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.
Continue reading “Retrotechtacular: One Does Not Simply String Up A Half-Million VDC Transmission Line”
How do you fix a shorted cable ? Not just any cable. An underground, 3-phase, 230kV, 800 amp per phase, 10 mile long one, carrying power from a power station to a distribution centre. It costs $13,000 per hour in downtime, counting 1989 money, and takes 8 months to fix. That’s almost $75 million. The Los Angeles Department of Water and Power did this fix about 26 years ago on the cable going from the Scattergood Steam Plant in El Segundo to a distribution center near Bundy and S.M. Blvd. [Jamie Zawinski] posted details on his blog in 2002. [Jamie] a.k.a [jwz] may be familiar to many as one of the founders of Netscape and Mozilla.
To begin with, you need Liquid Nitrogen. Lots of it. As in truckloads. The cable is 16 inch diameter co-axial, filled with 100,000 gallons of oil dielectric pressurised to 200 psi. You can’t drain out all the oil for lots of very good reasons – time and cost being on top of the list. That’s where the LN2 comes in. They dig holes on both sides (20-30 feet each way) of the fault, wrap the pipe with giant blankets filled with all kind of tubes and wires, feed LN2 through the tubes, and *freeze* the oil. With the frozen oil acting as a plug, the faulty section is cut open, drained, the bad stuff removed, replaced, welded back together, topped off, and the plugs are thawed. To make sure the frozen plugs don’t blow out, the oil pressure is reduced to 80 psi during the repair process. They can’t lower it any further, again due to several compelling reasons. The cable was laid in 1972 and was designed to have a MTBF of 60 years.
Continue reading “Find And Repair A 230kV 800Amp Oil-Filled Power Cable Feels Like Mission Impossible”