A fault in a power system generates economic losses, security problems, social problems and can even take human lives. Therefore, it is necessary to have an efficient fault location strategy to reduce the exposure tim...
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A fault in a power system generates economic losses, security problems, social problems and can even take human lives. Therefore, it is necessary to have an efficient fault location strategy to reduce the exposure time and recurrence of the fault. This paper presents an impedance-based method to estimate the fault location in transmission lines. The mathematical formulation considers the distributed parameters transmission line model for the estimation of the fault distance, and it is obtained by the application of Gauss-Newton method. Said method considers available voltage and current measurements at both terminals of the transmission line as well as the line parameters. Moreover, the method can be used for locating high and low impedance faults. Additionally, it is proposed an adjustable HIF model to validate its performance, which allows to generate synthetic high impedance faults by setting specific features of a HIF from simple input parameters. The error in fault location accuracy is under 0.1% for more than 90% of the performance test cases. The easy implementation of this method and encouraging test results indicate its potential for real-life applications.
This paper presents a high frequency phase variable model of electric machines obtained using finite element (FE) analysis. The model consists of the low frequency phase variable model in parallel with a high frequenc...
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This paper presents a high frequency phase variable model of electric machines obtained using finite element (FE) analysis. The model consists of the low frequency phase variable model in parallel with a high frequency winding branch. The resistance and inductance of individual winding turns are calculated by magnetodynamic FE analysis while capacitance is calculated by electrostatic FE analysis. With the obtained parameters, a distributed model was formed based on the winding arrangement. The order of the distributed winding model is reduced using the Kron reduction technique to form the lumped parameter high frequency winding branch. A Permanent Magnet synchronous motor (PMSM) with its operating inverter is used as an example. The developed model is then used to evaluate the motor-inverter interaction. The results show the ability of the developed model to represent the motor's high frequency behavior under different operating conditions.
Field approaches are employed to develop a mathematical model of a power network section. The facility consists of two electric power subsystems described with ordinary differential equations and presented as concentr...
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Field approaches are employed to develop a mathematical model of a power network section. The facility consists of two electric power subsystems described with ordinary differential equations and presented as concentrated parameter systems connected with a three-phase power supply line, presented as a distributed parameter system. The model of the electric power line is described with partial differential equations. Mathematically, the supply line model is described utilizing a mixed problem with explicitly indefinite boundary conditions. All electromagnetic state equations of the integrated system are introduced in their matrix-vector forms. The equation of the three-phase long supply line is expressed untraditionally as a system of two first-order differential equations as a function of long line voltage. Since the power supply line is part of the integrated system that includes two subsystems, the boundary conditions at the line's start and end are implicitly defined, avoiding the traditional application of the Dirichlet first-type boundary condition. An expanded system of ordinary differential equations that describe physical processes in both the supply and loading subsystems is used to calculate the boundary conditions. To this end, third-type boundary conditions, or Poincare's conditions, serve to describe the wave equation of the electric power line. Such an integrated model of an electric power system helps analyse transient processes across the supply line when the electric power system is switched on and is single-phase short-circuited at the final point of the electric power line. A comparison of computer simulation results with well-known software packages shows a convergence of approx. 96%.
The nonlinear tunneling of the optical similaritons through both dispersion and nonlinear barriers in a noncentrosymmetric waveguide exhibiting second- and third-order nonlinearity is studied. Within the framework of ...
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The nonlinear tunneling of the optical similaritons through both dispersion and nonlinear barriers in a noncentrosymmetric waveguide exhibiting second- and third-order nonlinearity is studied. Within the framework of an inhomogeneous quadratic-cubic nonlinear Schr & ouml;dinger equation with distributed group velocity dispersion, reciprocal of the group velocity, quadratic-cubic nonlinearity, and gain or loss, we demonstrate the existence of a rich variety of exact similariton solutions in the shape of bright, kink, anti-kink, W-shaped, and gray solutions. The results show that these self-similar waves involve certain control parameters in their amplitude, phase, width, and shift of the inverse group velocity, which enables us to control their evolution dynamics in the waveguide system through a suitable choice of these parameters. It is found that the parameter of reciprocal of the group velocity decides the phase shift and group velocity of these self-similar waves. Also, the stability of the solutions is discussed numerically. Results of this paper are helpful for enriching the similariton theory and understanding the dynamics of self-similar waves in systems with quadratic-cubic nonlinearities.
In this study, simulation and test results for lightning impulse voltage distribution in a dry-type transformer were compared for three different winding methods by using round, flat, and strip conductors. Distributio...
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In this study, simulation and test results for lightning impulse voltage distribution in a dry-type transformer were compared for three different winding methods by using round, flat, and strip conductors. Distribution of the voltage inside the transformer windings at high frequencies had a different behavior than that of at low frequencies. The transformer had non-linear voltage distributions at high frequencies due to the inner capacitance and inductance of its windings. The ladder network model was used for the analysis of high frequency signals for voltage distribution. The parameters of the model were calculated analytically and numerically using a finite element analysis (FEA) software. The analytical solution method of a matrix obtained from the ladder network model was presented. Finally, simulation and test results were given and compared.
