Pursuit

It is all part of the (New Zealand) experience. The West Coast has been wet. Real wet! Some areas can receive as much as 9000 mm (354 inches) of rainfall in one year. The reason is that New Zealand is smack dab in the middle of the roaring forties. The prevailing west-to-east winds cross the Tasman Sea and as the warm air hits the mountain range of the South Island, it rises, cools and then dumps lots and lots of rain on the western side of the Southern Alps. One of the things that this huge amount of rain creates is a multitude of lakes, rivers and waterfalls. Other than making for soggy camping, this water can be very useful in the production of hydro electricity. Since we have been traveling around the South Island, we have stopped and looked at lots of power generating stations along the way. After we left the iconic Milford Sound area, we took a boat ride across Lake Manapouri to the Manapouri Hydro Power Station, followed by a very scenic bus trip to the Doubtful Sound. As an electrician, I enjoy touring different power stations. I'm sure Tara could think of other things that might be more interesting, but she's a pretty good sport about my constant detours to see, "just one more power station". I'm sure she doesn't share my excitement about the different power stations. Some have been historic, some very small, and some have been very big. [TRL: I do find them interesting...most of the time]

Power stations are very interesting in how they work. The concept is very basic too. It may bore some, but here it is for those who may be thinking about building one as a hobby or simply can't get to sleep. A hydro power station works by harnessing the energy from falling water. The water held above a power station in a lake, river or reservoir is channeled through pipes or penstocks to the turbine below. The height from which the water falls from the reservoir to the turbine, known as head, determines the amount of energy that can be extracted from a given volume of water. The turbine spins as it extracts the energy from the water, turning it into mechanical energy that then spins the generator rotor. Similar to a car alternator, the generator rotor carries a set of electro-magnets that spin within a stationary set of insulated copper windings embedded in an iron core called the stator. The motion of the magnets within the stator generates electricity in the windings. [TRL: booorrring] Most large hydro generators generate at between 11,000 and 16,000 volts alternating current (AC), which is not suited to energy-efficient, long distance transmission of electricity. Instead, the generator is then connected to a transformer, which steps up the voltage - usually to 110,000 or 220,000 Volts AC. This makes long distance transmission more practical and energy efficient. The transformer connects to the national grid at the switchyard, which contains the circuit breakers and other connecting switches that allow the generator to be connected from the grid as required. After passing through the turbine and in turn spinning the generator, the water exits through an outlet tube or tailrace, back to the river, canal or downstream lake.

When the engineers designed the tailrace at the Manapouri power station, they must have been thinking about rugby or beers instead, because soon after the power station began generating electricity in 1972, it became apparent that it wasn't able to generate at the peak levels of 710 MW originally planned for. The station could only be safely operated at a peak capacity of 585 MW. Greater than anticipated friction between the water and the walls of the tailrace tunnel meant that the water couldn't escape fast enough and resulted in a loss of hydraulic head. Oops, better build another tailrace. What's another 1,500,000 man hours anyway? The hydraulic head should have been 178 metres, but was only 148 metres. A second tailrace had to be constructed parallel with the existing one at an additional cost of $200,000,000. The power output from the additional tailrace, generated from the same amount of water passing through the station, provided enough power for an additional 64,000 homes. The power station was refurbished in 2008 and can now produce 850 MW.

The Manapouri power station is the largest hydro power station in New Zealand. The generating units are housed in a cavern excavated from rock 200 metres below the surface of lake Manapouri. The road access tunnel to the generating station is over 2 kilometres long and 9 metres wide. It was built to fit the largest piece of machinery into it. Trucks had to back down the tunnel when delivering machine parts, which sometimes took up to seven hours. The biggest pieces were the transformers, weighing in at 138 tonnes each. It is an amazing engineering feat.

The idea of building the power station was originally suggested in 1904, but because of the remoteness of the location and the scale of the engineering task - drilling an outfall (tailrace) tunnel through 10 kilometres of Fiordland mountain - meant the project was shelved until the 1950s. The idea was revived when the Consolidated Zinc Pty of Australia set up an aluminum smelter in Bluff (145 kilometres away). The process of aluminum smelting requires a large amount of electricity. In the end, they could only afford to build the smelter, so the New Zealand government picked up the tab for the power station. The power station project took over 1,800 workers eight years to complete in extremely harsh conditions. The only form of travel to the Manapouri power station is by boat. All of the major equipment had to be brought in by ship via the Doubtful Sound and then across the Wilmot Pass road to Lake Manapouri. The first visitors were Maori (New Zealand's native population), who used the pass as a route to the seasonal food supply of the fiords. In 1770, Captain James Cook named the area Doubtful Sound - being doubtful that if he entered the fiord he would be able to get out again. Among the later explorers was Ernest Wilmot, who discovered the pass in 1897. The Wilmot Pass road is an engineering feat in itself. The cost was incredible at a cost of $2.00/inch. The views were incredible from the top overlooking the Doubtful Sound. It was a fantastic place to visit and to see how power can be generated from renewable resources.