Comparison between RF and electrical signals from the partial discharge activity of twisted pair cables at reduced pressures

A pressure-controlled test facility has been set up that allows the PD behaviour of polymer insulated twisted pair samples exposed to 50 Hz AC voltages in the range of 0 to 10 kV to be characterised. Resulting PD activity is quantified using the methods defined in IEC standard 60270 and by using a simple monopole antenna to detect the RF signals excited inside the pressure vessel by the discharges. This paper gives the results of preliminary tests performed on samples of wire insulated with Ethylenetetraflourethylene, Silicon Rubber and Polyvinylchloride in the pressure range between 103 and 105 Pa in atmospheric air. The dependence of PD inception voltage on the environmental pressure is reported. Changes in the behaviour of the PD activity; the correlations between the RF and electrical measurements and the frequency components of the RF signals as the applied voltage and pressure are varied are characterised and discussed

Zero-dimensional chemical kinetic simulation of ROS/RNSin pulsed pulsed-discharge exposed water

The concentration variations of reactive oxygen/nitrogen species in water, such as H2O2, NO2 −, and NO3 − generated by pulsed-discharge plasma exposure, are calculated using reaction rates of chemical reactions and acid-base equilibrium in water. The calculated concentrations and pH values are in good agreement with measured data within the range where the significant changes of the measured data are observed. The rate constant for ONOOH generation is estimated to be 7.8 × 103 M−2 s−1, and this value is in good agreement with previously reported values. The generation rates of H2O2, NO2 −, and NO3 − are estimated to be 7.70 × 10−7, 4.10 × 10−7, and 1.10 × 10−7 M s−1, respectively

FEA simulation studies of accelerated aging of power cables in water tanks

IEEE Standard 1407 provides guidance on accelerated insulation aging experiments on multiple medium voltage (MV) power cables using water-filled tanks. An applied cable current increases the temperature within the water tank and thus provides the accelerated aging conditions for the cables. Understanding the precise nature of the temperature distribution within the water tank and within the cable insulation is important to quantify and calculate the effective aging of the cables. This paper presents initial finite element analysis (FEA) simulation studies that evaluate the temperature distribution within a water filled tank and across submerged power cables when multiple cables are supplied with current. Two scenarios are evaluated and compared, namely the temperature profiles of cables when the water in the tank is treated (a) as a solid material, and (b) as a fluid with natural convection. The importance of applying effective water circulation mechanisms are also highlighted

Partial discharge detection and location for HVDC polymeric cables

This poster is concerned with use of partial discharge monitoring to provide information about the condition of the insulation of electrical cables used for HVDC transmission systems. Electrical cables are among the most fundamental components of any electrical grid, from large subsea international interconnectors, to the ‘last mile’ providing consumers with their electrical supply. The size, cost and current carrying capability are the main considerations when designing and selecting a cable, and in this regard the insulation of these cables is as fundamental as the conductor. Partial discharge (PD) measurement is becoming increasingly vital in monitoring the condition of cable insulation, providing valuable information about the health of the insulation, and predicting when insulation is likely to fail. The majority of this PD monitoring is performed on cable operating under AC conditions, however, with the increasing use of high voltage DC links, for subsea, or long land-based connections provides motivation for the increased use of PD monitoring on cables operating under HVDC. However, despite the increased intensity of research into PD in HVDC cables, there are significant knowledge gaps, preventing the practical application of PD monitoring techniques to HVDC cables. This poster describes the initial stages of a project to partially address these gaps in knowledge, by seeking to obtain results from PD measurements on cables of different insulation types under both AC and DC conditions. From this, recommendations on the use of PD monitoring for HVDC cables, with emphasis on insulation type, are will be provided, as well as recommendations for future research at both an academic and industrial level. The poster will detail the results of the initial literature review, as well as the design for the planned experimentation, and test rig

Polarity effects on breakdown of short gaps in a point-plane topology in air

Electrical breakdown in air in a point-plane topology involves complex processes that are still not fully understood. Unlike uniform-field topologies, the highly-divergent fields produced by point-plane topologies create pre-breakdown corona with volumetric space charge. It is known that space charges developed by corona discharge have significant impacts on the breakdown voltage in non-uniform electrode topologies. With large inter-electrode gaps (>cm) the breakdown voltage for a HV point cathode in air at atmospheric pressure is noticeably larger than a HV point anode. However, this paper shows that in shorter point-plane gaps in air (less than ~10 mm), in the air pressure range 0.1-0.35 MPa, an HV point anode has a similar breakdown voltage which eventually is surpassed by the HV point cathode as the inter-electrode gap is increased. The inter-electrode gap at which the HV cathode has a higher hold-off voltage is found to be dependent on the gas pressure and radius of the point electrode

Nanocomposites based on magnesium-oxide/aluminum-nitride/polypropylene for HVDC cable insulation

