HVDC Grid Requires Much More Economical Circuit Breakers

I think the crux issue holding up HVDC penetration right now is that so far, all HVDC projects rely on the AC grid for redundancy. That means that the maximum size of any HVDC project is artificially constrained by the local AC grid, and in effect guarantees that HVDC projects cannot carry more power than the biggest AC lines in the area. I wrote about that in several places, but this specific post gets at it directly:

http://elpipes.blogspot.com/2013/03/my-post-on-energy-collective-regarding.html

Some day, we'll have a meshed grid, but right now the next logical step is to a multi-terminal HVDC loop, with circuit breakers between each next-neighbor set of power taps. Such a setup is self-redundant. The circuit breakers are the problem. In spite of ABB's claim to have solved this problem:

http://ballisticbreaker.blogspot.com/2012/11/abb-announces-worlds-first-circuit.html

their solution is too expensive to work economically; I estimate their hybrid breaker will cost about one fourth as much per kW as a VSC-based AC/DC converter, about $35/kW (200 times as much as a comparable HVAC breaker). That is a big problem, and is one I'm working to solve with my Ballistic Breaker:

http://ballisticbreaker.blogspot.com/2014/12/first-ballistic-breaker-patent-has.html

It is not enough to just have HVDC circuit breakers at each power converter, to isolate it from the loop; for full protection and self-redundancy, one needs main loop circuit breakers and those must have higher capacity. Take as an example a 10 GW loop with ten power taps, each with capacity from -2 GW to +2 GW. Ten 2 GW breakers will not be adequate for self-redundancy; one needs main loop breakers rated at 10 GW BETWEEN the power taps, which increases the cost by a factor of 5 (approximately). Thus, a lower cost HVDC circuit breaker is crucial. 

This post describes how an HVDC loop can answer Germany's need to move offshore power to Southern Germany:

http://elpipes.blogspot.com/2014/02/article-in-natural-gas-electricity-on.html

Any circuit breaker for this application (HVDC supergrid) has a severe problem with current inrush in a fault. ABB in their hybrid breaker design has used a large inductor to delay the current inrush long enough to open the fast mechanical switch far enough to prevent re-striking. Unfortunately, an inductor stores energy as it slows the current inrush, and all this stored energy must be dissipated to open the circuit. A second way to slow the current inrush in a short circuit condition is via a superconducting fault current limiter (SCFCL). There are numerous patents in this area, and several known approaches to trigger the quantum mechanical transition of a superconductor to a conventional conductor or semiconductor. I believe the efforts of Paul Brown of Varian Semiconductor (now part of Applied Materials) are particularly promising, as Applied Materials is a new participant in this market, with no vested interest in the status quo, Here is Varian's recent patent. The use of SCFCLs as part of HVDC circuit breakers of other designs will reduce the cost of the main breakers by decreasing the maximum current that can develop before the circuit breaker completes its action (and therefore reducing the maximum rated current and voltage of the primary breaker).

Part of what is needed is to be able to carry a lot of power (10+ GW per line) in an underground transmission line; my solution for that is the elpipe, a sort of mashup of a powerline, a pipeline, and a train. I am now engaged in making elpipes (for underground HVDC transmission) and Ballistic Breakers (lower cost HVDC circuit breakers) work to make this vision possible. I have the support of a visionary investor (Jostein Eikeland) and his amazing startup company (Alevo) behind me. It will not be easy, but it looks feasible to me, from the inside.