Voltage Sag Indices Research Articles

Modeling of Adverse Weather Events in an Integrated Reliability and Power Quality Assessment of Distribution System Using Stochastic Diffusion Process

This paper presents the modeling of adverse weather events and their impact on the integrated reliability and power quality assessment of power distribution systems. With respect to previous works, stochastic modeling of adverse weather events is integrated into the Monte Carlo Simulation approach and its impacts on reliability and voltage sag indices are highlighted. In this paper, the aleatory and epistemic uncertainty are modeled into sampling of Time to Failure (TTF) using the Stochastic Diffusion Process. The Stochastic Diffusion Process, including the Jump diffusion is used to model the impact of adverse weather events on permanent and temporary failure rates. The proposed method is applied to the modified IEEE 34 node test feeder, and three case studies have been performed to investigate the impact of various uncertainties and adverse weather events. Numerical results for the IEEE 34 node test feeder are presented to quantify adverse weather impacts on both reliability and voltage sag indices.

An improved method for efficient controlling of the dynamic voltage restorer to enhance the power quality in the distribution system

This paper represents a low complexity of the DVR controller by using a robust differentiator named as approximate classical sliding mode differentiator (ACSMD) to overcome the drawback of the linear differentiator. Additionally, utilize a nonlinear sliding variable named arctan function (sigmoid function) in order to keep the magnitude of the load voltage approximately 1pu, the THD at the standard level, improve the robustness property and maintain the steady-state error within a small bound. The most important issues of the power system network are power quality, the major problems of power quality are voltage sag/swell and harmonics which cause tripping or malfunctioning of the equipment. This paper gives an economic and effective solution by utilizing the dynamic voltage restorer to protect the sensitive loads from the disturbances that happened in the system such as voltage sag/swell and harmonics. The proposed system of the DVR is investigated by utilizing MATLAB/Simulink to enhance the disturbances when it occurs in a distribution system. The presents DVR model is evaluated by utilizing some of the popular voltage sag indices.

The enhancement of power quality for the distribution system via dynamic voltage restorer

This paper represents a new configuration of the dynamic voltage restorer consists of approximate classical sliding mode differentiator (ACSMD) with the terminal sliding mode controller (TSMC) as the nonlinear sliding variable. In this study, the proposed structure of the DVR is utilized to maintain the magnitude of the load voltage at a constant value, maintain the system total harmonic distortion (THD), boost the robustness property and minimize the steady-state error. The power quality has received more interest due to the implementation of various industrial devices and critical loads at the distribution side. Nowadays, the main challenges in power quality in the system are voltage sags/swells, harmonics and voltage imbalance. Various devices are utilized to address these challenges. The dynamic voltage restorer is one of these devices. It is connected in series with the distribution system and injects a proper voltage magnitude to maintain the voltage load at the constant value. In this paper, the DVR model with the ASMF and TSMC is implemented in using MATLAB/Simulink. The proposed controller is evaluated using the standard voltage sag indices.

Energy demand and quality management of standalone diesel/ PV /battery microgrid using reconfiguration

Power quality has become one of the most vital challenges in the planning of smart distribution grids due to popularity and myriad applications of power electronic devices. This paper introduces a new method based on network reconfiguration to efficiently deliver the energy demand of standalone Diesel/PV/Battery microgrids with improved power quality. The feeder reconfiguration is performed to decrease power loss, decrease the total harmonic distortion (THD), and improve voltage sag indices. Mathematical models of Diesel/PV/Battery standalone system are integrated with harmonic power flow algorithms to implement the concept. Reconfiguration algebraic equations along with nonlinearities introduced by Diesel/PV/Battery standalone system are solved by means of Non-Dominated Sorting Differential Evolution Algorithm (NDSDEA). The proposed methodology is carried out on a 33-bus standalone microgrid. The results have shown that reconfiguration not only improves the overall performance of the standalone energy system but also is effective to improve the quality of power delivered to the significant consumers. The method has both economic and technical benefits for such islanded networks.

