HVDC Visit

This is one of those posts that nobody except me will find interesting. Sorry. I'm a nerd.

Some of my coworkers and I had the chance to go to one of our HVDC stations last week. HVDC stands for High Voltage Direct Current. Most of the power transmission lines in the world carry AC (alternating current) power. The cables along the large high-voltage AC power lines come in groups of three, plus a fourth wire which is at the top of the towers and is designed to carry lightning strikes safely to the ground without knocking out your power.

DC power lines are much more rare. They're typically used in situations where the power generator is hundreds of miles from the cities or industrial plants which will use the power. A long AC line will lose a certain percentage of energy per mile due to the characteristics of the line, and these losses can add up significantly over hundreds of miles. A DC line doesn't lose energy in the same way, but it requires some huge and expensive pieces of equipment to change the electricity from AC to DC at one end of the line, and vice versa at the other end. (The picture at the top is a good example, even though I got that picture off of Wikipedia since my pictures of this room didn't turn out very good. See that little person standing there at the bottom? Yeah, these things are huge!)

New Zealand only has one DC transmission line (actually two lines on the same path). Back in the 1960s, Auckland was growing and running out of nearby generation to support its energy consumption. There was plenty of cheap and environmentally clean hydro generation available in the lower part of the South Island, but since Auckland is in the north part of the North Island, there didn't seem to be a way of getting the "good" power from one island to the other. Proposals were made to build new coal-fired or gas-fired plants near Auckland, but then a group of engineers decided to take a chance on some brand new technology: HVDC lines. At the time, it was only the second HVDC line in the world and the first to use undersea power cables.

I think it's all pretty cool, and I know I have some (a few!) nerdy friends who agree, even if they won't admit it publicly. Here are some pictures from our site visit:

That huge piece of equipment in the picture below is a transformer that was brought to this site in the 1990s as part of a big upgrade project. We saw in a video how it was transported. Since it was too tall to be loaded onto a truck and driven under the underpasses (AND it weighs 330 tons, so a normal truck wouldn't be able to carry it anyway), it had to be hung between two trucks. The trucks looked like centipedes, with about 90 wheels each, and each of the wheels could move independently. It took five days to transport the transformer 17 kilometers (about 10 miles), and they had to do it in the middle of the night so it didn't snarl up traffic too much.