Why are modern street powerlines wrapped together?

[Nathi ORea]

TL;DR Summary

I have a few questions about why modern electrical street wires are wrapped in pairs.

Something I have noticed and have wondered for a fair while is how street powerlines are now wrapped around each other in pairs in my local area (Central Coast, NSW, Australia)In this first pic you can see how they used to be. 3 higher voltage powerlines, and the 4 lower voltage powerlines below (1 for each phase, and a neutral)

The next pic you can see how they seem to set up powerlines these days. Here is a place where it transitions from 4 separate lines to them wrapped in pairs.

Here is a little more down the road where you can see how the lower voltage powerlines are wrapped in pairs.

I guess i have a few questions about this
- Did insulation used to be more expensive, or not as good, etc, to allow this 'wrapping' kind of set up. Did better/cheaper insulation come about which allowed this to happen?
- Can anyone think of any advantages to wrapping the wires in pairs as opposed to being by themselves? Say such insulation did come along, what is the actual advantage of this... Like now you have to pay for insulation... Now there's bigger concern of a short between them.
- I would have thought that them being so close to each other would cause induction in the other wire, and muck up the flow of electricity somehow? I assume this must not be a problem?

I am just a high school science teacher who needs to learn about what he sees. Certainly no background in electricity.

 

[DrJohn]

Are you sure that's a power cable?
Google on twisted pair wiring. It's used in computing and telephone systems. (I'm not a physicist however, so I could be wrong.) It reduces background noise and interference in the transmitted signals.

 

[anorlunda]

In the 3rd picture, the lower lines are for phone/TV/Internet, not power.

The rule is that when power and phone share the same pole, the power lines are highest up, and the phone lines lower. The power lines provide shielding from lightning. You would be very unhappy if the phone/TV/Internet cables into your house carried lightning currents.

A second rule is that the maximum allowable voltage increases the higher up we go from the ground. That's primarily a safety reason. If someone or something touches those phone cables, the electric shock will probably not be lethal or start a fire.

 

[Baluncore]

That looks like 3 wire, three-phase distribution, at the top of the pole, maybe 11kV. There will be a transformer somewhere nearby that supplies the 4 wires below, being neutral plus 400V 3PH, which is equivalent to three separate 230V single phase lines relative to neutral.
The twisted two-wire cable from the pole to the house has neutral and one 230V phase.
Where a building requires more power, four wires are twisted together to deliver three phases and neutral.

Google Earth Street View makes it easier to see what is there. Please give a street address or the latitude and longitude of the location.

 

[Nathi ORea]

That looks like 3 wire, three-phase distribution, at the top of the pole, maybe 11kV. There will be a transformer somewhere nearby that supplies the 4 wires below, being neutral plus 400V 3PH, which is equivalent to three separate 230V single phase lines relative to neutral.
The twisted two-wire cable from the pole to the house has neutral and one 230V phase.
Where a building requires more power, four wires are twisted together to deliver three phases and neutral.

Google Earth Street View makes it easier to see what is there. Please give a street address or the latitude and longitude of the location.

Google Earth Linkhttps://earth.app.goo.gl/Xn6xEC
#googleearth

thanks for your reply.
All you just wrote I think is pretty spot on without knowing the exact numbers.

 

[Nathi ORea]

Are you sure that's a power cable?
Google on twisted pair wiring. It's used in computing and telephone systems. (I'm not a physicist however, so I could be wrong.) It reduces background noise and interference in the transmitted signals.

I just looked it up. It was interesting.

I am pretty sure they’re powerlines here but

 

[Nathi ORea]

In the 3rd picture, the lower lines are for phone/TV/Internet, not power.

The rule is that when power and phone share the same pole, the power lines are highest up, and the phone lines lower. The power lines provide shielding from lightning. You would be very unhappy if the phone/TV/Internet cables into your house carried lightning currents.

A second rule is that the maximum allowable voltage increases the higher up we go from the ground. That's primarily a safety reason. If someone or something touches those phone cables, the electric shock will probably not be lethal or start a fire.