Probabilistic Analysis of PV Generation Impacts on Voltage Sags in LV Distribution Networks Considering Failure Rates Dependent on Feeder Loading

The impact of photovoltaic distributed generation (PVDG) in the voltage sag indices of low-voltage distribution systems is assessed in this paper. A sensitivity study of these indices in relation to the penetration level of PVDG is performed considering the effect of the feeder sections loading on their failure rates. It is showed that, when this dependence is neglected, the indices are predicted with errors, especially for scenarios with large integration of PVDG. This study was performed using clustering techniques to model the uncertainty of solar irradiation, and the state enumeration method (SEM) is used to evaluate voltage sags indices. The results obtained by the clustering method and SEM were compared with those obtained with Monte Carlo Simulation based on the beta probability density function (pdf) model for solar irradiation. This comparison showed that the clustering model can obtain indices with precision comparable to those obtained with the beta pdf model, but with a significant reduction in CPU time.

Analysis of Voltage Sag Severity Case Study in an Industrial Circuit

This paper presents the results of a power quality study carried out in an industrial distribution system. The main objective of this study was to quantify the negative impact caused by voltage sags in industrial processes and its relationship to generated interruptions. A series of measurements of power quality variations were taken at the substation that feeds the circuit and at the point-of-common coupling of each industrial user. The new standard IEEE Std 1564-2014 “Guide for Voltage Sag Indices” was used to determine the indicators to assess the severity of voltage sags and also the calculation method. Sag severity was selected as it allows the calculation of the probability of voltage sags to generate interruptions in industrial processes or electrical equipment. Thus, an analysis of the quality of the supply voltage can be done. Severity was initially calculated at the substation that feeds the industrial circuit and later, at the point-of-common coupling of each user. Subsequently, the relationship between user interruptions and severity values was determined. Finally, recommendations of good engineering practices in industrial processes were done.

Power conditioning using dynamic voltage restorers under different voltage sag types

Voltage sags can be symmetrical or unsymmetrical depending on the causes of the sag. At the present time, one of the most common procedures for mitigating voltage sags is by the use of dynamic voltage restorers (DVRs). By definition, a DVR is a controlled voltage source inserted between the network and a sensitive load through a booster transformer injecting voltage into the network in order to correct any disturbance affecting a sensitive load voltage. In this paper, modelling of DVR for voltage correction using MatLab software is presented. The performance of the device under different voltage sag types is described, where the voltage sag types are introduced using the different types of short-circuit faults included in the environment of the MatLab/Simulink package. The robustness of the proposed device is evaluated using the common voltage sag indices, while taking into account voltage and current unbalance percentages, where maintaining the total harmonic distortion percentage of the load voltage within a specified range is desired. Finally, several simulation results are shown in order to highlight that the DVR is capable of effective correction of the voltage sag while minimizing the grid voltage unbalance and distortion, regardless of the fault type.

Economic analysis of losses due to voltage sag on industries using sensitivity method and comparison with cost of mitigation devices

Voltage sag indices are used to quantify the performance of the power supply during individual events for individual sites and the whole system. In this paper, a questionnaire is designed for survey and data is collected from the different industries. For calculating financial losses due to sag events, a probabilistic method is used. The aim of this survey is to find out the answer of some questions like an effect of voltage sag on Indian industries i.e., which type of industries suffers most. In this paper also losses due to voltage sag are compared with the cost of different mitigation devices.

A novel self-tuning control method based on regulated bi-objective emotional learning controller's structure with TLBO algorithm to control DVR compensator

DVR is one of the custom power devices for compensating power quality indices. A self-tuning controller with a bi-objective structure is presented for controlling the DVR compensator in order to improve the THD and voltage sag indices of a sensitive load in the network. In this paper, the emotional controller which is based on emotional learning of human brain is proposed for controlling the DVR compensator. This controller has such a structure that makes it capable of considering a second objective in the control process of the system. So far, this capability of the emotional controller has not been used in any researches. The results of the paper demonstrate that compensating and controlling the voltage THD signal in the control process has caused more improvement in the voltage sag of the sensitive load. It was reported that the performance of the emotional controller depends on the selection of the values of its coefficients. Therefore, in order to better improve the proposed controller, these coefficients are tuned by an optimization algorithm. Teaching–learning-based optimization algorithm is considered as optimization algorithm to regulate these coefficients. According to simulation results, it works significantly better than classic PI controller and some intelligent controllers that have introduced in other researches already.

