Showing papers in "IEEE Transactions on Power Delivery in 2001"
TL;DR: In this article, a simple equivalent circuit to represent the thermal heat flow equations for power transformers is presented, which uses a current source analogy to represent heat input due to losses, and a nonlinear resistor analogy to simulate the effect of air or oil cooling convection currents.
Abstract: A simple equivalent circuit to represent the thermal heat flow equations for power transformers is presented. Key features are the use of a current source analogy to represent heat input due to losses, and a nonlinear resistor analogy to represent the effect of air or oil cooling convection currents. The effect was first quantified in 1817. It is shown that the idea of "exponential response" is not the best way to think of the dynamics of the situation. It is also shown that one can consider ambient temperature to be a variable input to the system, and that it is properly represented as an ideal voltage source.
416 citations
TL;DR: In this article, the theoretical considerations of core flux transients were explored and algorithms were developed which allow controlled energization of most transformers without inrush current, which can potentially eliminate these transients.
Abstract: Transformer inrush currents are high-magnitude, harmonic-rich currents generated when transformer cores are driven into saturation during energization. These currents have undesirable effects, including potential damage or loss-of-life to the transformer, protective relay misoperation, and reduced power quality on the system. Controlled transformer switching can potentially eliminate these transients if residual core and core flux transients are taken into account in the closing algorithm. This paper explores the theoretical considerations of core flux transients, Based on these studies algorithms were developed which allow controlled energization of most transformers without inrush current.
312 citations
TL;DR: A new amending algorithm, poly-item cosine window interpolation, which is based on the interpolating algorithm proposed by V. Jain and T Grandke is presented, which improves the accuracy of the FFT, so it can be applied to the precision analysis for electrical harmonics.
Abstract: The fast Fourier transform (FFT) cannot be directly used in the harmonic analysis of an electric power system because of its higher errors, especially the phase error. This paper discusses the leakage phenomenon of FFT and presents a new amending algorithm, poly-item cosine window interpolation, which is based on the interpolating algorithm proposed by V. Jain and T Grandke. This new algorithm improves the accuracy of the FFT, so it can be applied to the precision analysis for electrical harmonics. The simulation result shows that applying different windows has different effects on the accuracy, and the Blackman-Harris window has the highest accuracy.
270 citations
TL;DR: In this paper, a small-signal model of the system, with a distribution line, is derived, which can be used for controller design where subcycle voltage transients are to be compensated.
Abstract: Controller design of a STATCOM-based voltage compensator requires a valid analytical model of the system. If phasor algebra is used for modeling, it is difficult to accurately describe the STATCOM behavior during compensation of subcycle transients in the PCC voltage. In this paper, a small-signal model of the system, with a distribution line, is derived. Predictions based on frequency-domain analysis are made, which are validated by experimental results. This model, therefore, can be used for controller design where subcycle voltage transients are to be compensated. It is shown that the voltage controller, so designed, can accomplish voltage sag mitigation. A discussion on the design of DC bus voltage controller-and experimental results showing its performance-is also included.
215 citations
TL;DR: In this paper, a threshold of eliminating the influences of noises is determined adaptively according to the background noises, and the abilities of the wavelet transform in detecting and localizing the disturbances can hence be restored.
Abstract: By means of the wavelet transform (WT), a power quality (PQ) monitoring system could easily and correctly detect and localize the disturbances in the power systems. However, the signal under investigation is often corrupted by noises, especially the ones with overlapping high-frequency spectrum of the transient signals. The performance of the WT in detecting the disturbance would be greatly degraded, due to the difficulty of distinguishing the noises and the disturbances. To enhance the capability of the WT-based PQ monitoring system, this paper proposes a de-noising approach to detection of transient disturbances in a noisy environment. In the proposed de-noising approach, a threshold of eliminating the influences of noises is determined adaptively according to the background noises. The abilities of the WT in detecting and localizing the disturbances can hence be restored. To test the effectiveness of the developed de-noising scheme, employed were diverse data obtained from the EMTP/ATP programs for the main transient disturbances in the power systems as well as from actual field tests. Using the approach proposed in this paper, remarkable efficiency of monitoring the PQ problems and high tolerance to the noises are approved.
