By Timothy Welch*
Another extreme weather event has highlighted the weak points in New Zealand’s critical infrastructure. As Cyclone Gabrielle ripped across the North Island, nearly 225,000 people lost power.
The cause is relatively obvious: many houses and buildings are connected to the power grid by overground power lines. Overhead wires, a common sight around many suburbs, are highly vulnerable to extreme weather events. When the winds pick up, limbs and trees fall, and power lines are dragged down.
But one solution is equally obvious: bury the power lines. With the threat of more frequent storms of increasing intensity, the risk to households, businesses and personal safety demands this option be seriously considered.
Power outages mean more than just the inconvenience of a dark house or a dead mobile phone battery. Many things we rely on, like fibre internet, home WiFi or even our ability to make emergency calls, depend on an electrical connection.
Loss of power puts refrigerators and freezers full of valuable food at risk. And many people rely on electricity for lifesaving medical devices in their homes. Battery backup only offers a short-term solution. When the power goes out, lives and livelihoods are put in danger.
Cyclone Gabrielle's strong winds and heavy rain have caused lines and trees to fall, causing widespread power outages over the upper North Island. https://t.co/CMq7X3c6u0
— Stuff (@NZStuff) February 13, 2023
Costs and benefits
Perhaps the main argument against burying power lines is the cost. And it’s true, putting thousands of kilometres of cable underground isn’t cheap. The fact is, reliable infrastructure is expensive.
However, while overhead power lines are cheaper to install in the short term, they carry a higher maintenance cost and are less reliable – especially in storms. If the cost to households and businesses from a loss of power is also considered, the economics of burying power lines become much more palatable.
Another argument against burying power lines is that in areas prone to earthquakes, underground lines are more vulnerable or more difficult to repair. This was certainly the case in the Canterbury earthquakes a decade ago.
However, studies have shown that better routing and reinforcement of underground lines can mitigate that risk. Major earthquakes are also far less common than weather events that damage overhead wires.
Earthquake-prone Japan recently announced a plan to bury 4,000km of powerlines by 2025. In shaky California, one utility company plans to spend US$10 billion burying power lines to prevent fires.
Denmark, Switzerland, Germany and the Netherlands have all buried most of their power lines. Unsurprisingly, they also have the lowest “system average interruption duration index” (SAIDI) values – a measure of the average duration of power outages per customer.
All four countries have a SAIDI value of less than 25, meaning the average customer experienced a power outage of fewer than 25 minutes. By comparison, Auckland’s electric distribution business Vector has a SAIDI of 161.9; Christchurch’s Orion scored 57.4; while the country overall averaged over 204 minutes per customer for an outage.
Spend now, save later
There are other good safety reasons for burying power lines, too. Even without trees nearby, power lines can arc in high winds, causing showers of sparks to rain down and potentially ignite fires. This happened in 2020 with the Lake Ōhau Alpine Village fire that burned 5,000 hectares and 65 structures and caused NZ$35 million in insurance losses.
Broken power lines carry massive voltages, which can maim or kill people. Falling power poles crush people and cars. Single-vehicle crashes into power poles also frequently result in critical and fatal injuries, and large power outages.
Utility poles can obstruct or narrow footpaths, making paths less accessible, particularly for people in wheelchairs. Overhead wires are often cited as an eyesore, and trimming trees around power lines is both ugly and damaging to the trees.
Right now, however, the most pressing reason for burying power lines is visible all around. At this point, it’s not clear how extensively cyclone Gabrielle damaged the power lines, but it will likely take days or weeks, not hours, to restore power to everyone.
In the coming weeks, workers will fan out across the North Island into precarious locations, lifted high above the ground in cherry pickers to mend lines and restore power. The work puts their own health and safety at risk, and we could eliminate this danger too with underground power lines.
Clearly it isn’t a good option for everywhere. High-powered transmission lines that bridge large spans in undeveloped areas are likely not viable economic candidates for under-grounding. But the long-term benefits of burying lines in cities and towns far outweigh the upfront costs. It should be given serious consideration before the next “storm of the century” hits.
