Connecting the land
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Connecting the land
It was one of the first HVDC transmission links in the world, motivated by the country’s long and stringy insular geography and its population distribution that is biased towards the North Island: New Zealand’s HVDC Inter-Island link transports hydropower produced on the South Island – which accounts for almost 60 percent of the nation’s total electricity generation – to the majority of the population (76 percent of the 4.5 million inhabitants) in the north.
Connecting the land
From Benmore substation the HVDC line travels 534 kilometers overland to the Marlborough Sounds area; three 350-kilovolt/500-megawatt submarine cables bridge the 40 kilometers of the Cook Strait from Fighting Bay to Oteranga Bay on the southern tip of the North Island where it continues for another 37 kilometers overland, bypassing the capital Wellington, to Haywards substation near Lower Hutt.
With businesses expanding and the population growing, there was a strong need to future-proof the backbone of New Zealand’s transmission system. And with the very real threat of potentially disastrous earthquakes – Wellington is built on a major fault line – there was an additional need to safeguard the bustling conurbation from major blackouts.
The 49-year-old Pole 1 has now been replaced with a new thyristor-based Pole 3, and Pole 2, installed in 1992, has been fitted with a new, state-of the-art control system. Siemens, under contract to Transpower, the government-owned grid management company, designed, built, tested, installed and commissioned the state-of-the-art converter and interconnector system – which had to be capable of withstanding a one-in-2,500-years earthquake event. Following the fatal earthquakes in Christchurch in 2010 and 2011, seismic requirements for buildings and key infrastructure had been toughened to the highest global standard.
“We had to apply the highest seismic standards in the design for this interconnect that is a major part of the New Zealand infrastructure,” says Gu¨nther Wanninger, the electrical engineer who headed the Siemens team in New Zealand for the four years of the project. “The seismic challenge was the biggest we ever had to face.” The whole equipment – including the valve hall, where the thyristor valves are suspended – had to be dampened to withstand massive seismic forces.
Aurecon, a New Zealand company with a worldwide reputation in seismic engineering, produced new designs for lead-rubber bearings, and sliders, to protect the long, deep piles on which the buildings and the equipment are mounted from both vertical and horizontal movement. Now the valve hall, for example, can move up to 700 millimeters horizontally without damage in an earthquake. Everything in the switchyard is similarly isolated from shocks.
“Aurecon tells me there is no building in the world that has such high seismic standards as the valve hall we have built for Transpower,” Wanninger says. “Recently there was an earthquake here in Wellington, reasonably big – 6.7 magnitude – but with the design we have applied, there was no effect at Haywards.”
The new Pole 3 has a continuous rating of 700 megawatts in both directions and, as with Pole 2, is capable of operating in bipole and individually in monopole configurations. The bidirectional design is needed because, in winter when power demands are high for heating, water stocks in the South Island dams feeding the hydroturbines can run low; rain becomes snow and snow does not melt until spring. Then, power from the North Island’s generators – geothermal, hydro, gas, wind and the sole New Zealand coal-fired station at Huntly – is needed to meet South Island needs. Siemens has made sure that New Zealand’s transmission is earthquake-proof.
Haywards converter station was furnished with a static reactive power compensation system, based on the SVC PLUS concept, as well as AC filters with the cutting-edge Siemens technology.
Static reactive power compensators (SVC – static VAR compensator), such as the one installed at Haywards, boost operational security and transmission capacity of power grids thanks to voltage stabilization and power feed-in in case of transmission losses. The SVC operates with innovative Modular Multilevel Converter Technology (MMC) from Siemens and is thus – with the help of high-power transistors (IGBT) – infinitely adjustable.
The building blocks of a new, more sustainable energy system.