Propagation of electromagnetic lightning transients modeling in the electrical network is not an easy task because of the large dimensions of its various equipment (length of power lines and ground ...wires, height of towers…). The full wave numerical methods well known in modeling, generally based on the mesh of the electromagnetic device to construct a system of equations, can prove to be cumbersome or even inapplicable to treat this problem. To study the lightning direct impact on a towers cascade equipped with its lines and earth connections, this article presents a realistic approach based on the transmission line equations. This new modeling, developed directly in the frequency domain, allows taking into account the frequency variations of the ground electrical characteristics in order to analyze properly the grounding systems transient behavior, particularly the Ground Power Rise during a back-flashover.
In a wind farm, the grounding circuit is a complex electrical system made up of several interconnected groundings. Its role is very important for the protection of the electrical equipment during a ...direct lightning strike. To contribute to the optimization of the conception of this complex grounding system in his real configuration (wind turbine towers, grounding grids, and several hundred meters of buried conductor wires …), we propose in this paper a realistic modeling. Realistic because, to model in all rigors using an electromagnetic field formalism a problem of propagation of electromagnetic transients in electrical device of large geometrical dimensions where the main environment (soil) is not homogeneous does not bring an appreciable advantage and consumes a very high calculation time. Also, the ideal for the engineer is to have a model that is easy to understand, accessible in its theory and obviously preserving the accuracy of the results and with very low computation time. In this work, to study the lightning surges in a wind farm, mainly to know the Ground Potential Rise and the distribution of the currents in the conductors, we use a modeling based on the transmission line equations. Our modeling is carried out by considering the effect of the frequency on the electrical characteristics (resistivity and dielectric permittivity) of the soil; the results we obtain are without loss of precision and with a very short calculation time.
•This paper presents a new modeling for analyzing transient grounding system behavior during a direct lightning strike.•The modeling that we propose makes it possible to treat even a complex ...grounding circuit like that encountered in wind farms where we have several interconnected groundings.•This modeling developed directly in the time domain considers the effect of frequency and ground ionization.•The modeling that we propose uses the transmission line equations with frequency dependence, the vector fitting technique and the Finite Difference Time Domain numerical method.•The modeling that we propose makes it possible to overcome the numerical disadvantages that may be encountered when implementing a full-wave electromagnetic formalism when the structure studied has large geometric dimensions, inhomogeneous and has open boundaries.
This paper presents a new model for analyzing transient grounding system behavior during a direct lightning strike. The modeling that we propose allows us to consider a simple grounding conductor buried horizontally or vertically, a grounding grid, wind turbine grounding system and grounding circuits for wind farms while including the aerial parts (towers and blades). This modeling is developed directly in the time domain taking into account the frequency dependence of the impedance and admittance of the wired conductors and of the electrical parameters of the soil (ρ, ε) and also considering the ionization of the soil. This formalism is based on transmission line equations, rational approximation by vector fitting and the Finite Difference Time Domain numerical method. The proposed formalism is verified considering both simulations and experimental results from available published researches. The Ground Potential Rise GPR in the grounding circuits of wind farms are discussed during the first stroke and also during the subsequent stroke whose frequency range generates more propagation of electrical waves along conductors. This formalism makes it possible to contribute to all knowledge/research of grounding systems.
Among several palmprint recognition methods proposed recently, coding-based approaches using multi-spectral palmprint images are attractive owing to their high recognition rates. Aiming to further ...improve the performance of these approaches, this paper presents a novel multi-spectral palmprint recognition approach based on oriented multiscale log-Gabor filters. The proposed method aims to enhance the recognition performances by proposing novel solutions at three stages of the recognition process. Inspired by the bitwise competitive coding, the feature extraction employs a multi-resolution log-Gabor filtering where the final feature map is composed of the winning codes of the lowest filters’ bank response. The matching process employs a bitwise Hamming distance and Kullback–Leibler divergence as novel metrics to enable an efficient capture of the intra- and inter-similarities between palmprint feature maps. Finally, the decision stage is carried pout using a fusion of the scores generated from different spectral bands to reduce overlapping. In addition, a fusion of the feature maps through two proposed novel feature fusion techniques to allow us to eliminate the inherent redundancy of the features of neighboring spectral bands is also proposed. The experimental results obtained using the multi-spectral palmprint database MS-PolyU have shown that the proposed method achieves high accuracy in mono-spectral and multi-spectral recognition performances for both verification and identification modes; and also outperforms the state-of-the-art methods.
A new approach is adopted in this paper for modeling the transient magnetic field, radiated by buried grid underlightning strokes. This approach summarizes each of threemethods: analytical formula, ...based on electrical dipole theory for determining radiated magnetic field in infinite conductive medium, modified images theory for taking into account the interface in the half space, and transmission line approach for determining the longitudinal and leakage currents. The model can be used to predict the transient characteristic of grounding systems because, it can calculate magnetic field in any points of interest, it is sufficiently accurate, time efficient, and easy to apply.
Induced Disturbance in Power Network by Lightning Kaouche, Senaa; Nekhoul, Bachir; Kerroum, Kamel ...
Journal of Communications Software and Systems,
03/2007, Letnik:
3, Številka:
1
Journal Article, Paper
Odprti dostop
In this work the transient analysis of a power network excited by indirect lightning is performed directly in time domain. Using the FDTD, we calculate induced currents and voltages in each node for ...a three-phase power network. The topological analysis of the network where each element (power line and lumped charge) is considered, allows deducing the matrix equation. In this electrical network matrix, power lines are represented by line equations, junctions and extremities nodes by Kirchhoff laws. The electromagnetic field emitted by lightning is represented in the second member of this matrix equation. The frequency dependence of the line parameters istaken in account while using time domain convolution.
Randomised pulse width modulation (RPWM) technique has become a viable alternative to deterministic pulse width modulation (DPWM). By spreading the power spectrum in a continuous noise, this new ...technique better complies with electromagnetic compatibility (EMC) requirements for conducted electromagnetic interferences (EMI) and allows reducing the emitted acoustic noise in variable speed drives (VSDs). The most popular RPWM schemes are randomised pulse position modulation (RPPM) and randomised carrier frequency modulation (RCFM). The combination (RCFM-RPPM) or dual RPWM (DRPWM) has also been proposed. In this article, we propose an optimised DRPWM (ODRPWM) for the three-phase inverter. First, the modulating principle is proposed, and then, a mathematical model of power spectral density (PSD) of the output voltage is developed and validated for the three schemes, namely RPPM, RCFM and RCFM-RPPM. PSD analysis shows that the proposed scheme is more effective on spreading PSD. Moreover, this analysis reveals optimal parameters of randomisation for a maximum spread of the PSD. The optimisation problem is then modelled and solved using two powerful non-linear methods.
The paper deals with transient analysis of grounding grids using two different approaches, wire antenna theory and modified transmission line model. The Pocklington integro-differential equations, in ...frequency domain, arising from the wire antenna theory are numerically handled via the Galerkin–Bubnov variant of indirect Boundary Element Method (GB-IBEM), while the transient response was obtained using inverse Fourier transform. The modified transmission line equations are treated using the finite difference time domain (FDTD) method. Some illustrative numerical results are presented and discussed in the paper.
The effect of one or two shield wires placed at the top of line, on induced currents and voltages generated by lightning on the horizontal and vertical configurations of both single circuit and ...double circuit transmission lines, for perfect ground, has been studied using the Transmission Line "TL" theory. In this paper, the lightning effect is included by two current sources located at the line terminations. The examples presented in this paper show that the presence of the shield wires reduces the overvoltage induced on the line which is related to several parameters.
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