M. Izzeddine

A new frequency domain arc furnace model for iterative harmonic analysis

This paper presents a new frequency domain arc furnace model for iterative harmonic analysis by means of a Newton method. Powerful analytical expressions for harmonic currents and their derivatives are obtained under balanced conditions of the power system. The model offers a three-phase configuration where there is no path for homopolar currents. Moreover, it contemplates continuous and discontinuous evolution of the arc current. The solution obtained is validated by means of time domain simulations. Finally, the model was integrated in a harmonic power flow where studies have been performed in a network with more than 700 busbars and 7 actual arc furnace loads.

A contribution for modeling controlled and uncontrolled AC/DC converters in harmonic power flows

The main object of this paper is to present a sequential method of adjusting the operating point of power converters within the framework of harmonic power flows. To do this, a unified formulation of previous work in the frequency domain has been developed, resulting in a set of compact and powerful analytical expressions for AC and DC magnitudes. Special attention has been paid to uncontrolled rectifiers. The proposed sequential method offers a more flexible and modular framework where AC and/or DC magnitudes can be used for defining the operating point. Moreover, it provides better convergence properties for iterative harmonic analysis (IHA). Newtons method or Gausss method can be applied for IHA without special considerations. Finally, the solution obtained has been verified by means of time domain simulation and measurements.

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.

A contribution for modeling static VAr compensators in iterative harmonic analysis

Static VAr compensator (SVC) with thyristor-controlled reactors (TCR) are used to control the voltage at bus SVC, while the nonlinear harmonic source is connected to the TCR busbar. This specific situation requires special treatment of the voltage control characteristic in the iterative harmonic analysis (IHA). A voltage control characteristic reduced to the TCR busbar is proposed. Under this condition, the operating point of the TCR in the IHA is treated in a way so the firing angle is adjusted to satisfy the voltage regulation characteristic. In this paper, a frequency domain TCR model is presented by means of a set of analytical expressions for harmonic currents and their sensitivities with respect to the harmonic voltages. An additional nonlinear equation is also derived for obtaining the firing angle under distorted voltage. A scheme of checking coherent operating points of TCR is also included for IHA.

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.

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.

A contribution for three-phase power flows using the current injection method

This paper presents a formulation of the load flow solution based on the current injection method using the Newton-Raphson algorithm. The current injection equations are written in rectangular coordinates and in terms of symmetrical components. Special attention is given to obtain great flexibility in representing different PQ loads and shunt elements. A new formulation of PV machines provides a more homogeneous structure of the Jacobian matrix. Moreover, with this PV machine representation, only the bus voltages are to be treated as unknowns and the discrimination between PQ and PV buses is not necessary.

Comparison of voltage sags prediction methods in power networks

This work aims to make a comparative analysis between two of the most used techniques for estimating voltage sags, the method of fault positions versus the Monte Carlo sampling technique. For the generation of voltage sags events, a short-circuit simulator is implemented with four stochastic input variables: fault rate, fault impedance, fault type, and location.

A novel educational proposal: Devising an electric power system

The study of electric power systems within the field of Electrical Engineering is usually approached by computer simulation because any actual test is quite complex to be implemented, especially with renewable energies. Having the aim to improve student learning about this topic, a new subject called “Devising an Electric Power System” was organized following a CDIO (Conceive-Design-Implement-Operate) approach. The subject is programmed for one academic year and based entirely on laboratory work. The students are divided into three teams. Every team would have to work on a power system that includes a solar PV generator and a pumping controlled drive, both connected to a three-phase grid. The third and last part of the subject is focused on “electric utility” business strategy. In the final day of the course a competition between the three teams takes place.

ANÁLISIS DEL EFECTO DE PROTECCIÓN SECUNDARIA EN HUECOS DE TENSIÓN

La influencia de la proteccion secundaria o de respaldo para la estimacion de los huecos de tension gravedad en sistemas de potencia se evalua mediante el uso combinado de la tecnica de Monte Carlo y el indice SARFI curva, teniendo en cuenta las referencias de compatibilidad mas utilizados como: ITIC, IEC 61000-4-11 y SEMI-F47. La generacion de los registros de los huecos de tension se desarrolla a traves de un simulador de corto circuito que involucra a cinco variables estocasticas: (i) la tasa de fallos, (ii) impedancia de falta, (iii) tipo de fallo, (iv) la ubicacion, y (v) solucion de la averia tiempo, evaluada en una simulacion virtual de monitoreo a largo plazo a traves del metodo de muestreo Monte Carlo. Ademas, los resultados del indice SARFI curva se estudian conjuntamente en tres redes electricas, dos redes IEEE prueba (24 y 118 barras colectoras) y la red nacional de energia de Ecuador (357 barras).