K. J. Sagastabeitia

New Method for Detecting Low Current Faults in Electrical Distribution Systems

In electrical distribution systems, low current faults may be caused by a high impedance fault or by the fault current limitation caused by the neutral to ground connection. In the former case, an indirect contact or insulation degradation give a high value of the fault impedance. In the latter, the neutral grounding may be either isolated or compensated. Nevertheless, these types of faults do not produce enough current so that the traditional overcurrent relays or fuses are not able to detect the fault. This paper presents a new methodology, based on the superposition of voltage signals of certain frequency, for the detection of low current single phase faults in radial distribution systems. The simulation analysis and laboratory tests carried out have proved the validity of the methodology for any type of grounding method.

Simulation by MATLAB/Simulink of active filters for reducing THD created by industrial systems

Nowadays, power electronics are widely used in industry for supplying loads with amplitude and frequency controlled voltage. These systems comprise mainly rectifiers and inverters, which, as non-linear loads, produce currents with high harmonic content. In order to fulfill the legislation concerning voltage harmonic distortion it is necessary to put in place corrective actions. Among these corrective actions active filters are one of the most effective. For the design of these filters simulation has been proved to be a very useful tool. In this paper, the simulation by MATLAB/Simulink of an active filter for the reduction of the harmonic distortion is analysed. Two examples are presented: a steel plant and an underground traction system.

Phase Asymmetry: A New Parameter for Detecting Single-Phase Earth Faults in Compensated MV Networks

Traditionally, the detection of high-resistance earth faults has been a difficult task in compensated medium-voltage (MV) distribution networks, mainly due to its very low-current fault. To date, several techniques have been proposed to detect them: using current injection in the neutral, superposing voltage signals, varying the value of the arc suppression coil, etc. These techniques use different detection parameters, such as fault resistance to earth, line asymmetries, or partial residual neutral voltages. In this paper, phase asymmetry is defined as a new parameter that can be used, together with the aforementioned techniques, in order to improve the reliability and efficiency of the detection process in single-phase earth faults, especially for compensated networks. The use of this parameter has been validated through extensive simulations of resistive faults up to 15 kΩ , with the use of RESFAL software, which is based on Matlab/Simulink.

Optimal Frequency Value to Detect Low Current Faults Superposing Voltage Tones

Single phase to ground low current faults (LCF) are difficult to be detected with common fault detection techniques. Therefore, several specific methodologies have been developed to identify LCF in an easier way. Among these methodologies, a method based on superposing voltage tones has been proposed. This method requires defining the frequency of the tones that have to be superimposed.

Overhead conductor monitoring system for the evaluation of the low sag behavior

The paper describes a monitoring system for the evaluation of the low sag behavior of the overhead conductors in operating lines. The monitoring system measures the conductor tension and temperature and it also measures the wind speed to evaluate the load in the conductor due to wind. This system includes a methodology for the analysis of the measured data and the comparison of these data with the theoretical values obtained by mechanical calculation.

Fault location system on double circuit two-terminal transmission lines based on ANNs

This paper presents a new approach to fault location in double-circuit two-terminal overhead transmission lines, using artificial neural networks (ANNs). The method presented enables the distance to be determined at which the fault occurs in a double-circuit two-terminal transmission line using the fundamental components of 50/60 Hz of the fault and pre-fault voltage and current magnitudes, measured in each phase of the reference end. The accuracy of the method has been checked using properly validated fault simulation software developed with MATLAB. This software allows generation of faults in any location of the line, to obtain the fault and pre-fault voltage and current values. With this value, the fault can be classified and the corresponding ANN activated in order to determine the fault distance.

Application of superimposed voltage in the detection of faults in resonant distribution systems

As a high percentage of the length of overhead lines corresponds to distribution lines, there is a strong probability that faults in overhead distribution lines will occur. When a fault occurs in a resonant grounded system, the short circuit current is below the threshold of the protection system. This means that the sensitivity of the protection system is not good enough to detect the fault and as a consequence the fault cannot be isolated. In this situation, the contact of a high voltage conductor with ground is a hazard to people. This is especially dangerous in the distribution lines as they are close to final customers. For this reason, it is fundamental to have at the power systems disposal devices that permit the detection of that type of faults. This work presents the definition of a new methodology for the detection of fault currents in resonant grounded systems based on superimposed voltage.

Factors that affect the sag-tension model of an overhead conductor

The sag-tension model of an overhead conductor in operation is analyzed. A monitoring system measures the conductor tension and temperature. With the measured data obtained in a pilot installation and considering the theoretical values obtained by calculation, the factors that affect the sag-tension model of an overhead conductor are analyzed.

Overhead line rating forecasting for the integration of wind power in electricity markets

Wind power has a significant impact on the operation of electricity markets in areas with high penetration of wind power. As the electricity market is planned some hours in advance, it is necessary to forecast the wind power. Besides, wind power forecasting techniques can be adapted for the overhead line rating forecasting. This can be useful for defining advanced strategies for grid operation and improve the wind power integration. This paper analyzes the similarities and differences between the wind power forecasting and the overhead line rating forecasting. Some overhead line rating forecasting experiences are described and the preliminary results of a pilot project are shown.