Glass as dielectric for high temperature power capacitors

ABSTRACTModern polypropylene film power capacitors are state of the art for power factor correction and many DC link applications, but their long-term commercial use is limited to temperatures of less than 85°C. The temperature limit is given by the dielectric polypropylene which has a melting point in the range of 140 to 170°C, while glass is much higher. Thus, the temperature limit could potentially be overcome by use of thin, alkali-free glass as dielectric. “Glass capacitors” employing ultra-thin and high purity glass layers are promising devices for high temperature applications in oil, gas, aerospace, hybrid electric vehicles, DC transmission, and pulsed power systems. This includes emerging power electronic systems using silicon carbide switches and diodes.This work analyzes and compares various glasses with a thickness of less than 50 µm by dielectric spectroscopy and elemental analysis. It is demonstrated that glass is attractive as dielectric for a wide frequency range up to 200°C. It argues that the dielectric losses are currently too great for thin glass to be used within a commercial power capacitor.While high temperature prototypes already exist, we demonstrate through our analysis that further developments are required to integrate this promising device into commercial systems. It is seen that even trace amounts of alkali materials can have an impact on losses. These losses must be further reduced through fundamental research into polarization/conduction mechanisms of various glass components.