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In this study, the dielectric properties of unfilled as well as nanofilled polystyrene-silicone rubber blends are evaluated. Accordingly, the preparation of polystyrene-silicone rubber blends is carried out considering three different concentrations of polystyrene (3, 7 and 10%wt). Also, the preparation of polystyrene-silicone rubber nanocomposites is carried out considering different two types of nanoparticles. These nanoparticle types are TiO2 and SiO2 with the same average particle size of 20 nm. Different nanoparticle concentration levels of 1.5, 2 and 3%wt are studied. The effect of thermal aging on the dielectric properties of unfilled as well as nanofilled polystyrene-silicone rubber samples is evaluated. The samples are subjected to thermal aging for two months at a temperature of 130 °C. The average breakdown strength as well as the breakdown strength at 10% and 50% probabilities is evaluated before and after the thermal aging process. The dielectric response includes relative permittivity and dissipation factor which measured and evaluated under thermal aging. The obtained results show that adding small amount of polystyrene to silicone rubber improves its dielectric properties. Finally, adding small amounts of TiO2 and SiO2 nanoparticles to polystyrene-silicone rubber blends give more improvements in its dielectric properties. [ABSTRACT FROM AUTHOR]

Electric cables play a crucial role in transmission and distribution systems. Polyvinyl chloride (PVC) is extensively used in cable insulation. In this work, PVC samples filled with nanosized ZnO and MgO particles are prepared. The effect of external electric field during sample preparation on the dielectric properties of PVC nanocomposites (NC) is evaluated. Accordingly, the samples are subjected to horizontal and vertical external electric fields during the preparation process. The evaluation is carried out considering different nanoparticle concentration levels. The studied concentration levels are 0.5, 1, 3 and 5 wt% for both adopted nanofiller types. Breakdown strength of the prepared NC samples is measured according to American society for testing and materials standard. Also, relative permittivity and dielectric loss of the prepared NC samples are measured. The evaluation is carried out considering horizontal and vertical electric fields. The obtained results show significant effects on the dielectric properties of the tested samples. Hence, the results show that the external electric field decreases relative permittivity and dielectric loss; however, it increases the breakdown strength of PVC NC. Applied horizontal electric field during sample preparation gives more improvement in dielectric properties of PVC NC compared to vertical electric field. Finally, the interpretation of the obtained results is highlighted and discussed. [ABSTRACT FROM AUTHOR]

Adding nanoparticles (NPs) to a base polymer matrix which is known as nanocomposites results in improving its dielectric properties. In this paper, the evaluation of polyvinyl chloride (PVC)/silica nanoparticles (SiO2) nanocomposites is carried out considering the effect of water absorption. PVC nanocomposites are prepared considering different filler loadings of SiO2 NPs (1, 2.5, 5, and 7.5 wt%). The preparation of PVC/SiO2 nanocomposites is chemically carried out by casting the solution. The chemical structure of PVC/SiO2 nanocomposites after water adsorption is investigated by Fourier transform infrared (FTIR) spectroscopy. The effect of water absorption is carried out by immersing nanocomposite samples in tap water. The AC breakdown strength of PVC/SiO2 nanocomposites is measured before and after water immersion. In addition, both dielectric constant (έ) and loss tangent (tan δ) are measured considering different frequencies before and after the water immersion. The results show that the dielectric properties of PVC/SiO2 nanocomposites are significantly affected by water absorption, where PVC/SiO2 nanocomposite sample with filler loading of 7.5 wt% is found to have lower water absorption compared to the other adopted filler loadings. Under the effect of water absorption, the breakdown strength of the base and PVC nanocomposite samples is decreased, and its value for PVC nanocomposite still exceeds the base polymer. Finally, the dielectric constant and dielectric loss of PVC samples are increased under the effect of water absorption. The increase in dielectric constant and dielectric loss is small at the higher filler loadings. [ABSTRACT FROM AUTHOR]

