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Showing papers on "Voltage sag published in 2002"


Journal ArticleDOI
10 Dec 2002
TL;DR: In this article, a matrix-based voltage sag detection method is proposed to detect the start and end of a voltage sag and any associated phase shift in the main control system of a DVR.
Abstract: Dynamic voltage restorers (DVRs) are used to protect sensitive loads from the effects of voltage sags on the distribution feeder. This paper presents and verifies a novel voltage sag detection technique for use in conjunction with the main control system of a DVR. In all cases it is necessary for the DVR control system to not only detect the start and end of a voltage sag but also to determine the sag depth and any associated phase shift. The DVR, which is placed in series with a sensitive load, must be able to respond quickly to a voltage sag if end users of sensitive equipment are to experience no voltage sags. A problem arises when fast evaluation of the sag depth and phase shift is required, as this information is normally embedded within the core of a main DVR control scheme and is not readily available to either users monitoring the state of the grid or parallel controllers. Previous research presented an additional controller, which required phase and sag depth information to manipulate the injection voltage vector returned by the main controller in order to prevent the DVR injection transformers from saturating. Typical standard information tracking or detection methods such as the Fourier transform or phase-locked loop (PLL) are too slow in returning this information, when either applied to the injection voltage vector, or to the supply voltages directly. As a result of this the voltage sag detection method in this paper proposes a new matrix method, which is able to compute the phase shift and voltage reduction of the supply voltage much quicker than the Fourier transform or a PLL. The paper also illustrates that the matrix method returns results that can be directly interpreted, whereas other methods such as the wavelet transform return results that can be difficult to interpret.

296 citations


Journal ArticleDOI
TL;DR: In this paper, a phase advance compensation (PAC) strategy for the DVR is proposed in order to enhance the voltage restoration property of the device, which requires only an optimum amount of energy injection from the DVM to correct a given voltage sag.
Abstract: The compensation capability of a dynamic voltage restorer (DVR) depends primarily on the maximum voltage injection ability and the amount of stored energy available within the restorer. A new phase advance compensation (PAC) strategy for the DVR is proposed in order to enhance the voltage restoration property of the device. The scheme requires only an optimum amount of energy injection from the DVR to correct a given voltage sag. Supply voltage amplitude and phase detection scheme as well as a phase advance determination scheme are also included. The resulting DVR design is shown to be superior in terms of lower storage energy need compared to the conventional in-phase boosting method. The analytical results are validated by laboratory tests carried out on a prototype of the restorer. The efficacy of the proposed method is illustrated.

199 citations


Journal ArticleDOI
10 Dec 2002
TL;DR: In this article, a dynamic voltage restorer (DVR) based on Space Vector PWM is described, which is able to compensate for any type of voltage sag and uses a phase-locked loop to track phase jumps during a fault.
Abstract: Control of a dynamic voltage restorer (DVR) based on Space Vector PWM is described. The control algorithm is able to compensate for any type of voltage sag and uses a software phase-locked loop to track phase jumps during a fault. The control algorithm restores the depressed voltages to the same phase and magnitude as the nominal pre-sag voltages and then gradually tracks to the phase of the depressed voltages. Experimental results are shown to validate the control algorithm using a three-phase prototype with a power rating of 10 kVA.

114 citations


Journal ArticleDOI
TL;DR: In this article, an adaptive form factor is applied to the DVR injected voltage, which minimizes the disturbance seen by a sensitive load, while at the same time preventing saturation, and removes the redundancy normally associated with their steady state operation.
Abstract: During the transient period at the start of a voltage sag, a DVR injection transformer can experience a flux-linkage that is up to twice its nominal steady-state value. In order to prevent the transformers from saturating it is normal to choose a rating flux that is double that of the steady-state limit. An alternative method is to limit the flux-linkage during the transient switch-on period, thus preventing saturation. It is shown through both simulation and experimental results that an adaptive form factor can be applied to the DVR injected voltage, which minimizes the disturbance seen by a sensitive load, while at the same time preventing saturation. The proposed method removes the need for rating the series injection transformers for the DVR transient switch-on period, and therefore removes the redundancy normally associated with their steady state operation. In economic terms, this may reduce the total cost of a DVR system, thus making it a more attractive solution for voltage sag mitigation.

