Short Duration Voltage Variations Research Articles

Power Quality Improvement of Micro Grid by Using DVR

Power quality is defined as the degree of voltage, current, frequency and waveform of power system under designed specification of the system. While transmitting the power from one end (generation) to another (load) utility has to face some power quality issues such as voltage sag, voltage swell, harmonics, inter-harmonics, voltage imbalance, voltage fluctuation, short duration voltage variation, long duration voltage variation, transient, power frequency variation, waveform distortion etc. These power quality issues directly effect on the efficiency of the power system and performance of the load equipment’s. Problems like voltage sag, voltage swell occurs due to sudden removal of large load from the system, energization of large capacitor bank or system fault like single-line-to-ground fault. These types of problems directly effect on equipment performance and accuracy, especially on sensitive equipment’s as computer, medical instruments, some electronic devices etc. To mitigate voltage sag, voltage swell problem in power system various devices are used such as DVR (dynamic voltage restorer) Key Words: Voltage sag, Voltage swell, Power quality, MATLAB simulation, Single-phase AC system, Single-phase AC load.

Impact of short-duration voltage variations on VSC-HVDC performance

The growing load demand globally necessitates increasing the penetration of renewable energy sources into electrical grids as well as interconnecting grids from different countries and even continents through HVDC transmission systems. Since these applications rely on power electronics devices, several power quality issues arise, namely voltage sags and swells. This paper analyzes the response of a VSC-HVDC transmission system that interconnects two asynchronous AC grids to short-duration voltage variations like sag and swell by adjusting the voltage of the controllable AC source. The system is simulated with the help of MATLAB/Simulink. The study records the effect of the manipulated AC voltage on the active/reactive powers and AC/DC voltages at both converter stations to evaluate the system stability due to these prevalent power quality challenges. The obtained results reveal that the system hardly withstands voltage variation for a short period.

Impact on Voltage Regulation in Medium Voltage Distribution Networks Due to the Insertion of Photovoltaic Generators

The objective of this paper was to analyze the impacts caused by the operation of voltage regulators in electrical distribution networks and to evidence the number of operations in the face of short-duration voltage variation caused by the high intermittency of the connected PV generators. A real LV and MV feeder was used, modeled in OpenDSS software, based on normative standards, adjustments, and technical maneuvers strategically used by the local utility. The analyses considered the temporal variations for the photovoltaic generators and different load demand profiles connected to the feeder. The feeder was submitted to the demand curves varying the load percentage, framing it in high and conventional (nominal) load according to the profiles of consumers and prosumers connected. The simulations made it possible to observe the exacerbated elevation in the number of maneuvers performed by the voltage regulators of the network. The single-phase voltage regulators stood out by the elevation of control operations, causing premature wear of the PV generation equipment connected to the most loaded phase. It was observed that discrepancies in the power flow in the lines and the voltage levels at the busbars. The creation of strategies and decisions to correct these impacts caused to transformers and regulators is possible.

Optimal allocation of power quality monitors considering short-duration voltage variations and parallel harmonic resonance conditions in power distribution systems

The proposed allocation methodology of Power Quality Monitors (PQMs) allows optimal monitoring of short-duration voltage variations and potential harmonic resonance conditions by defining strategic nodes in a Power Distribution System (PDS). The allocation methodology combines the Fault Position Method (FPM) and Harmonic Resonance Modal Analysis (HRMA) to obtain a binary covering matrix. The optimization process lately uses this matrix to determine the best installation nodes of the minimum number of PQMs that observe the considered power quality disturbances. From FPM, the remaining nodal voltages are studied for different short-circuits, which cause voltage sags and or swells. HRMA is used to calculate the modal impedances related to the critical modes and identify the respective harmonic frequencies of the PDS. The allocation problem is set as integer linear programming performed using a Branch and Bound algorithm. The proposed methodology was tested for 15 nodes PDS based on a CIGRÉ network and 24 nodes PDS derived from the IEEE 34 nodes test system. Results show that 2 to 4 PQMs are required for the 15 nodes PDS and 2 to 9 PQMs for the 34 nodes PDS to thoroughly observe the considered power quality disturbances.