In this paper, the role of the accumulated surface charge on the surfaces of nanoparticles on breakdown strength for liquid and solid dielectrics is presented. The breakdown strengths of a nanofilled liquid dielectric and a solid dielectric are evaluated. The evaluation was conducted considering different nanoparticle material types with different nanofiller loadings. Accordingly, the preparation of transformer oil nanofluid and silicone rubber nanocomposites was performed with different nanofillers of the same average particle size. Breakdown voltage was measured for all the prepared samples, both liquid and solid. The interpretation of the obtained results is presented. [ABSTRACT FROM AUTHOR]

Accelerated thermal ageing test on nanocomposites of polyvinyl chloride (PVC/SiO2) is conducted at constant temperatures of 110 °C and 140 °C. Accordingly, different PVC/SiO2 nanocomposite samples with different silicon dioxide (SiO2) filler loading are prepared. The preparation of the samples was carried out based on the solution casting technique. The loading concentrations of SiO2 in the investigating samples are 0, 1, 2.5, 5 and 7.5 wt%. The breakdown strength of the prepared PVC/SiO2 nanocomposite samples is evaluated before and after the thermal ageing test. The evaluation of breakdown strength is carried out based on American Society for Testing and Materials (ASTM) standard. Also, dielectric spectroscopy, which includes dielectric constant (έ) and tangent loss (tan δ) of nanocomposite, is performed before and after the thermal ageing test. Also, the mass losses during thermal ageing of all samples are evaluated. The results show that the breakdown strength, tan δ, and the dielectric constant (έ) of pure PVC and PVC/SiO2 nanocomposites are significantly affected by the thermal ageing test. Adding a small amount of SiO2 nanoparticles to PVC leads to improvement in its dielectric properties before and after the thermal ageing process as compared to the pure PVC. The mass loss of PVC/SiO2 nanocomposite during thermal ageing is less than that of pure PVC and confirms the obtained result from breakdown strength. [ABSTRACT FROM AUTHOR]

In this article, three-phase motor currents pass through a three-core cable are measured using a two-winding Rogowski coil. The two-winding Rogowski coil is externally fitted around the three-core cable without the need for removing its insulation layers. This results in reducing the measurement complexity. Two windings are fitted around a circular non-magnetic core considering 120o between their center points. The EMFs induced in each winding due to magnetic flux linkage between windings and cable cores are used to reconstruct the three-phase motor currents through the cable cores. In order to reconstruct cable currents, a current reconstruction algorithm is developed. Sensor design and the developed current reconstruction algorithm are theoretically and experimentally validated. Theoretical validation is carried out through Power Simulation Program (PSIM). Regarding the theoretical validation, a three-phase motor fed from a three-phase source is simulated. Motor feeding is carried out using a cable having three cores. The proposed Rogowski coil is simulated and the currents through the cable are theoretically reconstructed considering different operating conditions. Also, experimental validation is carried out considering the measurements of three-phase currents through the cable feeding a 15 HP, three-phase induction motor from a three-phase source. A designed two- winding Rogowski coil is used for sensing the measured currents and a Digital Signal Processor (DSP) is used for implementing the adopted current reconstruction algorithm. Finally, efficacy of the proposed two-winding Rogowski sensor as well as the developed current reconstruction algorithm is proved through the obtained results. [ABSTRACT FROM AUTHOR]

