A. Bojovschi

The influence of hanging water droplets on discharge activity, application to high voltage insulators

An investigation into the effect of hanging water droplets on a high voltage electrode is presented. This study is extended to a real life application of water droplets hanging on the sheds of high voltage ceramic insulators. The role of the water droplets on the partial discharge and flash over activity is considered. The results show that hanging droplets have a significant influence on corona discharges, which are visible between the sheds of insulators in a power network.

The Role of Fibre Orientation on the Electromagnetic Performance of Waveguides Manufactured from Carbon Fibre Reinforced Plastic

Aircraft skins manufactured from carbon fibre reinforced plastic (CFRP) can simultaneously support structural load and act as antennas. This offers the potential for disproportionately large antenna elements and arrays, and thus enhanced aircraft capability. The efficient design of such structures requires that the link between CFRP microstructure and electromagnetic performance be established. This paper presents a method of predicting the electromagnetic attenuation of waveguides manufactured from CFRP. The method considers both the orthotropic, complex conductivity of CFRP, high in the fibre direction and low transverse to it, and the local electric fields in waveguides, which vary with location and frequency. The method was validated experimentally using waveguides manufactured from aerospace grade IM7/977-3 prepreg tape with [0 90]s, [90 0]s and [±45]s ply stacking sequences.

Impact of electromagnetic radiation on cascaded failure in high voltage insulators

A cause of aging and cascaded failure of high voltage insulators is investigated by assessing the radiation propagating from a faulty insulator. The transfer of electromagnetic energy from corona discharge to healthy insulators situated on the same power pole is assessed. The results show that the high intensity of electric field associated with corona discharge on faulty insulators can lead to aging and finally failure of high voltage infrastructure.

A Loop-Type End-Launcher for Carbon Fiber Reinforced Polymer Waveguides

The analysis of an end-launcher type transition from coaxial to WR90 waveguides is presented. This transition is tuned to have the highest performance at the radar frequency of 9.375GHz. The characteristics of the transducer are investigated comparatively in 30cm aluminum and carbon flber reinforced polymer waveguides. The advantage of the proposed feed is that it does not require grounding to the broad wall of the waveguide compared to the traditional end- launcher loop feeds. This departure from the current loop feeds makes the proposed feed suitable for carbon flber reinforced polymer waveguides where a disruption in the broad wall would be undesirable.

Analysis of a carbon fibre reinforced polymer slotted waveguide array fed by a loop type end launcher

The investigations of an end-launcher transition in Carbon Fibre Reinforced Plastic (CFRP) WR90 waveguides is presented. The applicability of the feed for CFRP slotted waveguide antenna is addressed. Some of the aspects pertaining to the efficiency of CFRP slotted waveguide antenna and its use for radar applications are discussed. The results are presented in comparison with those obtained from the same concepts implemented in aluminium waveguides. A recently implemented anisotropic model for CFRP laminates, which describes the electrical anisotropy of the composite material, was used. The data obtained provide promising indicators for the potential use of slotted waveguide antennas made of CFRP for radar applications.

The reflectivity of carbon fiber reinforced polymer short circuit illuminated by guided microwaves

An investigation of the interaction between guided electromagnetic waves and carbon fibre reinforced polymer waveguide short circuits is presented. To determine the electromagnetic response of the composite waveguide short circuit, its anisotropic characteristics are considered. The reflection coefficients of the short circuit, at the reference plane, are about 0.98 over the whole 8 GHz to 12 GHz band. The results indicate the viability of carbon fiber based short circuits for lightweight waveguides.

Electromagnetic radiation spectrum from partial discharge in air-insulated medium voltage switchgear

The ability to accurately characterize the partial discharge events in switchgear systems can help to prevent effectively the breakdown of the system. In this work the electromagnetic radiation spectrum from partial discharge is investigated in the entire structure of medium voltage switchgear (Type D24-121114 of Driescher). The components of the switchgear simulated include voltage and current transformers, terminal studs, fuses, earthing switches, connection parts and the metallic enclosure. Finite Element Method has been used in this work. The partial discharge is situated on the surface of insulators being modeled by a Gaussian pulse. The intensity of the electromagnetic field which propagates from partial discharge is influenced by the switchgear components. The work shows that by analyzing the radiation spectra caused by partial discharge in a switchgear system the positioning of the electromagnetic sensors for fault detection can be optimized.