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Power Delivery, IEEE Transactions on

Issue 3 • Date Jul 2000

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Displaying Results 1 - 25 of 38
  • Analysis of grounding systems in soils with cylindrical soil volumes

    Page(s): 913 - 918
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    A theoretical model for the analysis of grounding systems located in soils with cylindrical soil volumes is presented for the first time. Exact closed-form analytical expressions for earth potentials due to current sources in different regions of such soil structures have been obtained. More precisely, the soil models considered contain horizontal semi-cylindrical soil volumes and vertical cylindrical soil volumes. Numerical results are presented for different grounding systems and for different types of cylindrical soil volumes. The results clearly show that these soil structures have a significant influence on the performance of grounding systems. The results obtained are in agreement with well-known simple case results and converge asymptotically to the uniform soil case View full abstract»

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  • An adaptive arc furnace model

    Page(s): 931 - 939
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    This paper presents an adaptive arc furnace model. The integrated model is divided into three parts, the supply system model, the nonlinear load model and the controller model. First, the supply system is represented by a set of linear differential equations. Simulation is achieved by a numerical method and the measurements are taken as the control input. Secondly, based on the arc melting process and typical arc furnace V-I characteristic, the arc furnace load is described as a current-controlled nonlinear resistance. The pattern of nonlinear resistance is controlled by the average arc length, which reflects the arc furnace operating condition. Finally, the rectangular approximation of arc voltage is adopted by the controller to generate the arc power-arc length and the arc current-arc length curves. This information combined with the arc furnace operation and measurement information is used for the control scheme to determine the arc length and arc furnace transformer tap. Thus, the proposed adaptive arc furnace model is suitable for different operating conditions. This model is also compared prith the existing arc furnace models, which provides its validity. The effect of arc furnace load on the power system is also studied through the proposed model View full abstract»

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  • A study of current-carrying capacity of drawlead cable in condenser bushing

    Page(s): 925 - 930
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    Temperature rise distribution at the drawlead cables in the condenser bushings was studied with a thermal model and actual thermal tests. Temperature rise of the hottest spot at the cables from the model is consistent with that from the tests within a 10% deviation. Factors that influence working current and overload capacity of the cable were studied. Current-carrying capacities of the drawlead cables with index 105 insulation are presented based on thermal basis of rating View full abstract»

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  • Electrical design parameters of all-dielectric-self-supporting fiber optic cable

    Page(s): 940 - 947
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    A lumped circuit model for calculating voltages and currents on all-dielectric self-supporting (ADSS) fiber optic cable near high voltage transmission lines has been developed. The model has been used to show that contamination levels, tower attachment points, relative ADSS and conductor sag and electrical phasing of the conductors are important parameters and must be considered in calculations, especially when determining the possibility of dry band arcs which could lead to cable damage View full abstract»

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  • Constrained least squares methods for parameter tracking of power system steady-state equivalent circuits

    Page(s): 1073 - 1080
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    The paper deals with the problem of the online parameter identification of power system harmonic equivalent circuits as seen from a bus at which a power electronic device is connected. Recursive constrained least squares methods are considered and models of different order are compared one to another. The proposed online identification procedure is able to identify both equivalent impedances and ambient voltage harmonics and to track their changes during normal operating conditions. Numerical applications evidence the performance of the proposed methods in terms of both steady-state accuracy and responsiveness to changes of the parameter values View full abstract»

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  • Overload prevention and loss minimization in managed distribution networks

    Page(s): 972 - 977
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    We present the concept of a “managed distribution network,” in which current flowing between a power distribution network and its supplies and loads is divided into “discretionary” and “nondiscretionary” components. The discretionary component is placed under the control of an energy management system, which communicates its requirements as current setpoints. The nondiscretionary component is determined by the external circuit itself, but is subject to authorization from the control system to ensure that demand never exceeds the available discretionary capacity. We develop a theoretical framework for the analysis of managed distribution networks, and its application to the problems of cable loss minimization and the anticipation and prevention of cable overloads View full abstract»

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  • Modeling of bipolar HVDC links in the harmonic domain

    Page(s): 1034 - 1038
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    A method for accurate calculation of the harmonics generated by a bipolar HVDC link is described. The method illustrates the importance of including detailed representation of the mutual coupling effects of DC transmission lines, even when smoothing reactors are included. The overall solution is achieved by means of a unified Newton algorithm in the harmonic domain View full abstract»

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  • On the need for strict second harmonic limits