Effect of adding nanofillers on transformer oil breakdown voltage and its thermal performance finds a great interest from researchers and scientists. The impact of oil circulation considering oil forced cooling method on nanoparticles stability in transformer oil is investigated. The stability is considered from breakdown voltage and thermal performance points of view. Titanium dioxide (TiO2) nanoparticles are chosen due to the safety of TiO2 nanomaterial as well as its good performance. First, the optimal concentration of nanosized TiO2 at which maximum breakdown voltage of nanofilled transformer oil is determined and chosen to study the effect of oil circulation on breakdown voltage as well as thermal performance of nanofilled oil. Two reduced experimental models are designed. The first model consists of a galvanized steel tank containing TiO2‐nanofilled transformer oil, at the pre‐determined optimal concentration. This tank is designed to simulate the natural oil cooled transformer. However, the second model that uses a similar tank is designed to simulate a forced cooled transformer. This model consists of a tank containing TiO2‐nanofilled transformer oil, at the pre‐determined optimal concentration, and an oil pump. Breakdown voltage and thermal performance considering the two adapted models are measured in a time period of 60 days. [ABSTRACT FROM AUTHOR]

In this article, a proposed non-invasive design of Rogowski coil to measure 3-phase currents through a 3-core cable is presented. Considering this design, there is no need to remove the insulation layers of a 3-core cable to measure its core currents. The adopted Rogowski coil design uses three separate coils wound at the same circular non-magnetic core with equal spacing between them. When the Rogowski coil is fitted around a 3-core cable, EMF is induced in each coil. The three induced EMFs are used to reconstruct the current passes through each cable core using a proposed current reconstruction technique. In order to validate the presented Rogowski coil design as well as the current reconstruction technique, theoretical verification is carried out using Power Simulation Program (PSIM) software. Hence, a 3-phase source feeds a 3-phase load is simulated. Also, simulation of the designed Rogowski coil as well as the adopted current reconstruction technique is carried out. The obtained theoretical results prove the accurate measurements of the Rogowski coil design and the introduced current reconstruction technique. For more validation, the Rogowski coil design is experimentally implemented. The implemented Rogowski coil is fitted around a 3-core cable that feeds a 3-phase load from a 3-phase source. The current reconstruction technique is implemented using a digital signal processing (DSP) board. The obtained experimental results give another evidence for the validity and efficacy of the proposed Rogowski coil design as well as the current reconstruction technique. [ABSTRACT FROM AUTHOR]

Oil‐paper composite is the main insulation system in oil‐filled transformers. In recent years, the use of nanotechnology to improve the electrical and thermal properties of transformer oil has become a field of research interest. In this paper, the electrical properties such as breakdown strength, volume resistivity, and dielectric response of nano‐filled oil‐paper insulation are evaluated. The evaluation is carried out on a double‐layer of oil‐paper composites insulation. The double‐layer samples are prepared considering different nano‐filler types. The studied nano‐filler types are Pb3O4, Al2O3, and SiO2 with average particle size 25 nm of each. For each nano‐filler type, oil‐paper samples with different concentrations (0.04, 0.06, 0.1, 0.2, and 0.4 g/L) are prepared. The effect of nano‐filler types on the breakdown strength, volume resistivity, and dielectric response of oil‐paper composites are highly evaluated. The results show that the filler types as well as filler permittivity affects the breakdown strength, volume resistivity, and dielectric response of oil‐paper composites insulation. Also, the results show that nano‐filler with high permittivity gives higher improvement in breakdown strength of Oil‐paper composite compared nano‐filler with low permittivity. Finally, the interpretation of all obtained results considering breakdown strength, volume resistivity, and dielectric response is highly reported. [ABSTRACT FROM AUTHOR]

In this paper, a proposed condition monitoring technique of high voltage insulators using Rogowski coil is presented. The proposed technique depends on the voltage signal that generated in Rogowski coil winding due to capacitive coupling between the insulator and the coil. A superimposed voltage signal is generated in the coil winding due to electromagnetic induction that occurs due to leakage current over the insulator surface during fog conditions. The output voltage signal from coil winding (i.e. due to capacitive coupling and electromagnetic induction) is directly analyzed using Fast Fourier Transform (FFT). The direct analysis of the output voltage signal from Rogowski coil without the need for current reconstruction reduces the complexity of signal processing. According to the obtained frequency spectrum of the output voltage signal, pollution level on insulator surface can be determined. In order to validate the proposed technique, an experimental setup is used. In experiments, high voltage pin type insulator is used and connected to a high voltage AC source. The insulator surface is sprayed with saline solution according to IEC 60815 standard to simulate different pollution levels. Also, the insulator surface is polluted with charcoal powder to simulate the non-soluble pollutants. For more validation, the experiments are extended to a cap and pin – type high voltage insulator. The obtained results show that the percent of 3rd/5th harmonics of the measured voltage signal increases with the increase in pollution level. Finally, the efficacy of the proposed technique is validated through the obtained results. [ABSTRACT FROM AUTHOR]

