Showing papers in "IEEE Transactions on Power Delivery in 1997"
TL;DR: In this paper, the optimal power flow control in electric power systems by the use of a unified power flow controller (UPFC) has been investigated and models suitable for incorporation in power flow programs are developed and analyzed.
Abstract: This paper deals with optimal power flow control in electric power systems by the use of a unified power flow controller (UPFC). Models suitable for incorporation in power flow programs are developed and analysed. The application of UPFC for optimal power flow control is demonstrated through numerical examples. It is shown that a UPFC has the capability of regulating the power flow and minimising the power losses simultaneously. An algorithm is proposed for determining the optimum size of UPFC for power flow applications. The performance of UPFC is compared with that of a phase shifting transformer (PST).
430 citations
TL;DR: In this paper, a wavelet compression technique for power quality disturbance data is presented, which is performed through signal decomposition, thresholding of wavelet transform coefficients and signal reconstruction.
Abstract: In this paper, the authors present a wavelet compression technique for power quality disturbance data. The compression technique is performed through signal decomposition, thresholding of wavelet transform coefficients and signal reconstruction. Threshold values are determined by weighting the absolute maximum value at each scale. Wavelet transform coefficients whose values are below the threshold are discarded, while those that are above the threshold are kept along with their temporal locations. The authors show the efficacy of the technique by compressing actual disturbance data. The file size of the compressed data is only one-sixth to one-third that of the original data. Therefore, the cost related to storing and transmitting the data is significantly reduced.
336 citations
Journal Article•
TL;DR: In this paper, the theoretical aspects of load modeling in harmonic penetration studies with a particular reference to the rotating part of load are discussed. And some guidelines are also provided for a correct use of the proposed model in system studies concerning harmonic penetration within electric distribution networks.
Abstract: This paper describes on improved model of rotating loads in complex load areas. The first section of the paper concentrates on the theoretical aspects of load modeling in harmonic penetration studies with a particular reference to the rotating part of load. The second section illustrates the results achieved from the experimental surveys conducted both in the laboratory and at a major industrial customer, in order to validate the model porposed in the field The third section describes the calibration stage of the proposed model based on results from a statistical survey conducted at manufacturers on parameter variation vs. frequency with a large sample of both LV and MV induction motors. Finally, some guidelines are also provided for a correct use of the proposed model in system studies concerning harmonic penetration within electric distribution networks.
334 citations
TL;DR: In this paper, a fault location and diagnosis scheme is proposed to accurately identify the location of a fault upon its occurrence, based on the integration of information available from disturbance recording devices with knowledge contained in a distribution feeder database.
Abstract: This paper presents new techniques for locating and diagnosing faults on electric power distribution feeders. The proposed fault location and diagnosis scheme is capable of accurately identifying the location of a fault upon its occurrence, based on the integration of information available from disturbance recording devices with knowledge contained in a distribution feeder database. The developed fault location and diagnosis system can also be applied to the investigation of temporary faults that may not result in a blown fuse. The proposed fault location algorithm is based on the steady-state analysis of the faulted distribution network. To deal with the uncertainties inherent in the system modeling and the phasor estimation, the fault location algorithm has been adapted to estimate fault regions based on probabilistic modeling and analysis. Since the distribution feeder is a radial network, multiple possibilities of fault locations could be computed with measurements available only at the substation. To identify the actual fault location, a fault diagnosis algorithm has been developed to prune down and rank the possible fault locations by integrating the available pieces of evidence. Testing of the developed fault location and diagnosis system using field data has demonstrated its potential for practical use.
291 citations
TL;DR: In this paper, a control strategy for the damping of electromechanical power oscillations using an energy function method is derived, which is shown to be effective both for damping large signal and small signal disturbances and are robust with respect to loading condition, fault location and network structure.
