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Power Delivery, IEEE Transactions on

Issue 2 • Date April 2010

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Displaying Results 1 - 25 of 85
  • Table of contents

    Page(s): C1 - 523
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    Freely Available from IEEE
  • IEEE Transactions on Power Delivery publication information

    Page(s): C2
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    Freely Available from IEEE
  • Ampacity Calculations for Deeply Installed Cables

    Page(s): 524 - 533
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (593 KB) |  | HTML iconHTML  

    In this paper, a new method is proposed for ampacity calculations of deeply installed cables. Two factors make these types of installations different from more common situations of cables located up to five meters underground. On the one hand, the time constant of the soil layer above the cable trench is very large, resulting in a very slow conductor temperature rise when the cable is first loaded, and, on the other hand, the weekly and yearly load-cycle variations can be taken into account to take the advantage of the greater laying depth. Both issues are explored in this paper. This paper introduces the concept of the equivalent laying depth which makes it possible to use the rating rules applicable to the steady-state conditions and avoid transient analysis. View full abstract»

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  • Processing of Harmonics and Interharmonics Using an Adaptive Notch Filter

    Page(s): 534 - 542
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (694 KB) |  | HTML iconHTML  

    A method for real-time detection and extraction of individual harmonic and interharmonic components in a power signal with potentially time-varying characteristics is presented. The proposed method, which is based on the concept of adaptive notch filter (ANF), adaptively decomposes the measured power signal into its constituting components independent of where their frequencies are located. The algorithm provides instantaneous values of the various estimated frequency components in addition to the values of their frequencies, amplitudes, and phase angles. The structure and mathematical formulation of the proposed technique, including guidelines for its parameter tuning, are presented and its performance is studied in a variety of scenarios where the power signal attributes, such as fundamental frequency and amplitude, undergo variations over time. This study confirms the desirable transient and steady-state performances of the proposed method. Compared with its recently proposed counterpart, the proposed method of this paper obviates the need for using a phase-locked loop (PLL), and hence, offers a more simplified structure which makes it more attractive from an implementation point of view. View full abstract»

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  • Control Scheme of Cascaded H-Bridge STATCOM Using Zero-Sequence Voltage and Negative-Sequence Current

    Page(s): 543 - 550
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    This paper presents a control scheme of cascaded H-bridge STATCOM in three-phase power systems. Cascaded H-bridge STATCOM has merits in point of switching losses, output harmonics, and the number of circuit components. But every H-bridge cell has isolated dc capacitors. So the balancing problem of capacitor voltages exists. Since STATCOM is often requested to operate under asymmetrical condition by power system faults, capacitor voltage balancing between phase clusters is particularly important. Solving this problem, a technique using zero-sequence voltage and negative-sequence current is proposed. By this scheme, the STATCOM is allowed to operate under asymmetrical conditions by power system faults. The validity is examined by digital simulation under one line and two-lines fault circuit condition. View full abstract»

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  • Load Signature Study—Part I: Basic Concept, Structure, and Methodology

    Page(s): 551 - 560
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    Load signature is the unique consumption pattern intrinsic to each individual electrical appliance/piece of equipment. This paper focus on building a universal platform to better understand and explore the nature of electricity consumption patterns using load signatures and advanced technology, such as feature extraction and intelligent computing. Through this knowledge, we can explore and develop innovative applications to achieve better utilization of resources and develop more intelligent ways of operation. This paper depicts the basic concept, features of load signatures, structure and methodology of applying mathematical programming techniques, pattern recognition tools, and committee decision mechanism to perform load disaggregation. New indices are also introduced to aid our understanding of the nature of load signatures and different disaggregation algorithms. View full abstract»

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  • Load Signature Study—Part II: Disaggregation Framework, Simulation, and Applications

    Page(s): 561 - 569
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    Load signatures embedded in common electricity consumption patterns, in fact, could render much information pertaining to the nature of the appliances and their usage patterns. Based on the proposed disaggregation framework, we use three advanced disaggregation algorithms, called committee decision mechanisms (CDMs), to perform load disaggregation at the metering level. Three random switching simulators are also developed to investigate the performance of different CDMs under a variety of scenarios. Through Monte Carlo simulations, we demonstrate that all CDMs outperform any single-feature, single-algorithm-based disaggregation methods. With sensitivity analysis, we also show that the CDMs are less sensitive to any load dynamics and noise. We finally demonstrate some applications of this technology in terms of appliance usage tacking and estimated energy consumption of each appliance. View full abstract»

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  • A Dynamic Synchrophasor Estimation Algorithm for Online Application

