Australian suburban power distribution

Question

In Melbourne, Australia I see a lot of utility poles like the one in the picture below. There are power lines on two levels. Three lines on the top level and four lines in the lower level.

I assume, that the lower level carries the three phases of AC plus the neutral line. From the lines on the lower level, all the lines to individual premises branch off, so I assume that these lines carry 230/400 V.

As there are only three lines on the top level, I assume, that these are the three phases of AC at a higher voltage. Is this the case?

Bonus question: Is the box at the top level a switch to disconnect the top-level power line?

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After my question has already been answered, I will nevertheless answer my own question. A couple of streets from where I took the initial picture, there is a utility pole, which would have answered my question all by its own. It even features the fuse holders mentioned in the accepted answer to my question.

Answer 1

The conductors at the top are a three-wire (delta), three-phase HV supply. In Australian suburbs, this is usually 11kV or 22kV. On Springvale Road in Glen Waverly, Melbourne, for example, it's 22kV. Where I live in outback Queensland, it's 11kV.

The object at the top of the pole is likely to be a sectionaliser - basically a switch with a few sensors and some crude logic. In the event of a fault, the sectionaliser will determine whether the fault is in front or behind of itself, and will lock out the faulty portion.

It could also be a simple fuse-holder, as Sparky256 suggests, though Australian utilities would normally use a simpler drop-out fuse holder, like the one shown below.

The conductors at the bottom are a four-wire (wye), three-phase + neutral LV supply. That would be 230/415 VAC, as you suggest.

The very bottom-most cable is usually telecommunications of some sort, i.e. phone lines.

Answer 2

The distribution standard for five continents is

• Distribution via 3-phase delta (no neutral) at various voltages
• A delta-wye transformer for the neighborhood (dozens of houses)
• The transformer taps all 3 phases
• 415V 3-phase "Wye" (230V to neutral) to each home - typically delivering 1, 2 or 3 phases depending on requirement.

North American strategy is totally different.

• Distribution via 3-phase delta at various voltages
• A single-phase center-tap transformer for the block (maybe a dozen houses)
• Each transformer taps 1 phase (2 wires of 3). The next transformer taps another phase etc.
• 240V split-phase (120 and 120) to the houses

The difference shows up when a customer wants something fairly big, like a machine shop. When a 5-continent user wants a big load, they drop him all 3 phases - if you ever notice larger on-demand water heaters always have three 240V hookups, that is why. This gives the European user 415/3phase. When a North American user wants a big load, she gets 240V single-phase, which is weak tea. If she needs bigger (typically US 480V or Canada 575/600), they have to fit a transformer just for her, and that has 5-digit expense.

North America does have all-electric homes in the snowbelt, and they provision staggering amounts of current to it - as high as 400A. Conductors the size of your thumb, and aluminum. (after we botched aluminum wiring, we un-botched it and it's now the standard for anything over about 100A.)

It is impossible for North America to retrofit to the 415/3phase system because the neutrals conflict. Well, not impossible -- the Philippines is doing it --but the neutral issues are driving them crazy and getting people killed.

Answer 3

Those are in-line fuses, rated 10 kV at 50 amps likely. The lines are too close to be over 10 kV, so they are likely local 7,200 VAC delta distribution lines. A single line can power about 50-60 homes. Notice the ceramic 'bells' the wires hang from.

At very high voltages there would be many bells in a row. They weigh about 20 pounds each, and are good for 10 kV each in terms of dripping water (rain) isolation by air gap. A 33 kV line would have many bells in a row.

The lower lines are likely 230/400 WYE. Notice the very small insulators, so the voltage has to be relatively low.

Note that foreign and USA standards can be very different.