Panayota Vassiliou

Learn More
The temperature dependent dielectric spectroscopy in frequency domain is compared to physicochemical and electrical tests that are periodically applied on highly insulating transformer oils. Complex permittivity and tandelta data are obtained as a function of frequency and operation temperatures, to demonstrate the polarization phenomena and the induced(More)
The monitoring of the complex permittivity of transformer oils as a function of frequency and temperature provides information concerning the state of the insulation. In this work, it has been investigated as a quality control method, providing service life estimations of power transformations. The formation of databases recording polarization effects in a(More)
Relative dielectric constant and dissipation factor (tan¿) values as a function of frequency have been measured for a variety of water types. The effect of water absorption on the permittivity properties of crystalline powders or nanopowders when exposed to various humidity levels is also examined. Powdered materials were characterized by XRD and were(More)
In this work the dielectric response of three commonly used polymeric insulating materials, namely polyvinyl chloride (PVC), polytetrafluoroethylene (PTFE) and high-density polyethylene (HDPE), was measured after applying combined action of UV-radiation and condensation (humidity and heat) in an Accelerated Weathering Tester apparatus. Test samples were(More)
Reference Cu-based alloy with chemical composition and micro-chemical structure similar to that of ancient alloys has been used for carrying out the artificial long-term degradation test based on chloride enriched soil (chemical+soil) degradation. The results show that such degradation procedure produces natural like "patinas" as the ones grown on(More)
UNLABELLED GOAL AND SCOPE: In order to realize surface consolidation of Pentelic marble on the Acropolis monuments, we have collected the criteria that have to be fulfilled by the methods and materials without side effects on the marbles (and other stones). When the existing methods and materials did not satisfy the requirements (criteria), we invented new(More)
The electrical contact characteristics are dominated by the interfacial transport processes, thermal generation and dissipation rates, mechanical fatigue during the operations, material phase transitions and migration effects as a result of transient phenomena during arcing. The work presented in this paper explores the possibility of using as electrical(More)
Based upon the quasi-equilibrium approximation, the validity of p-n junction modelling, has been experimentally investigated under synchronous electrical and optical excitation of silicon photo-diodes. The devices had areas of 8.2 mm and reverse bias saturation currents of the order of 10 A. Their current-voltage (I-V) response was exploited experimentally(More)
Relative dielectric constant and dissipation factor (tandelta) values as a function of frequency have been measured for a variety of water types. The effect of water absorption on the permittivity properties of crystalline powders or nanopowders when exposed to various humidity levels is also examined. Powdered materials were characterized by XRD and were(More)
In this work, commercial silver metal contacts welded on top of brass or silver plated copper substrates have been exposed to air rich in SO/sub 2/ and air rich in NaCl. Scanning Electron Microscopy (SEM) and Energy Dispersive Analysis (EDA) of the exposed contact surfaces were performed to identify the corrosion byproducts on top of the silver contacts,(More)