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Multifunctional carbon fiber-reinforced polymer (CFRP) composites are promising structural materials for lightweight applications. However, the low conductivity in the through-thickness direction of the composites limits its applications in the fields that require the high stability of composite against lightning strikes. This work presents the study on the synergetic effect of conducting polymer, polyaniline (PANI), and graphene nanoplatelets (GNP) for increasing the electrical conductivity of CFRP composites. PANI doped GNP flexible film is fabricated with the aid of compatible polymer polyvinylpyrrolidone (PVP), and its effect on the electrical conductivity of CFRP composites has been studied. About 250% in through-thickness conductivity has improved with 11 wt% GNP as a function of the composite. The incorporation of conductive film not only increases the conductivity of the CFRP laminates but also enhances the resistance against lightning strikes. Scanning Electron Microscopy (SEM), Thermogravimetric Analysis (TGA), three-point bending tests were used to analyze the morphology, thermal stability, and mechanical strengths of the composites. Finally, the observation of post-strike damage confirms the importance of through-thickness conductivity for mitigating the lightning strike damage.

Understanding the damage mechanisms of fiber-reinforced polymer matrix composite materials under high voltage conditions is of great significance for lightning strike protection and high voltage insulation applications of composite structures. In this paper, we investigated effects of the lightning impulse (LI) voltage and high voltage alternating current (HVAC) puncture on damage modes of the electrically nonconductive glass fiber-reinforced polymer (GFRP) matrix composite materials through experimental tests and numerical simulations. The LI and HVAC tests represent the lightning strike and high voltage insulation cable puncture conditions, respectively. Our experimental examinations showed that GFRP composite specimens subjected to the LI voltage test exhibited distinct damage modes compared with those in the HVAC puncture test. The GFRP composite material suffered more charring and fiber vaporization in the HVAC puncture test, whereas less matrix charring and fiber vaporization but severe fiber breakage and delamination in response to the LI voltage tests. The findings indicate that the thermal effect dominates the damage of GFRP composites inflicted by the HVAC puncture test, whereas the mechanical impact effect governs the GFRP composite damage in the LI voltage test. In addition, the electric arc plasma formation during the puncture of the GFRP composite material was modeled through solving Maxwell’s equations and the heat generation equations using finite element analysis. Simulation results provided insights on the effects of duration and intensity of the high voltage electric discharge on the composite damage.

For high voltage impulse testing, a standard lightning impulse is defined in IEEE Std. 4 and IEC 60060-1 as a double exponential waveform having a front time T1 = 1.2 μs ± 30% and time to half-value T2 = 50 μs ± 20%. It has been noticed that for a given specimen, it is possible to successfully pass a flashover test at one end of the T1 tolerance range while failing the same test at the opposite end of the tolerance spectrum. Consequently, a systematic approach was adopted to investigate this observation. Up-and-down tests were performed to define the disruptive discharge voltage (critical flashover voltage CFO, U50) for 1, 5, 10, and 15 unit glass insulator strings standard lightning impulses using the minimum acceptance front time value (T1 ≈ 0.84 μs). Tests were repeated using the maximum tolerance value (T1 ≈ 1.56 μs) to investigate the degree of divergence in the flashover value. Particular attention is given to the steepness (voltage-time characteristics) of the applied impulse to consider if tolerance criteria amendment is merited in a future standard revision. As the steepness impact is more renowned in non-uniform geometries, field homogeneity as a function of string length is also incorporated into the analysis.

Carbon Fiber Reinforced Matrix (CFRP) composites are promising alternatives of metal panels for various industries owing to their advantages. However, one of the main disadvantages of using CFRP composites compared to metal panels is their susceptibility to lightning strike, which is mainly due to the low electrical conductivity of resins used as the matrix for binding the carbon fiber fabrics. Since the low electrical conductivity causes substantial amount of Joule heating that damages CFRP composites, increasing the conductivity of the material would reduce the damage causes by lightning strikes. Nano-fillers such as Carbon Black (CB) and Carbon Nanotubes (CNT) are materials that can enhance the electrical conductivity of CFRP composites. A thorough understanding on impact of conductive nanofillers on the lightning strike damage characteristics is necessary for potentially reducing the lightning strike damage of the CFRP composites. There are numerous research groups that investigated the effect of adding the conductive materials to reduce the damage of lightning strike, but the ideal composition of the material for CFRP composites has not been determined yet.

