Araceli Hernandez

An analytical approach for stochastic assessment of balanced and unbalanced voltage sags in large systems

In this paper, voltage sags produced by balanced and unbalanced short circuits are analyzed by means of a new analytical method. The main feature of this approach is that contrary to the fault positions method, it does not require a preassignation of discrete fault positions along the lines. The developed algorithm has been applied to the 24-buses IEEE Reliability Test System (RTS) and to a real transmission system to illustrate its application. Results are analyzed and compared with the fault positions method. The mathematical formulation of the proposed approach is straightforward and different fault distributions along the lines can be effortlessly considered. The proposed method is adequate for the analysis of any size networks.

A new frequency domain approach for flicker evaluation of arc furnaces

In this paper, flicker magnitudes of rapidly varying loads are evaluated by means of a new frequency domain method. Analytical expressions of the instantaneous flicker sensation are obtained in terms of interharmonic voltages. The dynamic response of flicker magnitudes of such loads can be clearly described with this analysis, as well as the individual contribution of each interharmonic to the flicker sensation. The proposed method, applied to the voltages of DC and AC arc furnaces, provides very satisfactory results that have been validated with measurements performed with the standardized IEC flickermeter.

A Method for Voltage Sag State Estimation in Power Systems

This paper presents a new technique for voltage sag state estimation. The proposed method is based on estimating the number of voltage sags occurring at nonmonitored buses from the number of sags recorded at a limited number of monitored buses. This problem, contrary to the traditional state estimation where redundant measurements are available, is formulated as an underdetermined system of equations. In this paper, linear integer programming techniques are employed to solve this estimation problem. The performance of the proposed method is tested by means of several case studies applied in the IEEE 24-bus reliability test system (RTS) and in the IEEE 118-bus test system.

An Approach Based on Analytical Expressions for Optimal Location of Voltage Sags Monitors

This paper addresses the problem of identifying the optimal location for voltage sags monitors. The proposed approach is based on using a monitor reach matrix obtained from the solution of analytical expressions which are valid for any location of faults in the power system. This method provides the optimal number of monitoring devices and the best positions to place them in order to guarantee the observability of the whole system considering any type of fault (balanced or unbalanced). That is, the location of monitors obtained by means of the proposed algorithm ensures that any event leading to a voltage sag is captured by, at least, one voltage sag monitor. Several examples are provided showing the performance of the proposed formulation compared to other approaches.

A method based on interharmonics for flicker propagation applied to arc furnaces

In this paper, propagation in the network of flicker produced by rapidly varying loads is analyzed by means of a new frequency domain method. By this method, the flicker level can be determined at any bus of the network when one or several loads operate simultaneously. Flicker summation effect is considered and the results obtained are compared with the summation laws proposed by IEC. The propagation algorithm has been applied to the 14-buses IEEE network and to the Spanish transmission system. The method has been validated with measurements performed with the standardized IEC flickermeter.

A unified theory of uncontrolled rectifiers, discharge lamps and arc furnaces. I. An analytical approach for normalized harmonic emission calculations

Under certain assumptions, similar models can be applied for rectifiers and devices with electric arc characteristic. The analysis considers single and three-phase uncontrolled rectifiers with continuous and discontinuous evolution of the AC current. It leads to four possible situations which fit with the harmonic behaviour of discharge lamps, arc furnaces and rectifiers with capacitive DC smoothing. A very useful set of compact and powerful analytical expressions for different magnitudes as well as for the harmonics currents are derived. It offers a direct method of selecting different operating points with their corresponding harmonic emissions. Normalized diagrams and tables of these magnitudes are depicted in a friendly way. Over these diagrams, harmonic emission limits of standard IEC 1000-3-2 and IEC 1000-3-4 are specified for Class C and Class D single-phase equipment and for three-phase equipment. Passive solutions applied to the aforementioned rectifiers to comply IEC 1000-3-2 and 1000-3-4 are obtained in a direct and normalized way.

SVD Applied to Voltage Sag State Estimation

The method presented in this paper addresses the problem of voltage sag state estimation. The problem consists in estimating the voltage sags frequency at nonmonitored buses from the number of sags measured at monitored sites. Usually, due to limitations on the number of available voltage sag monitors, this is an underdetermined problem. In this approach, the mathematical formulation presented is based on the fault positions concept and is solved by means of the singular value decomposition technique. The proposed estimation method has been validated by using the IEEE 118 test system and the results obtained have been very satisfactory.

Neural Networks Applied to Solve the Voltage Sag State Estimation Problem: An Approach Based on the Fault Positions Concept

In this paper, the application of neural networks is proposed to solve the problem of voltage sags state estimation. This problem is based on estimating the voltage sags occurrence frequency at non monitored buses from the recorded voltage sags occurrence frequency at a limited number of monitored buses. The fault position method is used to formulate the optimization problem. The methodology is implemented by using Neural Networks routines from the Matlab® Neural Network ToolboxTM. Several case studies are showed in the IEEE-24 bus Reliability Test System (RTS).

Arc furnace characterization from an off-line analysis of measurements

The object of this paper is to present an exhaustive analysis of power quality measurements performed in an arc furnace. Main disturbances produced by the arc furnace are taken into account in accordance with IEC recommendations. In this way, the typical magnitudes of power quality analysis are evaluated using a statistical treatment. Other magnitudes such as different power components and power factors are also calculated in order to provide a scheme by which the disturbances of the arc furnaces can be characterized.

Iterative harmonic analysis of line side commutated converters used in high speed trains

This paper presents a model, in the frequency domain, of line commutated rectifiers used in traction applications. The model is described by means of powerful analytical expressions that take into account the operating point of such devices as single phase loads connected to three phase power systems. Special attention is paid to define the operating point in terms of power and DC current. The harmonic emission of each locomotive is represented by a harmonic current source coherent with the selected operating point. Several locomotives acting simultaneously at the same busbar are also considered. This model requires iterative harmonic analysis in order to obtain the final harmonic injections. Harmonic load flow calculations have been performed using this model in the IEEE 14 bus test system.