Nano-dielectric materials in electrical insulation application

High performance electrical insulation materials and structures must be free from unwanted and unpredictable dielectric breakdown through the insulator as well as surface flashover along the interface between the insulator and the ambient or vacuum. The last decade has witnessed significant developments in the area of nano-particulate and nano-dielectric materials, and significant effects of nano-scale fillers on electrical, thermal, and mechanical properties of polymeric materials have been observed. Surface flashover is one of the major issues in electrical insulation in power systems operating either in space (vacuum or partial vacuum) or atmospheric (earth-bound) environments. Thus, development of new and advanced materials to be used in power systems requires extensive studies on electrical insulation characteristics of these materials before they can be used in commercial systems. Most of the research in characterization of nano-dielectric materials has been for systems operating in atmospheric environment; there are limited or no data for systems using these materials in space environments. In this paper, we present experimental results of surface flashover characteristics of epoxy resin and epoxy resin cast with powdered Al/sub 2/O/sub 3/ in partial vacuum. The flashover studies were conducted separately using DC and AC signals. Surface flashover voltage and current waveforms of the samples and light emission waveforms and video images during the breakdown were recorded. Optical data collected by a video camera along with the PMT light emission data are analyzed and the results of the optical emission characteristics of surface flashover are presented along with the electrical data. The samples used in the experiments were produced by using either epoxy resin of known properties or by mixing known quantities of Al/sub 2/O/sub 3/ with epoxy. The electrode material placed over the dielectric samples was copper.

INTRODUCTION

Surface flashover across solid insulators in vacuum has been a research topic in the area of space power systems [1], [2]. One scenario where surface flashover in vacuum can be a problem is where a spacecraft operating in geosynchronous orbit (GEO) or low earth orbit (LEO) interacts with the local space environment resulting in the differential charging of the spacecraft. This charging can sometimes reach to electrical potentials of several hundreds to a few thousand volts. When this charging reaches a critical value, surface flashover on the solid dielectric insulator may occur, resulting in loss of high voltage isolation and causing damage to the space power systems on board. Similarly, surface flashover can also occur across insulators in the utility power system in partial vacuum and/or atmospheric pressures as well. In general, random emission of a small number of electrons at the cathode results in positive charging of the dielectric surface at the triple junction, thus initiating surface flashover across the dielectric.