Abstract: This paper examines improvement of power system dynamics by use of unified power flow controllers, thyristor controlled phase shifting transformers and thyristor controlled series capacitors. Models suitable for incorporation in dynamic simulation programs for studying angle stability are analysed. A control strategy for the damping of electromechanical power oscillations using an energy function method is derived. The achieved control laws are shown to be effective both for the damping of large signal and small signal disturbances and are robust with respect to loading condition, fault location and network structure. Furthermore, the control inputs are easily attainable from locally measurable variables. The effectiveness of the controls are demonstrated for model power systems.
279 citations
TL;DR: In this paper, it was shown that voltage sags experienced by three-phase loads such as adjustable-speed drives can be classified into four types, and each sag can further be characterized by a magnitude and a phaseangle jump.
Abstract: It is shown in this paper that voltage sags experienced by three-phase loads, such as adjustable-speed drives, can be classified into four types. Each sag can further be characterized by a magnitude and a phase-angle jump. Relations between fault type, sag type and load connection are presented. The transfer of sags through transformers is discussed. The magnitude and phase-angle jump of sags are directly related to the voltage in the faulted phase, or between the faulted phases, at the point-of-common coupling between the load and the fault.
240 citations
Journal Article•
222 citations
TL;DR: In this article, a unified model of a power system installed with three flexible AC transmission systems is established, and their effectiveness in suppressing power system oscillations is investigated by analysing their damping torque contributions.
Abstract: The static VAr compensator (SVC), controllable series compensator (CSC) and phase shifter (PS) are three of the options of power electronic devices, referred to as FACTS (flexible AC transmission systems) devices. They are becoming of increasing importance in suppressing power system oscillations and improving system damping. In this paper, a unified model of a power system installed with these three FACTS devices is established. Their effectiveness in suppressing power system oscillations is investigated by analysing their damping torque contributions to the power system. The work in this paper relies on the theoretical analysis of a general single-machine infinite-bus power system where the objective is to present an insight into the operation of the damping control of the FACTS devices.
219 citations
TL;DR: In this article, a wavelet technique is proposed for the analysis of the propagation of transients in power systems, and the advantages and disadvantages of the method are discussed and the way in which these analysis methods complement previously reported identification methods is described.
Abstract: In the literature, wavelet techniques have been proposed for the identification of power system transient signals (e.g., lightning impulse, and capacitor switching transients). In this paper, the wavelet technique is proposed for the analysis of the propagation of transients in power systems. The advantages and disadvantages of the method are discussed and the way in which these analysis methods complement previously reported identification methods is described. An example based on the discretized solution of a differential equation is given.
216 citations
TL;DR: In this article, a new method to discriminate internal fault from inrush current by the sum of active power flowing into transformers from each terminal was proposed, and the usefulness is confirmed by applying the method to the measured inrush and simulated fault data.
Abstract: To avoid the needless trip by magnetizing inrush current, the second harmonic component is commonly used for the blocking differential relay in power transformers. However, the second harmonic component in fault current is increased by the introduction of underground 500 kV lines. This paper describes a new method to discriminate internal fault from inrush current by the sum of active power flowing into transformers from each terminal. The average power is almost zero for energizing, but an internal fault consumes large power. To check the performance of this method, actual inrush current and voltage waveforms of a 500/154 kV transformer are accurately measured by digital equipment. The usefulness is confirmed by applying the method to the measured inrush and simulated fault data.
189 citations
TL;DR: In this paper, an evolutionary programming (EP) based fuzzy system development technique is proposed to identify the incipient faults of the power transformers using the IEC/IEEE DGA criteria as references, a preliminary framework of the fuzzy diagnosis system is first built.
Abstract: To improve the diagnosis accuracy of the conventional dissolved gas analysis (DGA) approaches, this paper proposes an evolutionary programming (EP) based fuzzy system development technique to identify the incipient faults of the power transformers. Using the IEC/IEEE DGA criteria as references, a preliminary framework of the fuzzy diagnosis system is first built. Based on previous dissolved gas test records and their actual fault types, the proposed EP-based development technique is then employed to automatically modify the fuzzy if-then rules and simultaneously adjust the corresponding membership functions. In comparison to results of the conventional DGA and the artificial neural networks (ANN) classification methods, the proposed method has been verified to possess superior performance both in developing the diagnosis system and in identifying the practical transformer fault cases.
