Voltage Sag Occurrence Research Articles

Analysis of the sensitivity of electronic active energy meters to voltage sags✰

This article presents a study on the sensitivity of electronic active energy meters when dealing with voltage sags, through the consideration of three distinct approaches. Initially, the analysis is performed for the two main power supply topologies found on the various commercially available energy meters. Following this, laboratory tests are performed that aim at obtaining the sensitivity curves, as well as the respective reset times after the occurrence of voltage sag, for six different energy meters. Finally, the sensitivity curves obtained for each of the meters under consideration are compared with real recordings of voltage sag events, acquired from a particular low voltage distribution system. The results found show that the sensitivity of electronic active energy meters can be very significant in some cases, where in practical situations this results in almost 1 h/week of unmeasured active energy consumed by consumers.

Estimation Method for Voltage Sag Occurrence Frequency Based on Calculation of Protection Operating Time Characteristics

Voltage sag occurrence frequency (VSOF) estimation includes the prediction of residual voltage and duration. The former has been well studied, whereas the latter presents many challenges, and is the main focus of this study. A method for estimating the VSOF based on the calculation of the protection operating time characteristics is proposed. First, this article adopts a recognition method for protection types based on monitored historical data. The protection type is recognized by dividing the fault electrical quantity (FEQ) into several intervals and calculating their mean standard deviation. Second, this article proposes a calculation method for the protection operating time characteristics. The FEQ and operating time samples are clustered based on the proposed algorithm. The density-based spatial clustering of applications with noise (DBSCAN) algorithm is enhanced by the Mahalanobis distance and K-nearest-neighbor (KNN) method. The least-square fitting and segmentation calculation of the operating time curve is performed in accordance with the clustering results. Finally, this study proposes a method to predict VSOF by considering operating time curves, different fault resistances, and generator scheduling, whereas the IEEE-30 test system is used to verify this method.

Quantitative evaluation method of power supply reliability considering voltage sag

Based on the analysis of the original quantitative evaluation system of power supply reliability, aiming at the influence of voltage sag on industrial users, a hierarchical quantitative evaluation system of power supply reliability considering voltage sag is proposed. The new index system aims to evaluate the reliability of the impact of voltage sag from the perspective of the structure, function and safety of industrial users. The specific evaluation methods are mainly composed of direct loss evaluation, indirect loss evaluation and potential safety hazard evaluation. Direct loss refers to the economic loss caused by the interruption of industrial process after the occurrence of voltage sag. Indirect loss refers to the economic loss caused by defective products due to the imperfect industrial production process. The potential safety hazard refers to the potential safety hazard of the production line where the important equipment is located after suffering voltage sag. This paper focuses on the rationality of quantitative evaluation with the principle of economic equivalence, the significance and internal relations of industrial user structure, function and safety index, and puts forward a reasonable calculation method. Through the case calculation, the layered evaluation results are consistent with the empirical conclusions, with applicability.

Power Quality Improvement In 8-Bus System Using DVR and D-STATCOM

The deterioration in the quality of the power supplied has the root cause of dilating gap between the supply and the demand. The occurrence of voltage sag and swell is predominant over other power quality issues like harmonics. The simulation of distribution network using FACTS devices for tempering the power quality issues is prevailing these days but there exist speculative theories which don’t provide effective and robust system on voltage stability and power quality control. This paper focuses on simulation of eight-bus system using D-STATCOM and DVR which is connected with closed loop PID and PI controller. The system is simulated to reduce the peak time, settling time and the steady state error thus proves to be effective in mitigating the voltage sag and swell occurring at the load point distribution system. The simulation is processed in the MATLAB software and the comparison of using PI and PID controller is tabulated and the system is implemented using the PIC16F84A micro-controller.

Optimization of DG Units in Distribution Systems for Voltage Sag Minimization Considering Various Load Types

The optimum installation of distributed generation (DG) units in distribution systems has always been challenging due to the continually increase of electrical energy demands. However, the improper installation of DG units may have negative impact on the power quality of the distribution system. Voltage sag is one of the most important power quality problems, which has the bad effects on the performances of different loads, especially on sensitive and uninterruptible loads. To mitigate the voltage sag problem in distribution systems, a new formulation is proposed for optimal location and sizing of DG units. Particle swarm optimization algorithm is employed to solve the problem. The minimization of the total power losses, total cost of DG units, improvement of the voltage profile, and the reduction in the voltage sag effect are considered as the main objectives. To involve the voltage sag occurrence in distribution system, a penalty is considered for interruption of each type of available load. Different types of load models such as industrial, residential and commercial loads are considered in the system. For the demonstration of the effectiveness of the proposed algorithm, 34-bus test system is considered as the case study. The proposed method results are shown that there is about 72% reduction in total power losses in the optimal configuration of DG units in the distribution system. It is observed that the total number of disturbed buses decreases to 4, which is equal to 12%, as the number of DG units increases. It can be seen that the total cost of the system is reduced from 36.250 to 31.824 M$, when the optimum number of DG units is increased from 1 to 5. The simulation results show the effectiveness of the proposed algorithm.