*Timothy Welch, Senior Lecturer in Urban Planning, University of Auckland. This article is republished from The Conversation under a Creative Commons license. Read the original article.
68 Comments
They are protected from water incursion by conduit;
https://emergencypreparednesspartnerships.com/pros-and-cons-of-underground-power-lines/
According to the above - 7-10 times higher cost to install and a bit trickier to fault find.
Not so simple.
Conduit would do nothing in a real flood. In fact afterwards it would keep the water hard up against the cables.
The issue here is at the ends where the cables are jointed, fused and tee offs occur. There are no waterproof connections here. Plus for cable networks transformers are usually ground mounted which would be ruined in a flood vs pole mounted ones.
Overhead is well clear of all this (except where it falls down).
Depends on the material used. If the conduit is uPVC then it's prone to brittle failure. Not sure if it's the case with electrical conduits, but often PVC pipes are rubber ring jointed which can pull out in seismic events. Material is also prone to slow crack propagation from rock impingement etc.
If PE100 (Polyethylene) is used, then it's electrofusion or butt welded forming a homogenous joint where the weld is stronger than the parent material. Can be directionally drilled in shots as long as you can fit on a drum. More exp per meter, but rated for 100 years+ in the ground.
Would be interesting to see accurate data about vectors network and where the faults were over the last week, if 70% of the network is already underground then it should be pretty easy to compared frequency of faults in above ground and underground sections in urban areas.
Your handle is quite the oxymoron.
Tim's article is far too brief, dangling a magical carrot to entice bunnies like you, tail-winded with one-eyed, highly improbable health & safety doomsday scenarios for above ground systems, whilst ignoring the even higher probability of accidents caused by persons blindly digging without checking (at least one can see the overhead lines).
Sure, for an entirely new, greenfield development of a significant scale, where it can be planned for, undergrounding is entirely feasible. Not so for existing, service-rich urban environments.
I can't even drill or trench for a new 100mm dia sewer line 5m long to 1/2 way across your average, quiet Auckland neighbourhood street to meet up with the Public main. The only real way to explain how impractical general undergrounding of powerlines is, would be to go through the exercise of documenting it, for a small neighbourhood. The complexities quickly compound and spiral out of control. Even if one could find an admissible solution on paper, everything changes once you're actually on Site. Oh, and then there's dealing with Nimby No-mates too, who thrives on negative energy and saying 'no'.
My cynical guess would be that the parts of Auckland where this is happening are quite happy to have their property value adding views cleansed a bit with the removing of overhead lines and don't mind the RAB being bumped up and the costs spread across everyone on that network.
Could of course be wrong.
Why would you drill a 5m run? The launch pit alone would probably be 1m of that, if not more for 100mm dia sewer due to the require angle of approach.
Power in streets would typically be 32 or 40 OD HDPE, maybe 63 OD for higher density. It comes on coils. It's flexible. This can be directionally drilled around existing services. It's no different than upgrading an existing ridermain and lateral feeds. Infact, why not install power underground at the same time existing ridermains are renewed?
Yep, on the face of it, it sounds a little silly. We'd drill short runs when a particular routing is non-negotiable & trenching becomes problematic. Something about AT being somewhat problematic to deal with when it comes to CAR (try waiting 1+ years for permission + attendant road cone purgatory, to open up a quiet Ak street) & something about cutting thru all the other service providers services (which I've witnessed). Ends up that drilling can be the only solution left. All on a case-by-case basis, however. We document one solution that appears to suit to get a Consent, then the Contractor chooses which way they want to do it, once they're on Site and have physically identified everything they need to work around (amazing how the actual location of services on Site can be completely different from documented as-builts).
Try dealing with power cables branching off the every existing house, routed around all the existing services at the required minimum separation. Can be done, but amazing how everyone backs off very quickly when the budget comes out.
A new, greenfield development? Sure, no problem.