TL;DR: In this article, a method to consider the dynamic changes in the network's topology for the coordination of directional overcurrent relays using linear programming is presented, and proper coordination constraints are included by using linear approximations for the relay dynamics.
Abstract: This paper presents a method to consider the dynamic changes in the network's topology for the coordination of directional overcurrent relays using linear programming The proper coordination constraints are included by using linear approximations for the relay dynamics The application of the methodology as well as the importance of considering the transient configuration changes are illustrated with a practical example and a test case consisting of a real industrial power system
TL;DR: In this article, a new model for conductors under simultaneous tensile and bending loads is presented, which takes into account the interlayer friction and the inter-layer slip in the conductor during bending and leads to a variable bending stiffness, i.e. a stiffness which changes with the bending displacement and the tension applied to the conductor.
Abstract: This paper presents a new model for conductors under simultaneous tensile and bending loads. The proposed conductor model takes into account the interlayer friction and the interlayer slip in the conductor during bending and leads to a variable bending stiffness, i.e. a stiffness which changes with the bending displacement and the tension applied to the conductor. The theoretical concept is validated by extensive tests using an innovative measurement setup, the "cable-scanner", which detects, by noncontact scanning of the conductor surface, the displacement and the curvature of the conductor axis.
TL;DR: The authors of this paper summarize the major possible alternatives and the reasons which may lead a utility to modify its original choices and the result of this analysis is the decision to change the neutral earthing of rural MV networks.
Abstract: Various neutral grounding techniques are applied in medium voltage distribution networks throughout the world. This is due to the fact that implementation of a particular grounding solution is the result of compromise between several objectives which are sometimes contradictory. The right compromise depends on the physical characteristics of the networks, type and density of load and the importance awarded to safety and power supply quality. Use of digital protection and automatic control systems may also have an impact on selection criteria. The authors of this paper summarize the major possible alternatives and the reasons which may lead a utility to modify its original choices. Developments by EDF are analyzed and the resulting potential benefits in terms of safety and power supply quality are indicated. The result of this analysis is the decision to change the neutral earthing of rural MV networks.
TL;DR: The TVA STATCON is the first of its kind, using GTO thyristor valves, to be commissioned in the United States, and is currently the largest installation of this type in the world.
Abstract: In 1995 a /spl plusmn/100 MVA static synchronous compensator (STATCON) was commissioned for the Tennessee Valley Authority (TVA) at the Sullivan substation in North-Eastern Tennessee, USA. This was an historic milestone in the initiative for flexible AC transmission systems (FACTS) promoted by the Electric Power Research Institute (EPRI). The TVA STATCON is the first of its kind, using GTO thyristor valves, to be commissioned in the United States, and is currently the largest installation of this type in the world. Commissioning tests have now been completed and the STATCON is operating continuously online. The demonstrated performance of the equipment has either met or exceeded expectations in all areas and has proven beyond doubt the viability of this type of equipment in high power transmission systems. This paper briefly reviews the STATCON installation and reports on the static and dynamic performance observed during commissioning.
TL;DR: In this paper, an artificial neural network (ANN) was applied to inrush detection and reconstruction of distorted secondary CT currents due to saturation, which improved the reliability of the protection operation.
Abstract: This paper suggests the possibility of improving digital power transformer protection. The establishment of inrush in power transformers is becoming unreliable in existing numerical protection. An artificial neural network (ANN) was applied to inrush detection. The saturation of protective current transformers (CT) cannot be totally eliminated despite proper dimensioning. ANN was used for the reconstruction of distorted secondary CT currents due to saturation. In both cases, an ANN was included in the protection algorithm as an extension of the existing methods, which improved the reliability of the protection operation. The paper presents the digital protection algorithm completed in this way and the laboratory equipment by means of which experimental results were obtained. The results confirm faster and more reliable recognition of transformer inrush, as well as satisfactory reconstruction of the distorted secondary CT currents.