107 citations


Journal ArticleDOI
TL;DR: In this paper, the effects due to short interruptions and voltage sags were investigated and some calculations on induction motor behavior were carried out, and the effect of short interruption and voltage sag sags on the performance of a standard three-phase squirrel-cage motor was carried out.
Abstract: An experimental study and some calculations on induction motor behavior were carried out. The effects due to short interruptions and voltage sags were investigated. A standard three-phase squirrel-cage motor of 5.5 kW, 1500 r/min, and 380 V was used. The presence of induction motor changes the voltage sag waveform and duration. Protection characteristic curves and contactor ride-through capability together with their improvement are also studied. The interaction between motor load, system hot-load pickup, and voltage sag magnitude determine the motor re-acceleration duration and magnitudes. Besides, on-sag and post-sag currents can reach levels higher than the direct start values. Post-sag overcurrent duration can last more than twice the normal start time period, having specific energies in the same order of magnitude.

107 citations


Journal ArticleDOI
10 Dec 2002
TL;DR: In this article, a new voltage sag compensator for powering critical loads in electric distribution systems is discussed, which employs a pulsewidth modulation AC-AC converter (four insulated gate bipolar transistors per phase) along with an autotransformer.
Abstract: In this paper, a new voltage sag compensator for powering critical loads in electric distribution systems is discussed. The proposed scheme employs a pulsewidth-modulation AC-AC converter (four insulated gate bipolar transistors per phase) along with an autotransformer. During a disturbance such as voltage sag, the proposed scheme supplies the missing voltage and helps in maintaining rated voltage at the terminals of the critical load. The approach does not employ any energy storage components such as bulk capacitors/inductors and provides fast response at low cost. Under normal conditions the approach works in bypass mode, delivering utility power directly to the load; this method of control allows the transformer to be rated only for transient conditions, thus reducing its required size. A four-step switching technique to drive the AC-AC converter is employed to realize snubberless operation. A design example is presented, and simulation results are shown for a three-phase 230-V 5-kVA system. Experimental results on a single-phase unit are discussed. The proposed approach can be easily integrated into a distribution transformer supplying critical loads.

105 citations


Journal ArticleDOI
TL;DR: In this article, the authors proposed a method for retrieving sag-related information from statistics originally prepared for other purposes, and provided an estimate of the total annual sagrelated cost for each of the companies considered in this study and for each customer category.
Abstract: The annual number and cost of voltage sags were determined for five Finnish distribution companies. The method of fault positions was applied for the calculation of voltage sag frequency. The economic consequences were assessed by multiplying the sag frequency and cost by the number of customers. The cost of a single sag was taken from a survey that had been carried out in three Nordic countries in the mid 1990s. This paper proposes a method for retrieving sag-related information from statistics originally prepared for other purposes. In addition, this paper provides an estimate of the total annual sag-related cost for each of the companies considered in this study and for each customer category. The total cost per company appeared to be much higher than had generally been assumed.

100 citations


Journal ArticleDOI
TL;DR: A systematic filter design method is proposed, the primary objective of which is to achieve specific harmonic performance while ensuring that the DVR inverter rating and the loading effect are minimized.
Abstract: The role of the inverter-side filter used in the dynamic voltage restorer (DVR) is examined. Using the circuit analysis method, it is shown that the selection of the filter parameters can affect the DVR inverter rating. Furthermore, with the DVR filter-series injection transformer combination, the loading effect of the filter on the restorer and the primary supply system has been quantified under normal as well as voltage sag conditions. A systematic filter design method is then proposed, the primary objective of which is to achieve specific harmonic performance while ensuring that the DVR inverter rating and the loading effect are minimized. Illustrative examples are also included.