Wavelet based real-time monitoring of electrical signals in Distributed Generation (DG) integrated system

In this paper, Hilbert-Huang Transform (HHT) and Discrete Wavelet Transform (DWT) based methods are employed on line to monitor the deviation in electrical quantities of the power system integrated with distributed generation. HHT employs an Empirical Mode Decomposition (EMD) method i.e. decomposition of the signal into Intrinsic Mode Functions (IMFs) in such a way that they are sorted from the highest frequency to the lowest frequency whereas, Wavelet Transform (WT) decomposes the signal into components that are indicative of signal details and trend. This paper presents a comparative analysis of HHT and DWT with the motive to provide the guidelines for deciding which one of these techniques is more suitable for Power Quality (PQ) event analysis in the case of Distributed Generation (DG) integrated system, in real-time domain. From the comparative analysis, it is observed that DWT is more precise in comparison with HHT in determining PQ events in real-time domain with high resolution. This work further explores the potential of WT for the real time application in measuring, monitoring, and analyzing the electrical signals during the occurrence of voltage sag, swell and harmonics. Real time implementation of WT necessitates signal sections to be serially processed. Towards the same, signal samples are collected in a buffer and then subjected to WT to extract the inherent details. The processing of the signal gives attributes that help in identifying the type of disturbance. Performance of the proposed method is tested through simulations on MATLAB/Simulink platform along with the experimental validation of the technique. Results reveal that the application of WT, in real time, can accurately detect the instant of disturbances with minimum delay to analyze the PQ issues.

Recloser placement optimization using the cross-entropy method and reassessment of Monte Carlo sampled states

This paper proposes an approach to optimize the location of reclosers in distribution feeders aiming to improve system reliability, minimize costs and reduce the occurrence of voltage sags. The approach is based on the cross-entropy method and the reassessment of sampled states generated using sequential Monte Carlo simulations. Results indicate the effectiveness of the approach, the importance of integrating reliability and power quality aspects to the analysis, and the computational gains of deploying a reassessment process of Monte Carlo sampled states instead of the conventional Monte Carlo simulation algorithm.

D-STATCON model for voltage sag mitigation

<span>Development of a FACTS device model for mitigating voltage sag is presented. It deals with a static synchronous condenser (STATCON) to be used in the AC distribution networks. Simulation with the help of a commercial software Matlab/Simulink was explored to investigate its characteristics and performance during the voltage sag occurrence. The considered main cause of voltage sag was the starting of high capacity asynchronous motor. A voltage source inverter based on the phase-controlled thyristor components was implemented in this application to compensate the change in reactive power of the system. The concerns have been put on the influence of initial operation point and DC capacitance. The study results show the capability of D-STATCON model to reduce the consequence of voltage sag following the starting of high-power asynchronous motor in the distribution network. A fast response of the condenser work confirmed the desired performance.</span>

Effect of Distributed Wind Generation on the Voltage Sag of Distribution Networks

As the issue of global warming is worsening, the shift towards using renewable energy resources is becoming more of an obligation rather than an option. With the continual decline in the cost of distributed small and medium-scale renewables and government sponsored programs, the outlook of growth of these converter-based resources remain high. Renewable energy resources are connected at the end-user terminals, in close proximity to the load at the distribution network. Such connection in the locale brings perceived benefits of transmission loss reduction, increased energy efficiency and improved voltage regulation. Yet, distributed renewable generation have noticeable effects on system’s power quality. This paper investigates the impacts of distributed wind generation on the voltage sag of distribution systems. A systematic approach is constructed to capture voltage sag occurrence incidents, due to wind generation connected at distribution nodes, and trigger the dynamic voltage restorer (DVR) into active operation mode to rectify the voltage sag problem. A test feeder system is represented using MATLAB/Simulink with wind turbines connected at several nodes of the system. A model for the DVR is developed in Simulink. It was then integrated with the test feeder system. Simulation results show that the incorporation of increased proportions of wind generation into the distribution network may give rise to negative operating conflicts as far as the voltage sag is concerned. Results manifest that the DVR is capable of effective correction of the voltage sag, caused by a three phase short-circuit fault, in presence of high penetration levels of variable wind generation connected at disparate locations in the distribution network.

