Rapid decomposition phenomena of polymer dielectrics in circuit breakers

Under short circuit condition or current interruption, polymer dielectrics in circuit breakers are exposed to high temperatures and pressure for a short period. The short-term exposure of polymer surface results in rapid decomposition. The surface resistance of the polymer is found to vary significantly after the exposure, whilst the arc resistance is not affected significantly. FTIR -depth profile analysis revealed that the surface chemistry is altered up to a depth of about 60mm. Through X-ray photoelectron spectroscopy of the polymer surfaces, it is inferred that the ratio of C-H and C-O vary significantly, depending upon the type of polymer. Interestingly, polyester displayed more oxidation on the exposed surface and, contrarily, polycarbonate surface was found to have more carbon and its by-products. The dielectric performance of the breaker is discussed in relation to the surface chemistry modification.