Thanks for your reply.

I am pretty sure they’re powerlines

 

[Rive]

As it turned out, those are called 'Aerial Bundled Cables'
link
Also: Wiki
Indeed, they seems to happen more and more frequently these days... I've also just noticed them not long ago.

 

[Nathi ORea]

As it turned out, those are called 'Aerial Bundled Cables'
link
Also: Wiki
Indeed, they seems to happen more and more frequently these days... I've also just noticed them not long ago.

That wiki article seems to be answering a lot of the questions I had. I have to process it in the morning but. It is 1:27 am here.

Thanks so much!

 

[Rive]

Thanks so much!

If not for your topic, I would have completely missed on the thing, so...

 

[Baluncore]

All you just wrote I think is pretty spot on without knowing the exact numbers.

I agree, NSW, Australia. -33.467579°, 151.361496° is a pretty spot.
I am in the same time zone, but on an island about 1000 km South of you.

My 11kV guess for the distribution voltage is probably correct, as the insulators have two discs.

Where houses need to tap off power, the neutral and three phases are run as four parallel wires, but for the run from the corner transition (-33.466474°,151.361884°), to the transformer (-33.466551°, 151.362578°), two twisted pairs are used. Those are the heaviest cables in the pictures.

Most telephone lines in Australia were buried underground, to keep them away from lightning and power poles controlled by another authority. I see no telecom lines in the pictures.

Note that the streetlights on every second pole are connected between two of the 400V phases and have no dedicated control wire running along the street.

 

[Nathi ORea]

Where houses need to tap off power, the neutral and three phases are run as four parallel wires, but for the run from the corner transition (-33.466474°,151.361884°), to the transformer (-33.466551°, 151.362578°), two twisted pairs are used.

I don't think this is the case. I did a Maccas run this morning, and had a bit of a look. There are household supplies where they have the bundled lines. Pictures are compressed when I upload them, so here is a couple of Google Maps links.

The first is at the transformer you're talking about. There is a household supply running overhead. https://goo.gl/maps/NxuyMhGpwz8TLwfg9

Here is the adjacent main road. Same thing. https://goo.gl/maps/Vvo8EEKb2NWHrUGT9

I am in the same time zone, but on an island about 1000 km South of you.

Is that island called Tasmania? lol

Most telephone lines in Australia were buried underground, to keep them away from lightning and power poles controlled by another authority. I see no telecom lines in the pictures.

I actually just noticed, through the whole process of this thread, that there are no telephone wires there. Along the part of the street where I live, they are still present. This Maps link sends you to where it seems to come out of the ground and then actually travels along the telegraph poles; https://goo.gl/maps/Y2FepRsehNRxKqwr7

Note that the streetlights on every second pole are connected between two of the 400V phases and have no dedicated control wire running along the street.

Could you explain this a little more. Are the lights connected between 2 phases, and not between a phase and ground as I think they would be in a home. I definitely do not have a strong background in electricity. What do you mean by control wire? Do you mean a separate supply wire for the street lights?

As it turned out, those are called 'Aerial Bundled Cables'
link
Also: Wiki
Indeed, they seems to happen more and more frequently these days... I've also just noticed them not long ago.

The Wiki article was good. Goes over some pros and cons. I am happy with that. I didn't want to become an expert in it... lol

I guess one question I had that Wikipedia does not explain is does electromagnetic induction occur between the wires because they are so close?

 

[Baluncore]

The first is at the transformer you're talking about. There is a household supply running overhead.

Yes. That house supply comes from the LV terminals of the transformer, where all the thick bundles originate.

Could you explain this a little more. Are the lights connected between 2 phases, and not between a phase and ground as I think they would be in a home.

I am not certain, but either is possible.

What do you mean by control wire? Do you mean a separate supply wire for the street lights?

What turns the lights on at night? Does each have a light sensor? Or is a code transmitted over the grid? I found one light that was turned on during the day in Street View. I will take another look when I get back from work.