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Power Delivery, IEEE Transactions on

Issue 2 • Date April 2011

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Displaying Results 1 - 25 of 98
  • Table of contents

    Page(s): C1 - 491
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    Freely Available from IEEE
  • IEEE Transactions on Power Delivery publication information

    Page(s): C2
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  • Risk-Based Assessment of Financial Losses Due to Voltage Sag

    Page(s): 492 - 500
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (674 KB) |  | HTML iconHTML  

    This paper investigates the factors that influence the outcome of financial-loss analysis in voltage sag studies. Focusing on industrial processes, this paper considers the effects of voltage sag profile estimation, plant-load profile modelling, and process cycle modelling on the financial risk associated with process failure. Based on voltage sag monitoring records, sag profile is probabilistically modeled for the estimation of future sag characteristic. Variations in financial risk due to varying process activities in different stages of a process (process cycle) and load profile are also investigated. The effects of the individual factors are analyzed through Monte Carlo simulation. The stochastic net present value method is introduced as a financial analysis tool. View full abstract»

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  • Extracting Load Current Influence From Infrared Thermal Inspections

    Page(s): 501 - 506
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    This paper presents some difficulties encountered when evaluating information obtained from infrared thermal inspections conducted in uncovered power substations. Technical, physical, and environmental factors are the main influences that have been identified. Based on field data and laboratory tests, mathematical models were derived to understand the load current variation influence on the thermal behavior of electrical components, which are suitable either to extract its influence or forecast the system behavior under specified conditions of interest. View full abstract»

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  • Transmission-Lines Shielding Failure-Rate Calculation by Means of 3-D Leader Progression Models

    Page(s): 507 - 516
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (632 KB) |  | HTML iconHTML  

    In this paper, by creating a 3-D model of power-line equipment and lightning leader progression models, an alternate procedure for calculating the shielding failure rate (SFR) of transmission lines is presented. The stepping nature of lightning downward leader is modeled according to field observations with the use of discrete line charges approaching the earth. A simplified self-consistent model for an upward connecting leader is also adopted to find the position of lightning incidence to the transmission line. The required electric field in an environment is computed by using the charge simulation method. A comparison has been made between the SFR calculated by proposed method and the values calculated by conventional electrogeometrical model. In addition, different previously proposed incidence criteria are implemented and compared. Some comparisons are also made between the calculated SFR and available field data for selected overhead lines. View full abstract»

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  • Nondetection Zone Assessment of an Active Islanding Detection Method and its Experimental Evaluation

    Page(s): 517 - 525
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    This paper analytically determines the nondetection zone (NDZ) of an active islanding detection method, and proposes a solution to obviate the NDZ. The method actively injects a negative-sequence current through the interface voltage-sourced converter (VSC) of a distributed generation (DG) unit, as a disturbance signal for islanding detection. The estimated magnitude of the corresponding negative-sequence voltage at the PCC is used as the islanding detection signal. In this paper, based on a laboratory test system, the performance of the islanding detection method under UL1741 anti-islanding test conditions is evaluated. Then, determining the NDZ of the method and proposing the countermeasure, the existence of the NDZ and the performance of the modified method to eliminate the NDZ is verified based on simulation results in PSCAD/EMTDC software environment and experimental tests. View full abstract»

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  • Value of Wind Power at Different Locations in the Grid

    Page(s): 526 - 537
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    Availability of wind energy which differs across locations primarily determines the appropriate location for installing windfarms. However, the grid location of windfarms must always be considered in an attempt to accurately quantify the benefits which can be achieved from windfarms during their lifetime operation to the supply network. The value of wind power is significantly affected by their penetration and concentration, and is further affected by their location within a network. This is because the location and penetration level of wind generation will result in a significant impact on power-flow distribution across the network. The objective of this paper is to measure the impact of grid location of windfarms on economic and operational parameters of a power system in the lifetime of a windfarm project. This paper first develops an assessment tool to quantify the economic and operational impact of wind power in the grid. This is followed by developing different scenarios in which different penetrations of wind power are installed at different locations in the grid, and it shows how the value of wind power is affected by location and network constraints. View full abstract»