By the time you factor in all services it can add up to roughly 1.5m of services "trench width". Minimum clearances from other services:
- Power 300mm parallel / 50mm when crossing
- Phone 300mm parallel / 150mm when crossing
- Water 300mm parallel / 50mm when crossing
- Sewer 500mm parallel / 50mm when crossing
But yes, the budget does to a certain degree make it prohibitive but I'd argue if overhead lines/poles have reached end of use, putting services underground would be far cheaper and less disruptive then pulling down the old poles/lines, running temporary power, and replacing with traffic management.
You seem to approach this too academically. In existing, services-rich urban areas, taking into account existing gas, telecoms, water, WW & SW assets as well as other physical constraints such as Private property, topology & geology) generally undergrounding in those areas is not 'cheaper' (possibly national catastrophies aside) and most certainly not less disruptive. If it was, it would have been done - amazing how cost drivers can change construction methodologies overnight. Again, this argument ignores wide open, services-sparse Public corridors where implementation of undergrounding is straight forward, but these tend to be the exception.
Fair points. I think the reason why it's not done more frequently is not due to physical constraints, you'll be surprised how sparse services actually are most of the time.
But the real reason is because the lines companies have bucket trucks, stockpiles of H5 timber or concrete power posts and task specific processes in place. They don't have a fleet of ditch witch directional drilling machines, with experienced operators, and stockpiles of orange PE duct, and why would they sub that work out at market charge rates?
Never said anything about premature replacement. But when those bunch of poles and transformers are up for renewal? There's the option of throwing in new poles, or directionally drilling some conduits and throwing it all underground. Guess what? The lines company doesn't own a single HDD rig, so they're going to use the equipment they have and put everything up on poles again.
So we'll end up with a mish-mash of overhead to underground to overhead on the distribution network.
Local storm, a few poles get taken out here and there, just drop in some underground cable.
Oops, driver took out a pole, lets underground between a couple of poles.
Major thunder storm blows a whole lot of pole mounted transformers, lets replace those with some ground mounted ones.
Or, the flipside, distribution networks are already a mish-mash of different aged assets from all the reasons above.
That should be easy to manage and maintain.
Despite the city’s long history of having most of its power cables underground, the city council agreed to the installation of the temporary overhead lines during the upgrades.
Seems like there is a study that could be done on life cycle costs given they have already undergrounded in some cities.
Befuddled - Agree whole-heartedly - the discussion so far has completely missed the losses inherent in undergrounding power cables. The capacitive and inductive losses go up significantly with voltage and distance so that undergrounding high voltage cables becomes impractical. Added to that is the cost of placing transmission lines underground. One example near me is a 220kV line put under a subdivision, as part of the permit, for only a few hundred meters cost in excess of 2 million - losses not significant, but if this was extended to kilometres then they become a major part of the discussion. There is a reason that the Cook Strait cables are DC and Haywards is required, DC has only I squared R losses - and the line is DC from Benmore for the same reason. DC is not practical within much of the rest of the network (maybe as yet).
Even at low voltages losses can become significant in underground cables - question then is who pays?
The trick is to generate power where its needed to avoid losses - solar for domestic at least!
PNCC already has a policy in their plan regarding this;
Policy 3.4. To require the placement of network utilities underground unless:
• there are natural or physical features or structures, or technological and operational constraints that makes underground placement impracticable or unreasonable;
• they are of a temporary nature and required for emergency purposes or critical events;
• they are of a nature that can only operate above ground;
• in the case of lines, they traverse any Rural Zone or roads within the Rural Zone.
I've lived in a few countries and electricity cables down a city street I've only seen in Port Moresby and Auckland. I asked a councillor about it a few years ago (when the slogan was something about making Auckland the world's most liveable city and was told the power lines are the property of Vector and they have no commercial incentive to bring them up to date.
https://www.vector.co.nz/personal/electricity/undergrounding-other-proj…
They are undergrounding existing lines, but its expensive and a long term project.
The trust which part owns Vector do have a program to underground small areas each year. Of the distribution voltage network. Only within the area that the Trust hails from (old AEPB area). But as mentioned, this is an incredibly slow process and is confined to a certain part of Vector's network. It's doing nothing on the formerly UnitedNetworks area. (North Shore, West Auckland).
