This paper proposes a comprehensive framework for defining operational classification criteria to evaluate the performance of electric power subtransmission systems. Based on the reliability indices estimated for a system taken as a reference and least squares regression analysis, an efficient way of classifying the adequacy of subtransmission networks is established. Using the proposed method, a judgmental scale for measuring the degree of severity index is obtained, which allows a quick check of the network’s operational performance, something that does not currently exist for subtransmission networks. The severity index is expressed in system minutes, i.e., the ratio between the expected unsupplied energy and the annual system peak load. The definition of an appropriate classification criterion represents an important support for decision making processes in the context of network planning and operation. Four real subtransmission systems, operated under a concession regulation by the same Brazilian public utility, are used to illustrate and analyze the use of the proposed method, and the obtained results are discussed.

Microgrids offer an innovative solution to modern energy challenges, providing enhanced reliability and resilience to distribution systems while accommodating the growing presence of distributed energy resources (DER). However, realizing the potential benefits of microgrids requires a comprehensive assessment of their complex technical and economic aspects. This paper introduces a dedicated techno-economic evaluation model for community microgrids (CMGs) while considering a consumer-centric internal market. Uncertainties arising from load variations and intermittent generation are addressed via Monte Carlo simulation (MCS). The proposed internal market model aligns with the Brazilian regulatory framework and enables currently unavailable innovations, such as a community internal market; however, the model can be adapted to the context of any system. We demonstrate the capabilities of the methodology by presenting a case study involving a real microgrid, where economic benefits are shared among all consumers. This study, derived from a research and development (R&D) project, underscores its practical relevance in advancing cleaner and more sustainable energy systems.

Assessing overvoltage due to lightning interactions with transmission lines is essential for the reliability of electric power systems. In this sense, the probability distribution of maximum lightning overvoltage is typically estimated considering the stochastic nature of lightning. This paper focuses on this problem by introducing a method offering reduced computational time and more flexibility. To do so, the proposed methodology effectively combines a modified version of the Unscented Transform method and probability density function reconstruction techniques based on Pearson and Johnson systems. Numerical results show that it estimates the probability density functions of maximum lightning overvoltage with considerable accuracy and reduced computational time. Also, they show that combining the Unscented Transform method and Pearson and Johnson systems is effective for reconstructing the probability density function of the maximum lightning overvoltage. As a result, the proposal emerges as a strong contender to replace the traditional methods in this context.

The lightning performance of transmission lines is a criterion of utmost importance to be evaluated in transmission system reliability. In order to accurately estimate the expected number of shutdowns, it is imperative to account for the stochastic nature of the lightning phenomenon. In this sense, the most widely used technique to estimate these shutdowns is the Monte Carlo method (MCM). Although the MCM is a trustful method, it has a huge drawback in terms of computational burden. Therefore, this paper proposes the use of an alternative statistical technique, the Unscented Transform method (UTM). This method achieves an approximate non-linear mapping by employing a set of points (associated with input statistical data), which are deterministically selected and weighted. The set of these points and weights is then used to estimate the lightning overvoltage across insulator strings, which represents a significant reduction in the number of samples evaluated in the process in relation to the application from MCM. In this paper, the MCM and UTM methods are applied and compared in the lightning overvoltage evaluation, which is carried out with the help of the Alternative Transient Program (ATP). From the studies conducted, it was found that the application of UTM in place of MCM allowed for significant computational gains while maintaining satisfactory levels of accuracy in the estimation of indicators.

The reliability evaluation of composite generation and transmission systems is a problem with high computational effort. The optimization of algorithms that carry out this assessment has historically been deeply studied, with emphasis on two approaches: (i) reducing the sample space necessary to represent the event of interest via variance reduction techniques (VRTs); and (ii) minimizing the computational effort of state adequacy analyses via machine learning classifiers. Although they have already been used together, no work has proposed using the knowledge produced by VRTs to improve the classifier performance. In this paper, a quasi -sequential Monte Carlo simulation is proposed, optimized by cross entropy and binary logistic regression techniques, in which the VRT output information is passed on to the classifier to improve the performance of the explanatory variables related to system failures. To validate the proposed method, several evaluations are carried out with a modified version of the IEEE RTS l996, with characteristics similar to those of modern interconnected systems.

The electric distribution sector is facing significant challenges in integrating distributed energy resources (DERs), with most assessment methodologies being primarily tested on standard feeders. However, given the nature of electric distribution systems, each feeder is unique and constantly changing, emphasizing the need for customized and updated feeder models for local quantitative studies. These studies encompass network operation, expansion planning, and DER integration. In response to this context, this paper proposes a methodology for extracting and processing information from public data to model up-to-date electric feeders. As these feeder models represent real operating circuits, they can be utilized by utilities, investors, and consumers. The proposed approach involves processing data from the Brazilian utilities’ geographic database (BDGD, in Portuguese) to develop structured simulations of distribution feeders using OpenDSS software. The BDGD standards are established by the Brazilian National Electric Energy Agency (ANEEL). In order to validate the methodology, two case studies are presented evaluating the impacts of distributed generation on real feeders from the Brazilian utilities: Minas Gerais Electric Power Company (CEMIG) and Bahia State Electricity Company (Neoenergia COELBA).

