SCHOTT solutions no. 2/2013 > Research & Development

When used as a a dielectric, glass-ceramic (in the foreground) can reduce the thickness of high-voltage capacitors significantly. This, in turn, increases their storage density, as this comparison between conventional (left) and innovative capacitors on the basis of glass-ceramic (right) shows. Photo: SCHOTT/C. Costard

Electrifying Glass-Ceramics

SCHOTT researchers have further developed glass-ceramics into highly promising dielectric materials for high-voltage capacitors. Power electronics for renewable energy, medical technology and laser applications are just a few of the areas that they can be used in.

Thilo Horvatitsch

Power electronics are becoming more and more important, to convert and transport electrical energy from offshore wind turbines, for example. Here, there is a clear trend toward increasingly higher power densities, by using semiconductor materials such as silicon carbide, for instance.
High-voltage capacitors on the basis of glass-ceramic are ideally suited for use in many applications, for instance offshore wind parks or computer tomography systems. Photo: Thinkstock
As the current densities continue to increase quite significantly, the temperatures inside these systems also rise, sometimes to as high as 200° C. Therefore, passive components such as capacitors located in the immediate vicinity must be able to resist high thermal loads. The dielectric materials available for high-voltage capacitors and how they behave when subjected to higher temperatures thus limit the power or make it impossible to develop a more compact design of the power electronics module. Against this backdrop, SCHOTT has succeeded in making the glass-ceramics material class usable as a dielectric for high-voltage capacitors for the first time ever. This new type of glass-ceramic offers significant advantages over the ceramics used as dielectrics in the past. For example, the fact that these new glass-ceramics are completely pore-free lends them extremely high dielectric strength of approximately 65 kV/mm. The dielectric material can thus be considerably thinner at a specific voltage. This, in conjunction with the high relative dielectric number, allows for very high capacity values for the capacitors. ”Thanks to these unique properties, the energy storage density can now be increased by a factor of up to 10 compared with conventional capacitor materials,” explains Dr. Martin Letz. The SCHOTT developer also expects to see this advancement be put to use at higher temperatures of up to 200°C and to produce more compact and lighter capacitor designs in the future.  According to Letz, ”The weight can be reduced by roughly 80 percent and it will still offer the same performance.”
Photo: Thinkstock
In addition to power grids, this opens up many different power electronics applications, such as computer tomography and laser applications in semiconductor processing and eye surgery. ”Our goal is to successfully launch this promising development in 2014,” says Dr. Jörn Besinger from SCHOTT Business Development. SCHOTT is currently working on two glass-ceramics for high-voltage capacitors. Tests are already being performed by renowned capacitor manufacturers. <
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