Retrotechtacular: One Does Not Simply String Up A Half-Million VDC Transmission Line

It takes strong and determined population to build a lasting civilization. If the civilization includes electricity and the inhabitants live in a hilly place with an often-unforgiving climate, the required strength and determination increases proportionally. Such is the case of the gentlemen who strung up the first half-million VDC transmission line across New Zealand, connecting the country’s two main islands.

Construction for the line known as the HVDC Inter-Island link began in 1961. It starts at the Benmore hydroelectric plant on the south island and runs north to Cook Strait via overhead cables. Then it travels 40km underwater to the north island and ends near Wellington. This is the kind of infrastructure project that required smaller, preliminary infrastructure projects. Hundreds of miles of New Zealand countryside had to be surveyed before breaking ground for the first tower support hole. In order to transport the materials and maintain the towers, some 270 miles of road were laid and ten bridges were built. Fifteen camps were set up to house the workers.

The country’s hilly terrain and high winds made the project even more challenging. But as you’ll see, these men were practically unfazed. They sent bundles of steel across steep canyons on zip lines and hand-walked wire haulage rope across gullies because they couldn’t otherwise do their job. Six of these men could erect a tower within a few hours, which the filmmakers prove with a cool time-lapse sequence.

Splicing the mile-long conductors is done with 100-ton compressors. Each connection is covered with steel sleeve that must be centered across the joint for optimum transmission. How did they check this? By taking a bunch of x-rays with a portable cesium-137 source.

Thanks for the tip, [Dave] and [Bryan Cockfield].


30 thoughts on “Retrotechtacular: One Does Not Simply String Up A Half-Million VDC Transmission Line

  1. HVDC lines are so cool. I was driving around through northern MN earlier this summer and saw a funky looking power line; hefty gauge with only two conductors. I looked it up later that day and it turned out to be the Square Butte line. I’ve always wanted to tour one of the converter stations, but so far it seems like they’re typically unmanned and quite dangerous.

  2. Ah, I long for the days of interesting documentaries like this, and not “Come dine with me”.

    If like me you would love to see inside they Haywards substation where the DC is converted to AC. For that look for the “Inter-Island Power (1966)” video.

    I used to regularly mountainbike under the northern end of the link, around where the truck was being pulled by the tractor…

  3. While it’s not a simple task, but it looks to me they simply strung up a half million volt HVDC transmission line anyway. :) Perhaps pratices have changed over fifty years, did the pull in that much line with out spooling it on layers so it pays out with trouble next time it’s used? Clearly they did.

  4. sitll using pretty much the same methods in india
    ( where l was recently bicycle-touring)
    they don’t bother to build such fancy camps though, workers simply live in tents
    ( l wanted to camp with them, but the logistics never quite worked out)

    1. DC is preferable for a number of reasons. Because it isn’t alternating, there is no need to worry about synchronisation, so if you are connecting between multiple grids they don’t need to be locked together. Power carried is higher for a given peak voltage with DC (as AC power is RMS of peak voltage, whereas DC power is directly linked to peak voltage), so for a given peak voltage the DC system carries 41% more power? You also need fewer conductors with DC as you don’t worry about carrying multiple phases. All this means less metalwork to fly. There are also other issues like the AC systems to do with Skin Effect, which effectively increases the conductor resistance in AC circuits as the power isn’t carried equally within the conductor, meaning you need more metal for the same power for AC than DC. More metal = more cost – both because it needs more source material AND heavier duty engineering to carry it.

        1. The reason Edison lost the “war of the currents” back in the day was because there was no good way of stepping DC up and down in voltage at the time. If they’d had high-power inverters and rectifiers available in the 19th century, AC power transmission might never have taken off.

          1. What the hell is wrong with you people. Because AC travels on the skin, this is why stranded wire increases surface area and is MORE capable of transmitting power. The higher the voltage the better for AC, and since a transformer is all that’s needed AC wins that battle hands down. One transformer and you can step down the super high transmission voltage 500kv to city wide transmission 20kv and another at each city block to 120v, keeping the voltage as high as possible, and easy to convert up or down. DC absolutely cannot do this. Not including AC single phase half-step amp wave is safer than DC.

      1. Also in buried and underwater transmission lines, AC systems has notable capacitive losses. The only advantage of AC over DC power lines is economic: It is a lot easier (and cheaper) to step up and down AC voltages than DC.

        1. It is, while you dodge most of the loss of the skin effect at 60Hz on the wire then due to the low frequency you’ll need huge expensive transformers, HVDC uses ultra high frequency transformers to be stepped up and down and has no skin effect on the wire, both of those factors (transformer cost and skin effect) are a balancing act with AC, the laws of physics aren’t known for handing out free lunches.

    2. When I was studying electrical engineering in the 90’s my lecturer told me they used DC for this line because it goes under water (through the Cook Straight), AC would be less efficient for this purpose.
      A wikipedia article on the topic states that capacitance between the lines is increased due to the dielectric properties of water (as opposed to air in overhead lines), therefore reducing the power factor of the system.

      1. DC just has huge flaws.
        And as for the skin effect with AC mentioned earlier, that’s an advantage in practice because you can use strong cores to carry the weight of AC lines and only the outer edge needs to carry the actual current.

        But sure AC does have a few disadvantages, like the synchronization, And I’m sure in some cases like your example HVDC might be the best solution, but still though, there is actually a reason why the entire planet selects to use AC most often, and it’s not mere coincidence.

        1. Dude, no one is claiming that DC is better for all transmission, but it is better for precisely this kind of high-power project. Chill out. AC is a hammer, quit pounding screws with it.

          And, yes, I do have an EE degree.

          1. You might not claim it, but it’s the internet, people will claim silly stuff and it’s picked up by other silly people and soon enough you are crucified if you aren’t on board and shout AC is always bad :/
            Then in the worst case scenario the politicians will start taking replacing all AC with DC…

        2. What huge flaws?
          DC was always superior from an engineering standpoint for bulk transmission of power, read, point A to B via wire, because DC has no skin effect and it’s rms voltage is the same as it’s peak voltage, which means smaller losses as the same wire at the same rate of power transmission will always pose less resistance to DC compared to AC.
          This is a fact, the laws of physics dictated so, and if you have to question it it’s only because you don’t know enough, even the basics, of electrical engineering.
          This was already known at the time of the war of currents but the reason why AC won is that it’s efficiency was bigger from production to consumption (a more holistic view that considered all factors) which offsetted it’s demonstrably worse on-wire transmission capabilities (just one factor), meaning, AC was correctly chosen at the time, it was the winner and rightfully so, not anymore tough, technology has moved on, the thing now is that upgrading would be incredibly expensive as all the AC networks and machinery would have to be replaced with DC networks and machinery, which is insane, we’re talking probably trillions of dollars here, it’s likely that the cost is so big that we can live with the inefficiencies of AC for hundreds of years before we could recuperate the losses of switching to DC.
          During the war of currents it was observed that DC needed much thicker wires, which leads the regular Joe’s of this world to think that that’s a characteristic of DC when it really isn’t, the approach was holistic as I said before and so the AC would be converted to higher voltage using transformers to then go across the thinner transmission lines, it was not economically viable at the time to convert DC to a higher voltage and brushless DC motors didn’t even existed at the time while AC ones did exist, were cheap, available and also very efficient, all of that has changed and is still changing.

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