Effect of short circuit switching on dielectric properties of vacuum interrupters
Short circuit current interruption may change the dielectric properties of vacuum interrupters during their service life. Therefore, in this work effects of the current interruption on the dielectric properties and contact erosion of the interrupters have been investigated. Contact material's evaporation during the flow of the vacuum arc before current zero may change the contact surface and cause some erosion after each operation. With the help of field electron emission current measurement the surface conditions of the interrupter contacts are compared between the new vacuum interrupters and interrupters which were previously subjected to interruptions with different arc current amplitudes and arcing time. With the help of Fowler-Nordheim diagram, surface parameters i.e. field enhancement factor β and emission area Ae are calculated and compared for each case. Field electron emission current inception voltage and breakdown voltage are compared for these cases as well.
$V\!{-}t$ Characteristics of Vacuum Interrupter After Large Current Interruption
Because of the contact material's evaporation and ejection of some metal particles out of the contact gap during the flow of the vacuum arc, the contact surface may exhibit some erosion after each operation of vacuum circuit breakers. In this paper, the insulation properties were investigated for vacuum interrupters with the rated voltage of about 10-kV operating voltage after short-circuit current interruption of more than 10 kA of 50-Hz current. The vacuum interrupter contacts were opened at either a current-zero point or an ac current peak. The latter involves greater arc energy at the short gap length compared with the former. After such interrupting duty, the characteristics were measured with the lightning impulse and rectangular impulse voltages as a function of polarity relative to that of the interrupting current. When the contact was opened at the current peak, the insulation properties deteriorated substantially compared with those of the new interrupter, and the polarity of the applied impulse voltage relative to that of the interrupting current has considerable effect.
AN ANALYSIS OF POLYMERIC THICK-FILM RESISTORS AS PRESSURE SENSORS
Abstract The strain-sensing characteristics of thick-film polymer-based resistors printed and cured on 96% alumina are presented. Two layout configurations have been analysed: planar and sandwich. Various strain-gauge characteristics have been studied, including the mechanical and temperature-dependent properties of the polymeric films. It has been shown that the planar polymer resistors exhibit low sensitivity, comparable to that of metal-foil gauges, whereas the MRM (metal-resistor-metal) configurations exhibit similar characteristics to those of cermet thick-film MRM gauges. It has also been observed that the mechanical properties of the polymeric films are significantly poorer than those of cermet-based gauges. This degradation in performance is attributed to the epoxy/pseudo-plastic structure of the polymeric thick-film resistor layer.