That sounds familiar. Slow progress, small investment, excludes North Shore.
In the last few years they have buried fibreoptic cable down our road. Could they have handled electricity at the same time?
If only we had an engineer in charge of Auckland City and its infrastructure.
Please! You can blow fibre cables down a tiny directionally-drilled conduit, and if they get near other services it ain't such a problem. You can't blow power lines and (something about induction) power lines CAN'T be too close to other services, lest those lines be livened too, so one is forced to trench. Therein lies the problem of retro-fitting underground power cabling in an already crowded urban environment - it just becomes entirely impractical. I do submit that for new, greenfield developments (ie: entire neighbourhoods), adequate infrastructure planning can make undergrounding feasible.
You do not need to trench for the conduit. Directional drilling is done all the time on power conduits, infact it's done all the time on watermains many times larger than your biggest power conduit. You see those big bright orange coils of pipe on a drum trailer? Typically 110mm od for HV transmission, 63od and smaller for residential.
They don't tow the trailer over a 100m long open trench dropping the pipe in along the way, if they did then good luck keeping the conduit straight prior to backfilling. It has a memory.
Acknowledged that drilling for cabling is very common and I myself specify thrusting for SW & WW pipes where suitable.
My negative comments around undergrounding of power cabling are in response to TW's silly article. I was even just discussing undergrounding of such cabling with a Vector manager as the cyclone approached. Their comments were that pretty much every retro-fitted undergrounding project got canned, once the budget came out and the developer / community had picked themselves up off the floor & suddenly decided that power poles weren't so bad after all. Why is it so expensive? Because of the complications I mention elsewhere, on this thread.
Yep.
By the way another hazard with undergrounding is the gas network. And there are street light poles which must remain. Plus are the connections to the houses undergrounded too? Who pays for any of this?
There is so much that is not included in this article that it isn't funny.
It would be a massive disruption, but how many roads in NZ cities still have overhead fibre, overhead power, and the various 3 waters asset that need upgrading to meet the medium/high density shoebox living they want to push us all into. Rip up everything at once and redo the whole lot in one go, or wait, and rip up the same street 5 times.
You know which the answer will be in NZ. :)
They've been undergrounding power cables in St Heliers (Auckland) which has resulted in more traffic congestion on narrow streets due to temporary traffic management. There are still street light poles to crash into, so I don't understand the author's comment about safety and single vehicle crashes into power poles. They also can still create a footpath obstruction.
Denmark, Switzerland, Germany and the Netherlands have all buried most of their power lines. Unsurprisingly, they also have the lowest “system average interruption duration index”
1) these countries are not located in earthquake prone zones
2) these countries have a mentality of doing high quality work at all levels
Bollocks conversation so far, including the original posit.
We are staring down the barrel of a no-fossil-fuel world.
Who TF thinks we'll be digging to fix, post FF?
Under accessible covers, sure. But I suspect that'll be cost-prohibitive.
What the writer - a senior knower of everything about sod-all (a siloed expert) forgets to assess, is local power production, and stand-alone resilience. Laughed today at a lady on RNZ - no power cuts; she's 100% off-grid. I haven't had a power cut in 20 years, same reason.
Why do so many folk leave so much in the way of assumptions, in their thinking?
Who says you need to be rural to be off-grid?
Who says income is related to being off-grid? (Answer - only those peddling OTT systems)
I pulled our system off for $5k in 2004/5, and even now, it wouldn't total more than 10k.
And I have done nearly 5 years in total, off-grid on boats; no property required.
Assumptions, assumptions. Straw-man denial constructs. Terrible impediments.
Go well.
Lots of stories of EV owners running their appliances from their cars during the outages.