191 citations
TL;DR: In this article, the practical considerations of core flux transients, performance of control strategies, and the application of circuit breakers to control transformer inrush transients are explored, and a closed-loop algorithm is proposed to eliminate these transients.
Abstract: For pt. I see ibid., vol.16, no.2, p.276-80 (2001). Transformer inrush currents are high-magnitude, harmonic-rich currents generated when transformer cores are driven into saturation during energization. These currents have undesirable effects, including potential damage or loss-of-life to the transformer, protective relay misoperation, and reduced power quality on the system. Controlled transformer switching can potentially eliminate these transients if residual core and core flux transients are taken into account in the closing algorithm. This paper explores the practical considerations of core flux transients, performance of control strategies, and the application of circuit breakers to control transformer inrush transients.
183 citations
TL;DR: In this paper, the top oil rise thermal model proposed in part I is valid, for a large power transformer in service, and there is a convenient way of estimating the parameters without removing the transformer from service.
Abstract: For pt.I see ibid., vol.16, no.2, p.171-5 (2001). This paper has two main objectives. One is to show that the top oil rise thermal model proposed in part I is valid, for a large power transformer in service. The second is to show that there is a convenient way of estimating the parameters without removing the transformer from service. A Manitoba Hydro 250 MVA OFAF transformer was chosen and instrumented with data-gathering equipment. Two twenty-four hour test runs were performed, one in February of 1999 and the other in July of 1999. The most basic parameter to be determined was the rated top oil rise but also found were the top oil line constant and the nonlinearity exponent, commonly given the symbol n. The results are very positive.
172 citations
TL;DR: In this article, a variable dead time control in adaptive single pole auto-reclosing (SPAR) is proposed to give rise to a high rate of successful reclosing by adapting to variable dead times.
Abstract: This paper presents a new concept, based on variable dead time control, in adaptive single pole auto-reclosing (SPAR). The proposed scheme can give rise to a high rate of successful reclosing by adapting to variable dead times. The significance of this algorithm is that it uses the waveform patterns of the voltage transients following initial breaker opening. The performance of this proposed method is tested under a variety of fault locations on the Korean 765 kV system, and the outcome of the study clearly indicates that variable dead time auto-reclosing scheme can be used as an attractive and effective means of better management and operation of a high voltage transmission system.
143 citations
TL;DR: In this article, a summary of the different communications technologies available for use or application with EMS/SCADA system projects is provided along with a brief description along with tables of the advantages and disadvantages of each and recommendations for choosing the most appropriate communication technology.
Abstract: The purpose of this Guideline Technical Paper is to provide a summary of the different communications technologies available for use or application with EMS/SCADA system projects. All of the various communication media are addressed with a brief description along with tables of the advantages and disadvantages of each and recommendations for choosing the most appropriate communication technology. The technologies discussed are: twisted pair metallic cable; coaxial metallic cable; fiber optic cable (either optical power ground wire (OPGW), all dielectric self supporting (ADSS), or wrapped types (WOC)); distribution line carrier (DLC); power line carrier (PLC); satellite (VSAT, LEO, others); leased service; VHF radio (mobile); point-to-point UHF radio; multiple address radio system (MARS) 400/900 MHz UHF radio; trunked mobile UHF radio; spread spectrum UHF radio (monitor frequency for potential interference before installation); and microwave radio (2-40 GHz).
131 citations
TL;DR: In this article, the use of artificial neural networks (ANN) to correct current transformer (CT) secondary waveform distortions is presented, which is trained to achieve the inverse transfer function of iron-core toroidal CTs which are widely used in protective systems.
Abstract: Current transformer saturation can cause protective relay misoperation or even prevent tripping. This paper presents the use of artificial neural networks (ANN) to correct current transformer (CT) secondary waveform distortions. The ANN is trained to achieve the inverse transfer function of iron-core toroidal CTs which are widely used in protective systems. The ANN provides a good estimate of the true (primary) current of a saturated transformer. The neural network is developed using MATLAB and trained using data from EMTP simulations and data generated from actual CTs. In order to handle large dynamic ranges of fault currents, a technique of employing two sets of network coefficients is used. Different sets of network coefficients deal with different fault current ranges. The algorithm for running the network was implemented on an Analog Devices ADSP3101 digital signal processor. The calculating speed and accuracy proved to be satisfactory in real-time application.
