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.
Dielectric Performance of Vacuum Interrupters after Switching
Vacuum interrupters are widely used in power distribution systems and have proven their outstanding reliability in service for medium voltage applications up to 40.5kV. The IEC or ANSI standard requires a power frequency voltage withstand of an interrupter mounted in a breaker of at least 80% of the rated value after type testing. Nevertheless there is an ever increasing demand from several markets that have additional requirements as full power frequency or even full lightning impulse withstand after switching operations. In this paper the authors present the results of an investigation on the evolution of the dielectric performance of commercial and prototype interrupters after short circuit interruption to an internal test procedure. The results will be compared with full scale short circuit interruption tests according to the IEC short circuit type tests and electrical endurance E2 of interrupters for rated voltages up to 40.5kV
Anode Phenomena in Metal‐Vapor Arcs at High Currents
The present investigation is concerned with the conditions associated with the development of an anode spot for metal‐vapor (vacuum) arcs. Chief among the aims of the investigation is the determination of the threshold current density for anode‐spot formation for a variety of electrode materials spanning a wide range of thermal and electrical properties. Electrodes of Sn, Al, Ag, Cu, Mo, and W were chosen for study in a plane‐parallel electrode geometry. Arcing was over one‐half cycle of a 60‐Hz current wave. The onset of anode‐spot formation was determined from high‐speed streak photographs of the discharge. An oscillographic record of the arc voltage was obtained simultaneously with the streak picture. From the data obtained particular interest attaches to the threshold current for anode‐spot formation, the threshold current density derived from it, and the arc voltage‐current characteristic. The threshold current densities (peak values) range from a low of 0.9×102 A/cm2 for tin to a high of 5.4×102 A/c...