TL;DR: In this article, the authors point out that the ability to double the power transfer of the uncompensated line applies also to the flexible AC transmission systems (FACTS), such as the STATCOM, the unified power flow controller (UPFC), the PWM asynchronous DC link, the thyristor-controlled series capacitor (TCSC), and the pWM series static VAr compensator have stabilized AC voltage support.
Abstract: Many controllers of flexible AC transmission systems (FACTS), such as the STATCOM, the unified power flow controller (UPFC), the PWM asynchronous DC link, the thyristor-controlled series capacitor (TCSC) and the PWM series static VAr compensator have stabilized AC voltage support. Thus, they can be sited at the mid-point of the transmission line, which has been proven by the late E.W. Kimbark, as the optimum location for shunt capacitor compensation. This paper points out that the ability to double the power transfer of the uncompensated line applies also to the aforementioned FACTS devices. The mid-point siting also facilitates the independent control of reactive power at both ends of the transmission line.
TL;DR: In this paper, the authors proposed two control issues: (1) regulation of the DC capacitance voltages and (2) their equalization to ensure the even sharing of voltage stresses in the gate-turn-off thyristors (GTOs), and (3) to prevent the degradation of total harmonic distortion (THD) factors, as all harmonic elimination strategies depend on equal voltages in their assumptions.
Abstract: Because of the high MVA ratings, it would be expensive to provide independent, equal, regulated DC voltage sources to power the multilevel converters which are proposed for STATCOMs. DC voltage sources can be derived from the DC link capacitances which are charged by the rectified AC power. This paper addresses two control issues: (1) regulation of the DC capacitance voltages and (2) their equalization. Equalization is necessary (i) to ensure the even sharing of voltage stresses in the gate-turn-off thyristors (GTOs), and (ii) to prevent the degradation of total harmonic distortion (THD) factors, as all harmonic elimination strategies depend on equal voltages in their assumptions. The strategies considered are: (a) the fundamental frequency method, and (b) the sinusoidal pulse width modulation method. Digital simulations are used to confirm the feasibility of the control methods.
TL;DR: In this article, a method of analysis to cope with this task is presented and motivated by application to a system with dual HVDC converters, and using the identified factors influencing the interactions, its practical realization is also illustrated.
Abstract: With the increased use of HVDC transmission systems in power systems, situations have arisen and will be even more frequent in the future, where several HVDC systems are located in the vicinity of each other It is evident that interactions between the different HVDC systems will occur in such configurations, and it is of importance to analyze such systems in a systematic way to ensure that there are no risks of adverse interactions A method of analysis to cope with this task is presented and motivated in this paper This method is demonstrated by application to a system with dual HVDC converters, and using the identified factors influencing the interactions, its practical realization is also illustrated
TL;DR: In this article, a variable window discrete Fourier transform (DFT) is used for frequency tracking and phasor estimation in a numerical relay, and a new technique for tracking the frequency is outlined.
Abstract: Digital generator protection is a complex and difficult problem. Analog and solid state methods have been successfully applied to generator protection in the past and implementation of these functions in a digital device is a continuing trend. This paper explores a new method to implement frequency tracking and phasor estimation in a numerical relay. A new algorithm is presented which utilizes a variable window discrete Fourier transform (DFT) for frequency tracking. Use of the DFT to compute the phasor estimates at a frequency other than the assumed frequency is outlined first. Next, a new technique for tracking the frequency is outlined. The paper concludes with testing of the new algorithm.
TL;DR: In this article, the authors present a method for predicting the net harmonic currents produced by a large number of electric vehicle (EV) battery chargers, which is stochastically formulated in order to account for randomness in individual charger start-time and battery state-of-charge.