With the increasing use of carbon fiber epoxy composite materials in the aerospace and wind energy industries, protecting these composite structures from lightning strike has become a vital and challenging task. Conventional lightning protection of carbon fiber composites requires the use of a surface layer of expanded metal mesh film. Such solution has shown disadvantages including (i) additional weight and cost and (ii) debonding between the mesh film and the composite laminate due to environmental aging. An alternative solution is adding lightweight conductive additives to epoxy resin instead of using heavy metal mesh. In this paper, we investigated effects of premixing highly conductive graphene nanoplatelets with epoxy resin on the overall electrical resistance and lightning damage response of composite laminates. Four carbon fiber composite laminate panels were fabricated using hand-layup followed by hot pressing, including two baseline panels without graphene nanoplatelets, two other panels with 0.5 and 1.0 wt. % graphene nanoplatelets, respectively. The quasiisotropic composite laminates were subjected to simulated lightning strikes with 100 kA impulse current. Both visual observation and ultrasonic inspection were carried out to identify the lightning strike damage and characterize the role of graphene nanoplatelets in mitigating lightning strike damage. Our results indicate that adding nanographene platelets significantly decreases the surface electrical resistance of the composite laminate and reduces the severity of the lightning strike damage.

Until recently, glass fiber composites (GFRP) were the preferred choice to prepare wind turbine blades due to their low cost compared to their counterpart carbon fiber composites (CFRP). However, to harvest the maximum wind energy, ever larger wind turbine blades are being manufactured. To support such a large structure carbon fiber composites CFRP have become the integral part of load bearing structures in the blade. In this work, we are proposing to utilize the low cost carbon fiber (LCCF), manufactured at Carbon Fiber Technology Facility (CFTF) of Oak Ridge National Laboratory (ORNL) as not only the cost effective alternative to the currently used carbon fiber (CF) but also as the lightning strike protection of the wind turbine blades. A textile-grade precursor was used to prepare LCCF. Wind turbines often get hit by lightning strikes due to their operating locations. LCCF can provide structural integrity to these gigantic structures and mitigate the effect of lightning strike on them by effectively dissipating the current. Two composite panels made of LCCF were tested against artificial lightning strikes of 100 kA and 200 kA (component A of lightning

Carbon fiber reinforced polymer matrix (CFRP) composite laminates are increasingly used as structural materials in the aerospace industry owing to their various advantages such as the corrosion resistant property, high specific strength and modulus, high fatigue strength and fatigue damage tolerance, low coefficient of thermal expansion, and light weight. Such an increasing use of CFRP composite laminates raises significant concern over lightning strike impact and necessitates the investigation of their lightning strike damage characteristics. The diameter of an actual lightning arc channel varies from several centimeters to several meters according to reported photographs and ionizing wave analysis. A thorough understanding on the material damage characteristics caused by a lightning strike impact is essential for reducing the lightning strike damage of the composite laminates while maintaining the mechanical properties. There have been numerous studies that investigated the effect of lightning discharges on aircraft composite structures, but the impact of the lightning channel diameter has not been systematically investigated. The goal of this research is to find the correlation between the diameter of electric arcs observed in lightning discharges and the level of damage it causes on CFRP composite laminates.

The common practice of assuming constant pressure in the dielectric strength estimation of hot gases is compared with that assuming constant number density. The dielectric strengths of dissociated gaseous He- H2-N2 mixture and $\mathbf{SF}_{\mathbf{6}}$ are estimated at various temperatures. The compositions of the dissociated gas species at temperatures as high as 5,000 K are obtained by minimizing the Gibbs free energy assuming local chemical equilibrium. The calculated mole fractions of the dissociated gas species and electron-scattering cross section data are used for calculating the density-reduced critical electric field that represents the dielectric strength of the gas mixtures. Through this study, it is shown that the dielectric strength of hot gases depends significantly on the two assumptions, and the assumption of constant pressure results in the underestimation of dielectric strength at high temperatures compared to the assumption of constant number density.

Accurate measurement circuit and high-frequency sensors with sufficient bandwidth are necessary for the analysis of individual partial discharge (PD) pulses. In this paper, a testbed is designed and constructed for the investigation of DC PD pulses. The testbed is equipped with a 50 ohm transmission line (TL) that terminate to an oscilloscope for measuring the charge displacement current generated by PD pulses. Besides the oscilloscope measurements, two types of electromagnetic field sensors (D-dot and B-dot) were developed to capture the EM fields of the PD pulses propagating through the TL. The main goal of this paper is to investigate the DC PD pulses through the EM fields and the corresponding discharge current pulses that are considered as calibrating signals for the developed D-dot and B-dot sensors. The results of DC cavity discharge measured by the constructed testbed and the EM field sensors demonstrate close agreement with the reference PD pulses measured via oscilloscope.