A Decision Making Methodology to Assess Power Quality Monitoring Index of an AC Microgrid Using Fuzzy Inference Systems

The power quality issues are challenging in microgrid due to the presence of various types of renewable energy resources unlike conventional power system. So, the main objective of this research is to quantify the power quality considering the fuzziness in variation of voltage, frequency, power factor and total harmonic distortion (THD) due to the occurrence of voltage sag, swell, interruption and unbalancing in three-phase AC microgrid feeding static and rotational loads. Therefore, a novel power quality monitoring index (PQMI) is proposed to determine the status of power quality. Total 256 numbers of rules are formed for fuzzy inference system (FIS) to assess PQMI considering the acceptable limits of above mentioned four input variables as per IEEE/IEC standards. The proposed methodology is verified through Mamdani and Sugeno type FIS using Matlab-Simulink software. It is also found that the proposed PQMI is significant to define the status of microgrid even during transition from grid-connected to islanded mode and vice-versa.

Dual 3-Phase Bridge Multilevel Inverters for AC Drives with Voltage Sag Ride-through Capability

One of the main power quality issues that can affect variable speed drives (VSDs) is the occurrence of voltage sags on their AC power supply. Voltage sags can affect the inverter nominal operation, leading to a malfunction of the AC motor. This paper presents an inverter with resilient capability to voltage sags. The topology consists of two conventional three-phase bridge inverters arranged to require just a single DC source. This inverter is also characterized by a voltage multilevel operation, providing the full advantages of multilevel converters without the need for level balancing. Associated with this AC motor driver, a control system based on a field-oriented controller with a vector voltage modulator that will enable voltage sag ride-through capability is proposed. The proposed control system does not require any changes in the occurrence of voltage sags. To verify the characteristics of the proposed drive and control system, simulation tests are provided. Simulation results confirm the voltage sag resilient capability of the proposed multilevel converter.

Stochastic Characterization of Voltage Sag Occurrence Based on Field Data

Computational methods for predicting voltage sags consider their occurrence as a Poisson process, although without confirmation from monitoring data, until now. In this paper, the stochastic nature of voltage sags is analyzed and discussed using monitoring data from 60 sites of the Portuguese Transmission Network, covering the years 2011–2015 (a total of 17 157 recorded voltage sags). A mathematical model to describe the voltage sag occurrence as a stochastic process is presented. The assumption of constant failure rates of the network elements implies that the occurrence of voltage sags is a Poisson process. However, that assumption is not valid if voltage sag clusters are included, as these imply considering time-dependent failure rates. Then, the time between voltage sags is described by an exponential distribution, if clusters are not included, and may be described by the gamma distribution, if including clusters. The boundaries of the adequacy of exponential and gamma distributions are assessed, based on monitoring data. The time of occurrence of monitored voltage sags are analyzed and results confirm that the Poisson process describes the occurrence of voltage sags when voltage sag clusters are disregarded. The gamma distribution fitting is also confirmed when clusters are included in the analysis.

Identification Method for Voltage Sags Based on K-means-Singular Value Decomposition and Least Squares Support Vector Machine

Voltage sag is one of the most serious problems in power quality. The occurrence of voltage sag will lead to a huge loss in the social economy and have a serious effect on people’s daily life. The identification of sag types is the basis for solving the problem and ensuring the safe grid operation. Therefore, with the measured data uploaded by the sag monitoring system, this paper proposes a sag type identification algorithm based on K-means-Singular Value Decomposition (K-SVD) and Least Squares Support Vector Machine (LS-SVM). Firstly; each phase of the sag sample RMS data is sparsely coded by the K-SVD algorithm and the sparse coding information of each phase data is used as the feature matrix of the sag sample. Then the LS-SVM classifier is used to identify the sag type. This method not only works without any dependence on the sag data feature extraction by artificial ways, but can also judge the short-circuit fault phase, providing more effective information for the repair of grid faults. Finally, based on a comparison with existing methods, the accuracy advantages of the proposed algorithm with be presented.

Optimal selection of voltage sag mitigating devices for micro‐level customer in distribution system

Power quality is a vital issue in distribution systems. Power quality issues have become important for the extensive use of sensitive equipment and integration of renewable generation. Several researchers have proposed for voltage sag mitigation devices to minimise financial losses arising from voltage sag. Augmentation of micro-level units like housing complex, super-specialty hospitals, rapid urbanisation has opened up demand for electricity. Modernisation in life has led to coextensive requirement for good quality power. Importance of micro-level consumers is to be considered while looking into the matter of optimal selection of voltage sag mitigation devices. In this study, a new framework is proposed for optimal selection of voltage sag mitigation devices to minimise voltage sag occurrence in a distribution system based on Nested Logit model. Nested Logit model has the essential characteristic for selection of optimal option by allowing equal preference to all the available customers' choice. This model gives unbiased and equal importance to all the available mitigation devices. The optimal selection of mitigation devices is obtained using aggregate forecasting. Voltage sag severity index is used for placement of optimally selected voltage sag mitigation device. Two case studies are described to validate the proposed approach.

