Breakdown and partial discharge characteristics of cotton and cellulose materials in liquid nitrogen

With increasing short-circuit power due to additional renewable energy feed-ins it is more and more important to use reliable fault current limiter to protect the power grid. To develop superconductive fault current limiters (SFCL) for high voltage level, new insulating materials for the use in liquid nitrogen (LN2) have to be investigated. Hence the dielectric strength and partial discharge (PD) characteristics of cotton and cellulose materials in LN2 were determined. Breakdown measurements show that the materials have the same or even higher dielectric strengths in LN2 compared to the use in insulating oil. Pure cotton material reaches in comparison to the other types under investigation the highest dielectric strength. Partial discharge investigations show that the mixture of cotton and cellulose materials has the highest values for inception and extinction voltage.