Grid-connected photovoltaic system to mitigate momentary voltage dip based on the balance between the active and reactive powers

With a great potential yet to be explored in Brazil, the grid-connected photovoltaic system, besides supplying the active power, can also contribute to improve the voltage level grid providing reactive power. Therefore, this work proposes to use a Grid-Connected Photovoltaic System (GCPVS) equipped with a control that uses the automatic voltage regulator (AVR) to balance the injection of the active and reactive powers, thus softening the short-duration voltage variation, more specifically the momentary voltage dip. For this purpose, the GCPVS was connected in part of a real distribution grid that attend the block 1106 South of Palmas city, state of Tocantins, northern region of Brazil. It is shown that the active and reactive power delivered to the grid can be controlled to help the power quality of the main grid during a disturbance. During a short-circuit situation, the active power is reduced, freeing up space from the inverter capacity for maximum supply of reactive power, in this way, helping the main grid to return to an adequate voltage level. The simulation results show that such voltage profile improvement is possible. Therefore, they confirm that photovoltaic systems, even though considered small, can also provide ancillary services to the low voltage distribution grid during abnormal conditions, adding to the actions normally performed by conventional power plants

A Novel Switching Methodology for Low Voltage Static Regulators

This paper presents a new switching methodology for low voltage static regulators. The switching method proposed in this paper differs from those found in the literature due to it not needing a measurement of the current signal in the transformer tap windings and/or in the static switches. This method simplifies the control, reduces the cost of implementation, and allows safe application onto grids with low loading and high harmonic current distortion. In order to analyze and evaluate the performance of the proposed methodology, the static voltage regulator presented in this article was implemented in a computer simulation and, later, a laboratory prototype was built. The topology, the operational principles, and the specifications of its constituent components are discussed and presented in this paper. In addition, the prototype of the equipment was tested under three different load conditions: operating under no-load conditions, supplying a purely resistive load and supplying a nonlinear load. For each of the three types of loads considered, the static voltage regulator’s performance was evaluated using specific measurements, which considered the occurrence of both long and short duration voltage variations imposed on the input of the equipment by a programmable power source. The obtained results show that—in the worst-case scenario—the tap changing process takes less than 4 cycles of the fundamental frequency to be concluded. In light of the obtained performance, the proposed switching methodology for low voltage static regulators is a promising solution for large scale use under varied applications.

Implementation of a Photovoltaic Inverter with Modified Automatic Voltage Regulator Control Designed to Mitigate Momentary Voltage Dip

The main objective of this research is to propose an active and reactive power injection control in order to mitigate voltage sags. The proposed control strategy works in conjunction with a modified version of an automatic voltage regulator (AVR), where it will act on the active and reactive powers injected by the inverter to reduce the effects of voltage sags. In this way, the control will avoid possible shutdowns and damage to the equipment connected to the grid. The voltage improvement can be perceived for consumers connected to the power system. Modifications in AVR model and parameters are performed to speed up its performance, thus identifying the short-duration voltage variations (SDVV) and, consequently, the control acts to alter the powers, decreasing the active power injection and increasing the reactive power based on inverter capacity during the momentary voltage dip (MVD). Finally, when the fault is cleared, all values return to the pre-fault condition, so that the inverter only operates with active power. A 75 kW three-phase grid-connected photovoltaic system (GCPVS) equipped with the proposed control was inserted in a distribution grid of the city of Palmas, state of Tocantins, Brazil, and all of the computer simulations were performed on the Matlab/Simulink®.

Optical Voltage Transformer Based on FBG-PZT for Power Quality Measurement.

