Voltages used in "neighborhood" power distribution

I suppose it is really up to your utility but they use 13,200v line to neutral here. (22,860Y) The other tap on the transformers is for 7,620v

In my area served by Los Angeles Dept. of P & L, the underground transformers are still 5000V to 240/120V. The one serving my home blew a few months ago. The linemen said there were still a few spares around, but they had a hard time locating one. They can "work hot" on anything 5KV or below.

The sub-division, just north of UCLA, is about fifty years old.

Probably 4800/8360 Wye system volts. We use that in our rural distribution but is losing to 27.6kV for higher loads over long distances.

The sub-division, just north of UCLA, is about fifty years old.

Well, at least I know that 38 kV isn't "crazy!"

"Next time" is talk with the "underground linemen" I will ask a few more questions.

It's a lot more difficult to start and maintain a conversation with a crew that's looking up into the air than a crew with two guys basically sitting in a ditch.

>

In UK, it's 11kV. However a suburban pad transformer will normally do 100 or more homes. Only in rural areas would it drop as low as 1 to 8 homes, and that would normally be pole mounted. Again, normally fed at 11kV, but there are some directly fed from 33kV.

I have a length of 11kV single core underground cable (normally

3 of them are used for a 3-phase supply). It's 150mm² Al cross sectional area. The Al core has a thin black semi-conducting layer around it. The bulk of the insulator is a thick layer of orange plastic, apparently XLPE (Cross-Linked Polyethylene), surrouded by another semi-conducting layer and earthed copper braid, and then the outer tough PVC sheath (red in this case).

With that many homes (100 or more) on one padmount transformer you must have severe voltage drops into the homes. Running 220v cables to the home at the end must incurr about 100 meters or more in length.

Ours, in the cities, with normal load density run up to about 13 homes on one transformer. The homes at the far ends get heavier wire to avoid voltage drop problems.

Does the centre conductor has strands of steel inside it? Ours has that for overhead distribution on HV lines. ACSR = aluminum conductor, steel reinforced. Not sure about U/G cables.

Translations: "centre" "center" (US); "aluminum" = "aluminium" (UK)

LOL

In plumbing they call XLPE it "PEX" = polyethylene cross linked.

When they terminat thos concentric/sheilded cables they built stress cones at the ends to avoid termination impedance transition shock. They flare every layer (except the conductor) out to 2.5 times it size before discontinuing the layer. This takes a lot of insualting tape, semi-con tape and braided conductor materials.

In UK, it's 11kV. However a suburban pad transformer will normally do 100 or more homes. Only in rural areas would it drop as low as 1 to 8 homes, and that would normally be pole mounted. Again, normally fed at 11kV, but there are some directly fed from 33kV.

I have a length of 11kV single core underground cable (normally

3 of them are used for a 3-phase supply). It's 150mm² Al cross sectional area. The Al core has a thin black semi-conducting layer around it. The bulk of the insulator is a thick layer of orange plastic, apparently XLPE (Cross-Linked Polyethylene), surrouded by another semi-conducting layer and earthed copper braid, and then the outer tough PVC sheath (red in this case).

Sorry, I meant 1000 metres instead of 100.

Ours, in the cities, with normal load density run up to about 13 homes on one transformer. The homes at the far ends get heavier wire to avoid voltage drop problems.

Does the centre conductor has strands of steel inside it? Ours has that for overhead distribution on HV lines. ACSR = aluminum conductor, steel reinforced. Not sure about U/G cables.

Translations: "centre" "center" (US); "aluminum" = "aluminium" (UK)

LOL

In plumbing they call XLPE it "PEX" = polyethylene cross linked.

When they terminat thos concentric/sheilded cables they built stress cones at the ends to avoid termination impedance transition shock. They flare every layer (except the conductor) out to 2.5 times it size before discontinuing the layer. This takes a lot of insualting tape, semi-con tape and braided conductor materials.

In UK, it's 11kV. However a suburban pad transformer will normally do 100 or more homes. Only in rural areas would it drop as low as 1 to 8 homes, and that would normally be pole mounted. Again, normally fed at 11kV, but there are some directly fed from 33kV.

I have a length of 11kV single core underground cable (normally

3 of them are used for a 3-phase supply). It's 150mm² Al cross sectional area. The Al core has a thin black semi-conducting layer around it. The bulk of the insulator is a thick layer of orange plastic, apparently XLPE (Cross-Linked Polyethylene), surrouded by another semi-conducting layer and earthed copper braid, and then the outer tough PVC sheath (red in this case).

--------------- Stress cones are not used to avoid "termination impedance shock" but, rather to control the voltage gradient in the region of the junction. The flaring is one way to do this. There are other ways.

"In cable installation, shielded power cables require electrical stress control when terminated. When the insulation shield is removed from a cable, high potential gradients are concentrated at the cutback point, causing high electrical stress. Electric field enhancement at these points can produce local discharges that could lead to either flashover along the insulation surface or dielectric breakdown causing cable failure. Cable terminations are designed to eliminate the stress concentration at the screen termination to avoid the break-down of the cable. In other words, the electrical field has to be controlled in a cable termination."

Out in the suburbs it is more like 2 - 4 houses on a transformer with a 13kv primary and a neutral. (wye distribution) They give each one about 12.5kva (25KVA transformer feeds 2 houses,

50kva feeds 4) There are 20 transformers on my leg, about 55-60 houses, all fed from one primary.

