Petru Nothingher

This paper is concerned with the measurement of electric fields at metal/insulator and metal/semiconductor interfaces using the thermal pulse method for space charge measurements. Simultaneous responses induced by the space charges and the variation of the surface temperature of samples are acquired, treated, and used. It is shown that and how through thorough and full decoupling and exploitation of such signals issued from an appropriate experimental setup, the values of the metal/polymer interface fields can be reached. On the other hand, the applicability of thermal methods for detecting charges at the interfaces of semiconducting materials is fully demonstrated.

When a charged human body stands up from a chair or walks in a room using an air conditioner, a malfunction or failure of electronic devices is caused occasionally by the static electricity. When the charged human body operates the electronic device by a charged hand, an instantaneous electrostatically high induced voltage is generated in the metal case of the electronic device. Such the induced voltage is generated in a metal case when a charged object of charged hand moves near the metal case. An experiment is conducted where an induced voltage is measured using a real experimental setup when a charged object moves away from the metal case to the left, right, or back. The voltage induced in the metal case is measured using a spark gap and an electromagnetic wave sensor. The results show that the voltages induced in the metal case are 0.6 times the voltage of a charged object when the charged object moves away from the metal case. The induced voltage of 6 kV is generated in the metal case for the charged hand of 10 kV. The results will be beneficial in solving the malfunction or failure of electronic devices caused by induced voltages.

This paper presents the results of a study regarding the influence of a Field Grading Material (FGM) on the electric field and temperature distributions in the insulations of a power cable joint model. The computation was performed at steady state for a cable joint insulation consisting of Ethylene Propylene Rubber (EPR) installed for a cable with Cross-linked Polyethylene (XLPE) insulation. The presence of the FGM layer leads to important modifications of the electric field values, especially near the corners of the cable joint inner semiconductive layer. The results also show that the maximum electric field and temperature values, as well as the surface charge density values present at the interface between the insulations are lowered by using a FGM layer. This leads to reduced electric stresses and charge injection. The reduction of the surface charge density values also reduces the values of the residual electric field and leads to a slowdown of insulation ageing.

The study of the electrical double layer in transitory regime seems to be a good way to reach a better understanding of its origin. Recent numerical studies have shown the importance of taking into account the thermal dependence of the liquid intrinsic properties, such as the electrical permittivity or ionic mobility. In this paper, a film of dielectric liquid trapped between two metallic plane electrodes is studies via its electrical current response to the thermal step.

When a liquid is put into contact with a solid, two charge layers of opposite signs appear at the interface. This Electrical Double Layer (EDL) is the result of electrochemical reactions occurring in the region separating the liquid and the solid. A bottleneck in understanding and quantifying the EDL and its behavior is the availability of direct methods allowing to fully measure the EDL charge and distribution. This paper concerns the use of the Thermal Step Method (TSM) as a tool for characterizing the EDL to complete the flow electrification method. Several dielectric liquids (cyclohexane, mineral oil and silicon oil) are subjected to thermal step measurements. The obtained results are analyzed and discussed with respect to literature and to numerical simulations.

Medium voltage underground cables were aged in air at temperatures between 70°C to 140°C. The changes of the structural properties of the crosslinked polyethylene (XLPE) insulating layer were characterized by physico-chemical techniques: Differential Scanning Calorimetry (DSC) and Fourier Transform Infrared Spectroscopy (FTIR). The performed analyses revealed chemical ageing (oxidation, chemical consumption of additives, post-crosslinking...) and physical ageing (migration of chemical species). The accelerated thermal tests on stripped XLPE samples showed, as expected, a mild oxidative degradation. In contrast, ageing tests conducted in the presence of the semi-conductive layers revealed a striking difference, with a migration of extra carbonyl species into the XLPE insulation.

This focuses on studying the applicability of the Thermal Step Method (TSM) in liquid dielectrics. The TSM is widely used on solid dielectrics, in which thermal conduction prevails. Experimental results and numerical simulations are employed to study the use of the TSM in dielectric liquids, particularly with respect to liquid convection and permittivity variation with temperature.