    Page(s): 967 - 971
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    Even harmonics, especially the second harmonic, cause waveform distortions characterized by asymmetries between the positive and the negative half-cycles. Certain single-phase converter topologies, when supplied with asymmetrically distorted voltage wave-forms, respond by injecting significant levels of direct current, even when the mean value of the voltage is zero. In turn the DC will bias transformers causing a host of undesirable effects. This paper concludes that the existing recommendations for permissible levels of the second harmonic must be stricter and proposes a ban on half-controlled three-phase converters View full abstract»

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  • A direction finder for power quality disturbances based upon disturbance power and energy

    Page(s): 1081 - 1086
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    While existing techniques are capable of automatically identifying and classifying various types of distribution-level power quality disturbances, they do not provide any information about the locations of the disturbance sources. This paper shows that it is possible to use sampled voltage and current waveforms to determine on which side of a recording device a disturbance originates. This is accomplished by examining the energy flow and peak instantaneous power for both capacitor energizing and voltage sag disturbances. The authors demonstrate the technique by testing it on both ATP-generated waveforms and actual field disturbance data. In both cases, they are able to accurately determine on which side of a recording device the disturbance originates. If enough recording devices are available in a network, the individual readings can be collectively used to pinpoint the locations of disturbance sources View full abstract»

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  • A novel fuzzy neural network based distance relaying scheme

    Page(s): 902 - 907
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    This paper presents a new approach to distance relaying using fuzzy neural network (FNM). The FNN can be viewed either as a fuzzy system, a neural network or fuzzy neural network. The structure is seen as a neural network for training and a fuzzy viewpoint is utilized to gain insight into the system and to simplify the model. The number of rules is determined by the data itself and therefore a smaller number of rules is produced. The network is trained with the backpropagation algorithm. A pruning strategy is applied to eliminate the redundant rules and fuzzification neurons, consequently a compact structure is achieved. The classification and location tasks are accomplished by using different FNN's. Once the fault type is identified by the FNN classifier the selected fault locating FNN estimates the location of the fault accurately. Normalized peaks of fundamental voltage and current waveforms are considered as inputs to all the networks and an additional input derived from the DC component is fed to fault locating networks. The peaks and DC component are extracted from sampled signals by the EKF. Test results show that the new approach provides robust and accurate classification/location of faults for a variety of power system operating conditions even with resistance in the fault path View full abstract»

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  • Statistical summation of the harmonic currents produced by a large number of single phase variable speed air conditioners: a study of three specific designs

    Page(s): 953 - 959
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    The variable speed air conditioner (VSAC) is a large domestic distorting load. We investigate the impact of a large number of VSAC's on domestic harmonic levels. We present a general method to build a harmonic numerical model of a passive filtered rectifier supplied by a distorted voltage; a statistical method to assess the total harmonic currents produced by a large number of units running at various power levels and supplied by various distorted voltages. These two methods are applied to a rectifier used by many VSACS. We also present results for two other rectifiers View full abstract»

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  • A busbar protection technique and its performance during CT saturation and CT ratio-mismatch

    Page(s): 895 - 901
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    This paper describes a digital technique for protecting busbars. The technique uses positive- and negative-sequence models of the power system in a fault-detection algorithm. While phase voltages and currents are used to detect faults, parameters of the power system are not used. An analysis of the performance of the proposed technique during CT saturation and ratio-mismatch conditions is presented. The performance of the technique was investigated for a variety of operating conditions and for several busbar configurations. Data generated by EMTP simulations of model power systems were used in the investigations. The results indicate that the proposed technique is stable during CT saturation and ratio-mismatch conditions View full abstract»

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  • Decreasing the commutation failure frequency in HVDC transmission systems

    Page(s): 1022 - 1026
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    In this paper we show how a fairly large proportion of those commutation failures that are due to single-phased short circuits to earth can be avoided. In a control circuit based on a digital signal processor (DSP) it is possible, with instantaneous results, to switch from a normal control strategy with equidistant firing pulses to a strategy that takes into consideration the potentially dangerous voltage changes on the supply lines, If the supply voltages are monitored continuously, it is possible to calculate the necessity of advancing the firing pulses to avoid commutation failures. In the paper such a calculation technique is described. The monitoring times may be approximately 50 μsec apart corresponding to a distance of 0.016 radians or about 1 View full abstract»

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  • Detection and measurement of power quality disturbances using wavelet transform

    Page(s): 1039 - 1044
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (248 KB)  

    This paper deals with the use of a continuous wavelet transform to detect and analyze voltage sags and transients. A recursive algorithm is used and improved to compute the time-frequency plane of these electrical disturbances. Characteristics of investigated signals are measured on a time-frequency plane. A comparison between measured characteristics and benchmark values detects the presence of disturbances in analyzed signals and characterizes the type of disturbances. Duration and magnitude of voltage sags are measured, transients are located in the width of the signal. Furthermore, meaningful time and frequency components of transients are measured. The whole method is implemented and tested over a sample representing recorded disturbances. Detection and measurement results are compared using classical methods View full abstract»