91 citations


Journal ArticleDOI
TL;DR: In this paper, the role of the inverter-side filter used in the dynamic voltage restorer (DVR) is examined, and a systematic filter design method is then proposed, the primary objective of which is to achieve specific harmonic performance while ensuring that the DVR inverter rating and the loading effect are minimized.
Abstract: The role of the inverter-side filter used in the dynamic voltage restorer (DVR) is examined. Using the circuit analysis method, it is shown that the selection of the filter parameters can affect the DVR inverter rating. Furthermore, with the DVR filter-series injection transformer combination, the loading effect of the filter on the restorer and the primary supply system has been quantified under normal as well as voltage sag conditions. A systematic filter design method is then proposed, the primary objective of which is to achieve specific harmonic performance while ensuring that the DVR inverter rating and the loading effect are minimized. Illustrative examples are also included.

81 citations


Journal ArticleDOI
07 Aug 2002
TL;DR: In this article, an analytical method was developed to determine the probability density functions of voltage sags caused by three phase faults across the network, taking 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.
Abstract: 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

67 citations


Proceedings ArticleDOI
05 Nov 2002
TL;DR: In this article, the VA requirement issues of series and shunt compensators of UPQC-Q and its performance is verified in a laboratory prototype are discussed and typical experimental results are presented to confirm the validity of the theory.
Abstract: Unified power quality conditioner (UPQC) is one of the major custom power solutions that is capable of mitigating the effect of supply voltage sag at the load end or the point of common coupling (PCC). It also prevents load current harmonics from entering the utility and corrects the input power factor of the load. The control of series compensator is such that it injects voltage in quadrature advance to the supply current, so that no active power is consumed by the series compensator at steady state. The UPQC employing this type of quadrature voltage injection in series is termed UPQC-Q. The present paper discusses the VA requirement issues of series and shunt compensators of UPQC-Q and its performance is verified in a laboratory prototype. The phasor diagram, control block diagram and typical experimental results are presented to confirm the validity of the theory.

Journal ArticleDOI
TL;DR: In this paper, the authors used the Computer Business Equipment Manufacturing Association (CBEMA) curve to evaluate the power acceptability or equipment sensitivity graph for repetitive sags, and found that the undervoltage part of the CBEMA curve follows very closely the expression /spl int/ /spl upsi//sup 2/ dt=k.
Abstract: Thunderstorms and lightning are large contributors to fault occurrence due to the fact that the spark stroke is repeated several times during a very short time interval. Lightning bolts are not the only origin for repetitive faults. Reclosers and recloser circuit breakers are among several types of cyclic loads that submit the system to a similar current pattern. The connected equipment may be able to withstand the first voltage sag but will drop out with the following one, if it arrives before the equipment reaches a stable situation or if the equipment self-recovers. The concept of recovering time was originally presented ten years ago without further development. The Computer Business Equipment Manufacturing Association (CBEMA) curve is the most widespread power acceptability or equipment sensitivity graph; however, its values are given in a one-event base so they cannot be applied for repetitive sag studies. The undervoltage part of the CBEMA curve follows very closely the expression /spl int/ /spl upsi//sup 2/ dt=k, which allows the extension of this criterion to repetitive sags. Results obtained are in good agreement with those previously published.

