Partial discharge (PD) magnitudes from classical detection techniques are expressed in terms of apparent charges. Signals from HF/VHF/UHF techniques on substation components are often hard to express in this quantity because of complex signal excitation and propagation channels. A method to calibrate PD signals obtained during online inductive detection in medium voltage belted cables is described. Online inductive detection implies that the impedances of components present in substations essentially determine the detected PD signal magnitude. The use of belted cables means, that the coupling of a PD event to the conductors not only depends on the PD site within the cross-section of the cable or cable accessory, but also becomes dependent on the momentary phase angle. In addition, during signal propagation the signal magnitude may alter according to the propagation modes of a multi-conductor cable. These aspects are studied quantitatively by the use of theoretical modelling in addition to offline and online experiments. PD diagnostic equipment including pulse injection capability allows online calibration with sufficient accuracy, irrespective of the actual substation arrangement.
An on-line partial discharge (PD) monitoring and location system for medium voltage cable circuits was developed previously. This paper explores ways to extend its range of application. The extension includes PD location method by time domain reflectometry (TDR) when reflections are not easily identifiable. The functionality of the PD monitoring equipment can also be widened by sensing other quantities related to the condition of the cable insulation using the same device. Dynamic cable temperature monitoring can be achieved by recording variation in the high frequency signal propagation velocity along the cable. Water ingress in paper-insulated lead-covered (PILC) cable decreases the cable's characteristic impedance while it increases the permittivity of the insulation. It can be observed by changes in the reflection pattern from the cable or by a lowered propagation velocity. Instead of recording reflection patterns in time domain, a frequency domain approach based on an impedance scan is investigated to be applied for cables in service.
An apparatus for studying metal crystal surfaces with ion scattering techniques is described. These techniques are low-energy ion scattering (LEIS) ion-neutralisation spectroscopy (INS) and low-energy recoil scattering (LERS). Angles of incidence and detection as well as the energies of incoming and outgoing particles can be controlled very precisely. Furthermore, coincidence measurements between scattered projectiles and electrons or between scattered projectiles and recoil ions can be performed. Ultraviolet photoelectron spectroscopy (UPS) and low-energy electron diffraction (LEED) are available as additional techniques.
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