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  • Predictive firing angle calculation for constant effective margin angle control of CCC-HVDC

    Page(s): 1087 - 1093
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    A capacitor commutated power converter (CCC) has superior commutation ability when compared to a line commutated converter used in a conventional HVDC power system. This paper models the commutating and post commutation period of the converter circuit in theoretical style, and formularizes the commutation and extinction equations with mathematical treatment. The equations express the relations among firing angle, overlap angle, effective margin angle, state variables and converter parameters, and compose nonlinear simultaneous equations. The fine CCC commutation characteristics are shown by using the equations to several commutation capacitor configurations. The authors propose the predictive firing angle calculation method for the constant margin angle control (Aγ'R) operation of a CCC-HVDC system as a practical application of the obtained equations. The obtained equations cannot be solved algebraically for their complexity, then convergence calculations of numerical analysis are assessed, but it is hard to secure the derivation to the various operating conditions. The authors propose to apply an approximate polynomial equation from the offline calculated characteristics to achieve the firing angle predicting equation. The design index for approximation polynomial of Aγ'R is presented to make the polynomials to low order. The suitability of the proposed predictive Aγ'R is studied with simulations by applying it to the converter controller and it can make the most of the CCC availability View full abstract»

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  • Performance evaluation of thyristor based static transfer switch

    Page(s): 960 - 966
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    Industrial customers are becoming more sensitive to variations of utility supply systems due to the growing demand for process controls in automated plants. One option to increase reliability and quality of AC power is to provide sensitive customers with access to two independent power sources. In this paper, a fast thyristor based static transfer switch (STS) is proposed which employs fast voltage-detection and thyristor gating strategies to connect the customer to either of the two sources. Performance of the designed STS system is evaluated using the Electromagnetic Transients for DC (EMTDC). Simulation results are verified by comparing them with experimental results View full abstract»

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  • A unified model for the analysis of FACTS devices in damping power system oscillations. III. Unified power flow controller

    Page(s): 978 - 983
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    For pt.II see ibid., vol.13, no.4, p.1355-62 (1998). This paper presents the establishment of the linearized Phillips-Heffron model of a power system installed with a unified power flow controller (UPFC). Two applications based on the Phillips-Heffron model are demonstrated: (1) study on the effect of UPFC DC voltage regulator on power system oscillation stability; and (2) selection of damping control signal for the design of UPFC damping controller View full abstract»

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  • Evaluation of current interharmonics from AC drives

    Page(s): 1094 - 1098
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    Distortion levels on power systems have been continuously increasing due to the increasing presence of power converters. The distortion currents injected by some converters can include interharmonics as well as harmonics. The generation of interharmonics in AC-DC-AC power converters is discussed, and a method to predict levels of current interharmonics is developed. The results show that very low interharmonic levels can be expected for a well designed PWM inverter operating with linear modulation and balanced load. Interharmonics can be expected in cases when the inverter is in overmodulation or when the inverter load is unbalanced. The paper also discusses the relative effects of DC link inductance and source inductance on interharmonic propagation View full abstract»

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  • Flash-over mechanism of SF6-gas type termination for DC power cable

    Page(s): 849 - 856
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    With the development of ±250 kV DC-XLPE power cable and flexible joint so far, there arose a need to develop other components for the construction of DC-power transmission. One of those is SF6 -gas type, horizontally installed termination. To supply the DC electric power with reliability and stability, we need to clarify the phenomena under DC voltage application in this system. This paper examines the flash-over (FO) phenomena under DC voltage application in the SF6-gas type, horizontally installed termination by using the model electrode in which the firefly of metal particle was imitated under the condition of charge accumulation on the epoxy bushing. In this examination, we confirmed experimentally that the behavior of metal particles was affected by the change of a field distribution due to the charge accumulation on the epoxy bushing, on the other hand, the metal particle promoted the charge accumulation on the epoxy bushing. Under these circumstances, FO initiated at the edge of the metal particle showing firefly, developed along the epoxy bushing surface. These seemed to mean that there was a synergetic effect of charges accumulation and behaviors of metal particle to introduce a FO. It was concluded that it was very important to be strongly aware of the existence of metal particles and its behavior in the SF6-gas type termination, when it was used under DC voltage application View full abstract»

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  • Noncharacteristic line harmonics of AC/DC converters with high DC current ripple

