* ABB says beats rivals Alstom, Siemens in breakthrough
* High voltage circuit breaker could improve green energy transmission
* Says solves DC current conundrum from birth of electricity (Adds detail, background)
By Caroline Copley and Chris Wickham
ZURICH/LONDON, Nov 7 (Reuters) - Swiss firm ABB announced a breakthrough in technology to carry electricity over long distances, making desert solar plants and ocean wind farms much more viable.
Its new circuit breaker makes it easier to send electricity through high-voltage direct-current (DC) lines into the grids that link power stations to consumers, the engineering company said on Wednesday.
DC lines are much more efficient over long distances than the alternating current (AC) lines that are largely used at the moment. They are also more compatible with some forms of renewable power generation.
But using DC lines widely has been impractical without a heavy-duty circuit breaker that can cut power when need be.
The search for such a circuit breaker has taken more than 100 years and ABB has been battling rivals Alstom and Siemens to invent one first - potentially giving it an important advantage in what it hopes will be a multi-billion dollar market for DC grids.
“If they’ve managed to do this it’s very significant,” said Roger Kemp, an engineering professor at Lancaster University in northern England. “DC transmission is a much higher efficiency way of moving electricity around.”
It could bring closer the idea of huge solar power arrays in the Sahara Desert supplying electricity to Europe, Kemp said.
ABB Chief Executive Joe Hogan hailed what he said was “a new chapter in the history of electrical engineering.”
High voltage DC is already used to connect wind farms to the power grid and for delivering power to offshore oil and gas platforms. But without a breaker, its use is very limited.
If you try to switch off direct current at the very high voltages needed for power transmission, it can cause a spark across the switch which simply keeps the electricity flowing. That is not a problem with alternating current because there is a window to interrupt the flow.
The challenge of breaking direct current can be compared to quickly stopping a truck hurtling down a highway at top speed, ABB’s chief power engineer, Claes Rytoft, said.
ABB’s circuit breaker works by combining mechanical and power electronics that are capable of interrupting power flows equivalent to the output of a large power station within five milliseconds - 30 times faster than the blink of a human eye.
Conventional AC grids are also not compatible with the DC power produced by many renewable sources, particularly solar energy. Computers, televisions and mobile phones also run on DC, meaning electricity has to be converted from AC.
The two systems have been at odds since their proponents, Nikola Tesla and Thomas Edison, battled for supremacy in the new technology a century ago.
Edison even electrocuted an elephant to highlight the dangers of Tesla’s AC power, but his rival’s system took off because it could transmit electricity further. At the time, DC power couldn’t carry power beyond a few city blocks.
High voltage DC can transmit 30 to 40 percent more energy than conventional overhead lines carrying alternating current, however, making it a better option for bringing power from distant sources.
ABB is in talks with utility companies to identify pilot projects for the technology over the next 12 months.
ABB has already installed a 2,000 km (1,250 mile) line in China that operates DC power while a 2,375-km HVDC project under construction in Brazil will be the world’s longest such transmission line when it comes online in 2013.
In Europe, high voltage DC is currently used to connect Britain and the Netherlands. The island of Majorca, whose tourists push up power demand every summer, was hooked up to the Spanish mainland in September 2011. (Editing by Matthew Tostevin)