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  • Partial-Discharge Characteristics of Free Spherical Conducting Particles Under AC Condition in Transformer Oils

    Page(s): 538 - 546
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    One of the major problems in the liquid insulation is the particle contamination, which can seriously degrade the withstand voltage of the insulation. The movement of conducting particles under operation voltage can generate incipient discharges that can lead to the complete failure of the insulation system during operation. The partial-discharge characteristics of the free spherical conducting particle in the quasiuniform electric field were studied in this paper in order to better explain the partial-discharge (PD) measurement signals for particle movement and implications for insulation diagnostics in power transformers. The phase-resolved partial-discharge (PRPD) pattern was measured and the PD inception voltage, PD charges, and PD frequency were studied under different applied voltages. The influence of oil aging degree to particle PD characteristics was also studied in this paper. It is observed that the PD pattern is different in a different particle motion stage and the number of particles has a significant influence on PD frequency and a slight influence on PD pattern. The particle is inactive in severely aged transformer oil. The PD charges and PD frequency (pulses number per half ac cycle) reduce with the aging degree of the oil sample. View full abstract»

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  • Accurate Noniterative Fault-Location Algorithm Utilizing Two-End Unsynchronized Measurements

    Page(s): 547 - 555
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    This paper presents a new two-terminal impedance-based fault-location algorithm, which takes into account the distributed parameter line model. The algorithm utilizes unsynchronized measurements of voltages and currents from two ends of a line and is formulated in terms of the fundamental frequency phasors of symmetrical components of the measured signals. First, an analytical synchronization of the unsynchronized measurements is performed with use of the determined synchronization operator. Then, the distance to fault is calculated as for the synchronized measurements. Simultaneous usage of two kinds of symmetrical components for determining the synchronization operator makes that the calculations are simple, noniterative, and at the same time highly accurate. The developed fault-location algorithm has been thoroughly tested using signals of Alternate Transients Program-Electromagnetic Transients Program versatile simulations of faults on a transmission line. The presented evaluation shows the validity of the developed fault-location algorithm and its high accuracy. View full abstract»

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  • Basic Principles Concerning the Experimental Evaluation of the Frequency-Dependent Parameters of Shielded and Unshielded Three-Phase Symmetric Cables

    Page(s): 556 - 564
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    The high-frequency domain characterization of overhead three-phase cables is a critical issue as far as power line carrier communications is concerned. In many instances a detailed knowledge of the electric and magnetic parameters of the cable is not available. Even if manufacturer cable-data are available, strong proximity effects among cable conductors do inhibit the utilization of closed-form expressions for the determination of the cable constitutive parameters, namely, the entries of the per-unit-length R, L, G , and C matrices. However, the determination of such parameters can always be made experimentally. In this paper, new measurement principles based on the cable excitation by independent propagation modes are presented and discussed. In the case of symmetric cables, the eigenvectors associated to the propagation modes are frequency independent, however, the propagation constants and surge impedances are not. The entries of the frequency-dependent R, L, G , and C matrices are retrieved from open and short-circuit cable measurements involving information on the modal propagation constants and modal surge impedances. For exemplification purposes, experimental results concerning a shielded three-phase cable for low voltage applications are provided. The results in this paper do not apply to buried cables where ground return phenomena would need to be accounted. View full abstract»

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  • Analysis of Underfrequency Load Shedding Using a Frequency Gradient

    Page(s): 565 - 575
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    Underfrequency load shedding is one of the most important protection systems, as in many cases it represents the last chance to prevent a system blackout after a serious disturbance occurs in a power system. In order to improve traditional schemes, many efforts have been concentrated on attempts to use the frequency gradient as an indicator for determining the lack of active power in a system. This paper concentrates on analyzing the factors that influence the gradient. Analyses have shown that the gradient can give misleading information about the active-power deficit, as long as certain factors are ignored or assumed to be constant. A draft of a gradient-based underfrequency load-shedding scheme is presented, which also highlights the problems associated with the use of gradient. On the one hand, a frequency gradient alone does not appear to be sufficient for the active-power deficit estimation. Nevertheless, for the actual load-shedding procedure it is found to be very useful. View full abstract»

