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Rogowski coils (RCs) are widely used to measure power or high frequency currents based on their design. In this paper, two types of RCs that are circular (traditional) and cylindrical shapes wound using wire covered by varnish are constructed. This construction is carried out to be suitable for monitoring the discharge current of the surge arrester installed in the distribution system. Concerning high frequency RC modeling for both types considering transfer function is introduced. Self-integrating for both types is attained. Therefore, the experimental tests using function generator for both coils are carried out to identify the parameters of the transfer function representing the introduced model. The measured signals for current and induced voltages are denoised for the parameter identification process. The denoised process is achieved using the MATLAB code 'wdenoise' while the parameters are estimated using the system identification toolbox. Verification of the proposed model is achieved using experimental results for the two coils. The sensitivity of the two coils is investigated based on the induced output voltage. The application concerning the two coils for monitoring the discharge current of the surge arrester is done. The results confirm the accuracy of the introduced RC model, as well as the performance of the cylindrical shape, is better than the traditional one. The simulation is carried out using MATLAB and ATPDraw programs. [ABSTRACT FROM AUTHOR]

Addition of lithium and manganese cations to borate glasses gives an essential enhancement of the dielectric properties. A strong challenge for energy storage devices is the high energy dissipation. Moreover, the ease of manufacture and the ability to control the glass composition make them significantly useful for a wide range of applications. Herein, borate glasses doped high polarizable BaTiO3 are synthesized by the melt-quenching method. The fully amorphous nature of all glasses is demonstrated. The density and molar volume are found to increase with increasing BaTiO3. The thermal stability study exhibits two glass-transition temperatures for the glasses containing BaTiO3. The most important optical parameters including band gap and Urbach energy are estimated. The BaTiO3-addition causes an initial reduction of band gap, however further addition makes the band gap wider. The activation energy for dc conduction is found to be between 0.98 and 1.07 eV. The dc conductivity decreases with incorporation of BaTiO3 due to the large sizes of barium and titanium ions compared to the size of boron ions, which reduces the ion mobility of the glasses. The influence of temperature, composition and frequency on the dielectric characteristics such as dielectric constant ε′, dielectric loss ε′′, loss factor tanδ and ac conductivity is investigated. The glasses of higher BaTiO3 content exhibit higher dielectric constant and lower dissipation factor (< 2%), which makes them excellent candidates for capacitors and energy storage applications. [ABSTRACT FROM AUTHOR]

This paper investigates the performance of the current model predictive control (CMPC) for controlling a two-stage transformerless grid-connected photovoltaic (PV) system under grid fault conditions. A maximum power point tracking (MPPT) controller was used to extract the maximum power of the PV panel. To stabilize the DC link and generate the reference current values, a proportionalintegral (PI) controller was used. The CMPC strategy was implemented to control the output current of the inverter that connects the PV system to the utility grid. The system and control strategy were simulated via a MATLAB/Simulink environment. The performance of the proposed control strategy was investigated under fault conditions between the three-phase two-level inverter and the grid. Moreover, to validate the capability of the CMPC, comparative case studies were conducted between CMPC, PI, and sliding mode control (SMC) under grid fault. Case studies' results showed that under grid fault, CMPC did not introduce any overshoot or undershoot in the PV output DC current and power. However, PI and SMC produced undershoots of almost 15 kW for the output power and 45 A for the output current. Under the fault conditions, the active output power and three-phase current recovery time of the inverter was 50 ms using CMPC, compared to PI and SMC with recovery times of 80 ms and 60 ms, respectively. Moreover, a voltage dip of 75 V at the DC link voltage was recorded with CMPC under faulty conditions, while the voltage dips for PI and SMC were around 180 V. [ABSTRACT FROM AUTHOR]

Ferroresonance occurrence represents a very dangerous phenomenon to electric power systems. Concerning the recent trend of the applications of gridconnected wind farms, this phenomenon can lead to undesired overvoltages stressing the wind farm components. In this paper, the ferroresonance overvoltages are studied and mitigated for the grid-connected wind farm. Single-pole switching of the breaker is considered, where it is the most famous reason behind the ferroresonance transient events in the electric power systems. During the ferroresonance period, the transient voltage of the network is increased to more than three times the voltage level and associated with harmonics. Surge arrester is suggested to mitigate the ferroresonance transient overvoltages, in which the arrester coordination setting of its residual voltage is selected to be 1.2 of the nominal voltage value. Evaluation of the dynamic interaction of the installed surge arrester with the ferroresonance overvoltages is investigated, and the mitigation is attained, successfully. Furthermore, the magnitudes of the harmonics created due to ferroresonance are reduced by installing the surge arresters, but they are not diminished completely. However, the arresters are found under stress if their dissipating energies exceed the withstand capability. The simulations are carried out using the alternative transient program/electromagnetic transient program (ATP/EMTP), and the waveforms are digitally processed using MATLAB software. [ABSTRACT FROM AUTHOR]

Epoxy is considered to be the most popular polymer and is widely used in various engineering applications. However, environmental considerations require natural materials-based epoxy. This necessity results in further utilization of natural materials as a natural reinforcement for different types of composites. Corn cob is an example of a natural material that can be considered as an agricultural waste. The objective of the present work is to improve the economic feasibility of corn cob by converting the original corn cob material into powder to be utilized in reinforcing epoxy-based composites. In the experiment, the corn cob was crushed and ground using a grain miller before it was characterized by scanning electron microscopy (SEM). The corn cob powder was added to the epoxy with different weight fractions (2, 4, 6, 8, 10 wt%). In order to prevent corn cob powder agglomeration and ensure homogeneous distribution of the reinforcement inside the epoxy, the ultrasonic technique and a mechanical stirrer were used. Then, the composite's chemical compositions were evaluated using X-ray diffraction (XRD). The mechanical experiments showed an improvement in the Young's modulus and compressive yield strength of the epoxy composites, increasing corn cob up to 8 wt% by 21.26% and 22.22%, respectively. Furthermore, tribological tests revealed that reinforcing epoxy with 8 wt% corn cob can decrease the coefficient of friction by 35% and increase wear resistance by 4.8%. A finite element model for the frictional process was constructed to identify different contact stresses and evaluate the load-carrying capacity of the epoxy composites. The finite element model showed agreement with the experimental results. An epoxy containing 8 wt% corn cob demonstrated the optimal mechanical and tribological properties. The rubbed surfaces were investigated by SEM to identify the wear mechanism of different composites.

This study is focuses on the investigation of the effect of using TiO 2 short nanofibers as a reinforcement of an Al matrix on the corrosion characteristics of the produced nanocomposites. The TiO 2 ceramic nanofibers used were synthesized via electrospinning by sol-gel process, then calcinated at a high temperature to evaporate the residual polymers. The fabricated nanocomposites contain 0, 1, 3 and 5 wt.% of synthesized ceramic nanofibers (TiO 2 ). Powder mixtures were mixed for 1 h via high-energy ball milling in a vacuum atmosphere before being inductively sintered through a high-frequency induction furnace at 560 °C for 6 min. The microstructure of the fabricated samples was studied by optical microscope and field emission scanning electron microscope (FESEM) before and after corrosion studies. Corrosion behavior of the sintered samples was evaluated by both electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques (PPT) in 3.5% NaCl solution for one hour and 24-h immersion times. The results show that even though the percentage of ceramic nanofibers added negatively control corrosion resistance, it is still possible to increase resistance against corrosion for the fabricated nanocomposite by more than 75% in the longer exposure time periods.