The emergence of nano dielectrics for specialized high voltage applications sparked off a variety of research activities, which proved that nano-fillers are capable of improving the electrical, thermal and mechanical properties of polymers. This paper primarily investigates the effect of addition of hBN (hexagonal boron nitride) nanoparticles into an epoxy polymer base by increasing fill-grade, from 0.2 to 5 % by volume, from two different standpoints: (a) characterizing the electrical space charge (S.C.) accumulation threshold under DC electrical fields, and, (b) demonstrating the alterations in material properties of the modified polymeric materials, from the unfilled polymer. Objective (a) is experimentally investigated by the pulsed electro-acoustic (PEA) technique, well known for determining spatial charge distribution in dielectrics. Objective (b) is investigated by determining the ultrasonic velocity response of the modified composites and unfilled polymer. The obtained results suggest a relation between electrical threshold fields for S.C. accumulation fill-grades, as well as the fact that incorporating stiff filler materials into brittle polymer bases leads to a tougher composite (capable of withstanding greater breaking stress levels), but with reduced ductility.

Partial discharge (PD) field tests are widely used for cable assessment or cable commissioning. Usually, these tests are carried out by means of off-line tests where PD pulses are measured with capacitively coupled PD sensors. In off-line single-sided cable measurements, time-domain reflectometry (TDR) is used to locate the source of the PD along the cable. However, when the PD pulses are originated at the cable ends, the TDR technique cannot, by itself, properly distinguish between PD pulses produced at the cable near-end or at the far-end. This paper describes three different methods that produce an unambiguous localization of PDs produced at the cable ends, complementing the TDR.

Many researchers have reported an improvement of the properties of polymer dielectrics by introducing nanofillers. However, the influence of ambient conditions and sample storage under different conditions are often not taken into account. The epoxy matrix itself is a polar polymer susceptible to water absorption, and the presence of hydrophilic nanofillers such as silica will enhance the uptake of moisture from the environment. The dielectric response both of neat epoxy resin and an epoxy-based nanocomposite under an electrical stress greatly depends on the amount of absorbed water. This study investigates the effect of water absorbance on the dielectric spectrum of epoxy-silica nanocomposites containing different concentrations of nanoparticles.

The design constraints of gas insulated switchgear(GIS) are changing due to an increasing power demand and decreasing available floor space for substations. Ideally, new GIS should operate at a higher nominal voltage with a minimal or no increase in size. Another ongoing development in the power industry is the desire to replace SF6 by an environmentally friendly gas which is preferably readily available and has relatively low production costs. Unfortunately these gases show a breakdown strength which is significantly lower than SF6. Coatings can prove to be a possible solution to this problem. The breakdown strength of GIS can be improved with the application of a dielectric coating on the electrode surfaces. In this paper, the influence of thick coatings on the breakdown strength of GIS is evaluated with negative lightning impulse breakdown tests. The tests are performed on a rod-plane electrode arrangement in which the rod electrode is coated. The coatings consist of a 10mm thick layer of epoxy or an epoxy based nanocomposite.

In gas insulated switchgear(GIS) SF6 gas is widely in use because it has good electrical insulation and arc interruption capabilities. Due to environmental constraints the desire to use alternative gases is continuously growing. This paper focuses on dry air as an alternative gas which unfortunately has a breakdown strength which is lower than the breakdown strength of SF6 at equal gas pressure. To improve the breakdown strength of dry air filled GIS, dielectric coatings can be applied to the electrodes. In this paper, the performance of GIS with thin coatings is evaluated through breakdown tests in a rod-plane electrode arrangement. Negative lightning impulse voltage is applied on the rod electrode and the gas pressure is kept constant at 0.9 MPa.