Hermann W. Dommel

A multiphase harmonic load flow solution technique

The operation of nonlinear devices under unbalanced load conditions may cause harmonic problems in power systems. A computer-based multiphase harmonic load flow solution technique for analyzing such problems is described. The harmonic load flows are obtained from iterations between the Norton equivalent circuits of the nonlinear elements and the linear network solutions at harmonic frequencies. Harmonics generated by static VAr compensators with thyristor-controlled reactors under unbalanced load conditions are used to illustrate the method. >

Matrix Representation of Three-Phase N-Winding Transformers for Steady-State and Transient Studies

Detailed transformer representations are needed in the analysis of electromagnetic transients and in the analysis of unbalanced steady-state conditions. This paper describes the derivation of mdels for three- phase and single-phase N-winding transformers in the form of branch impedance or admittance matrices, which can be calculated from available test data of positive and zero sequence short-circuit and excitation tests. The models can be used for many types of studies as long as the frequencies are low enough so that capacitances in the transformer can be ignored. The inclusion of saturation effects is briefly discussed.

Harmonics from Transformer Saturation

Saturation effects in transformers and shunt reactors can produce harmonics in power systems. Their magnitude can sometimes be found with an electromagnetic transients program, by going from an approximate linear ac steady-state solution directly into a transient simulation in which the nonlinear effects are included. In lightly damped systems, such simulations can take a long time, however, before the distorted steady state is reached. Therefore, another method was developed which uses superposition of steady-state phasor solutions at the fundamental frequency and at the most important harmonic frequencies, with nonlinear inductances represented as harmonic current sources. This method can either be used by itself, or as an improved initialization procedure for electromagnetic transients programs.

Guidelines for Modeling Power Electronics in Electric Power Engineering Applications

This paper presents a summary of guidelines for modeling power electronics in various power engineering applications. This document is designed for use by power engineers who need to simulate power electronic devices and sub-systems with digital computer programs. The guideline emphasizes the basic issues that are critical for successfully modeling power electronics devices and the interface between power electronics and the utility or industrial system. The modeling considerations addressed in this guideline are generic for all power electronics modeling independent of the computational tool. However, for the purposes of illustration, the simulation examples presented are based on the EMTP or EMTP type of programs. The procedures used to implement power electronics models in these examples are valuable for using other digital simulation tools.

Direct phase-domain modelling of frequency-dependent overhead transmission lines

A new wideband transmission line model, based on synthesizing the line functions directly in the phase domain, is presented. It includes the complete frequency-dependent nature of untransposed overhead transmission lines by means of recursive convolutions over a wide frequency range. The model belongs to the class of time-domain models and is designed to be implemented in general electromagnetic transients programs such as the EMTP. Because the synthesis of the frequency-dependent modal transformation matrix is avoided, the method requires fewer convolutions at each time step than full frequency-dependent modal-domain models. Simulations have been performed comparing the proposed model with existing line models, with field recordings, and with calculations from a frequency-domain program. The new model provides accurate answers in both steady-state and transient conditions.

Modelling of adjustable speed drives for power system harmonic analysis

A three-phase equivalent circuit model is developed to model adjustable speed drives (ASD) for power system harmonic analysis. The validity and accuracy of the model were verified by comparing simulation results with lab test results. Sensitivity studies are then conducted to determine the key factors affecting the harmonic characteristics of ASDs. Guidelines on modelling ASDs for harmonic distortion assessment are developed based on the results.

Re-examination of Synchronous Machine Modeling Techniques for Electromagnetic Transient Simulations

This paper re-examines the three synchronous machine modeling techniques used for electromagnetic transient simulations, namely, the qd model, phase-domain model, and voltage-behind-reactance model. Contrary to the claims made in several recent publications, these models are all equivalent in the continuous-time domain, as their corresponding differential equations can be algebraically derived from each other. Computer studies of a single-machine infinite-bus system demonstrate that all of these models can be used for unsymmetrical operation of power systems. The conversion of machine parameters is also discussed and is shown to have some impact on simulation accuracy, which is acceptable for most cases. When the models are discretized and interfaced with an EMTP-type network solution, the voltage-behind-reactance model is shown to be the most accurate due to its advanced structure.

Power system restoration — a bibliographical survey

Abstract In recent years, there has been an increasing number of major power system blackouts worldwide. As a consequence, interest in the investigation and development of new methods, tools, and models for power system restoration has grown considerably. This paper provides a bibliographical survey of the current state in research, development, and applications in power system restoration. The survey is subdivided into nine different sections, each section representing those subjects which are considered to be most relevant to that area. For each section a summary and an overview of relevant publications are given.

Overhead Line Parameters From Handbook Formulas And Computer Programs

Overhead line parameters can be calculated from handbook formulas, or with more general computer-oriented methods. At power frequency, the differences between the two approaches are usually negligible, but they can become large at higher frequencies. This paper discusses the causes of these differences for the engineer who wants to compare results from computer programs with those obtained from handbook formulas. It contains no new theories, but simply summarizes the experience gained in analyzing such differences over many years.

Methods of Interfacing Rotating Machine Models in Transient Simulation Programs

The electromagnetic transient programs (EMTP-like tools) are based on the nodal (or modified nodal) equations that enable an efficient numerical solution and, subsequently, fast time-domain simulations. The state-variable-based simulation programs, such as Simulink, are also used for studying the dynamics of electrical systems. Both the offline and real-time versions of these two types of simulation tools are widely used by the researchers and engineers in industry and academia to study the transient phenomena and dynamics in power systems with rotating electrical machines. This paper provides a summary of the interfacing techniques that are utilized to integrate the general-purpose models of electrical machines with the rest of the power system network for these studies. The interfacing methods are broadly classified as indirect and direct approaches. The paper also describes the numerical properties as well as limitations imposed by the interfacing of the commonly used machine models that should be considered when selecting the simulation parameters and assessing the final results.