LAPP answers questions like how to optimise cables and switchgear for this power type

Lightning bolts flash and electrical discharges fizz. Everybody in the room is wearing earmuffs and goggles. 400,000 volt experiments are being conducted behind fences several metres high. This is just another day in the laboratory at the Ilmenau University of Technology, where Berger heads up the Electrical Apparatus and Switchgear Group. “This is classic electrical engineering experiencing a rebirth,” he laughs. Frank Berger should know; you could call him the direct-current guru.

What looks like the command centre in a James Bond villain’s lair is a little nod from the for- mer German Democratic Republic. “I purposefully left it this way,” said Berger. With old-fash- ioned switchgear and measuring instruments. After all, his research topic of direct current is steeped in history: “From a physicist’s viewpoint, all of this was discovered about 150 years ago.” Now the focus is on the optimum price, use of materials and functionality. In other words: in light of new DC applications, what changes need to be made to components, their construction and materials, especially when used in low voltage?

THE ELECTRIC ARC RISK
There is a test that is spectacular in demonstrating the need for this research: in an experi- mental setup, an electric arc rotates between two rails at up to 80 km/h and a temperature of between 8,000 and 10,000 Kelvin. “When you pull a plug out of a socket charged with AC current when it is still on, nothing happens. If you did that to the same plug with DC current, the socket would burn and melt,” explained Professor Berger, demonstrating this statement.

This is the difference between alternating current, where the electric arc in the switching operation always quenches. This is due to the fact that zero-voltage switching occurs twice in a 50 Hz cycle of alternating current. So the Ilmenau-based scientists are working meticu- lously on specialised methods in instrument engineering that will force the switching arc to quench in direct current applications.

THE VISION FOR DIRECT CURRENT

PROGRESS THROUGH RESEARCH INTO CABLES
Cables are another research topic at Ilmenau University of Technology, in particular in ref- erence to the electrical fields that they are exposed to. After all, much of what has already been researched with regard to alternating current is uncharted territory with direct current. This is also the case for Professor Berger and his team, who are conducting experiments on Lapp’s cables in a specialised test bench.

Can AC cables also be used in DC networks? “In theory, yes,” Berger hesitates. “But there are differences that need to be considered. For example, we have seen that cables behave differently at high temperatures in DC voltage than in AC voltage.”

The lab tests by Frank Berger at the Ilmenau University of Technology in collaboration with the Lapp Group suggest that knowledge of one system cannot be simply transferred to the other – alternating current is not the same as direct current. Further research is needed to find out whether the revolution of electricity will also require a revolution for the components.