Voltage Sag Profile Research Articles

Voltage Sag Estimation for Distribution Systems Using Linear Machine Learning Models

This paper proposes a voltage sag estimation approach based on linear machine learning models. The proposed approach estimates the voltage sag profile on distributions systems with limited monitored buses. The approach takes advantage of the priory knowledge about the linearity of the problem to train and compare three linear models: Least Squares (LS), Ridge Regression (RR), and Absolute Shrinkage and Selection Operator (LASSO). The approach is tested on the IEEE-34-bus distribution system, and the performance of models is validated through the Mean Square Error (MSE). The results show that the proposed linear machine learning models capture the internal relationships of the problem and estimate the voltage sag with high accuracy on test data.

Multi-Objective Optimal STATCOM Allocation for Voltage Sag Mitigation

Voltage sags mitigation has become a significant concern for utilities due to the pressure from both customers and regulators recently. This paper proposes a novel multi-objective optimization formulation for STATCOM allocation problem to mitigate voltage sags. The allocation of STATCOM is formulated as a multi-objective optimization problem (MOP) with two conflicting objectives including the voltage sag performance and annual investment costs of STATCOM. To analytically evaluate the voltage sag performance in the optimization process, a mathematical voltage sag profile calculation model of power system with multiple STATCOMs is proposed and solved by nonlinear programming method. System Average RMS Variation Frequency index-X index is chosen to quantify the voltage sag performance for optimization. Sensitivity-based candidate bus selection is also performed as an essential step to reduce problem size. An improved multi-objective evolutionary algorithm (MOEA) called SPEA2+SDE (Strength Pareto Evolutionary Algorithm with shifting density estimation) is utilized to solve the proposed MOP model, so a set of Pareto optimal STATCOM allocations for voltage sag mitigation can be derived demonstrating the trade-off between two objectives and better supporting the decision-making. IEEE 30-bus system and IEEE 118-bus system are tested to demonstrate the effectiveness and feasibility of proposed method.

Voltage-Sag-Profiles-Based Fault Location in High-Speed Railway Distribution System

Operation parameters of the high-speed railway distribution system can be obtained from remote terminal units installed in box-type substations. Therefore, the voltage sag profiles may be utilized for fault location. This paper proposes a novel strategy for fault location in a high-speed railway distribution system by measured voltage data of existing box-type substations. The proposed method makes use of the difference between the calculated voltage and measured voltage at the end of the lines to locate the fault. Assuming that the fault occurs at any possible box-type substations along the lines, the faulted line section is identified with the defined difference sequence, and then the exact fault location can be obtained with a searching procedure in the identified fault section. Considering the effect of equivalent capacitance, each line section is modeled with the π model to improve accuracy of fault location. The validity of the proposed method is tested extensively in the simulation model of a real high-speed railway distribution system. The proposed method is not affected by fault type and fault resistance. Furthermore, comparing with the offline detection method of underground cables, it does not need any additional devices and will not interrupt the system operations.

Support vector classification and regression for fault location in distribution system using voltage sag profile

Fault location identification is an important task to provide reliable service to the customer. Most existing artificial intelligence methods such as neural network, fuzzy logic, and support vector machine (SVM) focus on identifying the fault type, section, and distance separately. Furthermore, studies on fault type identification are focused on overhead transmission systems and not on underground distribution systems. In this paper, a fault location method in the distribution system is proposed using SVM, addressing the limitations of existing methods. Support vector classification (SVC) and regression analysis are performed to locate the fault. The method uses the voltage sag data during a fault measured at the primary substation. The type of fault is identified using SVC. The fault resistance and the voltage sag for the estimated fault resistance are identified using support vector regression (SVR) analysis. The possible faulty sections are identified from the estimated voltage sag data and ranked using the Euclidean distance approach. The proposed method identifies the fault distance using SVR analysis. The performance of the proposed method is analyzed using Malaysian distribution system of 40 buses. Test results show that the proposed method gives reliable fault location.

Assessment of the Economic Value of Voltage Sag Mitigation Devices to Sensitive Industrial Plants

This paper investigates the economic value of voltage sag mitigation devices to end users. The focus is on sensitive industrial plants. Different types of power system faults are simulated on a typical British distribution network model to obtain voltage sag profiles at various locations in the network. The cost-effectiveness of various mitigation devices is investigated for industrial-size end users with various process characteristics and sensitivities, to obtain the optimal investment profile for each end-user plant. The sensitivity of the assessment to various levels of initial financial loss resulting from process interruption and network fault rates is also investigated. The findings would serve as valuable references for industrial end users who are considering investment in mitigation devices to reduce the financial losses caused by voltage sags.

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.

A generalized fault location method based on voltage sags for distribution network

AbstractAn enhanced fault location method based on voltage sag profiles for distribution networks is presented in this paper. In other previous methods, only a single measurement has been used. The proposed method can be used with any number of measurements in the network, making it more general. A new ranking approach that addresses multiple possibilities of the faulted section is proposed. Different case studies with various numbers of measurements are performed on a large 11‐kV network with the main feeder consisting of 42 buses to validate the method. The test results show that there is an improvement in terms of accuracy in detecting the faulted section in the first attempt for each additional measurement. Therefore, by utilizing the average value of each measurement, a better accuracy of fault location can be achieved. © 2013 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Development and Investigation of a Proposed Voltage Sag Index

A proposed voltage sag index based on power flow equations is developed and investigated in this paper. The index supervises the power quality of a system, through calculating the voltage sag profile caused by an increase in reactive demand due to induction motor starting. Mathematical equations representing the load angle of the system are also derived. The accuracy of the index is investigated for a range of load, transmission, and distribution line X/R ratio values as well as various motor loading levels. Results demonstrate the effectiveness and applicability of the proposed index.