Abstract—Polypropylene (PP) with high thermal stability and good electrical properties, has attracted much attention for its potential to take the place of cross-link polyethylene (XLPE) as HVDC insulation because PP is more easily recycled than XLPE due to its thermoplasticity. Due to the adverse effect of electric field reversal under HVDC application, there is a need to find the new polymer insulation material with higher thermal conductivity and good electrical performance. This paper investigates the effect of introducing aluminum nitride (AlN) and magnesium oxide (MgO) into PP on the electrical properties of the resulting the new nanocomposites. In the sample preparation, AlN and MgO were surface-modified by KH570 (γ- methacryloxypropyltrimethoxy silane) and then introduced into PP by the solution method to manufacture the nanocomposite materials. The measurements made were the voltage breakdown characteristics and the DC conductivity. The results obtained show that the combination of AlN and MgO can slightly decrease the DC conductivity of PP/AlN/MgO nanocomposites compared with pure PP. The breakdown strength was slightly decreased. which shows that the adverse effect of AlN on the electrical performance of PP can be compensated by introducing MgO nanoparticles. Hence, the new polymer with high thermal conductivity and good electrical properties could be manufactured by combining two kinds of nanoparticles. Keywords — nanocomposites, magnesium-oxide, aluminum-nitride, polypropylene, electrical performance

Measurements of mobility in aged mineral oil in the presence of nanoparticles

The addition of nanoparticles into insulating liquids has been a popular area of research for the last 20 years as improvements have been observed in the breakdown strength of aged insulating liquids. This paper reports on the changes in the conductivity and the mobility of charge carriers in oil as a result of ageing and how these are effected by the addition of nanoparticles to the aged insulation

Investigation of ozone generation using dielectric barrier discharges at 50 Hz, 2.6 kHz and 20 kHz

Experiments were conducted to investigate ozone generation (DBD) at different frequencies. A cylindrical DBD ozone generator with a discharge gap of 0.3 mm has been developed. 50 Hz AC power was used to provide power density of 44.2 W/m2. 2.6 kHz and 20 kHz AC energisation frequencies were employed to provide power densities of 2.37 kW/m2 and 19.08 kW/m2 respectively. Discharge current, optical emission signals and discharge power were obtained under three frequencies. Ozone concentration and production efficiency at different feed gas flow rates were measured and calculated. It was found that discharge mode was different for positive and negative half-cycle of the applied voltage. Results show that ozone production efficiency rises with an increase in the ozone concentration at 50 Hz, however this efficiency drops with an increase in the ozone concentration at 2.6 kHz and 20 kHz. For the same ozone concentration level, 2.6 kHz is more efficient than 20 kHz. The highest ozone production efficiency achieved in this work is 191.5 g/kWh at 50 Hz and the highest ozone concentration is 271 g/Nm3 at 2.6 kHz

Development of an antimicrobial blended white LED system containing pulsed 405-nm LEDs for decontamination applications

This study details the design, build and testing of a prototype antimicrobial blended white light unit containing pulsed red, yellow, green and 405nm LEDs. With a push for alternative methods of disinfection, optical methods have become a topic of interest. Ultra-violet (UV) light is widely known for its antimicrobial properties however; 405nm light has demonstrated significant antimicrobial properties against many common hospital acquired pathogens. In this study, a pulsed, blended, white-light prototype with a high content of 405 nm antimicrobial light, was designed, built and tested. Antimicrobial efficacy testing of the prototype was conducted using Staphylococcus aureus and Pseudomonas. aeruginosa, two bacteria which are common causes of hospital acquired infections. These were exposure to 3 different light outputs from the prototype and the surviving bacteria enumerated. Results showed that the mixed light output provided a much better CRI and light output under which to work. Also, the light output containing 405 nm light provided an antimicrobial effect, with decontamination of 103 CFUml-1 populations of both bacterial species. The other light content (red, yellow, green) had no beneficial or adverse effects on the antimicrobial properties of the 405nm light. The results suggest that with further development, it could be possible to produce an antimicrobial blended white light containing pulsed 405nm light that could supplement or even replace standard white lighting in certain environments

Thermoplastic materials aging under various stresses

The most popular cable insulation material used is XLPE due to its excellent electrical and thermal properties. However, it does not lend itself to ease of recycling. As a result of an increase in concern worldwide regarding environmental protection, it is the objective of this work to investigate whether a thermoplastic material could be used to replace XLPE for cable insulation. Among thermoplastic materials, HDPE is regarded as one with the most similar properties as XLPE. Although it is clear that the performance of polymeric material changes with different stresses, especially polymer nanocomposites aging process under AC electric field stresses, there are also not many publications on how a superimposed AC voltage would affect the insulation’s performance in HVDC power systems. This paper reports the dielectric properties of HDPE under thermo-electrical stresses. DC stress with and without a superimposed AC stress were applied in the experiments undertaken. The degradation of materials with change in frequencies are summarized and discussed