Jacinto Martin-Arnedo

Voltage sag stochastic prediction using an electromagnetic transients program

This paper presents a summary of the work performed by the authors on voltage sag analysis using a time-domain tool. The document describes a procedure for stochastic prediction of voltage sags based on the Monte Carlo method. A medium size distribution network is used to analyze the advantages of this approach, the convergence of the Monte Carlo method, the influence of protective devices and the importance of voltage sag indices. The limitations of the present version and the future work are also discussed.

Impact of distributed generation on distribution protection and power quality

The impact of distributed generation (DG) on voltage sags in a distribution network depends on the design of the protection system and the coordination between the different protective devices. DG changes the radial nature of distribution systems and affects the performance of the protection system. This paper summarizes the impact of conventional synchronous machine-based DG on the present protection practices for distribution systems, analyzes the effect of small generation units on voltage sags, and discusses the different alternatives for distribution and DG intertie protection design.

Voltage sag studies in distribution Networks-part I: system modeling

This paper is the first part of a work aimed at predicting the voltage sag performance of distribution networks using digital simulation and an EMTP-like tool. The paper discusses modeling guidelines for representing power distribution components in voltage sag simulations and details the approaches selected in this work. Different models for representing some components can be used to obtain voltage sag characteristics with similar accuracy. Test results are included to illustrate the performance of the developed models and support the selection of different modeling approaches.

Voltage sag studies in distribution networks - part II: voltage sag assessment

This paper is the second part of a joint paper aimed at predicting the voltage sag performance of distribution networks by estimating voltage sag indices. This part explores the characteristics of voltage sags caused by faults in a distribution network considering the effect of the protective devices installed in the network. The work is based on a Monte Carlo procedure implemented in a time-domain simulation tool. Several scenarios with a different coordination between protective devices have been analyzed. As expected, the main conclusions are that the protection system can have a significant influence on voltage sag characteristics and proper coordination between protective devices can reduce voltage sag impact on end-user equipment.

Voltage sag studies in distribution Networks-part III: Voltage sag index calculation

Power quality indices have been developed to assess the performance of a single site or an entire system. They can guide utilities to improve their systems and can be used by manufacturers to decide about equipment immunity. This paper is the third part of a joint paper aimed at predicting the voltage sag performance of distribution networks by estimating voltage sag indices. Two types of indices are analyzed in the present paper, they give, respectively, the average number of events and the average interruption duration of each kilovolt ampere served at the low-voltage level over the assessment period. Their values are obtained from a stochastic prediction using a time-domain simulation tool. The methodology used to obtain these indices and the analysis of the influence of the protective devices are the main contributions of this paper. The limitations of the present work are also discussed.

Expanding capabilities of EMTP-like tools: from analysis to design

EMTP-like tools are widely used for simulation of transients in power systems. The implementation of several features in some of these tools has significantly expanded their applications. Some of them can be now used to perform sensitivity analysis, select power components, or introduce modifications in a power system during a simulation. This letter describes the new features. Although the document is based on the ATP version, the concepts can be also applied to other tools of the family. A very simple example is included to illustrate the scope of new applications.

Voltage sag analysis using an Electromagnetic Transients Program

EMTP-type tools are widely used in power quality studies. This paper presents a summary of the work performed by the authors to adapt and apply the ATP version to voltage sag analysis. The document includes an introduction to the capabilities of this tool, a short description of the new modules developed for voltage sag analysis (stochastic prediction and index calculation), and some illustrative examples showing the advantages of the new ATP modules.

Load modeling for voltage sag studies

This paper investigates the influence of load modeling on voltage sag characteristics and compares the results of voltage sag calculation with different load models. It is shown that some voltage sag characteristics are strongly influenced by the models chosen for representing power system loads. Therefore, depending on the aims of the voltage sag study, load models need to be carefully chosen.

Distribution load flow calculations using time driven and probabilistic approaches

Distributed resources (i.e., distributed generation and energy storage) and some special loads (e.g., electrical vehicle) raise new challenges for load flow calculations in distribution systems. Intermittent and non-dispatchable generation units, complex time-dependent or asymmetrical loads require capabilities that until very recently were not available in many distribution software packages; for instance, capabilities for probabilistic and time driven simulations. This paper presents the work made by the authors to adapt OpenDSS, a free available distribution simulator, to perform these types of studies. The paper includes several examples based on a modified IEEE test feeder and a discussion about the potentialities offered by other tools for preparing input data.

Development and testing of a distribution electronic power transformer model

Conventional transformers are typically heavy, bulky and expensive. Their size can be significantly reduced by increasing the frequency of operation which allows a higher utilization of the magnetic core. A model of a high-frequency distribution transformer using power electronics is presented in this paper. Its impact on a distribution system has been analyzed under different types of faults. Several simulations have been carried out in order to validate the power quality control function of the transformer. The results show that the new transformer exhibits a very good performance, matching not only the functions of a conventional power transformer, but also providing additional capabilities to mitigate dynamic power quality problems.