Metallurgical aspects of contact materials for vacuum switchingdevices

Both the metallurgical aspects of contact materials for vacuum switching devices and their practical applications for important electrical load cases (circuit breaker, contactor, and load switch) are discussed. Because a vacuum contact material has to fulfil conflicting requirements, an optimization of the contact material with regard to the type of application is always necessary. The selection procedure for the different types of contact materials is discussed on the basis of experimental results. Cu/Cr-type contacts yield very good values for the breaking capacity of the circuit breakers used in the medium-voltage range. Optimization must attempt to improve the welding behavior and ability to withstand a high voltage after making short-circuit conditions. W/Cu-type contacts show a long service life in high-voltage contactors. Current chopping behavior, however, has to be optimized. WC/Ag-type contacts are a good choice for low-voltage contactors. The service life and breaking capacity, however, are not always satisfactory and need optimization     

Structural investigations of the ionic conductivity in zirconia single crystals by neutron diffraction at high temperatures and simultaneously applied electric field

In situ neutron diffraction studies of CaO and Y₂O₃ stabilized zirconia single crystals were performed at elevated temperatures and simultaneously applied DC electric field, i.e. lasting ionic current. Bragg data from Zr_0.85Ca_0.15O_1.85 (CSZ15) were collected at room temperature without electric field, at 1170 K and 1370 K without and with 3.5 V and 1.8 V, respectively, (field vector Ell[111]), which generated a current of 60 mA in each case. In case of Zr_0.70Y_0.30O_1.85 (YSZ15) the electric field vector was directed along [001]. At 1170 K three data sets were collected: without field, with 1.5 V (I=60 mA), and with 2.5 V (I=120 mA). Atomic displacement parameters (a.d.p.'s) were derived in the frame of a non-Gaussian Debye-Waller factor formalism for the oxygens. Corresponding probability density function (p.d.f.) maps and pseudo potential maps were calculated. Most probable curved diffusion pathways run close to 〈 100 〉, independent of the external field direction, applied voltage and the kind of dopant. With lasting ionic current the potential corresponding to p.d.f. >1% is lowered by about 0.06–0.07 eV.     

FT-IR studies on the mechanical response of the crystalline fraction in ultrastrong polyethylene tapes

FT-IR spectra of UHMW-PE tapes with different moduli have been studied in dependence of mechanical deformation and stress. Small spectral variations have been revealed in the difference spectra. Band shifts of the 730/720 cm^–1 doublet have been observed under stress relaxation and upon stretching. A clear correlation between the shift of crystalline bands and the Young's modulus could be determined. Polarized measurements demonstrated variations in the mechanical response of nearly perfectly oriented and non-oriented crystallites. Crosslinking was performed by blending the polyethylene with 10% polysilane and UV-irradiation of the drawn material. The band shift increases as the linkage between oriented crystal blocks is improved with higher draw ratios and chemical crosslinking.