Abstract: This paper presents a method for predicting the net harmonic currents produced by a large number of electric vehicle (EV) battery chargers. The problem is stochastically formulated in order to account for randomness in individual charger start-time and battery state-of-charge. The authors introduce a model that allows for partial harmonics cancellation due to diversity in magnitudes and phase angles. A general solution technique is presented along with an example using data from a commercially available EV charger. Their results show that a limiting distribution of 7-10 chargers is adequate for accurately predicting harmonic injection currents using the central limit theorem. They also show that the expected values of net harmonic currents are considerably less than the peak values that would have been realized if the same number of chargers were operated in unison.
TL;DR: In this paper, the development of an adaptive out-of-step relay, from the formulation of its concept to its field implementation at the Florida-Georgia interface, is described.
Abstract: The paper describes the development of an adaptive out-of-step relay, from the formulation of its concept to its field implementation at the Florida-Georgia interface. Adaptive relaying seeks to make adjustments to the relay characteristics as power system conditions change, thereby making the relay more attuned to the prevailing power system conditions. The work described here began as a theoretical examination of the out-of-step relaying application, its possible shortcomings, and the opportunities to make adaptive improvements. It is shown that for a system that behaves primarily as a two-machine power system, the out-of-step relay could be made more secure by applying the principle of equal area criterion. The paper describes the theory of such a relay, its hardware configuration, and the system as it is installed in the field. The newly developed technology of synchronized phasor measurements plays an important role in the realization of this relay. The paper includes a summary of the field experience gathered over a period of one year.
TL;DR: In this paper, a three-phase model for arc furnaces has been developed to fully represent the unbalances that are present in real industrial plants and which play a central role in the behavior of compensation devices such as SVCs.
Abstract: This paper presents a new arc furnace model which copes with the two main voltage disturbances normally associated with arc furnaces: voltage fluctuations; and harmonics. The model is based on the stochastic nature of the electric arc current-voltage characteristic. The model has been estimated from measurements made in two actual electric plants. Although a single-phase model has been normally proposed, this paper develops a three-phase model in order to fully represent the unbalances that are present in real industrial plants and which play a central role in the behavior of compensation devices such as SVCs. The model has been implemented using the SIMULINK environment in order to facilitate later simulation of advanced disturbance control systems. Finally, the simulation results are compared with actual data in order to validate the accuracy of the model.
TL;DR: In this paper, the authors present methods to determine the impact of momentary interruptions and storms on the reliability of an existing utility distribution system and explore the reliability impact of distribution automation.
Abstract: The goal of distribution system reliability assessment is to predict the availability of power at each customer's service entrance. Existing methods predict the interruption frequency and duration each customer can expect, but omit two major contributing factors: momentary interruptions and storms. This paper presents methods to determine the impact of each phenomena. These methods are then used to assess the reliability of an existing utility distribution system and to explore the reliability impact of distribution automation.
TL;DR: In this paper, the authors describe a new technique for sampling synchronisation in a numerical differential feeder protection relay, which uses a Global Positioning System satellite receiver for sampling synchronization at each end of the protected feeder.
Abstract: This paper describes a new technique for sampling synchronisation in a numerical differential feeder protection relay. The protection uses a Global Positioning System satellite receiver for sampling synchronization at each end of the protected feeder. The EMTP/ATP power system simulator was used to simulate a typical distribution feeder with faults at various locations. The current signals generated at both ends of feeder were used to evaluate the performance of the protection. These tests were carried out using a protection simulator. The results illustrate the effect of current transformer saturation on the sensitivity and stability of the protection. Finally it is shown that a precisely synchronized differential protection is fast, selective and accurate. On an internal fault it provides a high operating sensitivity, whilst it remains stable on all external faults.