Proceedings ArticleDOI
10 Dec 2002
TL;DR: In this article, a new economical sag/swell voltage generator suitable for the evaluation of high power custom power devices such as DVR (dynamic voltage restorer) and DSTATCOM (distribution static compensator) was designed to generate the several power quality disturbances in MVA power ratings.
Abstract: This paper describes a new economical sag/swell voltage generator suitable for the evaluation of high power custom power devices such as DVR (dynamic voltage restorer) and DSTATCOM (distribution static compensator). Proposed system was designed to generate the several power quality disturbances in MVA power ratings-sag, swell, under voltage, over voltage and harmonic distortions. The sag and the under voltage can be generated by voltage drop across a reactor, while its magnitude and durations can be controlled by the firing angle of TCR (thyristor controlled reactor). In the case of the swell and the over voltage, we need a step-up transformer. Output of the step-up transformer is regulated by TCR to obtain nominal voltage level. At any given instant, if the firing angle of TCR is retarded or stopped, then we can obtain the swell voltage or the over voltage disturbance. Also we can generate harmonic current by controlling firing angles of TCR, while keeping the system voltage level within the specified limits. In this paper, two identical three-phase wye-connected TCRs are connected to the secondary windings of two step-down transformers, one operated from wye-wye transformer, the other from delta-wye transformer. Harmonic filters (11/sup th/ and 13/sup th/) are added to reduce the voltage distortion when TCRs are operated. Simulation results are given for several cases of voltage sag and swell generations. Design guidelines are given for the TCR. Finally, conclusions are given.

Proceedings ArticleDOI
07 Nov 2002
TL;DR: In this paper, the evaluation of different control strategies applied to a dynamic voltage restorer (DVR) for the mitigation of voltage sags is presented, with the objective to analyse the influence of the chosen strategies on subjects such as the energy storage capacity or the inverter rating.
Abstract: Power quality (PQ) is one of the most important issues of modern electrical distribution. Power electronics can play a very significant role in the correction of PQ problems. This paper deals with the evaluation of different control strategies applied to a dynamic voltage restorer (DVR) for the mitigation of voltage sags. The objective is to analyse the influence of the chosen strategies on subjects such as the energy storage capacity or the inverter rating. First Matlab-Simulink/PSB has been used to test the characteristics of the different chosen compensation techniques. Then the simulation results and conclusions have been experimentally validated in a 10 kVA rated DVR. The paper shows the most important aspects that should be taken into account for the choice of a compensation algorithm for a specific application.

Journal ArticleDOI
TL;DR: In this article, the voltage sag magnitude is obtained taking into account the voltage drop across (ZI), and the normal coordination procedure is obtained by comparing the sensitive equipment (SE) dropout curve with the timevoltage characteristic (TVC) of the protective device.
Abstract: S ensitive equipment protection against voltage sags can be given for overcurrent protective devices, provided that careful coordination has been carried out. The inclusion of distributed resources (DR) in a distribution system creates the possibility of an important change in the coordination procedure. Overcurrent protection and voltage sag coordination studies are based on the upstream impedance of the point of common coupling (PCC) or system impedance (Z1). Voltage sag magnitude is obtained taking into account the voltage drop across (ZI). Sag duration depends on the operating time of the overcurrent protective device. The normal coordination procedure is obtained by comparing the sensitive equipment (SE) dropout curve with the time-voltage characteristic (TVC) of the protective device. TVC is obtained from the time-current characteristic using (ZI) as the the conversion factor. Under normal system conditions, (Zi) is approximately constant, but, in the case of distributed generation (DG), this impedance can change from a low value (utility plus distributed generators) to a high value when the nonutility generators are the only supply (emergency). The new scenario implies that the protective device TVC is changed into a zone that modifies previous methodologies and increases the SE dropout susceptibility. The new situation should be considered, since SE will be kept operating under emergency conditions. An example using fuses as protective device is illustrated in this article.