    Page(s): 570 - 578
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    A new algorithm for synchrophasor estimation is proposed to improve estimation accuracy under dynamic conditions. The real component of a constantly rotating vector and a low-frequency band-limited vector, which is linearized by Taylor series, is employed to model supplied signals in power systems. And dynamic characteristics of power systems are described in form of Taylor series' derivatives, which are calculated through consecutive phasors. The accuracy of phasor estimation was dramatically improved by the reassignment of estimation of short-time Fourier transform (STFT) with knowledge of these derivatives. Simulation results allow us to make the conclusion that the proposed algorithm improves the accuracy of phasor estimations under dynamic conditions dramatically, such as frequency ramping, low frequency oscillation, etc., at the cost of the calculation burden is a minimal increase whilst still meeting the requirements of the application for power systems. View full abstract»

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  • Reliability Modeling of All-Digital Protection Systems Including Impact of Repair

    Page(s): 579 - 587
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (394 KB) |  | HTML iconHTML  

    This paper explores the impact of including component repair on the reliability modeling of all-digital protection systems. It is shown that repairable and nonrepairable assumptions make a remarkable difference in the computed reliability indices of the mean time to failure (MTTF) and the mean time to first failure (MTTFF). Theoretical analysis of basic system structures consisting of two components is first examined. Then, a typical all-digital protection system architecture is modeled and numerically analyzed. Some interesting results are found by comparing reliability indices of MTTF and MTTFF and explanations of these results are provided. View full abstract»

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  • A Traveling-Wave-Based Protection Technique Using Wavelet/PCA Analysis

    Page(s): 588 - 599
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    This paper proposes a powerful high-speed traveling-wave-based technique for the protection of power transmission lines. The proposed technique uses principal component analysis to identify the dominant pattern of the signals preprocessed by wavelet transform. The proposed protection algorithm presents a discriminating method based on the polarity, magnitude, and time interval between the detected traveling waves at the relay location. A supplemental algorithm consisting of a high-set overcurrent relay as well as an impedance-based relay is also proposed. This is done to overcome the well-known shortcomings of traveling-wave-based protection techniques for the detection of very close-in faults and single-phase-to-ground faults occurring at small voltage magnitudes. The proposed technique is evaluated for the protection of a two-terminal transmission line. Extensive simulation studies using PSCAD/EMTDC software indicate that the proposed approach is reliable for rapid and correct identification of various fault cases. It identifies most of the internal faults very rapidly in less than 2 ms. In addition, the proposed technique presents high noise immunity. View full abstract»

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  • Application of Equal Area Criterion Conditions in the Time Domain for Out-of-Step Protection

    Page(s): 600 - 609
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (692 KB) |  | HTML iconHTML  

    A new procedure for out-of-step protection by mapping the equal area criterion conditions to the time domain is proposed in this paper. The classification between stable and out-of-step swings is done using the accelerating and decelerating energies, which represents the area under the power-time curve. The proposed methodology is simple and overcomes some of the difficulties associated with the previous techniques. The proposed approach is based only on the local electrical quantities available at the relay location, and does not depend on the network configuration and parameters. The proposed algorithm has been tested on a single-machine infinite bus and a three-machine infinite bus system using software simulations. A digital prototype of the relay has also been implemented on the hardware and its performance has been assessed in a closed-loop mode using a real-time digital simulator. The simulation results and the hardware testing results confirm the validity of the approach presented. View full abstract»

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  • Current Differential Protection of Transmission Line Using the Moving Window Averaging Technique

    Page(s): 610 - 620
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (351 KB) |  | HTML iconHTML  

    We propose a new approach to current differential protection of transmission lines. In this approach, we transform the instantaneous line current(s) by using a moving window averaging technique. If the time span of moving window is equal to one-cycle time, then the steady-state value of the transformed current is zero for a periodic signal which is composed of fundamental and harmonic frequencies. Signal distortions (e.g., a fault) cause the transformed currents to deviate from the nominal zero value. This permits the development of a sensitive, secure, fast, and yet simple current differential protection scheme. The scheme can be applied in toto to series-compensated transmission lines. Results on a four-machine ten-bus system and comparative evaluation with state-of-the-art methods brings out promise of the proposed method. View full abstract»

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  • Iterative Frequency Estimation Based on MVDR Spectrum

