Effective Field Grading at 200 °C of a Nonlinear Resistive Polymer Nanocomposite Coating for Medium-Voltage Power Modules

Medium-voltage silicon carbide power modules have the potential to enable a more renewable, resilient, and reliable electric grid. However, their electrical insulation, especially the partial discharge around the module's triple point, remains a challenge. To address this, we have applied a nonlinear resistive coating made of a polymer nanocomposite to the module's triple point and have shown its effectiveness in reducing the electric field stress at room temperature. In this research, we assessed the performance of the coating at high temperatures up to 200 °C. A test setup capable of measuring the partial discharge of a substrate at high temperatures was built. We found that from 25 °C to 200 °C, the coated samples maintained an 85% higher partial discharge inception voltage than that of the uncoated samples. The temperature dependence of the nanocomposite's electrical conductivity was measured and used in field simulations. Over the tested temperature range, the observed increase in partial discharge inception voltage agrees with the decrease in the simulated electric field stress caused by the nanocomposite coating. This research marks the first experimental demonstration of effective nonlinear resistive field-grading at 200 °C for medium-voltage power modules, potentially hastening their adoption in grid-tied applications.