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.
Stability of planar PEMFC in Printed Circuit Board technology
Abstract The use of planar PEMFCs in printed circuit board (PCB) technology with a thickness of less than 3.5 mm are presented. This planar design consists of an open cathode side which allows a completely passive, self-breathing operation of the fuel cell. Power densities of 100 mW/cm 2 at 500 mV with hydrogen as a fuel were achieved. A steady operation with this type of fuel cell was demonstrated over a week without any cell flooding. Since the electrical conducting elements of PCBs usually are made of copper, corrosion in the wet environment of a PEMFC is expected. Thus, a significant degradation in performance of fuel cells made of plain copper PCBs was seen in long-term operation. In order to avoid corrosion, the copper layer has to be coated. Fuel cells in PCB design with diverse coatings were tested in long-term operations up to 1000 h under load. Moreover, corrosion currents have been determined by the use of potentiodynamic scans. Promising coatings are electroplated Cr and Ni and a combination of Ni/Au.