Power Struggles and the Mediterranean Ring

‘The Mediterranean Ring’ would make a fitting title for a high-voltage action thriller where cut-throat crime gangs vie for control in the labyrinthine medieval medina’s of North Africa. Alas it is no such thing. And yet this project to connect the power grids of North Africa and Europe does boast a potentially destructive internal power struggle that could stymie its promise — clean power supplies for Europe, economic development for North Africa, and a much needed bond between neighbors.

MedRing’s power struggle spilled into the daylight on November 21, 2005 when power engineers activated a key electrical circuit linking Tunisia and Libya in a key test of the MedRing. For a moment nearly all of the AC power systems of North Africa operated synchronously with those of Europe. Power plants, transmission lines and controls from Syria to Morocco were in electrical conversation with those of the mighty UCTE, whose 240,000 kilometers of high-voltage lines connect 26 European countries. Add links to Turkey and the MedRing would have been complete.

Seven minutes later the grids had broken apart and the test had failed.

It was a tug of war between North African grid control systems that broke the synchronicity. Understanding why isn’t straightforward. Bear with me as I try because the failure of this early trial exemplifies the challenge inherent in connecting a robust power system like the UCTE’s — the world’s biggest — to much weaker grids such as those of North Africa.

Power demand naturally varies as factories start up or shut down and consumers switch appliances on and off. Automated generation control systems (AGCs) ramp power plants up and down to match the load, but there’s always some mismatch. Before the lines between Tunisia and Libya went live the power plants in Egypt to the East were generating slightly more power than was being consumed. Upon interconnection, the UCTE began absorbing this excess, sucking power across Tunisia, Algeria and Morocco like a giant electrical sponge.

Libya’s AGC, sensing over 100 megawatts of westward flow into Tunisia where it expected zero, compensated by ramping down Libyan power generation. Unfortunately Egypt’s AGC was answering a different call. Rather than tracking flows over its borders the Egyptian AGC was tuned to the frequency of AC power, which was dropping in Egypt as the UCTE absorbed its excess power. The Egyptian AGC initially fought back by ramping up generation, thus pouring even more excess power into Libya, then recognized the error and ramped down generation hard.

With power plants in both Libya and Egypt ramping down their grids suddenly were undersupplied with power, causing a power surge in from UCTE exceeding 150 MW. That slosh of power back into the East triggered protection plans on lines between Tunisia and Libya as well as Morocco and Algeria, opening the circuit and ending the ill-fated test. 

This unforeseen behavior took the power engineers involved (generally a notoriously cautious bunch) completely by surprise. Modelers checking for more complex problems overlooked the normal load deviations present in all power systems because, until now, power lines have always accomodated them. As one engineer involved summed up the failure put it: “It is very easy to ‘predict’ something once it has happened!”

North African power engineers believe the lines are strong enough now thanks to 400,000-volt infrastructure profiled in my feature story in this month’s print issue, “Closing the Circuit.” A second test is scheduled for the end of March or April 2009. What will they do if that fails? For that you’ll have to read the story (or wait for the thriller).

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This post was created for EnergywiseIEEE Spectrum’s blog on green power, cars and climate

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