    Page(s): 1060 - 1066
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    To investigate the basic mechanisms generating noncharacteristic line current harmonics of AC/DC converters with high DC ripple, the assumption of negligible small commutation is used. Thus, simple analytical models can be derived describing the effect of voltage unbalance in case of equidistant phase angle control and control angle asymmetry, respectively. By means of superposition of both components, the according behavior applying individual phase angle control is described. Finally, it is shown that the effect of resonance excitation in diode rectifier circuits can also be estimated using the proposed modeling. Comparing simulations confirm the validity of the approximations. However, the strong influence of the commutation especially on the negative sequent systems requires further investigations View full abstract»

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  • Aerial and grounding system analysis by the shifting complex images method

    Page(s): 1001 - 1009
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    This paper introduces a novel computer method for the analysis of both aerial and grounding systems of conductors. The computer method based on an hybrid approach, allows to incorporate into a single linear system both lumped and distributed circuit parameters, evaluated by a rigorous electromagnetic field analysis. The conductor system is replaced by a suitable set of elementary current sources. These may be plain or hollow, bare or insulated, freely oriented and interconnected in the three dimensional space, which is considered formed by two half spaces each one homogeneous, linear and isotropic (e.g., air and soil). Therefore the method does not pose geometric and topological limitations and enables to compute voltages and currents at the source (boundary) elements as well as vector potentials, electric and magnetic fields anywhere in the surrounding medium. The range of application of this method is sufficiently wide including any practical electric power system application. The method may be applied for frequencies up to 1 MHz, thus covering the frequency spectrum of a typical full lightning too. Results which are derived first in the frequency domain can be converted to the time domain by Fourier transform algorithms. In this way it is also possible to analyze the response to transient signals of both aerial and grounding systems having complex geometry View full abstract»

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  • A new method for protection zone selection in microprocessor-based bus relays

    Page(s): 876 - 887
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    Use of graph theory simplifies representation of complex bus arrangements in power system stations. This paper presents a new method, based upon graph theory, for selecting bus protection zones in microprocessor-based relays. We use a typical bus arrangement to illustrate the graphical representation of station arrangements, graph operations, and associated matrix operations. We also describe an implementation of the zone selection method and use two examples to demonstrate the advantages of the method. Using the status of switching devices in the station, the zone selection method provides the relay with real-time bus arrangement information. The bus relay uses this information to assign input currents to a differential protection zone and to select which breakers to trip for a bus fault or breaker failure View full abstract»

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  • A novel approach for auto-reclosing EHV/UHV transmission lines

    Page(s): 908 - 912
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (116 KB)  

    A technique to discriminate between the line charging inrush current and the current resulting on closing or auto-reclosing a faulted EHV/UHV transmission line is proposed in this paper. The technique is based on the voltage and current signals before and after the switching process. This technique is proposed to be a supplement to the main protection scheme View full abstract»

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  • Analysis of a novel method of current sharing in a resistive lightning protection terminal

    Page(s): 948 - 952
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    A new method, which simulates the lighting channel as a series network of R-C circuits, has been proposed by the authors. It successfully calculates the return stroke current with various added resistance values at the base of the lightning channel. The calculation shows that the peak current and current risetime along the channel are strongly influenced by the added resistance element at ground level. However, the larger voltage across this resistance element may cause the flashover along its surface and result in failure of current limiting. This paper describes the analysis and simulation of a novel method of current sharing following the termination of a lightning stroke onto a resistive lightning protection terminal. Such a system of resistance elements is essential to ensure that surface flashover does not occur across lightning rods and current limiting is successful View full abstract»

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  • Filtering dispersed harmonic sources on distribution

    Page(s): 1045 - 1051
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    Telephone company customers reported audible noise in their telephone service. Through measurements, analysis, and simulations, 540 Hz noise was found to be coupling from power distribution to telephone cables in a shared underground right-of-way. The source of the noise was small single-phase electronic loads dispersed throughout the power distribution system in the area. A passive shunt filter was designed using an existing capacitor bank. Installation of this filter reduced the noise to acceptable levels View full abstract»

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Aims & Scope

Installation and operation of apparatus, equipment, structures, materials and systems for the safe, reliable and economic generation, transmission, distribution, conversion, measurement and control of electric energy.

Full Aims & Scope

Meet Our Editors

Editor-in-Chief
Wilsun Xu
Ph.D., P.Eng.
Dept. Electrical and Computer Eng.
University of Alberta
(9107 - 116 Street)
Edmonton, Alberta T6G 2V4 Canada
wxu@ualberta.ca
Phone:780-492-5965
Fax:780-492-1811