Roughly two weeks ago it was an unusually hot in the Netherlands, with temperatures reaching 35°C (nearly 100°F). Meanwhile, I was in the city of Chongqing witnessing a type test for an 800kV UHVDC converter transformer for a 7,200MW DC-link (and part of China’s super grid), where temperatures also reached around 35°C. Millions of air conditioners were running at full power in Chongqing creating a high power demand. And in the Netherlands, more than 1,500MW of transit power was being transmitted from north to south Germany via the Netherlands and Belgium—due to limited transmission grid capacity in Germany—leading to a high loading level of the transmission lines (see the image below). In both cases, high temperatures caused the maximum loading capacity of the lines to be restricted, causing the power grid to operate closer to its (safe) limits.

Additional losses also occurred due to the transit power flow in the Netherlands. A typical 4 percent power loss, per 100km of the transmitted power at 400kV voltage level, gives roughly 90MW—assuming 1,500MW transit power and 150km Dutch transmission line is used. With an estimated duration of approximately 4 hours, this gives about 400MWh additional losses—which doubles the normal average loss.

In last week’s blog—Using Smart Grid to make a more efficient transmission & distribution network—I discussed techniques to reduce losses (i.e., better reactive power control, and more evenly loading of transmission & distribution connections). Reducing these losses would require an investment ranging from $20,000 (reactive power compensation, phase shifting transformer) to $75,000 (power electronics steering and control) per MW. It is obvious that these investments cannot be recovered from the reduced losses alone during the life time of the system. The advantage of employing such technologies lies in the combination of loss reduction and increased utilization of the power grid. In general, the availability of the electricity supply is improved, but the used technology has to be assessed carefully as a reduction is possible—due to undesired or unforeseen effects.

By: Peter Vaessen, principal consultant, Electricity Transmission & Distribution, DNV KEMA Energy & Sustainability

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