Electrical treeing is one of the main causes of crosslinked polyethylene (XLPE) cable failure. The current methods for locating electrical trees are mainly based on the partial discharge (PD) signal. However, PD signa...
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Electrical treeing is one of the main causes of crosslinked polyethylene (XLPE) cable failure. The current methods for locating electrical trees are mainly based on the partial discharge (PD) signal. However, PD signals are easily attenuated in the long cable and the PD test voltage may cause damage to the insulation. This work proposes an improved broadband impedance spectrum (BIS) method to locate electrical trees in XLPE cable. A mathematical model of a long cable containing local electrical tree degradation is established. The Gaussian signal is chosen as the simulated incident signal to reduce the spectral leakage. The location spectrum is obtained by multiplying the frequency domain function of the single-ended reflection coefficient and the Gaussian pulse. It has been found that the location spectrum of the local capacitance change can be characterized as a typical double-peak waveform and the spectrum of the local conductance change can be regarded as a typical single-peak waveform. Electrical tree experiments at different temperatures were carried out to initiate different types of electrical trees. A vector network analyzer (VNA) was used to test the high frequency capacitance characteristics in the treeing process. The location spectra of the 20 m long cable containing different types of electrical trees was calculated by the improved location algorithm. The results show that the location error of local electrical tree degradation is less than 3%. The capacitance of the sliced sample decreases with treeing time. The effect of the bush-pine tree on capacitance parameters is greater than that of the branch-pine tree. A typical double-peak is found in the bush-pine tree location spectrum and a single-peak is found in the branch-pine tree spectrum.
A fault on the DC side of a flexible HVDC system, along with the rise in short-circuit current, develops rapidly. With the gradual expansion of flexible HVDC technology to large capacities and long-distance transmissi...
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A fault on the DC side of a flexible HVDC system, along with the rise in short-circuit current, develops rapidly. With the gradual expansion of flexible HVDC technology to large capacities and long-distance transmission and offshore transmission scenarios, the problem of short-circuit current calculation considering the characteristics of line distribution parameters needs urgent attention. Therefore, in order to solve the problem of the inaccurate calculation of the short-circuit current on the DC side, the lumped parameter model is used in a flexible DC system for long-distance transmission. This study analyzes the transmission line structure on the basis of the general model of the MMC short-circuit current calculation on the DC side and establishes a mathematical model of a long-distance transmission line considering the characteristics of distributed parameters. Two impedance equivalent models for different length lines are proposed to facilitate the analytical calculation of the short-circuit current. A short-circuit current calculation method for a flexible HVDC system with long-distance transmission lines is proposed. Additionally, the correctness of the proposed method is verified through the comparison of the simulation values and calculation values. The results show that the error of the lumped parameter calculation is about 10%, and the error of the distributed parameter calculation is less than 2%.
It is considered a mechanical system composed of a string in cantilever having a pointwise damping. The discontinuous B(oundary) V(alue) P(roblem) is split in two coupled BVPs. Introducing the Riemann invariants and t...
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It is considered a mechanical system composed of a string in cantilever having a pointwise damping. The discontinuous B(oundary) V(alue) P(roblem) is split in two coupled BVPs. Introducing the Riemann invariants and taking into account their invariance along the characteristics, a system of continuous time difference equations with two delays is associated to the coupled BVPs and a one-to-one correspondence between the solutions of the two mathematical objects is proven. Then a theorem on exponential stability for the difference system is obtained. The stability depends on the arithmetic properties of the delay ratio. The aforementioned one-to-one correspondence is then used to establish exponential stability of the classical solutions of the coupled BVPs. Some conclusions and a sketch of open and future research subjects end the paper.
The study is aimed at the optimal control design of longitudinal motions for a rectilinear elastic rod with free ends. Several piezoelectric actuators are attached along its axis. The control is carried out by piezoel...
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The study is aimed at the optimal control design of longitudinal motions for a rectilinear elastic rod with free ends. Several piezoelectric actuators are attached along its axis. The control is carried out by piezoelectric normal force acting in the cross section. We assume that this force changes piecewise constantly in space, and the intervals of constancy have no gaps and are equal in length. Given an arbitrary initial state and periodic terminal conditions, the optimal control problem is to minimize the mean mechanical energy stored in the rod over a fixed time horizon. For a uniform rod, the minimal admissible horizon is found, and the exact optimal control law is presented.
The paper presents the control problem for a hyperredundant arm, a tentacle model. The difficulties determined by the complexity of the nonlinear integral differential equations are avoided by using a very basic energ...
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The paper presents the control problem for a hyperredundant arm, a tentacle model. The difficulties determined by the complexity of the nonlinear integral differential equations are avoided by using a very basic energy relationship of the system. A PD control laws are discussed. Numerical simulations for spatial and planar tentacle models are presented.
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