    Page(s): 621 - 630
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    Frequency estimation is an important task in a power system since the frequency deviation is a yardstick for the power system abnormal operating conditions. This paper presents a new frequency-estimation algorithm based on the minimum variance distortionless response spectrum that has advantages of accuracy, fast convergence, and modest complexity. To reduce complexity without a trade off of accuracy, an iterative searching method is introduced. An adaptive step-size method is also introduced to reduce gradient noise. Complexity of the proposed algorithm is O(K) or O(K 2) depending on environments where K is the dimension of correlation matrix. When compared with other conventional adaptive algorithms, simulation results show that the proposed algorithm improves convergence speed, and has lower frequency estimation error in cases of high signal-to-noise ratio. View full abstract»

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  • Unsynchronized Fault-Location Scheme for Nonlinear HIF in Transmission Lines

    Page(s): 631 - 637
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    The general aim of this paper is to develop an accurate fault-location scheme that can solve the problems affecting the accuracy of the existing conventional fault locators achieving easier maintenance and restoration time reduction as well as economical aims. This consequently helps to fit the new deregulation policies and competitive marketing. This investigation successfully applies zero-sequence current (3I 0) from the two terminals for earth high impedance fault (HIF) location, or negative-sequence currents from the two terminals of one faulted phase for line-to-line fault location. The HIF location is determined within only a maximum time of one cycle. The proposed scheme is insensitive to variations of different parameters, such as fault type, HIF behavior, wide-range transmission-line parameters variation, and fault inception angle. Staged fault testing results demonstrate that the proposed algorithm has feasible performance. View full abstract»

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  • Automated Graph-Based Methodology for Fault Detection and Location in Power Systems

    Page(s): 638 - 646
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (234 KB) |  | HTML iconHTML  

    This study investigates how the model-based fault detection and location approach of structural analysis can be adapted to meet the needs of power systems, where challenges associated with increased system complexity make conventional protection schemes impractical. With a global view of the protected system and the systematic and automated use of the system's analytical redundancy, faults are detected and located by more than one means. This redundancy can be used as a confirmation mechanism within a wide-area protection scheme to avoid unnecessary or false tripping due to protection component failure or disturbance. Furthermore, this redundancy turns the sensor configuration problem into an optimization problem with regard to fault detection and location. The effectiveness of different system topologies can then be compared on the basis of the optimal number of sensors they require. The principle of structural analysis is described in detail and illustrated on a simple power system model. Pertinence of the approach is demonstrated through simulation. View full abstract»

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  • Adaptive Noise Mitigation in Impulsive Environment: Application to Power-Line Communications

    Page(s): 647 - 656
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1134 KB) |  | HTML iconHTML  

    In this paper, we address the general issue of asynchronous impulsive noise mitigation and its application over coded power-line communications (PLC). As is well known, PLC channels usually suffer from significant degradation due to impulsive interference generated by electrical appliances. The use of a level limiter is a simple and intuitive technique, widely used to mitigate the noxious effect of impulsive noise in these channels. However, the determination of the clipping threshold remains, most of the time, empirical, and the impulse statistics are usually assumed to be known. In a previous study, we proposed an original threshold determination based on signal detection theory, using the well-known false alarm and good detection tradeoff. Here, we further investigate the proposed optimization method in closed form. We compare two tradeoff criteria by means of a receiver operating curves analysis. We clearly show that the resulting decision fits well with encountered bit-error rate performances. We also evaluate the influence of impulsive noise statistics estimation on the performance of the proposed approach. To do so, we assess the robustness of the classical method of moments on Gaussian mixture estimation. It clearly appears that the estimation method is reliable for reasonable values of the impulse occurrence. As one of the main results of this paper, we make a proposal for impulse statistics estimation under ??severe?? conditions (i.e., for very rare impulse events, based on impulse detection over corrupted OFDM symbols). Subsequently, we propose a general scheme of automatic impulse mitigation, according to the disturbance ratio of the environment. Finally, the performance of the approach is evaluated over the Home-Plug AV (HPAV) physical layer. View full abstract»

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  • Optimal Resource Allocation Based on Resource Factor for Power-Line Communication Systems

    Page(s): 657 - 666
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (526 KB) |  | HTML iconHTML  