Carbon fiber composites are paving the way for light weight, high strength structures in the aerospace industry. While the benefits of carbon fiber composites are undeniable, they also have their drawbacks. Crippling damage due to lightning strikes is one of them. The current solutions to reducing the damage due to lightning includes adding expensive and heavy copper mesh into the laminate. A potential solution to this problem would be to add a lightweight conductive additive to the epoxy resin instead of a copper mesh. Carbon nanotubes are chosen as the additive to create an electrically conductive resin matrix and hence increase the overall electrical conductivity of the composite. Increasing the conductivity will decrease the damage owing to a faster dissipation of lightning-strike-induced Joule heating, and more importantly increase the residual strength. In this work, we quantified the increase in conductivity through measuring the electrical resistance using the four-probe method. Results showed that the electrical resistance of the sample with carbon nanotube additives is 31% lower than the one with no additives when the same resin system is used. In addition, lightning strike tests have also been carried out with both samples using an artificially generated waveform A impulse current with a peak of 100 kA. The current results showed no visible damage to both the samples with and without CNT additives in the epoxy. Time-resolved camera images taken for the lightning strike tests showed that

In recent years, demand response programs have attracted attentions for reducing network peak. Demand Response (DR) is the variation of energy consumption by customers in response to incentives, aiming to reduce consumption at peak hours. In general, DR methods might be based on price or incentive; this paper studies Interruptible/Curtailable (I/C) Demand Response Program. In this paper, the effect of changes in incentives and penalties on the implementation of I/C service on the microgrid is studied considering different uncertainties. The microgrid studied in this paper can exchange power with the upstream network. Effect of implementing I/C service in different modes on operation cost, customer profit, load factor, and peak reduction is evaluated in this paper. To prove the effectiveness of the presented method, this model is implemented on an 11-bus microgrid in a 24-hour period, and the results are investigated.

– Due to the increasing need of electrical energy and environmental issues corresponding to fossil fuels such as global warming, renewable energy sources attracted a lot of engineers and researchers to themselves. Among renewable energy sources, wind energy as the most accessible energy source, has been among the most popular research topics in recent years. Doubly-Fed Induction Generator (DFIG) is a commonly used configuration for variable speed Wind Energy Conversion Systems (WECSs) because of its independent control of active and reactive powers and extensive range of wind speed variations. In this paper, a Pulse Width Modulation (PWM) rectifier and a Z-Source Inverter (ZSI) are used as Grid Side Converter (GSC) and Rotor Side Converter (RSC), respectively. Z-Source Inverter is a newly proposed power electronic converter which has solved the limitations and disadvantages of conventional voltage source and current source inverters. A modified Space Vector Modulation (SVM) technic based on Sliding Mode generator power control is used to control the switching pattern of the ZSI. To verify the effectiveness of the proposed control system, simulations result in MATLAB/Simulink software are presented. Different wind speeds as well as independent control of active and reactive powers are examined through these simulations.

This study aims to classify and compare AC and DC partial discharge (PD) based on PD pulse waveform analysis. To achieve this goal, we designed a testbed that enables precise measurements of individual PD pulses. The testbed is used for collecting data from four different types of PDs including cavity, surface, corona, and floating potential discharges generated by individual PD source samples. All samples were examined under AC, positive DC, and negative DC electrical stresses, through which we captured thousands of PD pulses. We classify the waveforms of each PD type into representative groups associated to their discharge mechanisms. The statistical data of the measured pulses are utilized to identify the differences between AC and DC PDs while the clustered patterns of PD amplitude versus their temporal characteristics serve as a means to classify the types of PDs under AC and DC electrical stresses.

Lightning strike damage tolerance of carbon fiber reinforced polymer (CFRP) composites is prone to misinterpretation. This study demonstrates that the design of lightning strike testbeds can be a major cause of the misinterpretation. The risk of misinterpretation originates from the lack of standards clearly defining testbed design requirements including electrode size and ground electrode edge configuration. Here we report the impact of electrode size and ground electrode edge configuration on the damage characteristics of CFRP matrix composite laminates caused by simulated lightning strikes. The results suggest that the level of damage is influenced by discharge current amplitude, discharge diameter, and the existence of electrical insulation covering ground electrode edges. Specifically, the damage increases with increasing discharge current amplitude and decreasing discharge diameter. Most importantly, we report that electrically insulating the edges of ground electrode prevents lightning discharge current from bypassing CFRP matrix composite laminate samples and directly striking the ground electrode. Experiments conducted without electrically insulating the edges resulted in considerably lower sample damages than those resulted from experiments conducted with the electrically insulated ground electrode edges. Our findings suggest that electrode size and ground electrode edge configuration have significant influence on the results of lightning strike experiments.

