D. Van Dommelen

Usefulness of DC power flow for active power flow analysis

In recent days almost every study concerning the analyses of power systems for market related purposes uses DC power flow. DC power flow is a simplification of a full power flow looking only at active power flows. Aspects as voltage support and reactive power management are not considered. However, such simplifications cannot always be justified and might sometimes be unrealistic. In this paper authors analyze the assumptions of DC power flow, and make an attempt at quantifying these using indexes. Among other, the paper answers the question of how low the X/R ratio of line parameters can be, and what is the maximal deviation from the perfect flat voltage which still allows DC power flow to be acceptably accurate.

Analysing time-varying power system harmonics using wavelet transform

This paper presents the possibilities offered by the dyadic-orthonormal wavelet transform used in the multiresolution analysis of voltage- and current-signals. This transform proves to have some advantages over the classical FFT-based algorithms, when used in electric power quality assessment and the analysis of waveforms. Practical examples using waveforms generated by energy saving lighting equipment, remote-control signals and an adjustable speed drive, are presented.

Experimental and numerical analysis of fast transient phenomena in distribution transformers

Transformers can be damaged by transient overvoltages causing internal resonances in the windings. The study of these oscillations implies a total system approach, including transformer, distribution network, circuit breaker, etc. In this paper, the results of experimental investigations and numerical analysis are presented, explaining the possible occurrence of internal winding resonances. The experimental part consists of laboratory experiments and on-site measurements in a substation. The numerical analysis is carried out using a preprocessing programme that translates the geometrical transformer data into a duality-based model for use in ATP. This approach can be used to investigate different system designs.

The registration of harmonic power by analog and digital power meters

This paper discusses the measurement error of energy meters operating under harmonic distortion. A system to determine the magnitude of the error caused by an individual harmonic is used to generate curves on which the error introduced by different frequency components is displayed. An algorithm using these data to predict the resulting measurement error of a linearly operating energy meter registering under circumstances of any known harmonics in the voltage and the current is presented.

Bifurcation analysis of three-phase ferroresonant oscillations in ungrounded power systems

The study of power networks prone to ferroresonant oscillations by means of simulation turns out to be a tedious task. Therefore, a direct calculation of the stability domains of the various oscillation modes is preferable. In this paper, the software package AUTO is used to determine the periodic solutions of the differential equations describing a typical three-phase network in which ferroresonance has occurred. A small modification of the system equations is introduced to approximate the quasi-periodic oscillations by periodic ones, without major impact on the position of the stability domains. Finally, an example of the automated dimensioning of a damping circuit using a continuation scheme is presented.

Influences of large penetration of distributed generation on N-1 safety operation

The incentive to operate less polluting energy sources and the electricity liberalization has opened opportunities for the increasing penetration of distributed generation (DG) in the power system. Due to the locally available resources and small scale, DG units are mostly connected at the distribution level. This does not only have impact on the distribution system operation, but on the transmission system as well. In this study, the impact of DG on N-1 safety (contingency) of the transmission system is studied in detail with different DG technologies at given penetration levels.

Penetration level of distributed energy resources with anti-islanding criteria and secure operation of power system

Many recent blackouts might raise a concern on how the introduction of distributed energy resources or distributed generation (DG) into the network influences its secure operation in terms of dynamic performance. The anti-islanding criteria of DG may harm the secure operation of the power system. In this paper, the maximum penetration level of DG is determined using a dynamic study. Tested systems are used to study. The results show that the protection settings have an influence the maximum penetration of DG and the system secure operation

Simulation of losses in LV cables due to nonlinear loads

Companies active in distribution or transmission of electrical energy know the power losses in their HV and MV cables. Users have no idea of the magnitude of the cable power losses in their electrical installations. Nevertheless cable power losses can be a significant part (3%-5%) of the total power consumption. Nonlinear loads (ASD, CLF, IT-equipment,...) are often installed with the aim of rational energy use. However, one is not aware of the increase of cable losses due to the nonlinear load. A software tool is developed in order to enable companies to simulate the supply system losses of their present or future electrical installation in an easy way, including the use of both active or passive filter systems. In this paper the power losses in LV cables are analyzed, including the impact of nonlinear loads. A simple model is proposed in order to calculate power losses in a quick way. The model uses an equivalent resistance, taking into account frequency dependency by means of a correction factor only dependent on the conductor cross section and not on the current harmonic spectrum. The model is validated by experiments. Deviations less than 5% are found. Because of the suitability of the model for a wide range of harmonic spectra, power losses can be easily calculated with sufficient accuracy without the knowledge of the current harmonic spectrum. The paper also includes a sensitivity analysis of parameters influencing cable losses and some practical recommendations to reduce cable losses.

Comparison of transmission tariff methods in a free market for electricity

One of the outstanding issues in the liberalisation of the electricity market is the way in which transmission costs are translated into tariffs. The transport grid is seen as a natural monopoly, and thus the transmission tariffs should be regulated. Ideally, the tariff structure should lead to economic efficiency, it should enable the grid owner to cover his costs, and it should be nondiscriminatory and transparent. The present study compares three basic alternative methods of transmission pricing-postage stamp, distance related and nodal-in the light of these requirements, and presents a tariff proposal for Belgium. Special attention is paid to cross-border transmission.

A postage stamp transmission tariff with marginal loss based incentive

Transmission tariffs are an essential element in creating a competitive market for electricity. They should provide incentives leading to an optimal use of the limited transmission capacity, something which is not at all the case with the postage stamp tariff as it is used in all European countries at the moment. The authors propose a modified postage stamp transmission tariff. Consumers and generators are charged for the impact they have on grid losses and congestion, through a weighted marginal loss tariff component. The applicability of this tariff is tested for the Belgian grid. The sensitivity of the results to load, transit and generator unit commitment is studied. The results also allow studying the appropriateness of projected sites for new generation and load, and help in identifying weaknesses in the grid.