    The optimal multilayer, multiobjective resource allocation model for multiuser and multitraffic orthogonal frequency-division multiplexing (OFDM)-based power-line communication (PLC) systems is analyzed with the restrictions of maximal total power, constant rates for every real time (RT) user, minimal rates for every non-real time (NRT) user, maximal upper limit of power and number of bits for every subcarrier in each OFDM symbol. A bit-loading lookup table resource allocation algorithm with rate- and margin-adaptation is proposed based on resource factor, which first assigns fairly Pareto non-dominated resources for all RT users according to resource factor so as to attain their constant rates, second computes the relevant remaining power and non-used subcarriers for every Pareto solution and assigns fairly them for all NRT users so as to attain their minimal rates, third also computes the relevant remaining resources and assigns them so as to achieve the maximal sum of the allocated rates for all NRT users, lastly selects out the globally optimal solution according to the order of partial information. Based on the typical power-line channel, the simulation results illustrate that the proposed algorithm outperforms the existed multiuser bit-loading greedy algorithm and it realizes better the multiple aims of resource allocation in OFDM-based PLC systems. View full abstract»

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  • Design and Evaluation of a Dual Impedance-Adapting Power-Line Communications Coupler

    Page(s): 667 - 673
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    Historically, the unpredictable on-off switching of loads has been a major obstacle to low-voltage power-line communications. Some researchers have gathered valuable data and have proposed statistical models in order to try and mitigate these sudden changes in access impedance. Others have proposed network conditioning in order to ??block off?? harsh loads from the power-line network by means of series filters. These filters are expensive, as they have to be rated at the typical current that is drawn by the load to be `blocked off'. Also, in many cases, these are the very loads than need to be monitored and controlled for home automation. This paper investigates the possibility of utilizing a simple, dual coupler to diminish the impact of switching loads on data transmission. First, the design of a suitable dual coupler is demonstrated, using a commercially available high-frequency transformer. Next, laboratory as well as live 220-V measurements are done for 50-?? modems at frequencies below 1 MHz. These measurements confirm that the proposed dual coupler can help to counter the impact of switching power-line loads by means of (i) improved transmission when a certain network point is loaded and (ii) more predictable (lower) power-line impedance levels-facilitating more accurate overall impedance adaptation. View full abstract»

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  • M-FSK Carrier Gain Adjustment for Improved Power-Line Communications

    Page(s): 674 - 679
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1101 KB) |  | HTML iconHTML  

    This paper describes carrier gain adjustment (CGA) in the CENELEC A-band, a counter-measure against the negative impact of a transmitter coupling circuit's filter characteristic in this band. As the CENELEC A-band lies very close to the power waveform frequency, a steep -40 dB/decade coupler filtering slope is present in the lower parts of this band. Therefore, different symbol carriers (of different frequencies) are exposed to different attenuation factors. With linear amplification, only the least attenuated carrier can be amplified to the maximum level allowed by regulations, whilst the other carriers will be transmitted below the maximum level. Conversely, all carriers are exposed to similar noise levels, present on the power-line. CGA however, counters the unequal attenuation effect of the transmitter coupling circuit, by amplifying all carriers to an equal, maximum amplitude. As carrier gain adjustment is directly linked to the frequency response of the transmitter coupling circuit, this coupler needs to be characterized before implementing CGA. As measuring rod for this study, the performance of orthogonal M-ary frequency shift keying without coding, in the presence of white noise, is used. Results show that under the above conditions, carrier gain adjustment proves successful in equalizing the attenuating effect of the transmitter coupling circuit, thereby improving overall performance. View full abstract»

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  • Robust Narrowband Interference Rejection for Power-Line Communication Systems Using IS-OFDM

    Page(s): 680 - 692
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (312 KB) |  | HTML iconHTML  

    In this paper, two narrowband-interference (NBI) rejection methods are formulated for power-line orthogonal frequency-division multiplexing (OFDM) communications. The inherent NBI suppression capability of the OFDM system is improved upon through the application of a spreading sequence (i.e., IS-OFDM) and further improved through the utilization of NBI filtering implemented at the OFDM receiver. A block least-mean-square (BLMS) algorithm, called cyclic prefix BLMS (CP-BLMS), is constructed for time-domain NBI filtering and a corresponding fast BLMS (FBLMS) algorithm, called linear FBLMS (LFBLMS), is also presented which performs the NBI filtering in the frequency domain. The fast implementation reduces the computational burden of the additional filtering process for a large number of subcarriers without impact on filter performance. Both simulation and theoretical analysis demonstrate the bit-error rate improvement of the proposed approaches compared to previous methods. Numerical results from theoretical analysis also illustrate the speed advantage of the LFBLMS algorithm. View full abstract»

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  • Noise Resistant OFDM for Power-Line Communication Systems

    Page(s): 693 - 701
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (296 KB) |  | HTML iconHTML  