Electrical substations are susceptible to several electromagnetic surges. Short-period surges due to lightning strikes at or near the substation typically present fast transients. Thus, one concern in the studies investigating this stress is the definition of voltage used to ensure safety inside (and near) a substation under fast or very fast transient phenomena. This work deals with the electric field due to impulse currents injected in buried conductors and the difference between considering the traditional step voltage definition proposed by IEEE standards and a more rigorous definition (line integral of the total electric field, which corresponds to the vector sum of the conservative and non- conservative components). The current distribution and originated electric field are evaluated by using a well-established electromagnetic model. According to the results, significant differences can be found in the analyzed configurations for fast phenomena.

Microgrids have emerged as a popular solution for electric energy distribution due to their reliability, sustainability, and growing accessibility. However, their implementation can be challenging, particularly due to regulatory and market issues. Building smaller-scale microgrids, also known as nanogrids, can present additional challenges, such as high investment costs that need to be justified by local demands. To address these challenges, this work proposes an economic feasibility assessment model that is applied to a real nanogrid under construction in the Brazilian electrical system, with electric vehicle charging stations as its main load. The model, which takes into account uncertainties, evaluates the economic viability of constructing a nanogrid using economic indicators estimated by the Monte Carlo simulation method, with the system operation represented by the OpenDSS software. The model also considers aspects of energy transactions within the net-metering paradigm, with energy compensation between the nanogrid and the main distribution network, and investigates how incentives can impact the viability of these microgrids.

Abstract The still growing share of intermittent renewable sources in the electric energy matrix is a factor that greatly increases the complexity of modelling electrical power systems. Although its exploitation is conditioned to the geographic location where the natural resource emerges itself, when this location coincides with the grid‐edge of the system, close to the consumer, the composite reliability assessment is exposed to the combination of two problems: (i) representation of the intermittent energy availability of generators; and (ii) failure event rarity. To address the first problem, a fast Monte Carlo tool capable of representing chronological aspects can be used. For the second problem, an efficient variance reduction technique that adapts well to the composite problem of generation and transmission must be established. Therefore, a quasi‐sequential Monte Carlo simulation tool aided by importance sampling via the cross‐entropy method is proposed as an efficient and robust procedure for evaluating the composite reliability of systems with renewable participation at grid‐edge. The method is evaluated through a modified version of the IEEE Reliability Test System ‐ 1996, which presents renewable generation in consumer load buses and rarity in the composite failure.

The grounding grid transient behavior is an important substation design criterion. This behavior is determined through interaction with impulsive currents typical of lightning. Based on the technical literature, the behavior in question is determined considering fixed current waves, with median parameters (peak values and front and tail times etc.). Therefore, important statistical-probabilistic characteristics of lightning currents, such as correlations and statistical regressions, are not included. From this perspective, this paper includes research into the sensitivity of impulsive impedance and effective area values of substation grounding grids in relation to the waveform of currents typical of the first return strokes. The results (original) illustrate significant sensitivity of the grids transient behavior in relation to those mentioned statistical-probabilistic characteristics, considering a wide range of resistivities in both current injection points considered in this study.

The Monte Carlo method (MCM) is the most widely used statistical approach to evaluate the lightning performance (LP) of overhead transmission lines (OTLs). However, the MCM has a very high computational burden, making LP studies time consuming. To overcome this difficulty, this letter proposes a new alternative approach for calculating the the lightning overvoltages (LOs) using the unscented transform method (UTM). This letter compares the UTM and MCM for calculating LO in insulator strings of OTLs through extensive tests carried out using the Alternative Transients Program (ATP). Such LO evaluation is an essential requirement for LP evaluation of a transmission line. The results indicate that the UTM significantly reduces the processing time to generate LOs while its accuracy is similar to that of the MCM.

One of the challenges faced by Brazilian distribution utilities to enable the connection and operation of microgrids (MGs) is the absence of a solid set of technical standards in the country. An alternative has been to use and adapt existing standards applied to micro- and mini-distributed generation. In this context, this paper presents an analysis of the development status of norms, standards, and general requirements for the connection and operation of microgrids, as well as a proposal for the regulation and structuring of technical and operational requirements related to the implementation of microgrid projects. Some critical points highlighted in the paper include: the modes of operation, the minimum requirements for the different modes of operation, interoperability of systems, a conceptual model with attribution of responsible actors for the decentralized management of microgrids adapted to the institutional standards of the Brazilian sectorial model, a proposal for a standard connection structure considering the point of connection (PoC) implanted using multifunctional relay and recloser, procedures for technical feasibility assessment (operational studies) of MGs connection, and, finally, a discussion of operational issues of storage systems in a microgrid environment.