Today, with the movement of power systems towards competition and breaking the monopoly, the importance of ancillary services like reactive power and voltage control has increased. One of the most important services is power reactive service. Independent System Operator (ISO)has to provide reactive power in deregulated environments which are considered one of the six ancillary services of power system which should be provided by the ISO to improve system security. ISO is responsible to provide reactive power in deregulated environments. Purpose of this paper is to present a method for pricing reactive power. In this method, reactive power pricing is performed based on Financial Transmission Rights (FTRs). The novelty of this study is that it has offered a new method for pricing reactive power based on FTR. Reactive power pricing methods presented so far have not considered congestion costs of the transmission system but this method considers congestions costs also through considering FTR. In this paper, results of this method are evaluated on a standard IEEE-30 bus test system and compared with current pricing method used for pricing reactive power in Iran.

Due to their complicated dynamics coupled with kinematics and non-holonomic underactuated behavior, spherical robots cannot unveil their full maneuverability when linear controllers are applied. Because of that, position and trajectory tracking of spherical robots have been the main challenges recently tackled in the literature. In this paper, two controllers are introduced to provide the effective path following of a 2-DOF spherical robot. A sliding mode controller (SMC) and a fuzzy sliding mode controller (FSMC) are designed and compared. The Lyapunov stability theorem is employed to analyze the stability of the controller and the tracking error. The simulation results indicate that the spherical robot controlled by the proposed methods is capable of moving to a desired point from any given initial point with minimum tracking error.

In this paper a controller is designed for voltage source converters (VSC) using Nyquist array. Real systems existing in industry are nonlinear systems with multiple inputs and multiple outputs (MIMO). Such systems are always affected by different undesired factors like noise and distortion. But multivariable control design for linear systems is based on theories which are robust against noise, disturbances and uncertainties. DC and AC part of VSC are affected with disturbances which should be controlled. Thus, a Nyquist array is applied to VSC to study design and analysis of multivariable control based on the presented theories. The proposed controller is illustrated by simulation.

This paper deals with a reliable control technique to control wind generator. The wind generator’s structure is categorized as a complicated nonlinear system. The accurate scheme of this system cannot be obtained, so the model has high uncertainty and nonlinearity. So, controlling of this system becomes more attractive for scholars; however, many of approaches were given for regulating of wind generators explore these kind of systems in a normal weather situations. In practice several generators operate in an unpleasant weather condition. For having a realistic controller, is assumed that there are uncertainties in the model, for this purpose wind generator is recommended in the cold climate, also with the ice on generators blades. A promising controller is modeled, in order to control the pitch angel of wind. Finally, simulation outcomes will be provided to confirm the presented control approach.

Optimal microgrid operation is one of the most important challenges for microgrid operators. Decreasing the operation cost while the problem constraints are fulfilled is the aim of operators in this challenge. The demand response program in presence of uncertainties in different components of the microgrid is also attracted a lot of attention in recent years. In this paper, the impact of running Direct Load Control (DLC) program and different positions of installing storage units on microgrid are investigated. The microgrid is connected to the up-grid and DLC demand response program (DLC-DRP) is modeled based on price elasticity and customers benefit as well as finding the proper location of installing storage units (batteries) by considering various factors, is the objective of this paper. GAMS optimization software and Mixed Integer Non-Linear Programming (MINLP) technic have been deployed to achieve this goal. To verify the performance of the proposed method, the results of running DLC-DRP on an 11-bus microgrid in 24 hours period has been analyzed.

In this paper, simultaneous employment of electrical vehicle-to-grid (V2G) and wind power generation in security constrained unit commitment (SCUC) problem are considered. SCUC problem as one of the most highlighted research area in electrical power system provides a commitment scheduling table for the generation units in which generation operator aims to maximize system security as well as to minimize generation costs along with the satisfying system and units constraints. The technology of V2G as a new energy resource absorbed remarkable consideration, recently. V2G reduces the dependence of generation procedure to the small and costly thermal units and subsequently has tremendously impact on diminishing operation costs as well as ameliorate of load vacillations management. Besides the V2G, utilization of renewable energies like wind-based generation gained considerable attention in last decade. In this paper, simultaneous employment of V2G and wind power in scheduling and operation of power systems considering the uncertainty of wind generation is presented. Numerical results of independent use of V2G and simultaneous utilization of V2G and wind-based generation are provided and effects of such the obligations on the reduction of generation costs and enhancement of operation indexes and penetration of wind farms in power systems are investigated.