    In this paper, we present a new approach to noise suppression for power-line communications based on orthogonal frequency-division multiplexing (OFDM). Previous work for wireless systems has suggested that augmentation of OFDM using spreading codes prior to modulation offers some narrowband interference (NBI) resistant capabilities. We present a study of the performance of such a system for power-line networks-well known to be affected by such noise. Termed interference suppression OFDM (IS-OFDM) and its counterpart NBI avoidance (NBIA), we also present a further modification of these techniques in order to improve NBI suppression performance. The proposed algorithm, orthogonal narrowband interference avoidance (ONBIA), avoids narrowband interference on contaminated subcarriers while preserving the orthogonality of the spreading code. Both theoretical analysis and simulation results demonstrate the improvements of ONBIA over the standard IS-OFDM and NBIA methods across a wide range of interference-to-signal ratios (ISR). View full abstract»

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  • Wideband Indoor Transmission Channel Simulator for Power Line: WITS Software

    Page(s): 702 - 713
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (3024 KB) |  | HTML iconHTML  

    Advanced communication technologies has allowed the power-line communication (PLC) channel to be a transmission medium that enables the transferring of high-speed digital data over the classical indoor electrical wires. The development of PLC systems for Internet, voice, and data services requires measurement-based models of the transfer characteristics of the power-line network suitable for performance analysis by simulation. In this paper, a statistical-based and deterministic PLC channel frequency model was proposed. This model has the advantage of using only one parameter: the channel class. Related software is also developed. In this paper, this model is further improved to represent the measured impulse responses, and related software is developed. First, a PLC channel classification is realized, and an average magnitude and phase channel model by class is proposed. Second, the multipath behaviour of the PLC channel is introduced: a statistical-based channel magnitude generator is built, and a refined phase model is suggested. Finally, the related software is briefly described. View full abstract»

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  • Efficient Secure Group Communications for SCADA

    Page(s): 714 - 722
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    Modern industrial facilities have command and control systems. These industrial command and control systems are commonly called supervisory control and data acquisition (SCADA). In the past, SCADA system has the closed operating environment, so this system were designed without security functionality. These days, as a demand for connecting the SCADA system to the open network increases, the study of SCADA system security is an issue. A key-management scheme is essential for secure SCADA communications. Several key-management schemes for SCADA also have been proposed. Recently, advanced SCADA key-management architecture (ASKMA) was proposed. While previous studies do not support message broadcasting and secure communications, ASKMA supports it. Although the overall performance of ASKMA has many advantages compared to previous studies, it can be less efficient during multicast. In this paper, we propose ASKMA+ which is a more efficient scheme that decreases the computational cost for multicast communication. ASKMA+ reduces the number of keys to be stored in a remote terminal unit and provides multicast and broadcast communications. View full abstract»

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  • Capacity of Overhead Medium Voltage Power Line Communication Channels

    Page(s): 723 - 733
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    This paper considers broadband transmission via the overhead medium voltage (MV) grid. The MV broadband over power lines (MV/BPL) channels considered are three-phase overhead MV lines above lossy plane ground. To determine the end-to-end transfer function of any MV/BPL configuration the scattering matrix method is adopted. Various topologies of MV/BPL transmission channels have been studied with regard to their end-to-end signal attenuation and capacity. The analysis and relevant simulations reveal that broadband transmission via MV power lines depends drastically on the MV grid topology and the power constraints imposed to suppress electromagnetic interference to other services. A modification to the fixed spectrum allocation/all-protection model to regulate BPL emission is proposed employing power masks adaptive to locally existing wireless services. View full abstract»

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  • Power-Frequency Voltage Withstand Characteristics of Insulations of Substation Secondary Systems

    Page(s): 734 - 746
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    The insulation of secondary system in substation, including secondary cables and devices, have to endure the high ac power-frequency voltage during the short-circuit fault. The ac withstand characteristics of the secondary cables and devices are experimentally investigated and discussed in this paper. The insulation breakdown mechanism of relays can be classified into three modes: air gap breakdown, creeping discharge, and solid insulation breakdown, that of the microcomputer protection device is solid state component damage. The ac power-frequency breakdown voltages of the microcomputer protection device, the small-size electromagnetic and solid-state relays all are as low as about 2 kV. The statistic method to obtain the withstand voltage of long communication cable from experimental data of short cables is proposed. The minimum 3-s withstand voltages of secondary system are 6.5 kV and 2 kV, respectively, this should be considered in substation design. What's more, the volt-second characteristics of the power-frequency withstand voltage of the secondary cables and devices are analyzed and compared in detail, which would be important in the selection of secondary cables and devices. At last, the method how to guarantee high ac breakdown voltage of electromagnetic and solid-state relays and microcomputer protection device is suggested. 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