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Accurate transient stability assessment (TSA) and effective preventive control are important for the stable operation of power systems. With the superiorities in precision and efficiency, data-driven methods are widely used in TSA nowadays. Data-driven TSA model can be adopted in the stability constraint of preventive control optimization, but existing methods are mostly iteration-based methods, which may result in low efficiency, sometimes even non-convergence. In this paper, an analytical representation method of data-driven transient stability constraint is proposed based on a nonparametric regression model built for TSA. Key feature extraction and dominant sample selection are proposed to reduce the scale of the TSA model, and bi-level linearization is applied to further modify it. Optimal preventive control model is then formulated as a Mixed-integer Linear Program (MILP) problem with the linearized analytical data-driven transient stability constraint, which can be solved without iterations. An overall procedure of data-driven TSA and preventive control is finally developed. Case studies show that the proposed method has high accuracy in TSA and can achieve effective preventive control of power system with high efficiency.

Fluorides and their CO $$_{2}$$ mixtures are considered as promising choices of SF $$_{6}$$ -substitute gases due to their low global warming potentials and high dielectric strength. This paper investigates physical and chemical properties and breakdown characteristics of different common fluorides and their mixtures for application in the power system. For dielectric characteristics of fluorides and their mixtures, their power frequency breakdown voltages are determined experimentally, and the results are compared with SF $$_{6}$$ . For physical and chemical characteristics, the saturated vapor pressures, global warming potentials (GWPs), toxicities, prices of fluorides and their mixtures are calculated, and the corresponding characteristic curves are obtained. Based on characteristics mentioned above, a method for obtaining the optimal gas parameters of a specific fluoride mixture is proposed, which can be used as a feasible solution to find an SF $$_{6}$$ alternative gas that meets the application requirements. The results show that CO $$_{2}$$ mixtures with hexafluoropropene (HFP), 1,1,1,2-tetrafluoroethane (HFC-134a) and perfluoroisobutyronitrile (C4-PFN) are three types of good SF $$_{6}$$ -substitute gases. HFP/CO $$_{2}$$ mixtures with HFP component ratios 0.32 to 0.6 are suitable for applications at 0.1 to 0.3 MPa. HFC-134a/CO $$_{2}$$ mixtures (HFC-134a component ratios from 0.16 to 0.2) are suitable for applications at 0.3 to 0.5 MPa. C4-PFN/CO $$_{2}$$ mixtures (C4-PFN component ratios from 0.09 to 0.12) could be used for the applications at 0.1 to 0.5 MPa, regardless of the gas price.

Aircraft stealth by avoiding radar detection relies on shape and materials, but these are ineffective in attenuating electromagnetic (EM) waves in the ultrahigh frequency (UHF) band. This article investigates broadband EM wave attenuation in dielectric-barrier discharge (DBD) plasmas. We used a simplified collisional-radiative model to determine the electron density distribution using 2-D emission spectra and found that the gas pressure has a great effect on electron density. An empirical relationship between the gas pressure and electron density is given. We introduce a parameter optimizing method for multilayer plasmas that combines the attenuation characteristics of EM waves in plasma. We also establish an ideal multilayer plasma model to calculate the EM wave attenuation in the UHF band. The results show that multilayer plasmas can effectively enlarge the effective attenuating frequency range of EM waves and also attenuate UHF EM waves. On the basis of the calculation results, we propose a single-layer plasma generator. A large-area and homogenous plasma under medium-to-high gas pressure can also be created by discharge with argon or a mixture of argon and helium.

Environmental friendly fluorinated compounds and their mixtures with CO 2 are considered as a typical category of SF 6 -substitute gases, due to their low global warming potentials and good dielectric strength. This paper investigates the breakdown characteristics and physical and chemical properties of HFC-134a (1,1,1,2,3,3,3-Heptafluor-opropane) and its mixtures theoretically and experimentally, which are compared with those of SF 6 . The results show that the HFC-134a mixtures with CO 2 are suitable for the power application with pressure 0.1 MPa, such as medium voltage power equipment. Espeically for the power application with 0.3MPa, the HFC-134a/CO 2 mixtures with the same pressure or a higher pressure could have equivalent insulation as SF 6 , whose GWPs are almost one twenty-third that of SF 6 . For the power application with 0.5 MPa, the HFC-134a/CO 2 mixtures with the liquefaction temperature -15°C and pressure 0.6 MPa could have equivalent insulation as SF 6 .

In order to formulate a reasonable scheduling plan of virtual power plant (VPP), a prediction method of photovoltaic (PV) output based on K-means and improved BP neural network is proposed. Firstly, the structure of virtual plant for peak regulation is introduced. Then, the historical data of PV is clustered by K-means to distinguish different weather conditions. To improve the prediction accuracy, genetic algorithm (GA) is used to improve the BP neural network. Finally, a short-term prediction model based on improved BP neural network is established in Matlab. The simulation results show that using clustered photovoltaic data and improved BP neural network to predict the output of PV on similar days has a higher prediction accuracy.

In recent years, the rapid development of wind power generation and the low load growth rate have brought challenges to the peak regulation of power grid in Northeast China. In order to solve the peak regulation problem, virtual power plant (VPP) is proposed to participate in the peak regulation auxiliary service market in Northeast china, especially for deep peak regulation. Firstly, two modes of peak regulation in Northeast China are introduced in this paper, which are thermal power unit and VPP. With the definition of the peak regulation capacity for VPP, the Optimal Scheduling Model of VPP participating in peak regulation ancillary service is established. The simulations are carried out in MATLAB. The results show that the economy of peak regulation is significantly improved in peak regulation auxiliary service based on VPP.

