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 study, the insulation properties were investigated for vacuum interrupters with the rated voltage about 10 kV operating voltage after short circuit current interruption more than 10 kA of 50 Hz current. The vacuum interrupter contacts were opened at either current zero point or a.c. current peak. The latter involves greater arc energy at the short gap length compared with the former. After such interrupting duty, the V-t 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, insulation properties deteriorated substantially compared with the new interrupter, and the polarity of the applied impulse voltage relative to that of the interrupting current has considerable effect.
ELECTROMAGNETIC DESIGN OF A RADIO FREQUENCY QUADRUPOLE FOR THE FRONT END TEST STAND AT RAL
The goal of the RAL front end test stand is to demonstrate cleanly chopped bunches of a 60mA H − ion beam at 3MeV. The acceleration of the H − ions from 65keV to 3MeV will be done using a radio frequency quadrupole (RFQ) operating at a resonant frequency of 324MHz. The two types of RFQ considered were a 4-vane and a 4-rod. The 4-vane has a higher Q-value but the post-production adjustment is limited. The 4-rod design is easier to manufacture but requires complicated cooling at 324MHz. The results of electromagnetic simulations using CST Microwave Studio are presented for the 4-vane type and 4-rod type RFQ.