Journal Article•
TL;DR: In this article, a technique of estimating the secondary current corresponding to the current transformer ratio under CT saturation is presented, which can improve the sensitivity of relays to low level internal faults, minimize the instability of relay for external faults, and might ultimately assist in reducing the dimension of the required CT core cross section.
Abstract: Current transformer (CT) saturation may cause relays to malfunction. The conventional method to deal with the problem is overdimensioning of the core so that CTs can carry up to 20 times the rated current without exceeding 10 % ratio correction. However, this not only reduces the sensitivity of relays, but also increases the CT core size. This paper presents a technique of estimating the secondary current corresponding to the CT ratio under CT saturation. The proposed algorithm can improve the sensitivity of relays to low level internal faults, minimize the instability of relays for external faults, and might ultimately assist in reducing the dimension of the required CT core cross section.
TL;DR: In this article, a new wideband transmission line model, based on synthesizing the line functions directly in the phase domain, is presented, which includes the complete frequency-dependent nature of untransposed overhead transmission lines by means of recursive convolutions over a wide frequency range.
Abstract: A new wideband transmission line model, based on synthesizing the line functions directly in the phase domain, is presented. It includes the complete frequency-dependent nature of untransposed overhead transmission lines by means of recursive convolutions over a wide frequency range. The model belongs to the class of time-domain models and is designed to be implemented in general electromagnetic transients programs such as the EMTP. Because the synthesis of the frequency-dependent modal transformation matrix is avoided, the method requires fewer convolutions at each time step than full frequency-dependent modal-domain models. Simulations have been performed comparing the proposed model with existing line models, with field recordings, and with calculations from a frequency-domain program. The new model provides accurate answers in both steady-state and transient conditions.
TL;DR: In this paper, a frequency domain arc furnace model for iterative harmonic analysis by means of a Newton method is presented, which offers a three-phase configuration where there is no path for homopolar currents.
Abstract: This paper presents a new frequency domain arc furnace model for iterative harmonic analysis by means of a Newton method. Powerful analytical expressions for harmonic currents and their derivatives are obtained under balanced conditions of the power system. The model offers a three-phase configuration where there is no path for homopolar currents. Moreover, it contemplates continuous and discontinuous evolution of the arc current. The solution obtained is validated by means of time domain simulations. Finally, the model was integrated in a harmonic power flow where studies have been performed in a network with more than 700 busbars and 7 actual arc furnace loads.
Journal Article•
TL;DR: In this article, a model for predicting the flashover voltage of ice-covered insulators energized with ac voltage is presented, taking into account the variation of ice surface conductivity as a function of freezing water conductivity.
Abstract: A model for predicting the flashover voltage of ice-covered insulators energized with ac voltage is presented in this paper. The model takes into account the variation of ice surface conductivity as a function of freezing water conductivity. The effects of the length of the arc on its own characteristics, as well as the ac arc reignition condition, were determined in a laboratory investigation using triangular ice samples. The model is applied to a short string of 5 IEEE standard insulator units. There is an excellent concordance between the 50% flashover voltage calculated from the mathematical model and the experimental results.
TL;DR: In this paper, the authors describe the characteristics of energy absorption of surge arresters on power distribution lines due to direct lightning strokes using the EMTP, the effect of an overhead ground wire and the influence of the installation position of a surge arrester on the energy absorption are investigated quantitatively.
Abstract: The authors describe the characteristics of energy absorption of surge arresters on power distribution lines due to direct lightning strokes. Using the EMTP, the effect of an overhead ground wire and the influence of the installation position of a surge arrester on the energy absorption are investigated quantitatively. The analysis shows that: (1) an overhead ground wire is more effective in preventing damage to surge arresters than increasing the withstand capabilities of surge arresters by a factor of two; (2) the energy absorption without an overhead ground wire is about 3/spl sim/5 times larger than that with one; and (3) in the case of direct lightning strokes to an overhead ground wire, the energy absorption of surge arresters installed at the termination of a line is approximately 2.3 times larger at its maximum than that of arresters installed in the midst of a line.