123 citations
TL;DR: In this article, the authors present an analysis of proposed methods for tracking the fundamental power frequency to see if they have the performance necessary to cope with the requirements of future protection and control equipment.
Abstract: This paper presents an analysis of proposed methods for tracking the fundamental power frequency to see if they have the performance necessary to cope with the requirements of future protection and control equipment and are robust enough to cope with the more demanding nature of modern power system conditions. The analysis shows that the linear estimation of phases, decomposition of single phase into orthogonal components and discrete Fourier transform perform extremely well but they all suffer from a periodic error in the estimated frequency if it departs from the assumed frequency. This can be cancelled using a low pass filter although it would introduce delays and obscure any real oscillations in the fundamental frequency. Alternatively, averaging over three phases could be used but higher harmonics in the oscillation of the estimation would be present.
TL;DR: In this paper, a system is proposed to locate faults on transmission lines using the traveling wave phenomenon, where an ANN is used to estimate the fault location based on the modal information.
Abstract: A system is proposed to locate faults on transmission lines using the traveling wave phenomenon. Prony method is used to analyze the voltage or current signal at the local bus and extract its modal information. This information represents the traveling wave generated by the fault and can be used to estimate its location. Artificial neural networks (ANNs) are used to estimate the fault location based on the modal information. Two schemes are presented: the first with a voltage input signal; and the second with a current input signal. Training and testing data are obtained by ATP-EMTP simulations. Tests were done to study the effect of fault resistance variation and fault incidence angle on both schemes. The system has the advantages of utilizing single-end measurements, using either a voltage or current signal; no pre-fault data is required.
TL;DR: In this paper, the authors derive a novel algorithm which combines the appropriate analog low pass filter and modified full cycle DFT (FCDFT) or half cycle DFT (HCDFT), to remove the decaying dc in a voltage or current signal.
Abstract: Protecting transmission lines frequently involves applying distance relays. Protective relays must filter their inputs to reject unwanted quantities and retain signal quantities of relevant interest. Accuracy and convergent speed of filter algorithm are essential for protective relays. A widely applied filter algorithm, the discrete Fourier transform (DFT) can easily remove integer harmonics using simple calculation. However, the voltage and current signals contain serious harmonics and decaying DC during the fault interval. In addition, the decaying DC and higher order harmonics seriously decrease the precision and convergence speed of fundamental frequency signal from DFT. In this investigation, the authors derive a novel algorithm which combines the appropriate analog low pass filter and modified full cycle DFT (FCDFT) or half cycle DFT (HCDFT) algorithm to remove the decaying dc in a voltage or current signal. Using the Electromagnetic Transients Program (EMTP) simulates the transient responses of transmission lines during the fault period. Applying the proposed algorithm in distance relays effectively suppresses the decaying DC and quickly decomposes the accurate fundamental frequency components.
TL;DR: The paper presents a new approach for the protection of power transmission lines using a minimal radial basis function neural network (MRBFNN) using a sequential learning procedure to determine the optimum number of neurons in the hidden layer without resorting to trial and error.
Abstract: The paper presents a new approach for the protection of power transmission lines using a minimal radial basis function neural network (MRBFNN). This type of RBF neural network uses a sequential learning procedure to determine the optimum number of neurons in the hidden layer without resorting to trial and error. The input data to this network comprises fundamental peak values of relaying point voltage and current signals, the zero-sequence component of current and system operating frequency. These input variables are obtained by a Kalman filtering approach. Further, the parameters of the network are adjusted using a variant of extended Kalman filter known as locally iterated Kalman filter to produce better accuracy in the output for harmonics, DC offset and noise in the input data. The number of training patterns and the training time are drastically reduced and significant accuracy is achieved in different types of fault classification and location in transmission lines using computer simulated tests.
TL;DR: In this paper, the Numerical Electromagnetic Code (NEC-2) is applied to the electromagnetic analysis of tall structures hit by lightning, where a lightning channel is represented by a vertical conductor that is loaded by series inductance and resistance so as to simulate the slow propagation velocity of a current wave on the lossy channel.