Proceedings ArticleDOI
06 Oct 2002
TL;DR: The vanadium redox-flow battery (VRB) as mentioned in this paper is a rechargeable battery with a quick response time and an outstanding high-rate charge and discharge performance for short time periods.
Abstract: The vanadium redox-flow battery (VRB) is a rechargeable battery. The VRB has a quick response time and an outstanding high-rate charge and discharge performance for short time periods. The capacity of the VRB can be easily specified by increasing or decreasing the quantity of electrolyte. By utilizing all these features, the VRB can form an effective system to maintain power quality, such as a voltage sag compensation system, a stabilizing system for output fluctuations of wind turbines. SEI delivered a VRB to a semiconductor plant as a voltage sag compensation system in April 2001. This system normally operates at the rated output of 1.5 MW as a load leveling system. Should a voltage sag occur, it can deliver 3 MW for 1.5 seconds. This VRB has already completely compensated 20 voltage sags. SEI delivered a VRB for the project of The New Energy and Industrial Technology Development Organization (NEDO) in March 2001, and it is under evaluation at a WT power plant of Hokkaido Electric Power Company. The VRB's rated output power is 170 kW, and it can be operated up to a maximum power of 275 kW. The VRB has already been found to demonstrate good performance.

Journal ArticleDOI
TL;DR: In this paper, a simple method is presented that allows us to transform the information of starting current/time characteristics to voltage sag depth/time characteristic that are directly comparable with the sensitive equipment susceptibility curves (CBEMA and other curves).
Abstract: Voltage sag produced by an induction motor starting current is a main cause of sensitive equipment dropout. The use of a motor starter reduces the voltage sag depth but increases its duration. The subsequent connection to full voltage produces a new sag separated from the first one by a few seconds. A simple method is presented that allows us to transform the information of starting current/time characteristics to voltage sag depth/time characteristics that are directly comparable with the sensitive equipment susceptibility curves (CBEMA and other curves). The method also allows one to consider motor repetitive starts and different starting cycles.

Proceedings ArticleDOI
06 Oct 2002
TL;DR: Voltage sag tolerance levels were measured for samples of three equipment categories sensitive to sags: contactors, PCs and gas discharge lamps as mentioned in this paper, which justifies more generalized conclusions on performance of these device categories as well as more statistical approach to the issue.
Abstract: Voltage sag tolerance levels were measured for samples of three equipment categories sensitive to sags: contactors, PCs and gas discharge lamps. An up-to-date voltage waveform generator was used to produce and repeat the events as necessary. Remaining voltage and sag duration were the test variables. For contactors also the effect of point-on-wave of sag initiation was studied. The results were rather well convergent with earlier studies by other institutes. This justifies more generalized conclusions on performance of these device categories as well as more statistical approach to the issue. This kind of typical equipment sensitivity data is needed as a library for the future sag assessment methods.

Proceedings ArticleDOI
10 Dec 2002
TL;DR: In this paper, a new DVR circuit topology has been presented which has the ability to mitigate long duration voltage sags with comparatively small energy storage capacitors, and a closed loop controller that consists of an inner current loop and an outer voltage loop has been incorporated into the DVR inverter to maintain the load voltage at a desired level.
Abstract: Highly automated production processes are particularly susceptible to voltage disturbances in the power system. Series compensation in the form of dynamic voltage restorer (DVR) is used to mitigate these voltage disturbances. The compensation capability of a particular DVR topology depends on its voltage injection ability and maximum energy storage. This paper presents a new DVR circuit topology which has the ability to mitigate long duration voltage sags with comparatively small energy storage capacitors. The proposed DVR is equipped with a line-side current forced reversible rectifier that helps to maintain the DC-link voltage under voltage sag conditions. A closed loop controller that consists of an inner current loop and an outer voltage loop has been incorporated into the DVR inverter to maintain the load voltage at a desired level. Simulation and experimental results are presented to demonstrate the efficacy of proposed DVR multiloop controller for various voltage sags.