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  • Estimation of Cost of Downtime of Industrial Process Due to Voltage Sags

    Page(s): 576 - 587
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    This paper describes a methodology to estimate post process failure cost of downtime (COD). COD can be estimated using either historical or direct online costs (direct and restart costs) as input to the model. Application of the proposed COD estimation model is illustrated on an actual industrial process that experienced several downtime events due to voltage sags in its electric supply. Raw financial data obtained from industrial collaborators are normalized and used as an input to developed software for COD estimation. Several case studies, including influence of simultaneous manufacturing of different product variants and optimization (minimization) of COD are presented and discussed in detail. View full abstract»

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  • Identifying Transformer Inrush Current Based on Normalized Grille Curve

    Page(s): 588 - 595
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    A novel algorithm for discrimination between inrush currents and internal fault currents by utilizing the normalized grille curve is proposed. First, the calculation method of the normalized grille curve is presented. Then, two schemes to discriminate the inrush currents from the internal faults in the time and frequency domains are, respectively, developed. A total of 268 experimental measurements have been tested on an YNd11-connected transformer. The results indicate that the proposed technique is able to reliably and accurately distinguish inrush currents from internal faults with easy implementation. Furthermore, the new method is not affected by the saturation of current transformers. View full abstract»

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  • Reliability-Based Transmission Line Design

    Page(s): 596 - 606
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (572 KB) |  | HTML iconHTML  

    It is well known that environmental loads, e.g., wind and ice, acting on power transmission lines are highly uncertain, as are the structural strengths of the towers supporting the lines. The design of such systems must take uncertainty into account in order to achieve acceptable reliability at a reasonable cost. The paper presents a simulation-based methodology for the optimal design of a transmission line which considers uncertainties in both environmental loads and structural resistance. The methodology is developed and illustrated for the simple problem of determining the optimal span length required for designing against tower failure. Wind, ice, and tower resistances are simulated over the extent of the transmission line and over the design life of the transmission system. Total expected system cost, along with the estimated probability of lifetime failure, are produced for a range of possible span lengths, allowing an informed decision regarding the optimum span length for the tower strength limit state. View full abstract»

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  • Analysis of Five-Legged Transformer Used for Parallel Operation of Rectifiers by Coupled Circuit-Field Approach

    Page(s): 607 - 616
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    This paper deals with the modeling and analysis of a five-legged rectifier transformer that is used for parallel operation of two three-pulse rectifiers, specifically, for low-voltage high-current applications. The five-legged system is compared with the conventional rectifier system consisting of a three-legged transformer and interphase transformer (IPT). Ensuring equal current sharing between the rectifiers and obtaining output voltage with a higher pulse number are the two major requirements which are satisfied in the conventional system. A mathematical explanation for the five-legged system satisfying the mentioned requirements is given. The system is treated as a strongly coupled circuit field one, where a nonlinear finite-element model of the five-legged transformer is coupled with nonlinear circuit equations. IPT-like behavior of the five-legged rectifier transformer is also investigated. The stated theory and analytical expressions are validated experimentally on a 12-V, 5000-A rectifier system. View full abstract»

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  • Numerical Analysis of the Induced Corona Vibrations on High-Voltage Transmission Lines Affected by Rainfall

    Page(s): 617 - 624
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    Droplets formation on high-voltage transmission lines affected by rainfall amplifies the corona discharges from the conductors. The induced corona vibrations intensify the fatigue of high-voltage conductors and supporting elements. The alternating presence of space charge and the ionic wind associated with the corona discharge are the main causes of this phenomenon. The objective of this paper is to validate a numerical simulation method to investigate the effects of different parameters (electric field strength and polarity, rain intensity, transverse wind velocity) on the amplitude of the induced corona vibrations. The finite element method was used to develop the numerical model of the conductor movement under the action of mechanical and electrical forces, while time discretization was made with the finite difference method. The numerical simulation results were in good agreement with the experimental data available in the literature. The model enables better comprehension of the induced corona vibration mechanism. View full abstract»