Abstract: The Numerical Electromagnetic Code (NEC-2) is applied to the electromagnetic analysis of tall structures hit by lightning. The advantage of the analysis using NEC-2 is that it can accurately compute the current distribution along a conductor system by the method of moments. The waveforms of the lightning currents measured on freestanding tall structures are well reproduced, and the computed waveforms of the electric and the magnetic fields at some distance from the structure hit by lightning agree fairly well with the measured waveforms. In the analysis, a lightning channel is represented by a vertical conductor that is loaded by series inductance and resistance so as to simulate the slow propagation velocity of a current wave on the lossy channel. This representation is demonstrated to be quite effective.
TL;DR: In this article, a branch-current-based state estimation model for a distribution system is proposed, which is based on the concepts presented by Baran and Kelley (see IEE Trans. on Power Systems, vol.10, no.1, p.483-91, 1995).
Abstract: A highly-linear branch-current-based state estimation model for a distribution system is proposed in this paper. This algorithm is based on the concepts presented by Baran and Kelley (see IEE Trans. on Power Systems, vol.10, no.1, p.483-91, 1995). Baran and Kelley proposed a novel branch-current-based approach to solve distribution state estimation. However, the treatment of current magnitude measurements and the complicated gain matrix by Baran and Kelley greatly degrades its value in real-world applications. The approach presented in this paper substantially revised the original method. A new algorithm with constant gain matrix and a decoupled form was developed. Tests have shown that the proposed method is robust, efficient and needs minimal storage requirement. The new algorithm provides a very good theoretical foundation for developing more applications and research in this area.
TL;DR: In this paper, a generalized, optimal, and flexible control strategy (OFC) for harmonic compensation of utility lines is proposed, which provides a unified and highly flexible compensation framework has the ability of programming for perfect current harmonics compensation, or (UPF) accomplishment, or other newly defined objectives such as maximizing the power-factor subject to some adjustable constraints on the level of current harmonic and unbalancing via an online optimization algorithm.
Abstract: This paper gives a new insight into the concept of load compensation under distorted voltages. Achieving both unity power factor (UPF) and perfect compensation of current harmonics are not possible where competition will arise between these two important factors. Through evaluating the present control strategies, a generalized, optimal, and flexible control strategy (OFC) for harmonic compensation of utility lines is proposed. The proposed control strategy, which provides a unified and highly flexible compensation framework has the ability of programming for perfect current harmonics compensation, or (UPF) accomplishment, or other newly defined objectives such as maximizing the power-factor subject to some adjustable constraints on the level of current harmonics and unbalancing via an on-line optimization algorithm. The strategy can fulfill the IEEE-519 standards requirements, while guaranteeing the best achievable power factor and optimum required rating for the compensator. Theoretical concepts and practical features of the proposed control strategy have been shown through extensive simulation studies using MATLAB/SIMULINK programs.
TL;DR: In this article, a first zone algorithm for distance protection of series compensated lines is presented, which detects faults with the reach of 75-85% of the line length by measuring two distinctive impedances, using three adequate regions on the impedance plane and applying appropriate logic functions.
Abstract: This paper presents a new first zone algorithm for distance protection of series compensated lines. The algorithm detects faults with the reach of 75-85% of the line length by measuring two distinctive impedances, using three adequate regions on the impedance plane and applying appropriate logic functions. The algorithm estimates instantaneous values of the voltage drop across the series capacitors online, and compensates for this signal when calculating the impedance valid for faults behind the series capacitors. The other impedance (without compensation) is calculated for faults in front of the series capacitors. An explicit selecting procedure for the two impedances is not required since the presented relaying method asserts directly the fault within or outside the first zone. The algorithm is presented in detail and extensively tested using the EMTP model of a 400 kV 300 km transmission line. The enclosed results demonstrate high speed, dependability and security of the new algorithm.
TL;DR: In this article, a simple series LC circuit tuned at the net frequency, with the capacitor shunted by a metal oxide varistor (MOV), proved to be a well suited limiter to reach the goal.
Abstract: Short circuit current limitation in distribution utilities can be an effective way to improve power quality, since the expected voltage sag amplitude during faults can be dramatically reduced A simple series LC circuit tuned at the net frequency, with the capacitor shunted by a metal oxide varistor (MOV), proves to be a well suited limiter to reach the goal In the paper, the properties of such a circuit are analyzed and its operation is investigated through computer simulation The relevant pro and con aspects are outlined and discussed
TL;DR: In this article, the most important diagnostic methods for monitoring metaloxide surge arresters in power systems are described in detail, such as measuring of the V-I-characteristics or analysis of the third harmonic content of the leakage current.