For example, one person ran their fridge, freezer, LED lights, laptop and router plus a water pump from their car for a day and use 10% of their EV battery. Currently limited to plugging stuff directly into the car using a V2L (Vehicle to Load) adaptor NZ EV Owners | Anyone with V2L in their EV will be doing well in Gisborne atm | Facebook or a DIY setup of an inverter running off the 12V battery (which gets constantly topped up by the drive battery).NZ EV Owners | **Emergency Power from an EV** | Facebook
Future bi-directional chargers like this one (developed in Christchurch) bidirectional-ev-charger-white-paper (enphase.com) will allow the whole house to be powered. It can detect an outage, island off your home and use solar and your EV battery to keep the electrons flowing. Also has the ability to become a virtual power plant allowing you to arbitrage the electricity pricing to generate income (i.e. discharge the EV during grid price spikes and recharge it when cheap. A Tesla trial in the US (using PowerWalls) has generated USD500 per user in the first year Tesla Powerwall owners made up to $500 in the first year of the virtual power plant | Electrek
No problem. As long as the ComCom allow the cost to be passed through at current values, then I'm sure Vector and other would go ahead. Whether the consumers would like to bear the additional cost is another story.
You can produce as many magical SAIDI figures from overseas but the busk stops when you cost converting from overhead to underground.
Of course as an academic the cost is not usually a factor, especially if AN Other has to pay for it.
Hang on, I live in a bit of Auckland that doesn't get a dividend. Why should I pay extra when others have had millions of dollars of dividends that could/should have been put back into modernisation and resilience? Maybe those areas could just go without a dividend for a few years.
I'm very happy to be living in a suburb with all services running underground. No ugly power or phone lines spoiling the skyline.
Power cuts here are rare, usually just planned maintenance outages for the above ground neighbourhoods that the supply runs through.
Not a simple thing to retrofit though, given the supply has to be trenched fairly deep to every house in the area.
Can't see it ever being cost effective for rural supply.
Please take a look at the impact of the (primarily) tree damage in northland - currently 54 areas without power, and have been this way for 4 or 5 days straight, even after 2 good, fine days for repairs the number of outages are actually still increasing.
https://northpower.com/electricity/current-outages
Some of the above is from slips, some from flooding, but most of it is from multiple tree strikes. So to get an area repaired it's not just one tree and one fix, it's dozens of trees and dozens of repairs just to get one area live again.
By the time an entire line is fixed there's another tree down over the line.
I think we're going to see some very significant changes following this regarding trees around power corridors.
And as for Napier. Wow, Major access bridges built no higher than the flood plains they serve. Hindsight has shown that to be a really dumb design flaw.
Really useful comment.
And I'd add - yes, I too am stunned by (what appears to be) the inadequacy of many bridges, but I also wonder what year they were designed and built. Many are possibly 30-50 years old now and what might have been a 1 in 50 or 1 in 100 year flood back in those days is how they were designed. Very different story today - more people, more precipitation, less permeable surfaces upstream. And, already sodden ground.
Perfect storm.
Great in theory, scuttled in practice. Overhead lines in many (most?) areas imply overhead to the house. So in addition to the lines company cost, to u/g the trunks and distributors, every such household faces its own private cost to convert. Double whammy, and as Befuddled points out, in actuality much u/g infrastructure is un- or poorly documented. So add a risk premium and significant contingencies. Counsel of perfection....
And while we are at it, another couple of 'solutions' to demythologize. Microgrids cannot exist without the frequency, voltage, and power factor controls of a conventional grid, or face having to implement all of these on a 24/7/365.25 basis. Good luck. Off grid with mini hydro, solar, etc is a low total power affair. Interested to know PDK's annual kwh consumption. Then ask if that is acceptable to a majority. Or to an actual productive enterprise running induction motors, heating, lighting....
Acceptable to a majority?
Bloody anthropocentric arrogance.
We are overshot, and planet-forcing. But you think 'acceptable' to a temporarily overconsuming echelon, is a worthwhile yardstick?
Spare me.
I went ahead and investigated what energy frugality is, because it is coming to us all. Turns out it's quite a good life - you don't even need to mount straw-persona arguments to support it.
Yes, we'll all get there like it or not - kicking and screaming and bemoaning our foolishness - reminiscing about the good 'ol days.
Talk to any 50+ year old scallop lover in the top of the south. Zero comes quickly and we will all ask, how did that happen?
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