This paper investigates the spatially characteristics of an atmospheric-pressure surface dielectric barrier discharge plasma by optical emission spectroscopic diagnostics. With the increase of distance from the upper electrode, both N2 vibrational temperature and electron density are greatly elevated and in the ranges of 0.15~0.4eV and 0.5~4×1012cm-3, respectively. The dependence of the electron temperature on distance from upper electrode appears non-monotonic, and the electron temperature is in the range of 1.7~3eV.

Sulfur hexafluoride (SF6), the widely used insulation medium, is a strong greenhouse gas. The SF6/N2 mixture is expected to be an alternative gas and has been used in power equipments due to the low liquefaction temperature and environmental impact. In this paper, SF6/N2 gas mixture breakdown characteristics are studied with a lifting metal particle in the gap. The distorted field distribution is calculated by finite element method (FEM). The critical electrical fields for both the static breakdown and breakdown in the particle motion are obtained from the streamer criterion. The results show that the critical distance for the breakdown in motion decreases with increasing SF6 gas fraction and pressure, and it appears a saturation with high SF6 gas fraction and pressure.

With a large number of DFIG wind turbines connected to the power grid, in order to improve the frequency fluctuation caused by its decoupling, this paper first analyses the current situation of DFIG wind turbines participating in the primary frequency modulation of power grid, and establishes the corresponding model based on the above analysis. According to the commonly used inertial control methods, a frequency modulation method for auxiliary power grid of DFIG wind turbines based on improved frequency control strategy is proposed. Through the simulation of actual power grid model, the grid frequency fluctuation has been effectively alleviated after adding frequency control link to DFIG wind turbines, and it is concluded that the higher the wind power penetration, the more significant the frequency improvement effect.

The presence of metal particles in power equipment may cause gas discharges and threaten insulation reliability. The discharge phenomenon in the presence of particles involves complex physical processes. To describe these processes, a numerical method is proposed to analyze the relationship between the motion of the particle and the discharge at the same time. First, processes including the generation of the first electron, the formation of a streamer corona, the transition from the streamer to the leader, and the leader propagation are considered. Voltage–time characteristics are calculated with particles of different shapes. Then, the characteristics of the particle motion driven by the Coulomb force are analyzed. Finally, the threshold field for partial discharge and the breakdown in the presence of the particle are discussed taking into account the voltage–time characteristics and the analysis of the particle motion mentioned above. The results demonstrate that there is a threshold field when breakdown occurs in the presence of a long and narrow particle at the negative electrode before the particle leaves the electrode.

The perfluoronitriles and its mixtures have great dielectric strength and are environmentally friendly, which are considered as a typical class of alternative gases. This paper investigates the frequency breakdown characteristics of C4-PFN/CO2 mixtures in the nonuniform electric field. The influences of the electric field distribution, pressure and the C4-PFN component ratio on the dielectric strength of C4-PFN/CO2 mixtures are studied, which is compared with the cases for SF6 under the same conditions. It is shown that the sensitivity of C4-PFN/CO2 mixtures to the nonuniform electric field increases with the increase of the C4-PFN component ratio. For C4-PFN/CO2 mixtures containing more than 5% C4-PFN, the sensitivity is much greater than that of SF6.

CF3I-N2 mixtures have garnered much attention as potential SF6-substitutes due to their excellent dielectric strengths, and the dielectric strength of SF6-N2 mixtures has a good synergy effect. This paper attempts to propose an approach of adding a small amount of SF6 to improve the dielectric strength of the CF3I-N2 mixture, by making an all-around consideration of dielectric strength, impact on the environment and the limitations of engineering pressure and the lowest ambient temperature. The influences of adding different amounts of SF6 on the electron energy distribution function, the reduced ionization, attachment and effective ionization coefficients, the critical reduced electric field strength and critical electron temperature of ternary SF6-CF3I-N2 mixtures are investigated by Boltzmann analysis. Then the relations of the critical electric fiend strength, mixed ratio and saturated vapor pressure of the ternary SF6-CF3I-N2 mixture are built and analyzed. The results demonstrate that an effective improvement of its dielectric strength can be obtained by adding a small amount of SF6 into the CF3I-N2 mixture, and that a proper choice of the mixed ratio and the gas pressure of the ternary SF6-CF3I-N2 mixture can provide a comparable dielectric strength to pure SF6.

Stealth technology plays an important role in modern military conflicts, and because of its many practical advantages, plasma stealth technology has gained a lot of attention. In this paper, we describe our study of the reflection and absorption characteristics of waves propagating in multilayer plasma slabs. Our results show that positive effects on the attenuation can be obtained by optimizing the plasma parameters and by increasing the number of plasma layers. We also found that multilayer plasma slabs can effectively widen absorption bands, especially for low frequency bands.

The dielectric breakdown properties of CO2-O2 mixtures at different O2 concentrations and gas pressures were studied in this paper, with electron detachments from negative ions taken into consideration. The influences of the electron detachment on the reduced effective ionization coefficients αeff/N, the critical reduced electric fields (E/N)cr, the critical electron temperature Tcr, the breakdown reduced electric fields (E/N)breakdown, and the breakdown electron temperature Tbreakdown were analyzed for the CO2–O2 mixture. Based on the results, it was found that an enhancement in αeff/N and a decrease in (E/N)cr and Tcr were caused by the electron detachment, which appeared to be more significant at relatively low E/N and low gas pressures. With the increase in the pd product, both (E/N)breakdown and Tbreakdown in the CO2–O2 mixture decreased first and then tended to be a constant at relatively high pd products.