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A high impedance fault (HIF) normally occurs when an overhead power line physically breaks and falls to the ground. Such faults are difficult to detect because they often draw small currents which cannot be detected by conventional overcurrent protection. Furthermore, an electric arc accompanies HIFs, resulting in fire hazard, damage to electrical devices, and risk with human life. This paper presents an analytical model to analyze the interaction between the electric arc associated to HIFs and a transmission line. A joint analytical solution to the wave equation for a transmission line and a nonlinear equation for the arc model is presented. The analytical model is validated by means of comparisons between measured and calculated results. Several cases of study are presented which support the foundation and accuracy of the proposed model.

A high-impedance fault is generated when an overhead power line physically breaks and falls to the ground. Such faults are difficult to detect and locate in electric power systems because of the small currents and voltage drops involved, which cannot be detected by conventional protection. Furthermore, arcing accompanies highimpedance faults, resulting in fire hazard, damage to electrical equipment, and risk to human life. This article presents an analytical description of the interaction between the electric arc associated with high-impedance faults and a transmission line. A joint analytical solution to the wave equation for a transmission line and a non-linear equation of the arc model is found for the case of an arbitrary reflection coefficient at the substation end, and a methodology for high-impedance fault detection and localization is proposed. The developed model is validated by means of a comparison with measurements. The comparison demonstrates the accuracy and effectiveness of the proposed model.

One of the most critical issues in the evaluation of power systems is the identification of critical buses. For this purpose, this paper proposes a new methodology that evaluates the substitution of the power flow technique by the geodesic vulnerability index to identify critical nodes in power grids. Both methods are applied comparatively to demonstrate the scope of the proposed approach. The applicability of the methodology is illustrated using the IEEE 118-bus test system as a case study. To identify the critical components, a node is initially disconnected, and the performance of the resulting topology is evaluated in the face of simulations for multiple cascading faults. Cascading events are simulated by randomly removing assets on a system that continually changes its structure with the elimination of each component. Thus, the classification of the critical nodes is determined by evaluating the resulting performance of 118 different topologies and calculating the damage area for each of the disintegration curves of cascading failures. In summary, the feasibility and suitability of complex network theory are justified to identify critical nodes in power systems.

This paper presents a new PWM strategy for the control of active and reactive power flow, applied to a threephase power inverter connected to a microgrid. Power quality and reactive compensation are essential in the integration of renewable energy sources in small grids (stand-alone mode or connected to the utility grid). The control algorithm of the gridconnected system is applied for voltage control. This technique provides independent control of the active and reactive power flow in the utility grid while maintaining constant the DC-link voltage. As a novelty, a Generalized Discontinuous PWM technique is implemented in the control algorithm of the gridconnected converter. Losses in the converter are reduced while the efficiency of the equipment is increased. As a technological innovation, in addition to the power flow control technique, a modular multilevel converter (MMC) is introduced. The main purpose of the system is to improve voltage unbalance and harmonic compensation in stand-alone grids. Some advantages of the model developed here include the cellular concept, easy thermal design, increased system efficiency and improvement in the system expansion capacity. The simulation model has been developed and tested using MATLAB/Simulink software.