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  • Influence of Sensor Information Accuracy on Condition-Based Maintenance Strategy for GIS/GCB Maintenance

    Page(s): 625 - 631
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1018 KB) |  | HTML iconHTML  

    Condition-based maintenance (CBM) is a new maintenance strategy for the reliable operation of aged power equipment. Although CBM has been applied for various equipment, the accuracy of condition information from sensors has not yet been sufficiently discussed. Specifications of reliable information are still not clear and CBM sensors have not widely been applied on actual power substations. The influence of condition information accuracy is treated in this paper. The authors describe results with a comparison of the CBM gas pressure sensor and the existing gas pressure sensor in reference to the problem with SF6 gas leakage detection. As result of the experiment, an SF6 gas leakage of less than 0.1 per year might be detected by using the CBM gas pressure sensor. The authors conclude that a special sensitivity and long-term stability performance of the CBM gas pressure sensor are very important for the reliable operation of power substations under the CBM strategy. View full abstract»

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  • Effect of Transfer Coefficients on MV and LV Flicker Levels

    Page(s): 632 - 639
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    It has been suggested that the recommended flicker planning levels provided in IEC 61000 3-7 and IEEE 1453 are too restrictive for high-voltage and extra-high-voltage networks. The premise of this argument is based on a perceived increase in low-voltage (LV) flicker compatibility level. Some believe that flicker measurements made in Europe over a period of several years support the notion of an increased LV compatibility level; however, measurements performed by the authors in North America indicate otherwise. Analysis of authors' measurements suggests that the lack of customer complaints is due primarily to the effect of flicker transfer coefficients, rather than a presumed increase in LV compatibility level, and supports the continued use of Pst95%=1.0 as the LV flicker compatibility level. View full abstract»

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  • Discussion on Useless Active and Reactive Powers Contained in the IEEE Standard 1459

    Page(s): 640 - 649
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  • Hourly Scheduling of DC Transmission Lines in SCUC With Voltage Source Converters

    Page(s): 650 - 660
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (531 KB) |  | HTML iconHTML  

    This paper presents the modeling of high-voltage direct current (dc) transmission systems with voltage-source converters (VSCs) in security-constrained unit commitment (SCUC). The impact of VSC-DC transmission system on the economics and the security of integrated ac/dc transmission systems is discussed. The nonlinear ac/dc equations are linearized and the Newton-Raphson method is utilized to solve the linearized network in the base case and contingencies. The SCUC solution will determine the optimal hourly schedule of controllable VSC-DC transmission systems in electricity markets. Numerical examples show the efficiency of the proposed model. View full abstract»

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  • Islanded-Mode Control of Electronically Coupled Distributed-Resource Units Under Unbalanced and Nonlinear Load Conditions

    Page(s): 661 - 673
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1796 KB) |  | HTML iconHTML  

    This paper proposes a voltage- and frequency-control strategy for the islanded operation of dispatchable electronically coupled distributed-resource units, based on a discrete-time mathematical model which is also valid for variable-frequency operation. The proposed control strategy utilizes a combination of deadbeat and repetitive control to enhance the performance of the control system under unbalanced and/or distorted load currents. Moreover, a new approach is proposed to maintain the effectiveness of the repetitive control under variable-frequency operational scenarios. Furthermore, the control strategy employs feedforward compensation techniques to mitigate the impact of load dynamics on the regulation process. The performance of the proposed control strategy is demonstrated for single- and multiunit islanded networks, through digital time-domain simulation studies in the PSCAD/EMTDC software environment. View full abstract»

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  • The Effectiveness of Compensated Passive Loops for Mitigating Underground Power Cable Magnetic Fields

    Page(s): 674 - 683
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2434 KB) |  | HTML iconHTML  

