1,721,003 research outputs found
Modelling partial discharge in gaseous voids
No full textThe measurement of partial discharge (PD) activity is a commonly used tool to quantify the health of electrical insulation material in high voltage plant. Models of PD activity have been developed in order to provide insight into the physical conditions present in PD systems. Modern PD models typically use the approach taken in the work of Niemeyer in early 1990's, and so far have been primarily limited to investigating PD activity from simple controlled experiments. PD models have typically focused on PD activity in gaseous voids, which is also the case in this thesis.In this work a new PD activity model was developed. It addressed several of the shortcomings present in other PD activity models in order to provide a more physically accurate description of PD phenomena and to extend the scope of the model. The model was validated against experimental data in the literature, and was then used to simulate PD activity from a three-phase cable experiment, which is indicative of the more complex PD systems present in operational plant. However, despite this contribution it became evident that many of the assumptions and concepts used in the model, despite having a basis in the literature, have limited justification.A drift diffusion model was then used to test some of the physical concepts that are employed when modelling PD in voids. The results showed that many of these concepts may be erroneous, with discrepancies between the canonical reasoning and the simulation results. For example, the residual electric field, the electric field after a discharge, is significantly lower than the estimates used by PD activity models in the literature. It is concluded that in their current form PD activity models may not be t for purpose, and it is suggested that a new approach to modelling PD activity is required moving forward
Improving models of partial discharge activity using simulation
No full textIn the literature models of partial discharge (PD) activity have been used to successfully replicate PD data from experiments under controlled conditions. To reduce computational cost PD models are forced to make assumptions about the discharge physics, including the surface charge distributions and magnitudes at a dielectric boundary due to a discharge. In this work a drift-diffusion model is used to simulate a single discharge inside a spherical air filled void at atmospheric pressure surrounded by epoxy resin. It was found that the discharge comprised of an electron avalanche that transitioned into a positive streamer, a result seen in previous work on dielectric barrier discharges. Furthermore, although the surface charge density distributions are approximately bipolar with respect to the symmetry axis, there is a notable asymmetry in the electric field and charged particle distributions during the discharge. Future improvements and possible insights from the results are then discussed
Plasma dynamic simulations of partial discharges within electrical tree structures
No full textThis paper is a preliminary investigation into the physical mechanisms of PD within gaseous tubules in a needle-plane electrode arrangement. It is intended as a simple representation of an experimental system which formed electrical trees. A drift diffusion model is used to simulate plasma dynamics, where it is assumed that the gas within the tubule is atmospheric pressure air. The findings were in reasonable agreement with the existing literature on the tubule length required to initiate a PD. The PDs were found to be positive streamers, which propagated towards the needle tip at negative applied voltage polarity, and away from the needle tip at positive voltage polarity. There a number of possible developments for future work with the ultimate aim of improving simulations of electrical treeing in high voltage plant
Dataset for Simulating Partial Discharge Activity in a Cylindrical Void using a Model of Plasma Dynamics
No full textPlot data for journal paper "Simulating Partial Discharge Activity in a Cylindrical Void using a Model of Plasma Dynamics" published in Journal of Physics D: Applied Physics, all data files are in MATLAB .mat format.</span
Simulating partial discharge activity in a cylindrical void using a model of plasma dynamics
No full textPartial discharge (PD) activity models typically use simplified descriptions of individual discharges to develop a model of discharge activity. This approach neglects the plasma dynamics of the discharge, and requires the use of multiple assumptions. In this work, plasma dynamic simulations of individual PDs are used to inform a PD activity model for discharges within a cylindrical cavity bounded by low density polyethylene (LDPE). Specifically, by considering the plasma dynamics of the discharges it is possible to determine: surface charge density distributions, apparent charges, the inception electric field and the residual electric field. The resulting PD activity model had only a single adjustable parameter, relating to the availability of seed charges, and was able to produce phase resolved PD (PRPD) patterns that were comparable with experimental data. Good agreement was also observed between the measured and simulated PD extinction voltage. The shortcomings of PD activity models are discussed including the poor understanding of the seed charge generation rate. Nevertheless, the model does allow robust conclusions on the PD dynamics in the experiment. The main contribution of this work is to show how simulations of plasma dynamics can be used to provide additional insight PD activity
