing red hot at night when everyone has plugged their electric cars in to charge.

Yes, I know I'm making light of it, but this new reliance on electricity as the answer to everything bothers me.

Anyone else? Or just me?

It won’t work

A large portion of the LV distribution network is getting on for 100 years old in cities etc, I worked on an LV fault last night and 6 houses were fed off an .0225 three phase cable, three of those were fed off a single phase .0225 cable, two off a .01 single phase cable.
.0225 is around 15mm, .01 is 6-7mm
This is pretty standard and it will just burn out

[dglcomp]

Originally Posted by Roger Ramjet

Quote: No, not really. USA residential supplies are generally single phase, 3 wire, with 120 volts between either live pole and the earthed neutral, and 240 volts between the two live wires.
Domestic lighting and general purpose small power circuits are 120 volts, distributed equally between the two live wires.
Heavier loads such as cookers, water heaters, clothes dryers and central air conditioning are on 240 volt circuits.
So a 200 amp supply has a capacity of 48 kw.

Blocks of flats generally have a 3 phase 4 wire supply with 120 volts between any phase and neutral, and 208 volts between phases.
Each dwelling has any two phases and the neutral for smaller homes, or all three phases and neutral for larger homes.
The drawback of this system is that very few appliances are made for 208 volts, it is usual to utilise 240 volt loads and accept reduced performance.
broadgage is offline Report Post Reply With Quote

Very interesting Broadgage, clearly the American's appear to have a mixed local distribution network. What puzzles me is where houses or flats are on the same distribution cable, how can two different line voltages of 240 & 208 volts exist .....so are they connected to different supply transformers in the substation.

Rog

I believe the American system is all down to the transformer used, normal domestic 120/240V systems will use a centre tapped transformer run off one phase, similar to what you what we'd have in a 110V site transformer but with 120V on each leg, I believe flats must use 3 phase as it's needed for the lifts and it's simpler just to use that supply for everyone.

[broadgage]

If for some reason a detached house was connected to the same substation as a block of flats, it would receive 120 volt/208 volt service just like the flats. This is rare but examples do exist.
Detached houses are more often supplied from relatively small pole mounted transformers, either one transformer per home, or one per small group of nearby homes.
Blocks of flats often have the 3 phase high voltage utility supply brought into the building, to a utility owned transformer either in the basement, or in an outdoor enclosure.

3 phase, 4 wire service at 120/208 volts is the norm for smaller business premises also.

Large offices and works generally have a 3 phase supply at 277/480 volts, with customer owned transformers to produce 120 volts for portable appliances. Fixed lighting equipment would be 277 volt in such premises. 277 volt incandescent lamps, and 277 volt ballasts for fluorescent and discharge lamps are sold.
This higher voltage is prohibited in homes.

The accepted colour code for single phase 120/240 volts is white for neutral, with black and red for the two live conductors.
For three phase 120/208 volt, white for neutral and black, red, and blue for the three phases.

For 277/480 volts, gray for neutral and brown, orange and yellow for the three phases is the norm.

Other systems exist, including 3 phase 4 wire delta, and 3 phase 3 wire delta with one phase earthed, known as "corner grounded delta".

[Roger Ramjet]

Fascinating Broadgage... clearly a right mixed bag.b
So getting back to the OP, would the high voltage UG cables feeding the utility transformers have multiple differing values as well & also, would they come from independent power stations on my presumption that the USA does not have a National Grid ?

Rog

[broadgage]

Many different high voltages are used by American utilities, but that is a regional thing. WITHIN a region high voltages are more or less standardised.

Supplies to customers may be single phase, 3 wire 120/240 volt
Three phase four wire at 120/208 volts.
Three phase four wire at 277/480 volt.
Three phase, four wire delta at 120/240 volt (rare)
Corner grounded delta, various voltages. (rare)

But the HV supply into the various types of transformer will be standard.

They do have a national grid, but local utilities distribute the power at different high voltages, often for historical reasons. A lot of HV distribution uses 3 phase, 4 wire with a neutral. Contrary to UK practice where HV is almost always 3 wire.

Frequency is now virtually standard at 60 cycles. But within living memory California used 50 cycles, and some industrial supplies were 25 cycles.