    This paper analyzes the possibility of using compensated passive loops to obtain a high mitigation effectiveness of the magnetic field generated by underground single-core cables. With that aim, several loops arrangements are simulated in a case study, including new ones called enchained loops, whose geometry reminds short-circuited conductors at both ends, but with the advantage of requiring smaller compensating capacitors. The results show a drastic spot reduction in several configurations, but with the drawback of high sensitivity to parameters. This aspect should be taken into account in the final design, so a design procedure is proposed that includes measures to alleviate this problem. Eventually, a comparison using shielding with high-conductivity material is provided. View full abstract»

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  • Measurement of VFTO Based on the Transformer Bushing Sensor

    Page(s): 684 - 692
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    Disconnector switching operations in large gas-insulated switchgear (GIS) systems may produce very fast transient overvoltages (VFTOs), causing high electric stress to other apparatuses in the substation, such as power transformers. This paper presents a VFTO measuring technique based on a transformer bushing sensor, which consists of the transformer bushing (C1) and a capacitor sensor (C2) installed at the test tap of transformer bushing. In order to solve the problem of the frequency limitation of the transformer bushing sensor for measuring VFTO, a convolution model on the square-wave response of the transformer bushing sensor is introduced to obtain the frequency response of the transformer bushing sensor, and a deconvolution model based on the incremental Wiener filter is applied to reconstruct the input transient voltage waveform at the tip of the bushing by using the output signals from the bushing sensor. A 110-kV transformer bushing sensor and a fast transient overvoltage source are built in our laboratory. The results from the laboratory indicate that a transient voltage can be measured correctly based on our technique with the 110-kV transformer bushing sensor. A 750-kV transformer bushing sensor is built in a 750-kV substation. The measuring results from the 750-kV substation by using our technique show that the peak value of the VFTO produced by the disconnector (AIS) switching off operations is about 775 kV, and the dominant oscillating frequencies of the VFTO are 3.5 MHz, 1.6 MHz, and 650 kHz. View full abstract»

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  • Corona Onset Voltage of Bipolar Bundle Conductors of HVDC Transmission Line

    Page(s): 693 - 702
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    In this study, the corona onset voltage (COV) of bipolar bare overhead bundle conductors for transmission lines has been investigated using numerical calculations and gas discharge theory. First, an accurate numerical method, the charge simulation method, was used to calculate the electric field distribution in the vicinity of bare sub-conductors in bundles. Then, the electric field values and a criterion from the gas discharge theory were used to evaluate the onset voltage for monopolar positive or negative coronas on the bare sub-conductors. The monopolar criteria for single conductors have been further developed for use in bipolar bundle conductors with a rational demonstration. The bipolar COVs obtained are in good agreement with the literature data for laboratory models and full-scale test lines. Furthermore, some numerical results for the COVs influenced by the different effect factors of the bundle conductors have also been discussed. View full abstract»

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  • A Control Strategy for Islanded Microgrids With DC-Link Voltage Control

    Page(s): 703 - 713
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    New opportunities for optimally integrating the increasing number of distributed-generation (DG) units in the power system rise with the introduction of the microgrid. Most DG units are connected to the microgrid via a power-electronic inverter with dc link. Therefore, new control methods for these inverters need to be developed in order to exploit the DG units as effectively as possible in case of an islanded microgrid. In the literature, most control strategies are based on the conventional transmission grid control or depend on a communication infrastructure. In this paper, on the other hand, an alternative control strategy is proposed based on the specific characteristics of islanded low-voltage microgrids. The microgrid power is balanced by using a control strategy that modifies the set value of the rms microgrid voltage at the inverter ac side as a function of the dc-link voltage. In case a certain voltage, which is determined by a constant-power band, is surpassed, this control strategy is combined with P/V -droop control. This droop controller changes the output power of the DG unit and its possible storage devices as a function of the grid voltage. In this way, voltage-limit violation is avoided. The constant-power band depends on the characteristics of the generator to avoid frequent changes of the power of certain DG units. In this paper, it is concluded that the new control method shows good results in power sharing, transient issues, and stability. This is achieved without interunit communication, which is beneficial concerning reliability issues, and an optimized integration of the renewable energy sources in the microgrid is obtained. 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.

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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