Journal ArticleDOI
TL;DR: In this article, a low-cost approach to provide ride-through capability for critical loads has been explored, where the output of the inverter is synchronized with the utility input and is regulated by keeping the DC-link voltage regulated, too.
Abstract: A low-cost approach to provide ride-through capability for critical loads has been explored. The approach provides continuous power to the load under two operational modes. Normal mode allows the load to be connected directly from the utility power supply, as long as it remains undisturbed. Once a voltage sag appears, the load is transferred to an inverter that provides the ride-through mode. The output of the inverter is synchronized with the utility input and is regulated by keeping the DC-link voltage regulated, too. An external energy source can be incorporated in the DC-link to provide ride-through during short-term power interruptions. Results show that the detection of the disturbance is quick, and the transfer between operational modes is seamless, causing no evident problems to the load. High efficiency is only achieved by applying the ride-through operational mode during the disturbance duration. Reduced size and low cost are additional characteristics of the proposed approach.

Journal ArticleDOI
TL;DR: In this paper, a Monte Carlo based approach is presented to evaluate the maximum voltage sag magnitude in series capacitor compensated radial distribution systems, taking into account the uncertainty of several factors associated with the practical operation of a power system.
Abstract: Voltage sags, also known as dips, are important to industrial reliability. This paper presents a Monte Carlo based approach to evaluate the maximum voltage sag magnitudes in series capacitor compensated radial distribution systems. In this context, investigations have been conducted on a sample distribution system model taking into consideration the uncertainty of several factors associated with the practical operation of a power system. The Power System Blockset of MATLAB is used in the simulation studies.

Patent
12 Dec 2002
TL;DR: In this article, a voltage sag and over-voltage compensation device for an AC electric power distribution system employing cascaded switching devices and a pulse-width modulated transformer is presented.
Abstract: A voltage sag and over-voltage compensation device for an AC electric power distribution system employing cascaded switching devices and a pulse-width modulated transformer. Each stage of the cascaded switching device includes a switching element located within a full-bridge rectifier circuit to allow bi-directional switching through each switching element (i.e., switching through the same switching element during the positive and negative portions of the AC voltage cycle). Each full-bridge rectifier also includes a snubber circuit connected in parallel with a corresponding switching element to absorb the current discharge caused by switching the input power supply to the transformer through the corresponding switching device under non-zero current conditions. On the output side, the voltage sag and over-voltage compensation device includes a filter capacitor to smooth the voltage-corrected AC power supply toward a sinusoidal power supply at the system frequency, and a notch filter to remove noise created by the switching elements.

Proceedings ArticleDOI
07 Aug 2002
TL;DR: In this article, a summary of the work performed by the authors to adapt and apply the ATP version to voltage sag analysis is presented, including an introduction to the capabilities of this tool, a short description of the new modules developed for voltage sagging analysis (stochastic prediction and index calculation), and some illustrative examples showing the advantages of new ATP modules.
Abstract: EMTP-type tools are widely used in power quality studies. This paper presents a summary of the work performed by the authors to adapt and apply the ATP version to voltage sag analysis. The document includes an introduction to the capabilities of this tool, a short description of the new modules developed for voltage sag analysis (stochastic prediction and index calculation), and some illustrative examples showing the advantages of the new ATP modules.

Proceedings ArticleDOI
07 Aug 2002
TL;DR: In this paper, a static series compensator for voltage sag mitigation is proposed, which has the capability to supply nonlinear loads, based on isolation of harmonic components of the load current, compensates for the effect of current harmonics circulating on the filter reactor.
Abstract: In this paper, a static series compensator for voltage sag mitigation is proposed, which has the capability to supply nonlinear loads. The control system, based on isolation of harmonic components of the load current, compensates for the effect of current harmonics circulating on the filter reactor. The latter would reduce the compensation capability of the device and introduce harmonic frequencies in the load voltage. The system also has the capability to filter out harmonic components in the supply voltage. Simulation results, obtained by using actual voltage sag recordings, are presented.