Abstract: Various diagnostic methods-either on-line or off-line-for monitoring of metal-oxide surge arresters in power systems are known. In most cases they are based on the measurement of the leakage current. This paper describes the most important ones in detail, such as measuring of the V-I-characteristics or analysis of the third harmonic content of the leakage current. Their advantages and weak points, respectively, are discussed, based on the most recent investigation results on the change of the V-I-characteristics due to electrical and nonelectrical stresses. It turns out that almost none of these commonly applied methods really work satisfactorily under either technical or economical aspects. As an alternative the temperature of the MO-insert is proposed to be used for diagnostics purposes. This is made possible by newly developed passive temperature sensors, which can be remotely accessed without any hardware connection to the environment. It is shown how the temperature can be used for monitoring of all kinds of degradation, energy absorption, thermal stability or even pollution performance.
TL;DR: In this paper, the authors investigated the impact of the integration of EGs on the settings of electrical feeders emanated from the substation to which EGs are connected, and also covered the dynamic behavior of EG caused by disturbances on the host network.
Abstract: Since the late 1970s, intensive efforts have been made to utilize renewable energy sources to generate electric power. On the other hand, economical pressure experienced in recent years has led to the development of high efficiency combined heat and power schemes to use the normally wasted heat to generate electric power. Generators used under both schemes can be either synchronous or asynchronous types and when they are integrated into utilities' distribution networks (DNs) they are commonly known as "embedded generators" (EGs). Previous experience has shown that the integration of EGs into DNs could create safety and technical problems. They may contribute to fault currents, cause voltage flicker, interfere with the process of voltage control, etc. This paper reports an investigation to determine the impact of the integration of EGs on the settings of protective devices of electrical feeders emanated from the substation to which EGs are connected. This study also covers the dynamic behavior of EG caused by disturbances on the host network. Results obtained from several case studies presented and discussed.
TL;DR: In this article, the authors developed analytical expressions for the admittances and impedances of a static synchronous compensator (STATCOM) as a function of frequency, including the conventional positive and negative sequence admittance as well as transfer admittance where a positive sequence current generates a negative sequence voltage at another frequency.
Abstract: The paper develops analytical expressions for the admittances and impedances of a static synchronous compensator (STATCOM) as a function of frequency. The expressions include the conventional positive and negative sequence admittance as well as transfer admittances where a positive sequence current generates a negative sequence voltage at another frequency. These results are then corroborated using the tool of electromagnetic transients simulation. The expressions are shown to be valid for six-pulse as well as higher pulse number configurations. The impact of the STATCOM's control system on the admittance is also investigated.
TL;DR: The past and present uses of relay models are reviewed and the various types of models, what information is required to build such models and the model validation process are discussed.
Abstract: This paper reviews the past and present uses of relay models. It discusses the various types of models, what information is required to build such models and the model validation process. Examples of present and possible future use of software models are given.
TL;DR: In this article, a digital technique for improving the accuracy of instrument current transformers is presented, where the exciting current required by the transformer in every kind of steady state operation can be determined by simply acquiring the secondary current, provided that the examined CT has been preliminarily identified.
Abstract: In the paper a digital technique for improving the accuracy of instrument current transformers is presented. Since the exciting current can be considered as the main error source, its evaluation can allow the compensation of its detrimental effects to be obtained. The exciting current required by the transformer in every kind of steady state operation can be determined by simply acquiring the secondary current, provided that the examined CT has been preliminarily identified. A simple scalar model for the CTs magnetic core, taking into account saturation as well as hysteresis and eddy currents phenomena, has been implemented in a software compensation routine. This allows us to improve the accuracy in the reproduction of the primary current, in the case of both sinusoidal and distorted current waveforms (provided that DC components are not present). Many experimental tests, under different practical situations, have been performed. The results clearly show that the proposed technique is able to significantly reduce, in comparison with traditional methods, the errors introduced by current transformers.
TL;DR: A flywheel energy storage system which performs both functions and presents a novel control scheme using both sinusoidal pulse width modulation as well as a boost converter to regulate the critical load voltage on the feeder is considered.