Optimal Reconfiguration of Electrical Networks by Applying Tabu Search to Decrease Voltage Sag Indices

This article presents a methodology for electrical network reconfiguration to minimize voltage sags indices. The voltage sag analysis is carried out by means of an analytical method. A tabu search algorithm is implemented to find the optimal configuration in an electrical system to decrease voltage sags indices. The proposed algorithm is implemented in MATLAB® (The MathWorks, Natick, Massachusetts, USA). Several case studies in IEEE test systems of 57 and 118 buses are presented showing the performance of the proposed methodology.

Assessment of Voltage Sag Indices Based on Scaling and Wavelet Coefficient Energy Analysis

The two main voltage sag indices are magnitude and duration, defined in terms of the well-known rms voltages. The spectral energy of the voltages provides the same voltage sag indices of the rms voltage analysis and less computational effort is required. However, neither of them provide point on wave of sag initiation and recovery. This paper presents a wavelet-based methodology for the characterization of voltage sags, where the spectral energy of a voltage is decomposed in terms of the scaling and wavelet coefficient energies. The scaling coefficient energies of the phase voltages are used for voltage sag characterization, providing sag indices (magnitude and duration) in agreement with the definition. However, the analysis of the wavelet coefficient energies of such voltages provides additional information for the identification of the point on wave of voltage sag initiation and recovery as well as important parameters for power system protection and voltage sag mitigation devices. The performance of the proposed wavelet-based methodology was assessed with actual data and it was scarcely affected by the choice of the mother wavelet. Therefore, a compact mother wavelet can be used for voltage sag analysis with computational effort equivalent to the rms method and in agreement with practical applications. The maximal overlap discrete wavelet transform presented better performance than the discrete wavelet transform. All of the equations provided in this paper were developed for real-time analysis.

New approach for power lines performance estimation based on load variation due to voltage sags

The power line performance has traditionally been assessed in terms of its efficiency and reliability. The increase of the effect of voltage sags on sensitive loads, maybe located far away from the faulted line, is the reason to carry out a new analysis of power line's performance. A new method to evaluate the power line performance, based on voltage sag indices, is proposed. The voltage sag indices suggested to assess power lines performance are the load variation, the non delivered energy and the total cost due to voltage sags. The proposed power line performance is compared with the traditional performance based on power line outages. The results show that the proposed method can change the assessment of power lines performance and therefore the utility focus for investment.

Multiphase transmission line modeling for voltage sag estimation

This paper presents a novel approach for voltage sag indices calculation based on instantaneous voltage estimation. The estimation uses traditional state estimation where redundant measurements are available. The estimation is based on time domain state estimation which uses time domain modeling of the power network. The time domain current monitoring is used to have linear mapping and to achieve high performance of voltage sag estimation. The fault estimation procedure is prior of the voltage sag estimation. This paper shows a possible for fault instance detection, fault location identification and fault type estimation method that are required to estimate voltage sag for different line models utilizing residual analysis and topology error processing. Lumped parameter and distributed parameter transmission line modeling are developed to estimate instantaneous voltage at a three-phase power system in time domain. Magnitude and duration of voltage sag as main indices are calculated from the estimated instantaneous bus voltage. The performance of the novel approach is tested on IEEE 14 bus system and the results are shown.

Voltage sag index calculation: Comparison between time-domain simulation and short-circuit calculation

This paper describes a case study where voltage sags indices are estimated using Monte Carlo approach combined with ATP (Alternative Transient Program) and short-circuit calculation program. Voltage sag magnitude and frequency are used to evaluate the correlation between both programs. The results indicate that time-domain simulation and short-circuit calculation gives similar voltage sag indices. Considering the high correlation between the results, short-circuit calculation programs are preferable over the time-domain simulation tools as the modelling for time-domain simulation is more complex, time consuming, and rarely covers the whole network.

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.

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 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.