Optical Current Transformers (OCTs) and Optical Voltage Transformers (OVTs) are an alternative to the conventional transformers for protection and metering purposes with a much smaller footprint and weight. Their advantages were widely discussed in scientific and technical literature and commercial applications based on the well-known Faraday and Pockels effect. However, the literature is still scarce in studies evaluating the use of optical transformers for power quality purposes, an important issue of power system designed to analyze the various phenomena that cause power quality disturbances. In this paper, we constructed a temperature-independent prototype of an optical voltage transformer based on fiber Bragg grating (FBG) and piezoelectric ceramics (PZT), adequate to be used in field surveys at 13.8 kV distribution lines. The OVT was tested under several disturbances defined in IEEE standards that can occur in the electrical power system, especially short-duration voltage variations such as SAG, SWELL, and INTERRUPTION. The results demonstrated that the proposed OVT presents a dynamic response capable of satisfactorily measuring such disturbances and that it can be used as a power quality monitor for a 13.8 kV distribution system. Test on the proposed system concluded that it was capable to reproduce up to the 41st harmonic without significative distortion and impulsive surges up to 2.5 kHz. As an advantage, when compared with conventional systems to monitor power quality, the prototype can be remote-monitored, and therefore, be installed at strategic locations on distribution lines to be monitored kilometers away, without the need to be electrically powered.

Optimized Method for Locating the Source of Voltage Sags

Short-Duration Voltage Variations (SDVVs) are the power quality disturbances (PQD) that mainly affect industrial systems, and are originated for various reasons, in particular short circuits over large areas, even those originating in remote points of the electrical system. The location problem aims to indicate the area or region or distance from the substation that is connected to the source causing the voltage sags, and is a fundamental task to ensure good power quality. One of the strategies used to determine the location of sources causing SDVVs and for an implementation of machine learning algorithms in modern distribution networks, called Smart Grids. Monitoring a Smart Grid plays a key role, however mostly it generates a large volume of data (Big Data) and as a result, multiple challenges arise due to the properties of this data such as volume, variety and velocity. This work presents an optimization through genetic algorithm to select meters which already exist in the Smart Grid, using a voltage sag location method in order to reduce the data obtained and analyzed throughout the localization process. Optimization was evaluated through a comparison with a non-optimized localization method, this comparison showed a difference between the hit rates of less than 1%.

Power Quality Issues and Mitigation for Electric Grids with Wind Power Penetration

Large penetration of wind energy systems into electric-grids results in many power quality problems. This paper presents a classification of power quality issues, namely harmonics and short-duration voltage variation observed due to the integration of wind power. Additionally, different techniques and technologies to mitigate the effect of such issues are discussed. The paper highlights the current trends and future scopes in the improvement of the interconnection of wind energy conversion systems (WECSs) into the grid. As the voltage variation is the most severe power quality issue, case studies have been presented to investigate this problem using steady-state time-series simulations. The standard IEEE test system namely IEEE 123-node test feeder and IEEE 30-node grid are solved under different operating conditions with wind power penetration. Typical daily load profiles of a substation in Riyadh, Saudi Arabia, and an intermittent wind power generation profile are used in all case studies. Mitigation of voltage variations due to wind intermittency is achieved using reactive power compensation of the interface inverter. The results show the effectiveness of these approaches to avoid voltage variation and excessive tap setting movements of regulators and keep the voltage within the desired operating conditions.

Investigation of Main and Secondary Transformers on Mitigation of Voltage Sags, Swells and Interruptions in Unbalanced Medium Voltage Distribution Systems

—Since voltage interruptions, sags and swells are Power Quality (PQ) disturbances with great economic impact, studies that seek alternatives to mitigate its effects have been conducted extensively. The PQ Brazilian standard names these disturbances as Short-Duration Voltage Variations (SDVVs), classified them in terms of magnitude, duration, and frequency of occurrence. These parameters are used to calculate the Impact Factor (IF) of SDVVs, a severity-characterization index of their incidence. In this context, this work assesses the influence of three-phase transformer winding connection and neutral grounding on the quantities of SDVVs and the IF observed by an industrial consumer in a distribution system. Fault simulations at ATP-EMTP perform the study, considering two different winding connections for the secondary transformer and applying a grounding resistance to the neutral of the main transformer of the distribution system. The SDVVs are verified in two different ways: phase-to-ground and phase-to-phase voltages. It is observed that there are differences in these quantities and for the value of the IF due to the winding connection of the secondary transformer, the value of the neutral grounding resistance of the main transformer and the ways of voltage verification.

