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Has ABB Solved the 100-Year 'War of the Currents'?

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The Swiss company has thrown down a possible power breakthrough.

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Industry experts say the breaker technology represents a breakthrough and that it appears to be viable, but noted that the costs could slow adoption.

"ABB has changed the game," Norman MacLeod, technical director of HVDC at Parsons Brinckerhoff said. "DC can now do what AC guys have been doing for 120 years."

ABB's Ligi acknowledged that the hybrid HVDC breaker has not yet been brought to market. The next step is going to be deploying the technology in a pilot project. That is in discussions, Ligi said, but he declined to give details. Regarding cost, he said it is difficult "to put a number at this stage as pricing will depend on numerous factors."

The other players in the field, Alstom (PINK:AOMFF) and Siemens (NYSE:SI), are also working on DC breakers, but ABB is ahead of them, MacLeod said.

Alstom is working on a DC circuit breaker – until recently, MacLeod worked at Alstom –a nd expects to finish testing in March 2013. Alstom confirmed it is working HVDC breaker for introduction in March 2013.

Siemens, he said, is tight lipped about its efforts. And, in fact, Siemens did not return requests for interviews.

But even after ABB's DC circuit breaker hits the market, the cost could slow its deployment. "The hybrid breaker is the size of a tennis court and costs millions and millions of euros," MacLeod said.

One of the attractions of DC transmission is its greater efficiency over long distances.

DC line losses are about half of those of AC lines, depending on voltage and distance. The cross-over point is about 800 kilometers (about 500 miles), the distance beyond which the economics tilt toward DC, MacLeod said.

In addition to lower line losses, DC lines do not require the equipment that AC lines do to maintain voltage. For instance, among other things, reactive power, which can be a costly and contentious issue for AC lines, is not an issue with DC lines.

DC power lines also require a smaller footprint than do AC lines, which require three lines for each of its three phases. DC power has only one polarity, noted Kiran Kumarswami, a manager with consulting firm ICF International. So a single DC cable could replace three AC cables required to deliver the same power, he said.

It is DC power's single polarity, in fact, that presents the technical challenge of creating a DC circuit breaker. AC power cycles, that is, it travels in three waves that are schematically depicted as sine curves. An AC circuit can be broken when the power passes through the zero point of the curve. DC power does not cycle, so there is no zero point.

"For DC power you have to do it the hard way: Make it go to zero with power electronics so you can open a mechanical switch to isolate the circuit, but you still have to deal with the energy so the third part is a surge arrestor to absorb the energy," MacLeod explained. That is why it is called a "hybrid" breaker; there are three different parts. "It's a complicated beast," MacLeod said.

So far, ABB has tested its hybrid breaker, but it has yet to be proven in a commercial application. To be tested, the circuit breaker would have to be in place 24/7, and "it could be waiting years to do its job which just takes 5 milliseconds," MacLeod said.

As noted, cost could be an impediment to deployment until greater adoption drives down costs. But as MacLeod said, the hybrid breaker would make it possible to put Norwegian hydropower, English wind power and Spanish solar power into a DC grid and move it all around the Europe.

Going back to the highway and exit ramp analogy, it would be possible to build a DC line to move wind power from Wyoming to load in Las Vegas with an exit in Salt Lake City. But the project would be expensive, requiring eight hybrid circuit breakers.

Not that such a grid would be electrical nirvana. "Once you start mixing these switches into the network, how do you coordinate them?" Marija Ilic, professor of electrical and computer engineering at Carnegie Mellon University, asked. "Breakers react to flow and don't care about coordinating the wider area," she said.

Time will tell if and when the greater efficiency of HVDC will warrant the investment in hybrid breakers to make a DC line that rivals, or even outperforms, an AC line. But for now, ABB seems to be the first out of the gate in reaching that goal.

This article by Peter Maloney originally appeared on Platts' The Barrel.

Follow @PlattsPower on Twitter

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