Many day-to-day operation decisions in a smart city need short term load forecasting (STLF) of its customers. STLF is a challenging task because the forecasting accuracy is affected by external factors whose relationships are usually complex and nonlinear. In this paper, a novel hybrid forecasting algorithm is proposed. The proposed hybrid forecasting method is based on locally weighted support vector regression (LWSVR) and the modified grasshopper optimization algorithm (MGOA). Obtaining the appropriate values of LWSVR parameters is vital to achieving satisfactory forecasting accuracy. Therefore, the MGOA is proposed in this paper to optimally select the LWSVR's parameters. The proposed MGOA can be derived by presenting two modifications on the conventional GOA in which the chaotic initialization and the sigmoid decreasing criterion are employed to treat the drawbacks of the conventional GOA. Then the hybrid LWSVR-MGOA method is used to solve the STLF problem. The performance of the proposed LWSVR-MGOA method is assessed using six different real-world datasets. The results reveal that the proposed forecasting method gives a much better forecasting performance in comparison with some published forecasting methods in all cases. [ABSTRACT FROM AUTHOR]

In this study, determining the location of coating defects and severities is evaluated using measurements along the Jordanian buried gas pipeline. Induced alternating current (AC) voltages and current densities along the pipeline are investigated using analytical and practical data under normal operation of the overhead transmission line. Since the induced AC voltages depend on the load currents, it is worthy to determine the actual load current during the lifetime of the pipeline. Accordingly, the forecasting of pipeline‐induced AC voltages is investigated using the least square method. The investigation is carried out in order to expect the future effects on the gas pipeline. The mitigation of induced AC voltage based on inserting polarisation cells (PCs) along the pipeline is evaluated. The results show that an agreement between the measured and calculated induced AC voltages is achieved with and without PCs. Based on the forecasting of induced AC voltages and current density along the pipeline, determining the number of PCs and allocations is suggested for the future years. This study increases the lifetime of the pipeline as well as decreases the maintenance cost. [ABSTRACT FROM AUTHOR]

In this study, determining the location of coating defects and severities is evaluated using measurements along the Jordanian buried gas pipeline. Induced alternating current (AC) voltages and current densities along the pipeline are investigated using analytical and practical data under normal operation of the overhead transmission line. Since the induced AC voltages depend on the load currents, it is worthy to determine the actual load current during the lifetime of the pipeline. Accordingly, the forecasting of pipeline-induced AC voltages is investigated using the least square method. The investigation is carried out in order to expect the future effects on the gas pipeline. The mitigation of induced AC voltage based on inserting polarisation cells (PCs) along the pipeline is evaluated. The results show that an agreement between the measured and calculated induced AC voltages is achieved with and without PCs. Based on the forecasting of induced AC voltages and current density along the pipeline, determining the number of PCs and allocations is suggested for the future years. This study increases the lifetime of the pipeline as well as decreases the maintenance cost. [ABSTRACT FROM AUTHOR]

