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
PULSE: a high-repetition-rate linac driver for x-ray FELs
We describe a staged concept for a linac-based freeelectron laser providing coherent tuneable VUV and soft X-ray output with pulse lengths down to 10 fs or less. Use of 1.3 GHz cryomodules operated with CW RF will allow flexible pulse patterns at potentially very high repetition rates up to 1 MHz. We consider the options for FELs that may be included in a facility of this type.