Simulating surface charge dynamics
No full textSurface charge dynamics can play an important role in electric field distributions in both AC and DC insulation systems. In this paper the theory behind surface charge dynamics is introduced with a particular focus on the calculation of surface divergence; an operator which is used to determine movement of charge constrained to a surface. A detailed discussion of the model implementation is provided and validated against an analytical solution. Surface charge dynamics in AC and DC insulation systems are then investigated. Assuming the measurement data in the literature is representative it is demonstrated that surface currents have the capability to significantly alter electric field distributions in voids, even over the timescales of an AC cycle
DC conductivity characteristics of core-shell nanoparticles filled epoxy nanocomposites
No full textEpoxy-based nanocomposites are extensively used for High-Voltage Direct Current (HVDC) insulation. Incorporating inorganic nanoparticles can modulate interfacial traps, but the influence of core-shell architectures remains unclear. Here, we investigate field-dependent DC conductivity in epoxy composites filled with conventional SiO2, Al2O3, TiO2 and SiO2-coated core-shell counterparts (SiO2@SiO2, Al2O3@SiO2, TiO2@SiO2) filled with a total surface area of ≃ 5.82 m2. Samples were fabricated via shear mixing and cured at 80 ◦C (2 h) and 125 ◦C (3 h). J-E measurements (1–10 kV mm−1) were analysed using power-law and Poole-Frenkel/Schottky empirical fits. Currents were fit with stretched-exponential decay to extractrelaxation time (τ ) and stretch exponent (β). Conventional SiO2 and Al2O3 demonstrated sub-Ohmic low-field behaviour and higher transition fields, while TiO2 remained near-Ohmic. Core-shell composites demonstrated Ohmic drift in all cases and raised transition fields to 3.6-4.1 kV mm−1, with significantly accelerated de-trapping (τ ≃ 6.2-6.4 s, β ≃ 0.52-0.54). Findings demonstrate that silica shells result in homogeneous traps, extending the Ohmic regime and deferring space-charge-limitedconduction without compromising core-driven conductivity enhancement
The use of thermal and load data to identify large autotransformers that have aged and degraded electrical insulation
No full textThis paper reports on the use of thermal and load data to identify large autotransformers that have aged and degraded electrical insulation. The top oil temperature rise and the oil time constant at rated load are used to guarantee that the transformer temperature will not exceed the thermal limits at the rated capacity. The thermal parameters from a heat run test are typically supposed to be unchanged over the lifetime of the transformer. Nevertheless, the thermal behaviors could be affected by the degradation of electrical insulation. Those parameters are recalculated by fitting operational measurements, which comprised of load profiles, winding temperature indicator (WTI) measurements and ambient temperature, to the IEC 60076-7 model. Significant increases in the thermal parameters indicate that there is a possibility that the autotransformer has aged and degraded electrical insulation.</p
Estimation on degradation rate of insulating paper in power transformers using historical load and thermal data
No full textLife expectancy of power transformers is limited by the integrity of insulating cellulosic paper wound around transformer winding. The insulating paper is subjected to thermal, electrical and mechanical stresses. There are three main factors causing degradation in the paper, i.e. moisture, oxygen and temperature. In this work, the degradation rate due to temperature is only discussed. That means that transformer life could be shortened or extended by adjusting loads which results in higher or lower temperature conditions. The temperature, namely the hot-spot temperature is typically used to estimate the relative ageing rate and loss of insulation life. Being able to estimate the hot-spot temperature accurately given load and weather data helps operators to plan about transformer replacement properly. This could also reduce costs of early replacement due to a conservative estimation. In this work, thermal models have been developed using machine learning techniques to learn thermal behavior from historical data. The data are comprised of the hot-spot temperature estimated by winding temperature indicator (WTI), load profiles, ambient temperature, rainfall, wind speed and direction and solar radiation. The proposed method has been validated using data for five 400kV/275kV, four 400kV/132kV and two 275kV/66kV autotransformers and has been shown to work effectively
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