Studying the effect of adding nanosized ZrO2 to mineral transformer oil on the AC breakdown voltage is presented. The study is carried out considering different concentration levels of nanosized ZrO2. These concentrations are 0, 0.001, 0.002, 0.003 and 0.006%w. The AC breakdown voltage of both nanofilled and base oil is measured according ASTM D1816 standard at room temperature. The evaluation is carried out based on AC breakdown voltage for the nanofilled and base oil considering average and Weibull statistical techniques. Both 50 and 10% breakdown voltage probabilities are obtained and analysed for all samples. Also, the effect of temperature (to take the effect of real operating conditions) on breakdown voltage of base and nanofilled oil is experimentally evaluated. The studied temperatures are 50, 80 and 130°C. The obtained results show that the performance of nanoparticles is significantly affected by increasing the temperature of nanofilled transformer oil. Finally, a proposed mechanism for the effect of temperature on the nanofluids breakdown strength is introduced. [ABSTRACT FROM AUTHOR]

This paper presents a dynamic model to compute the DC flashover voltage for a fixed washed high voltage insulator. This model provides a combination between the static flashover and dynamic arc models. The proposed model takes the pollution layer resistance variation with time during washing into consideration. This variation is experimentally measured at different equivalent salt deposit density (ESDD) values. A mathematical equation for computing the pollution resistance variation with time during washing process is proposed. The DC flashover voltage is computed using the proposed flashover model at different pollution levels. The proposed flashover model is experimentally validated considering the adopted ESDD values. Also, the obtained results show a good agreement between the proposed model and experimental results. The effect of washing water flow rate on flashover voltage is preliminary investigated. Finally, the present study improves fixed washing systems and decreases the flashover during the washing process. [ABSTRACT FROM PUBLISHER]

In this paper, the impact of surge arresters and ferromagnetic ring on the magnitude as well as the steepness of lightning overvoltages in gas insulated substation (GIS) are investigated. This investigation is carried out through modeling of a typical 380-kV GIS using ATP/EMTP for very fast transient overvoltages. Two scenarios of lightning strikes, backflashover and shielding failure are considered. Also, the impact of ferromagnetic ring on the surge arrester performance is evaluated. The evaluation is carried out considering surge arresters located at entrance, and at transformer terminals of GIS. Finally, the effect of ferromagnetic ring parameters on the arresters performance is evaluated and discussed. The obtained results show that the presence of ferromagnetic ring can affect the rating selection of GIS surge arresters. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In this paper, a developed method for measuring power frequency ac current using Rogowski coil is presented. The proposed method uses a differentiator in order to reconstruct the current that is intended to be measured. This method gives accurate results as well as it requires only few samples to successfully reconstruct the power frequency current. These advantages are investigated by experimental testing using two different designs of Rogowski coil. The first Rogowski coil has a higher number of turns as compared with the second one. In addition, a digital signal processor is integrated with the coil to implement the proposed reconstruction method. The obtained results give an evidence for the proposed method validity as well as its efficacy. [ABSTRACT FROM PUBLISHER]

This study presents theoretical as well as experimental studies in order to obtain interpretations about the role of nanoparticles in the breakdown mechanism of transformer oil. The published breakdown mechanisms for nanofilled transformer oil are briefly discussed in order to highlight the points of agreement and disagreement with these mechanisms. Moreover, a proposed breakdown mechanism for nanofilled oil is presented depending on a proposed particle charging mechanism that is theoretically discussed and experimentally validated. Finally, the obtained experimental results prove the efficacy of the proposed theoretical mechanisms. [ABSTRACT FROM AUTHOR]

SUMMARY The wind turbine is subjected to lightning due to its geographical location and size. The struck wind turbine suffers from backflow current-overvoltages affected by the grounding system. This issue is highlighted in this paper, and, therefore, the grounding system of the wind turbine is modified. In order to accurately examine the proposed grounding system, we present a model that takes into account both soil ionization and frequency-dependence effect. Also, wind farm components, such as wind turbine down conductor, transformers, surge arresters, overhead, and distributed line, are modeled using high-frequency models. More factors affecting backflow current-overvoltages are analysed such as the lightning inception angle, in-service and out-of-service wind farm, and the number of wind turbines. The simulation is carried out using ATP/EMTP software. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]