Abstract: Due to technological advancements, the flywheel energy storage system is becoming a viable alternative to electrochemical batteries. Two potential applications of flywheel systems are for voltage support and as an uninterruptible power supply. The two applications are both useful to protect critical loads on distribution feeders. Therefore, it may be useful to look at the possibility of combining both functions into one system. This paper considers a flywheel energy storage system which performs both functions and presents a novel control scheme using both sinusoidal pulse width modulation as well as a boost converter to regulate the critical load voltage on the feeder. Dynamic voltage compensation is achieved by injecting voltage through series transformers rather than by connecting the system in shunt, to minimize the amount of kVA required by the flywheel system. Simulations are provided using the Electromagnetic Transients Program to validate the concept.
TL;DR: In this article, a finite impulse response artificial neural network (FIRANN) was used as differential protection for a real three phase power transformer, and three FIRANNs were designed, trained and tested.
Abstract: This paper presents an application of a finite impulse response artificial neural network (FIRANN) as differential protection for a real three phase power transformer. Three FIRANNs are designed, trained and tested. The first one has an output which identifies internal faults from any other cases like inrush current and external faults. The two others FIRANNs, each have two outputs that classify between internal and external faults, so that a backup protection is included. These FIRANNs have six inputs, one for each sampled current signal from both transformer sides. The sample rate selected is 2 kHz for a 50 Hz power frequency. All FIRANNs were trained to have a 3.5 ms fault detection time, which is considered as a very fast protection. The test results show very good behavior of the FIRANN as a differential protection and it is planned to build a prototype.
TL;DR: In this article, a modified Mayr-type dynamic arc equation was presented to calculate the DC interruption limits for the Kii-Channel HVDC link under construction in Japan, which is equipped with metallic return transfer breakers in one converter station.
Abstract: The Kii-Channel HVDC Link under construction in Japan is equipped with metallic return transfer breakers (MRTBs) in one converter station. A new MRTB for an interrupting current of 3500 A DC was developed. To interrupt a DC current, a method that produces a current zero point by superimposing a self-excited oscillatory current on a DC arc current was employed. For this purpose, a LC circuit was coupled in parallel to a SF/sub 6/ gas circuit breaker. Developing a SF/sub 6/ gas circuit breaker that has a large arc voltage drop gradient against currents permitted a large oscillatory current to be generated. A modified Mayr-type dynamic arc equation was newly presented. The DC interruption limits calculated using this equation agreed with the measured values.
TL;DR: In this paper, a goal programming approach was used to achieve compromises among various engineering objectives, such as minimizing the SAIFI and ASIFI indices by identifying types and locations of protective devices, and achieving a reasonable trade-off between a decrease in the SAI index and an increase in MAIFI index by identifying where a fuse saving scheme should be applied.
Abstract: The number, type and location of the protective devices on a distribution feeder have a direct effect on the system reliability. In earlier work, a technique was developed to design a protective system in order to minimize the SAIFI index. This paper extends earlier results by using a goal programming approach to achieve compromises among various engineering objectives. The design goals are: (1) to minimize the SAIFI and ASIFI indices by identifying types and locations of protective devices; and (2) to achieve a reasonable trade-off between a decrease in the SAIFI index and an increase in MAIFI index by identifying where a fuse saving scheme should be applied. Numerical examples highlight the approach.
TL;DR: In this article, an artificial neural network based methodology is proposed for power systems fault location, each of them being responsible for detecting faults involving a limited number of components, and the proposed methodology is tested using a test system and a real Brazilian system.
Abstract: In this work an artificial neural network based methodology is proposed for power systems fault location. Several artificial neural networks are employed, each of them being responsible for detecting faults involving a limited number of components. The proposed methodology is tested using a test system and a real Brazilian system. Indexes based on the Hamming distance are also proposed for feature selection and analysis.
TL;DR: In this paper, a new method that handles multiple hypotheses is presented for fault diagnosis using sequence of event recorders (SERs) to quantify the certainty of hypotheses, a method to calculate their credibility is provided.
Abstract: In this study, a new method that handles multiple hypotheses is presented for fault diagnosis using sequence of event recorders (SERs). To quantify the certainty of hypotheses, a method to calculate their credibility is provided. The proposed techniques are integrated in a generalized alarm analysis module (GAAM) and have been tested with numerous scenarios from the Italian power system.