Transmission versus distribution: who owns the poles and wires

Drive along the Hume Highway between Yass and Wagga and you’ll pass under a line of steel towers strung with conductor thick as your wrist, running at 330,000 volts. Twenty minutes later, in a Wagga side street, you’ll see a wooden pole with a transformer the size of a wheelie bin feeding six houses at 230 volts. Same electricity, same grid, two completely different businesses own those wires. That distinction, transmission versus distribution, is one of the most misunderstood bits of plumbing in the National Electricity Market, and it’s worth getting precise about because it explains a good chunk of what shows up on your power bill.

The line on the map that matters #

Transmission is the high-voltage backbone: the freeways. Distribution is everything downstream of the zone substation: the suburban streets and driveways. The regulatory boundary usually sits somewhere between 66 kV and 132 kV, depending on the state, and below that voltage a different company, with a different licence, different assets and a different regulatory reset, takes over. It sounds like a technicality. It isn’t. TransGrid in NSW and Powerlink in Queensland run networks measured in gigawatts of transfer capacity across hundreds of kilometres. Ausgrid, on the other hand, is managing a spaghetti of low-voltage cable under footpaths in Newtown, worrying about a transformer that’s been running hot on a 40-degree day in Merrylands. Both are essential. Neither can do the other’s job.

Transmission: the freeways of the grid #

The five mainland NEM states each have a single transmission network service provider, or TNSP: TransGrid in NSW, Powerlink in Queensland, AusNet in Victoria (which also runs some distribution, more on that oddity below), ElectraNet in South Australia, and in Tasmania and the west, TasNetworks and Western Power do a combined job because those systems are smaller and, in WA’s case, not even connected to the NEM. These networks carry bulk power, often hundreds of megawatts down a single circuit, from generators to load centres and between regions. When AEMO dispatches the market every five minutes, as I’ve written about how the NEM dispatches power, it’s the transmission network doing the physical work of moving that dispatched megawatt from a wind farm in western Victoria to a smelter in the Illawarra. Congestion on those lines is also a big part of why wholesale prices swing so violently between regions — a constrained interconnector can strand cheap generation on one side of a state border while the other side pays through the nose.

Distribution: the last mile, literally #

Distribution networks step voltage down, again and again, until it’s usable in a house or a small factory. In NSW that’s Ausgrid (Sydney, the Hunter, the Central Coast), Endeavour Energy (greater western Sydney, the Blue Mountains, the Illawarra) and Essential Energy (the rest of regional NSW, which is an enormous, thinly populated, expensive network to run). Victoria splits distribution five ways between CitiPower, Powercor, United Energy, Jemena and AusNet. Queensland has Energex around Brisbane and the southeast and Ergon Energy for the rest of the state, both now sitting under the government-owned Energy Queensland umbrella. South Australia has one, SA Power Networks. These are the businesses that answer the call when a storm brings a gum tree down across the line on your street, and they own the asset that ultimately decides whether your rooftop solar export gets curtailed on a sunny Sunday, which matters a great deal if you’ve read our piece on who really pays for solar.

Who actually owns this stuff #

Ownership across this sector is a genuine mixed bag, and it’s changed a lot over the past decade or so. Some networks never left government hands: Powerlink, Energy Queensland, Essential Energy, TasNetworks and Western Power are all state-owned. Others were partially or fully privatised through long-term lease transactions, mostly in the 2010s. TransGrid was leased out by the NSW government in 2015 to a consortium of infrastructure and superannuation investors. Ausgrid’s majority interest went to a consortium including AustralianSuper and IFM Investors in 2016, with the NSW government retaining a minority stake. AusNet, which uniquely straddles both transmission and distribution in Victoria, was taken private by a Brookfield-led consortium in 2022 after a contested takeover process. SA Power Networks sits with a consortium that includes CK Infrastructure. None of that ownership structure changes the physics, but it does change who’s arguing with the Australian Energy Regulator about how much they get to earn on the asset base, and that argument is where your bill gets decided.

The AER decides what they can charge you #

Every TNSP and DNSP operates as a regulated monopoly, which means you can’t shop around for your poles and wires provider the way you can for a retailer. In exchange, the Australian Energy Regulator sets, roughly every five years, a maximum allowed revenue for each network based on the value of their regulated asset base, a return on capital, and forecast operating costs. This is not a small line item. Network charges, transmission and distribution combined, typically make up somewhere between a third and half of a residential bill, which is one reason the AER’s annual Default Market Offer determination gets so much attention each year. It’s also why network businesses have such a strong incentive to justify capital spending on poles, wires and substations: under the current regulatory framework, a bigger asset base broadly means a bigger allowed return, which is exactly the kind of structural tension the AER’s resets are meant to keep honest.

A worked example: why 500 MW doesn’t mean 500 MW at your switchboard #

Here’s where the power-versus-energy distinction actually bites, and it’s worth being careful with the numbers rather than waving hands. Say a 500 MW wind farm in the Riverina is dispatched at full output for an hour. That’s 500 MWh of energy delivered in that hour, moved along a transmission line rated for, say, 1,000 MW of thermal capacity, so there’s plenty of headroom. That energy then gets split across dozens of distribution feeders on its way to homes and businesses, each rated in the tens of MVA, not hundreds. A suburban zone substation might be rated at 40 MVA and serve 15,000 homes. If every one of those homes tried to charge an EV at 7 kW simultaneously on a summer evening, you’d hit 105 MW of instantaneous demand against a 40 MVA asset, and the network would trip long before it ever became a transmission problem. That’s the entire argument behind managed EV charging and the current push described in our piece on the Consumer Energy Resources roadmap: the constraint of the future isn’t the freeway, it’s the last few hundred metres of suburban street.

Why the split matters for the transition #

AEMO’s Integrated System Plan is the document that lays out how much new transmission the NEM needs to connect renewable energy zones to load centres, and the 2024 edition put the figure in the tens of billions of dollars over the coming two decades. Let’s be careful with that number, because the ISP gets updated every two years and the next full release is due this year, so the headline figure will move once construction costs and delivery timelines are reassessed. What won’t move is the underlying logic: wind and solar sit in places the old coal-fired grid was never built to reach, and someone has to string new high-voltage line to get there. That’s squarely a transmission problem, and it’s a large part of why projects like South Australia’s renewables build-out needed serious network investment alongside the generation itself.

Distribution networks have a quieter but arguably harder version of the same problem: absorbing millions of small, uncoordinated devices, rooftop solar, batteries, EV chargers, on infrastructure designed for one-way power flow from a substation outward. I’d argue the distribution side gets less attention from commentators than transmission simply because there’s no single dramatic transmission line map to point at, no equivalent of a REZ announcement. But my honest read, after a few years watching AER determinations roll through, is that the distribution reset process is where the more consequential fights over cost allocation are actually happening, even if it never makes the front page.

None of this is glamorous engineering. It’s closer to municipal plumbing than rocket science, and I say that as someone who finds long solo bike rides oddly similar to reading network revenue proposals: both reward patience over any single burst of effort. But next time your bill arrives with a line item for network charges, you’ll know it’s really two separate businesses, running two separate assets, both regulated, both necessary, and neither one substitutable for the other.

— Anjali Rao, Grid & Storage Correspondent

Photo by American Public Power Association on Unsplash