Effect of recovery time of fault current limiter on over current from distributed generator in micro grid after voltage sag

AbstractThis paper describes an effect of recovery time of fault current limiter on over current from a micro grid system which is interconnected to a power distribution system. We have assumed that the semi-conductor type fault current limiter is installed between the micro grid system with the synchronous generator and the power distribution system, measured the over current after a voltage sag occurrence in the power distribution system and a recovery of fault current limiter by experiments in our laboratory. Finally, it was found that the introduction of recovery time for fault current limiter after voltage sag is useful for suppressing the over current from the distributed generator.

Evaluation of Resistance Type SFCL on Reduction of Destructive Effects of Voltage Sag on Synchronous Machine Stability

Electrical power quality has become an essential part of power systems and electrical machines. True identifying and regarding power quality and how to check the related destructive points are of utmost importance. Most of the time, providing the quality of power for sensitive load which requires the voltage to maintain a sinusoidal waveform at rated voltage and frequency is the main point to be considered. On the other hand, protecting power supply against resulting turbulences can be regarded. Voltage sag is one of the destructive issues in power quality problem to be taken into account. Not only can it have some undesirable effects on the sensitive load, but it also has some undesirable effects on synchronous machine as a power supply. In this study, SFCL was used in order to reduce the destructive effects of voltage sag on the performance of synchronous generators. To achieve better understanding, a simple model composed of synchronous generators, SFCL and load is used with the help of MATLAB/SIMULINK software. By creating voltage sag which results from 3-phase short-circuit voltage, current, torque, speed and angle load changes of synchronous generators were simulated and discussed. It was done in condition with/without SFCL. The results illustrate that using SFCL in synchronous generator output can improve its performance during occurrence of voltage sag.

Power Quality Enhancement in Microgrid

This paper deals with the mitigation of voltage sag and harmonic profile improvement in a microgrid system. The microgrid system contains a hybrid combination of PV array, Battery interfaced with a cascaded multilevel inverter through a boost converter. The microgrid feeds a non-linear balanced load. The occurrence of voltage sag in the microgrid is compensated using the reference current for mitigation by using the SRF theory. The proposed power quality conditioner can compensate the voltage variations and harmonic profile distortions caused by the load changes. The efficacy of the proposed power quality conditioner in the microgrid system is validated through the MATLAB/Simulink.

Voltage Sags Drain Your Profit, but Solutions are Available

ABSTRACT Voltage variations, in particular voltage sags, cause unplanned production stoppages that cost North American industry over $200 billion per annum. Electrical utilities cannot readily prevent the occurrence of voltage sags, which are more frequent during stormy weather. It is usually not practical for the utility to provide correction for a network, or even for individual customers. Companies that regularly invest millions in production equipment often ignore or greatly underestimate the cost of their unplanned stoppages. The article reviews the latest active voltage conditioning solutions that keep critical equipment running, avoid the unplanned stoppage costs, and provide a very attractive financial payback.

Load Current Model of Electric Apparatus Based on Load Voltage Characteristics during Voltage Sag

This paper describes the measurement-based load current model of electric apparatus after a voltage sag occurrence. The terminal voltage and load current of a personal computer (PC), an inverter fluorescent light and an incandescent light were measured to find out the dependences of load characteristics on the voltage sag. The magnitude of the load current after voltage sag depends on both the magnitude of residual voltage and the time period of voltage sag. In order to make it possible to take account of these transient load characteristics in the power quality estimation, a load current model is proposed. The load current waveform is obtained using the database of harmonic component of load current and time variation in the parameters of load voltage characteristic. The proposed model enables us to estimate the load current within an error of about 5% when the voltage sag occur.

Voltage Sag Detection Based on Rectified Voltage Processing

An algorithm for voltage sag detection based on rectified voltage processing is presented and its performances are evaluated by means of simulated and real voltage waveforms (recorded at some low-voltage busbars and measured on a scaled prototype of a voltage support system). The algorithm is intended to detect voltage sag occurrence and to trigger the disconnection of the faulty supply network and subsequently the connection of a voltage support system. The algorithm is very convenient in terms of memory storage and computational requirements and may be implemented on low-cost platforms. The results show that the time for detection is very short and always less than a quarter of the supply voltage period.