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Uncertainties in microgrid topology, protection system, and communication links involve accidental variables that affect the protection coordination of a microgrid. To resolve this issue, a method is proposed that uses a decision tree after each fault to ensure a robust protection coordination. The decision tree creates an optimal composition of strategies, such that for each unsuccessful strategy,...
Power systems are usually subjected to some changes in connections during operation, which leads to varied short-circuit levels in different parts of them and Directional Overcurrent Relays (DOCRs) may be subjected to miscoordination by changing short circuit levels. Therefore, all network topologies should be considered for coordination among overcurrent relays in a power system. Reduction of operating...
In addition to the advantages of distributed generation (DG) sources, also it would have disadvantages such as harmonic distortions generation and changing in short-circuit current. Harmonic distortion generation may exceed from permissible harmonic level and cause problem. Furthermore, the change in short-circuit current can cause performance of incorrect in the over-current relays. In first, this...
A new approach based on a ground penetrating radar is proposed to detect and locate a metallic object hidden in a lossy ground. In this approach, the object is illuminated by a dipole antenna and the resultant scattered electric field is monitored at a distance above the ground. The detection and locating of the object are based on the simulation results obtained using a full-wave solution of the...
A modeling technique is presented to efficiently evaluate field penetration through small apertures within a metallic cubic enclosure. The technique utilizes the moment method solution to calculate current distribution on enclosure surface area and the modal expansion technique to find field distribution over the slot aperture. In this way, one can obtain the equivalent magnetic current along the...
The effect of cellular phone handset dimensions on radiation patterns, impedance and resonance frequency is investigated. The handset body is modeled by an appropriate three-dimensional wire-grid structure with a 2/4 monopole antenna as its radiating source. The governing electric field integral equation (EFIE) is solved in the time domain, using the method of moments (MoM). The validity of the model...
The paper adopts a comprehensive modeling technique to investigate the effect of frequency-dependent characteristics of grounding system in a grid-connected photovoltaic (PV) system on the overvoltages caused by lightning strikes on the nearby overhead line. In this technique, the frequency response of grounding system is determined using an electromagnetic approach based on the method-of-moments...
We propose a method for optimal placement and sizing of distributed generation (DG) sources in an existing distribution network. The method, which uses the genetic algorithm, provides improved network parameters (i.e., voltage profile, power losses, and short circuit levels) while keeping the existing coordination of protection devices unchanged. An important feature of the proposed method is the...
An efficient technique is proposed to incorporate the frequency-dependent characteristic of wind turbine grounding system in ElectroMagnetic Transient Program (EMTP) for lightning transient studies. In this technique, first, the frequency response of grounding system is determined using an electromagnetic approach based on the method-of-moments solutions of the governing Maxwell's equations. To avoid...
In this paper a time-domain (TD) method-of moments (TD-MoM) technique is applied to evaluate the transient penetrated electric field through a rectangular aperture in a perfect electric conductor (PEC) rectangular enclosure. Solution technique is the marching-on-in-degree (MOD) method that calculates the unknown surface electric currents on the enclosure surface. Since the structure is resonant, mathematical...
In this paper a time-domain (TD) method-of moments (TD-MoM) technique is applied to evaluate the transient penetrated fields through a rectangular aperture in a perfect electric conductor (PEC) plate. The incident wave is assumed to be a Gaussian plane wave. Here, by using weighted Laguerre polynomials, as entire-domain temporal basis functions, the MoM based technique is modified to a technique called...
In this Paper, shielding effectiveness of an enclosure is analyzed by an efficient hybrid finite difference frequency domain (FDFD) and method of Moments (MoM) technique. The enclosure is loaded with a realistic microstrip transmission line (MTL). The susceptibility of the load is also studied to show the effect of external interference plane wave. In our proposed FDFD solution, lumped elements are...
Currently most of the electrical and electronic equipments use switching mode power supplies (SMPS) as their input power source. SMPS increase power - volume ratio using high switching frequencies which it cause producing sever radiated and conducted electromagnetic interference (EMI) in the environment. Therefore, SMPS must satisfy the requirements of electromagnetic compatibility (EMC) standards...
The transient scattering of a thin wire buried in a half-space is calculated by a novel Time-Domain Mixed Potential Integral Equation (TD-MPIE), using complex-time Green's functions. The TD-MPIE is solved by MoM in time domain along with a Marching-On-in-Time (MOT) procedure. The excitation is a Gaussian plane wave and Band-Limited Second-Order Lagrange (BL-2L) functions are used as Temporal Basis...
The transient response of a dipole above a lossy ground is calculated with a new formulation of the Method of Moments (MoM) in time domain, based on a novel representation of the Time-Domain Mixed Potential Integral Equation (TD-MPIE), using complex-time Green's functions. The TD-MPIE is solved by MoM in time domain along with a Marching-On-in-Time (MOT) procedure. Quadratic B-spline (QB) functions...
This paper presents the effects of a small satellite structure on the characteristics of Quadrifilar Helical Antennas (QHAs). The antenna is first analyzed in free space in order to achieve the desired radiation pattern using Method of Moment (MoM). Two antennas are then simulated in the presence of the satellite structure for two different distances from the satellite surface. It is shown that performance...
This paper proposes a modeling technique that predicts the output signal of an open-ended rectangular waveguide probe when scanning a long crack. The technique is based on a circuit approximation model and hence remarkably reduces the computation burden. In this model, the waveguide probe is replaced with a transmission line, the crack is replaced with a shorted transmission line, and the interface...
A sub-domain method of moment formulation is proposed to model the problem of an open-ended coaxial probe radiating into a conducting metal with a surface-breaking crack. As opposed to the conventional model, the proposed formulation is capable of treating effectively the unknown magnetic current over the arbitrary shaped common aperture. This feature will remarkably improve the computation time,...
This study presents a robust and efficient approach for derivation of non-symmetrical closed-form Green's functions for microstrip structures. In this method, the discrete complex image technique is used to extract the closed-form expressions for stratified Green's functions. The surface-wave poles in these expressions are first extracted using a recursive contour integration method. The remainder...
In this paper, a new robust numerical technique is presented to solve the Time Domain Electric Field Integral Equation (TD-EFIE) via a time domain Method of Moments (TD-MoM) for infinite conducting cylinders in free space illuminated by a TM-polarized Gaussian plane wave. Both of the temporal and spatial basis functions are rectangular. By employing Galerkin's method in spatial domain and point matching...
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