Risk-Based Assessment of Financial Losses Due to Voltage Sag

This paper investigates the factors that influence the outcome of financial-loss analysis in voltage sag studies. Focusing on industrial processes, this paper considers the effects of voltage sag profile estimation, plant-load profile modelling, and process cycle modelling on the financial risk associated with process failure. Based on voltage sag monitoring records, sag profile is probabilistically modeled for the estimation of future sag characteristic. Variations in financial risk due to varying process activities in different stages of a process (process cycle) and load profile are also investigated. The effects of the individual factors are analyzed through Monte Carlo simulation. The stochastic net present value method is introduced as a financial analysis tool.

Estimation of system voltage sag profile using recorded sag data

AbstractThe influence of voltage sags on electrical equipment has become a major issue because of the widespread use of voltage‐sensitive devices. In order to reduce the influence of voltage sags at each customer's site, it is necessary to identify the drop in receiving voltage due to lightning strikes on transmission lines. However, it is hard to directly measure the sag level at every load node.In this report, a new method of efficiently estimating the system voltage sag profile is proposed, based on symmetrical coordinates. In the proposed method, limited sag data recorded at each substation in the power system are used for the estimation. Since the number of recorded nodes is generally far less than the number on the transmission route, a fast method is developed to calculate only the recorded faulted voltage by applying the reciprocity theorem for the Y‐matrix. Furthermore, an effective screening process is used to select limited candidates for the faulted transmission line.Results using the IEEJ East10 standard system and actual 1700 bus system are presented, showing that the estimation accuracy is sufficiently acceptable with lower computational effort. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 173(4): 9–19, 2010; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.21061

Non-linear representation of voltage sag profiles for fault location in distribution networks

Fault location for distribution networks with multiple laterals would requires additional information such as from fault indicators and protective devices. As SCADA systems to provide such information are limited in 11 kV or lower voltage distribution networks, effective fault location method that only use information from a measurement at primary substation is needed. This paper presents the application of calculated non-linear voltage sag profiles and voltage sag measurement at primary substation to locate a fault in distribution networks. The proposed method firstly identifies the faulted section. From the indentified section, fault distance is calculated. The method has been tested under different fault scenarios that include various fault resistance, loading variation and data measurement errors. The results indicate the possibility of using this method to support automatic fault management system.

観測電圧に基づく瞬低時系統電圧分布推定手法の開発

The influence of voltage sag to electric equipment has become big issues because of wider utilization of voltage sensitive devices. In order to reduce the influence of voltage sag appearing at each customer side, it is necessary to recognize the level of receiving voltage drop due to lightning faults for transmission line. However it is hard to measure directly those sag level at every load node.In this report, a new method of efficiently estimating system voltage sag profile is proposed based on symmetrical coordinate. In the proposed method, limited recorded sag data is used as the estimation condition which is recorded at each substation in power systems. From the point of view that the number of the recorded node is generally far less than those of the transmission route, a fast solution method is developed to calculate only recorder faulted voltage by applying reciprocity theorem for Y matrix. Furthermore, effective screening process is incorporated, in which the limited candidate of faulted transmission line can be chosen.Demonstrative results are presented using the IEEJ East10 standard system and actual 1700 bus system. The results show that estimation accuracy is sufficiently acceptable under less computation labor.

A Modified Sag Characterization Using Voltage Tolerance Curve for Power Quality Diagnosis

This paper newly defines a voltage sag duration considering the voltage tolerance characteristics of individual electrical device for power quality (PQ) diagnosis. The conventional sag characterizing method has the possibility to overestimate voltage sag in case of nonrectangular sag. Furthermore, it cannot take the voltage tolerance characteristics of individual device into account. The proposed method utilizes the monitored parameters (V/sub sag/,V/sub avg/,d) at PQ monitor and the minimum voltage (V/sub min/) of voltage tolerance curve. The voltage sag profile is approximated using k/sup th/ order radical root function and finally the sag duration is modified from this function. The proposed method is applied to the nonrectangular sag due to induction motor reacceleration. It effectively evaluates the actual effects of voltage sag on the customer equipments whether the sag is rectangular or not.

A Modified Voltage SAG Duration for Power Quality Diagnosis

This paper newly defines a voltage sag duration considering the voltage tolerance characteristics of individual electrical device for power quality (PQ) diagnosis. In PQ diagnosis, the magnitude and the duration of voltage sag are important parameters that characterize the voltage sag event. The conventional sag characterizing method has the possibility to overestimate the voltage sag. Furthermore it cannot take the characteristics of each device into account. The proposed method utilizes the minimum voltage of voltage tolerance curve. The voltage sag profile is approximated and the modified duration is newly defined considering the voltage tolerance characteristics. The proposed method is applied to the non-rectangular sag originated from induction motor starting and proved to be effective for PQ diagnosis. The modified voltage sag duration can be applied to stochastic analysis of PQ diagnosis and will give more realistic understanding to the customers.

Analytical approach to probabilistic prediction of voltage sags on transmission networks

Quantification of voltage sags at a location of interest is the basic requirement for assessing the compatibility between equipment and electrical supply. An analytical method is described that has been developed to determine the probability density functions of voltage sags caused by three phase faults across the network. The method takes into account the impact of fault positions along transmission circuits and patterns of generation associated with the corresponding load demands on the voltage sag profiles. The developed algorithm is applied to the IEEE 24-bus reliability test system to verify the technique and illustrate its application.