In this paper, the influence of the transmission tower and the frequency-dependent soil parameters on the grounding potential rise (GPR) waveform is evaluated. This evaluation is performed using a physically consistent electromagnetic model that determines the transient behavior of the grounding system submitted by lightning, together with the Alternative Transients Program for the representation of aerial elements (tower, phase cables and shield wires). This model was developed in the frequency domain and, in this way, allows the inclusion of frequency-dependence of soil electrical parameters. In this sense, three formulations of the dependence in question are considered, widely disseminated in the literature, and determined through systematic measurement processes. The results illustrate that the concomitant inclusion of the tower and the frequency-dependence substantially modifies the GPR waveforms, when compared with those in which isolated grounding is considered, especially for soils with high resistivity values and for first return strokes. This is of most importance when evaluating personal safety criteria in the transmission tower vicinity. In these situations, the GPR waveforms should be determined by considering the presence of the tower and not only with the isolated grounding, since the transient step and touch voltages are directly associated with GPR.

The assessment of distribution systems performance is a key factor to guarantee the continuity of energy supply. Hence, understanding the impacts that lightning can generate in this type of system is a matter of relevant importance. Therefore, this work aims to investigate the impact of grounding resistance on the distribution line lightning performance considering induced overvoltages. The present work is based on the theory proposed by Sune Rusck and later extended by J. O. Paulino. For this analysis, the Monte Carlo Method was also used in a computational routine to estimate the number of expected shutdowns of a distribution line. Thus, simulations were carried out with different values of grounding resistance and the number of shutdowns was calculated as a function of these values. According to the results, the value of the grounding resistance significantly impacts the expected number of shutdowns for a given distribution line.

In power system planning studies that involve the search for optimal investments with low risks for the power grid, probabilistic reliability assessments provide very useful tools and indices. A challenge faced in the application of these tools is related to the computational effort demanded by the evaluation process, especially when the combined effects of failure of generation and transmission equipment are considered. In this context, the present work proposes a new method for efficient estimation of the main composite reliability indices by combining Binary Logistic Regression (BLR) technique, a machine learning tool used for binary data classification, with the non-Sequential Monte Carlo simulation (NS-MCS) method. In addition, a computational parallelization strategy is incorporated to the proposed method to improve even more the efficiency of the composite reliability assessment. The performance of the proposed approach is analyzed by evaluating composite reliability indices for the IEEE-RTS considering two different generation and load scenarios, in addition to a real large-scale power system. The results obtained are compared with those using the NS-MCS method in its conventional version.

The overhead transmission lines are subject to several transients events, such as atmospheric discharges. For this, the study of electromagnetic transients in transmission lines is fundamental to know the response of this element before the electrical power system in cases of unexpected requests. In the existing line models in electromagnetic transient softwares, a required step is the fitting of the functions that model the line in rational functions. Therefore, this paper aims to analyze the difference between two methods of rational approximation in the study of electromagnetic transients in a single-phase overhead transmission line. The two methods used are: i) Asymptotic Bode Fitting (ABF); ii) Vector Fitting (VF) . The analyzed models are computed considering a frequency spectrum from 100 Hz to 10 MHz. According to the results, the use of the most complex model, VF, can lead to mean square errors up to 36 times smaller than those resulting from the use of the traditional ABF implemented in electromagnetic transient software, such as ATP.

Transmission towers are an essential component for the functioning of a country’s electrical system. In countries with a large extension of transmission lines and a high incidence of lightning, problems related to the interaction between lines and lightning are quite intense. Thus, it is of fundamental importance to develop models that compute the response of the transmission system when an electromagnetic transient is established. This article aims to present the revised Jordan formula for calculating the surge impedance of a vertical conductor, and its extension to calculate the surge impedance of multiple vertical conductors. Neumann integrals are also applied to calculate the self and mutual surge impedances of vertical conductors. The results of surge impedances, of typical towers of 138 kV transmission lines, from the application of modified Jordan formulas and Neumann integral equations are compared. According to results, for 138 kV transmission towers, the percentage differences are smaller than 1%, proving the accuracy of Jordan’s modified analytical formulas.

For the study of lightning performance of distribution lines, the correct assessment of indirect flashes plays an important role. Thus, this paper considers the frequency-dependent soil electrical parameters in a previously developed approximate formula for the peak value of lightning-induced overvoltage on overhead lines. This approach consists of using a specific frequency (based on the lightning front time) to estimate the ground conductivity. Since the proposal is easy to implement and fast to run in any computational environment, it is a practical engineering tool. According to the results, it is possible to note the importance of applying models that take into account the variation of soil parameters with frequency, since overvoltage reductions for high resistivity soils above 35% were verified.

Indirect lightning strokes represent and important source of damage for overhead distribution systems. For the correct evaluation of lightning-induced overvoltages, the frequency dependence of the electrical parameters of the soil should be considered. Therefore, this paper proposes a simplified approach which selects a representative frequency according to the front time of the current waveform at the base of the lightning channel and takes advantage of an approximate formula for the lightning-induced overvoltage peak which is available in the literature. The most relevant strengths of the proposed method are the simplicity of implementation and the reduced process time, which is extremely lower than that required by more sophisticated numerical methods. These characteristics make the proposed approach a simple and practical tool. The results show overvoltage decreases above 35 percent for soils of low conductivity. Therefore, the frequency dependence of the electrical parameters of the soil plays an important role.