Sure sounds like an echo.

"In cable installation, shielded power cables require electrical stress control when terminated. When the insulation shield is removed from a cable, high potential gradients are concentrated at the cutback point, causing high electrical stress. Electric field enhancement at these points can produce local discharges that could lead to either flashover along the insulation surface or dielectric breakdown causing cable failure. Cable terminations are designed to eliminate the stress concentration at the screen termination to avoid the break-down of the cable. In other words, the electrical field has to be controlled in a cable termination."

---------------

In Finland the most important distribution voltages to the transformer are 20 kV and 10 kV (three phase power, voltage between phases).

20 kV is the most commonly used voltage for both overhead lines and cables on modern installations. 10 kV is used on some older installations (especially on the center of big cities like Helsinki).

Complete opposite. With a 1-2MVA transformer, nothing I can do at home with varying the load makes the slighest difference to the voltage. Variations are very much less than in the US. OK, I'd expect 4 times less due to twice the voltage and half the current, but it actually seems much better than even that. Maybe we use thicker street conductors, I don't know?

[1000m] Probably 500m max.

If you look at a tiny village here with overhead supply, you might find a pole mount transformer in the middle with a street mains heading in each direction down the road. With reasonably modern installs (like last 25 years), the same thick conductors run right along the road feeding the taps right to the last house.

We don't use the edison system - our street distribution is all

3-phase 240/415V Wye (or Star as it's known here). I don't know the construction of overhead cables. From the ground, there are two distinct styles - older use 4 separate conductors (sometimes the neutral is uninsulated, sometimes all uninsulated, sometimes all insulated). Newer use a thick bundle of 4 insulated cables twisted quite tightly together.

**1** You must be referring to another form of transformer, usually called a "substation or distribution transformer" other than what most called the "street transformer". Street distribution transformers are the last transformation in voltage feed your house with 120/240vac (in N.America) and I have never seen one at 1-2MVA. The poles won't hold them up. It doesn't work well in distribution systems for residential. I did note some confusion here and this is why I asked.

- You don't run this low voltage 1000m to a house as the copper would be too expensive.

- You don't supply a residence with that high of a fault capacity using a trnasformer and copper that big. Explosions result.

**2** ACSR has nothing to do with an Edison system. Houses do not use 240v/415wye feeds in North America. Where are you located?

**3** The cable bundle you refer to is called "quadriplex"

Thanx

**1** Complete opposite. With a 1-2MVA transformer, nothing I can do at home with varying the load makes the slighest difference to the voltage. Variations are very much less than in the US. OK, I'd expect 4 times less due to twice the voltage and half the current, but it actually seems much better than even that. Maybe we use thicker street conductors, I don't know? [1000m] Probably 500m max.

If you look at a tiny village here with overhead supply, you might find a pole mount transformer in the middle with a street mains heading in each direction down the road. With reasonably modern installs (like last 25 years), the same thick conductors run right along the road feeding the taps right to the last house.

**2** We don't use the edison system - our street distribution is all 3-phase 240/415V Wye (or Star as it's known here). I don't know the construction of overhead cables. From the ground, there are two distinct styles - older use 4 separate conductors (sometimes the neutral is uninsulated, sometimes all uninsulated, sometimes all insulated). Newer use a thick bundle of 4 insulated cables twisted quite tightly together.

If you read back through the thread, you'll see this branch was talking about pad mount transformers in the UK. I think that's where your confusion is.

Yes, but being on the end of a 500m run from the transformer would cause quite a bit of drop between the transformer and you, esp. with your neighbors also present as loads. You must have serious sized conductors running down your streets.

It would be 4 times worse (that is, intolerable) at 120V vs, 240V, true, but at such distances even 240V would have problems.

Not really- it has nothing to do with terminal "impedance transition shock" which is what I questioned.(whatever you mean by that-please clarify) but a lot to do with the distribution of electrostatic stress ( steady state low frequency AC or DC) - rather than "impedance transition" [Which I consider as the change from the characteristic impedance of one cable to that of a different cable]. The use of flaring (see Rogowski profile) is commonly used in HV applications- again for elimination of high electrostatic stresses. The reference that I gave does provide a mathematical analysis. Is it faulty? Do you have data otherwise?

As to its effectiveness for frequency surges where the effects of an impedance change and reflections is important -possible but, in practice, it appears to be secondary or negligable with respect to the electrostatic situation. Possibly such grading in a double cone (as is the practice) may be beneficial but I have no knowledge of any analysis of this with respect to surges in a power cable situation. Do you? I would be interested. -- Don Kelly cross out to reply

There are many different voltage levels and schemes in effect. it depends on where you are, North America, UK or elsewhere as well as load density (roughly houses per km along the line) and single/three phase distribution. Different strokes for different people or conditions. Beyond the technical factors there are historic factors which which have generated a lot of inertia, attitude problems as well as economic problems in making changeover to a world wide uniform approach. Pity Japan with both 50 and 60 Hz systems -cheapest solution is an asynchronous back to back DC link. :)

Whoever accomplishes that will rule the civilized world. ITER (the closest to that) does not sound so hopeful. This post is outlandish and done. RR

Ah, yes, Randy or proteusiiv No capitals or" I am Proteus"?

You can't be Proteus(n) - you make marginally more sense than he/she/it does. However sensible engineering doesn't compete with BS in ruling the world.