Multi-Objective Approach for Power Quality Monitor Allocation With Symmetry in Short-Duration Voltage Variations

In this paper, we present a new approach for solving the problem of power quality monitors (PQMs) optimal allocation, for the monitoring of short-duration voltage variations caused by a fault condition in a power grid system. The problem is treated in a multiobjective perspective with two optimal criteria: minimization of the number of PQMs and maximization of the number of identified faults. Non-identification of an event can occur as a result of symmetry conditions in the network, i.e., in cases where two or more faults generate the same signals in some buses, which leads to ambiguity in the monitoring results. Symmetry increases the complexity of both the problem formulation and solution. The problem is described as a multiobjective discrete optimization problem and is solved by the algorithm for bicriteria discrete optimization within reasonable computational time. That approach was tested in power grids of different characteristics and sizes. The results demonstrate the proposed methodology applicability for solving the problem in real-size networks.

Fault location in distribution systems from analysis of the energy of sequence component waveforms

This study presents a technique to locate the source of faults in distribution systems, i.e. to pinpoint where the fault has occurred along the distribution system. More specifically, it localises the origin of short duration voltage variations (SDVVs) in a distribution system. Fault location (its origin) is estimated solely from the voltage waveforms during the fault. More specifically, the energies of the instantaneous symmetrical components corresponding to the voltage waveforms are used to estimate the fault location. The proposed localisation strategy considers that the signal records during a fault are captured at the feeder start node and at other nodes scattered along the distribution systems. Simulation results show the feasibility of the proposed technique to accurately localise the origin of faults in distribution systems.

Modelling and Simulation of Current Source Converter based Dynamic Voltage Restorer for Voltage Regulation cum Harmonics Mitigation

The modern electric power distribution system faces lots of power quality (PQ) problems such as short and long duration voltage variations, voltage imbalance, waveform distortions, impulsive and oscillatory transients and voltage flicker etc. The custom power devices (CPD) have been designed and developed with the aim of mitigating these problems. The major CPDs introduced so far include distribution-static synchronous compensator (D-STATCOM), dynamic voltage restorer (DVR), unified power quality conditioners (UPQC), active power filters (APF) etc. However, most of these CPDs are designed and implemented using voltage source converter (VSC) topology. Although lots of research works have been carried out for realizing DVR system based on VSC topology, not much research work has been reported on the application of CSC topology in DVR system over the last one decade. Through this paper, it has been attempted to develop a model of DVR system based on CSC topology capable of performing dual power quality enhancement tasks viz. voltage regulation and harmonics mitigation at a power distribution system catering power to a variety of loads. The DVR system has been modeled and simulated in the MATLAB / Simulink platform and the simulation results reveal the effectiveness and validity of the proposed model for use in power distribution system.

Adaptive Threshold for Electrical Disturbances Segmentation

The detection of the electrical signal discontinuities in the oscillographies recorded in substations and/or points of common coupling allows their segmentation, which is crucial for implementation of automated methods for detection, classification, location and storage by classes of disturbances in electric power systems. In this context, this study provides a way of determining an adaptive threshold that allows the segmentation of voltage or current signals based on Wavelets decomposition. The disturbances considered in this work were the short-duration voltage variations, impulsive and oscillatory transients, and harmonic distortions. The signals were synthetically generated. Moreover, white noise was added on the signals. Thus, a Symlet Wavelet was applied to the signals in order to denoise them. In the sequence, a Daubechies Wavelet was used to decompose the filtered signals. So, to determine the initial and final points of each segment, an adaptive threshold was established based on the energy and entropy of energy for the second level of decomposition. Thus, the number and position of each segment were determined according to the intersections of the detail curves and the thresholds found.

Location of faults generating short-duration voltage variations in distribution systems regions from records captured at one point and decomposed into damped sinusoids

This study investigates the detection and localisation of faults provoking short-duration voltage variations - sags (dips) and swells - in small power distribution networks. It aims to accomplish those tasks by capturing fault records, voltage and current waveforms, at just one point in the system, the substation. The main objective is to classify the fault type and locate the fault origin occurring in a given region of a power delivery network. For that purpose, fault inception is triggered by a sensitive phase-locked loop. Then, the captured signals are decomposed using damped sinusoids of arbitrary temporal support by means of an adaptive decomposition algorithm. Subsets of the parameters defining the damped sinusoids are used for classifying the fault type and indicating the fault location. The fault-type classification is obtained by using support vector machines, whereas the fault location is obtained by means of an artificial neural network. The simulation results for a simple but actual power distribution system with three possible places for fault occurrence are presented. The exact fault-type classifications were obtained while a correct localisation of 85- of the faults was accomplished.