Journal Article
TL;DR: In this paper, two new methods, which are the average method of the d q conversion of instantaneous voltages and the low pass filter method for single phase voltage sag, are proposed.
Abstract: The correct detection of the voltage sag characteristics (its magnitude,duration and phase angle jump) is of great importance for the power quality evaluation and its mitigation.The existing methods including RMS voltage,peak voltage,fundamental voltage component and single phase average voltage are introduced.A fictitious three phase system is created from a reference single phase voltage by a 60 ° delay.With the d q conversion of voltages,two new methods,which are the average method of the d q conversion of instantaneous voltages and the low pass filter method of the d q conversion of instantaneous voltages,are proposed.The proposed methods can instantaneously quantify the phase angle jump,magnitude and duration for single phase voltage sag.By simulative calculation,the applicability of different methods is compared in detail.The result shows that the proposed methods possess the superiority of fast dynamic tracing performance and they are suitable for the analysis of voltage sag and the real time test of DVR.

Proceedings ArticleDOI
R. Cao1, E.R. Collins1
06 Oct 2002
TL;DR: In this article, the effects of different load types on the behavior of AC motor drives during voltage sags are analyzed and the authors explore torque and speed variations of constant, linear and quadratic loads during a voltage sag and subsequent voltage drop on DC-bus of the drive.
Abstract: Voltage sags are a frequent cause of disrupted operations for many industrial processes. This paper analyzes the effects of different load types on the behavior of AC motor drives during voltage sags. Voltage sags cause a voltage drop on the DC-bus of a drive, which may cause the drive to misoperate or trip offline. The tripping or failure of a drive due to a voltage sag affects the output torque of a drive-fed induction motor and, thus causes the connected load to operate abnormally. The impact of voltage sags on a load depends on the behavior of the drive, the type of load, the motor's inertia, etc. This paper discusses mathematical models for a drive, induction motor and various loads. It explores torque and speed variations of constant, linear and quadratic loads during a voltage sag and the subsequent voltage drop on DC-bus of the drive.

Proceedings ArticleDOI
20 Oct 2002
TL;DR: In this paper, a semiconductor circuit breaker is proposed to switch fast enough to keep voltage disturbance within acceptable limits in a short-circuit scenario, and the realization of the switch with state-of-theart semiconductors and its impact on the grid is analyzed.
Abstract: State-of-the-art mechanical circuit breakers in medium-voltage systems only allow handling of short-circuits if the short circuit power of the grid is limited Using delayed turn-off times, the circuit breaker can be coordinated with lower level protection gear Hence, a high availability of the grid can be guaranteed However, during a short-circuit a significant voltage sag can be noticed locally in the medium voltage grid Sensitive loads such as computers will fail even when voltage returns within a few seconds The proposed semiconductor circuit breaker is able to switch fast enough to keep voltage disturbance within acceptable limits The realization of the switch with state-of-the-art semiconductors and its impact on the grid is analyzed in this paper


Proceedings ArticleDOI
10 Dec 2002
TL;DR: In this article, the authors present new converter topologies for low-power voltage sag compensators, based on the elimination of the series transformer and the utilization of converter structures with reduced number of semiconductor switches.
Abstract: This paper presents new converter topologies for low-power voltage sag compensators, based on the elimination of the series transformer and the utilization of converter structures with reduced number of semiconductor switches. The main aspects for the specification of the components and a design example are described, along with a simulation study, including the evaluation of the operation of the proposed compensators with nonlinear loads.

Proceedings ArticleDOI
06 Oct 2002
TL;DR: In this article, the authors describe computer simulations used as an initial phase in process of designing a three-phase voltage sag generator and investigate the influence of various parameters, different circuit topologies and different control strategies.
Abstract: The paper describes computer simulations used as an initial phase in process of designing a three-phase voltage sag generator. The influence of various parameters, different circuit topologies and different control strategies is investigated and discussed in the paper. The main results and conclusions are illustrated numerically and graphically. The investigation resulted in selection of optimal design and control parameters for voltage sag generator. The PSCAD/EMTDC software environment was used in all computer simulations.