Practical Aspects of Performance Tests on Power Quality Analyzers

This paper aims to provide analysis for qualification and quantification of causes related to results deviations in relation to a default value eventually recorded by power quality analyzers while the calibration tests are performed by the Power Quality Group of the Federal University of Uberlândia. Specifically, it is shown the method effects for calculating the RMS voltage while the time and short-duration voltage variations amplitude are quantified. Additionally, it is presented the differences between the various methods available to quantify the voltage unbalances, as well as the impacts due to different methods of calculating the RMS average recorded by the power quality analyzer.

Measurement and Analysis of Electric Power Quality for Commercial Vessels

Owing to more and more sensitive loads installed in modern ships, ship owners and builders have been faced with rising numbers of complaints about the quality of power. However, the existing power monitoring facilities installed onboard for recording deviations of power parameters is only over steady-state conditions due to limited capacity of measurement equipment and ignores short-duration phenomena. To understand the true supply quality in ships, a power quality (PQ) monitoring technique is employed in this paper. The PQ parameters including short-duration and long-duration voltage and frequency variations in a practical commercial vessel power system under different operating conditions are analyzed and their statistic data are reported. Through PQ measurement and analysis, the quality of supply can be quantified and assessed according to classification society standards. Analysis model developed in this paper can assist them in understanding true supply quality in ships for further determining proper PQ mitigation options.

Hybrid Method to Assess Sensitive Process Interruption Costs Due to Faults in Electric Power Distribution Networks

This paper shows a new hybrid method for risk assessment regarding interruptions in sensitive processes due to faults in electric power distribution systems. This method determines indices related to long duration interruptions and short duration voltage variations (SDVV), such as voltage sags and swells in each customer supplied by the distribution network. Frequency of such occurrences and their impact on customer processes are determined for each bus and classified according to their corresponding magnitude and duration. The method is based on information regarding network configuration, system parameters and protective devices. It randomly generates a number of fault scenarios in order to assess risk areas regarding long duration interruptions and voltage sags and swells in an especially inventive way, including frequency of events according to their magnitude and duration. Based on sensitivity curves, the method determines frequency indices regarding disruption in customer processes that represent equipment malfunction and possible process interruptions due to voltage sags and swells. Such approach allows for the assessment of the annual costs associated with each one of the evaluated power quality indices.

Método híbrido para o cálculo dos custos de interrupções em processos eletro-eletrônicos causados por faltas em sistemas de distribuição de energia elétrica

Neste trabalho é apresentado um método híbrido para análise de riscos de interrupções em processos sensíveis provocadas por faltas nos sistemas de distribuição de energia elétrica. Com a utilização deste método, são avaliados índices relativos às interrupções de longa duração e às variações de tensão de curta duração (afundamentos e elevações) em cada consumidor da rede de distribuição de energia elétrica. O método permite, de forma inovadora, a obtenção, para cada ocorrência na rede, dos valores de magnitude da tensão e da duração do evento. Em cada barra do sistema, as freqüências de ocorrências de cada índice são obtidas e classificadas por faixas de magnitude e duração. O método parte de um conjunto de informações de configuração, de parâmetros da rede e dos dispositivos de proteção e, através de um conjunto de simulações aleatórias de curto-circuito, é possível mapear as áreas de risco relativas aos fenômenos de interrupção e variações de tensão de curta duração (VTCDs). Dispondo ainda do conjunto de curvas de sensibilidade dos processos industriais, avaliam-se as freqüências de disrupções de processos, esperadas por ano no ponto analisado, isto é, o número de vezes que um processo é interrompido pelos eventos de curta duração considerados, para então serem avaliados os custos anuais associados.