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Power Delivery, IEEE Transactions on

Issue 3 • Date Jul 2001

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Displaying Results 1 - 14 of 14
  • Comparison of generator circuit-breaker stresses in test laboratory and real service condition

    Page(s): 415 - 421
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (184 KB) |  | HTML iconHTML  

    The paper shows that there may be substantial discrepancies regarding delayed current zeros and circuit-breaker arc energies when exposing a generator circuit-breaker to a short-circuit in a real system or in a test lab. Depending on the pre-loading of the generator in the real system the degree of asymmetry may be far higher than that being adjustable in a test lab. Based on realistic generator data the courses of the short-circuit currents have been simulated for various cases also taking into account the arc voltages of different circuit-breaker types. For the same breaking current zero crossings may be delayed for several periods and arc energies may be substantially different in the real system compared to the test lab. Improved generator modeling is indispensable for correct simulation of such phenomena and explains more over “voltage depression” View full abstract»

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  • A precise calculation of power system frequency

    Page(s): 361 - 366
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (204 KB) |  | HTML iconHTML  

    A precise digital algorithm based on discrete Fourier transforms (DFT) to estimate the frequency of a sinusoid with harmonics in real-time is proposed. This algorithm, that the authors call smart discrete Fourier transforms (SDFT), smartly avoids the errors that arise when frequency deviates from the nominal frequency, and keeps all the advantages of the DFT e.g., immunity to harmonics and the recursive computing can be used in SDFT. These make the SDFT more accurate than conventional DFT based techniques. In addition, this method is recursive and very easy to implement, so it is very suitable for use in real-time. The authors provide the simulation results compared with a conventional DFT method and second-order Prony method to validate the claimed benefits of SDFT View full abstract»

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  • Finite element analysis of internal winding faults in distribution transformers

    Page(s): 422 - 428
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (253 KB)  

    With the appearance of deregulation, distribution transformer predictive maintenance is becoming more important for utilities to prevent forced outages with the consequential costs. To detect and diagnose a transformer internal fault requires a transformer model to simulate these faults. This paper presents finite element analysis of internal winding faults in a distribution transformer. The transformer with a turn-to-earth fault or a turn-to-turn fault is modeled using coupled electromagnetic and structural finite elements. The terminal behaviors of the transformer are studied by an indirect coupling of the finite element method and circuit simulation. The procedure was realized using a commercially available software. The normal case and various faulty cases were simulated and the terminal behaviors of the transformer were studied and compared with field experimental results. The comparison results validate the finite element model to simulate internal faults in a distribution transformer. View full abstract»

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  • Evaluation of frequency tracking methods

    Page(s): 367 - 371
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (96 KB) |  | HTML iconHTML  

    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 View full abstract»

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  • Removal of decaying DC in current and voltage signals using a modified Fourier filter algorithm

    Page(s): 372 - 379
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (260 KB) |  | HTML iconHTML  

    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 View full abstract»

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  • Analysis of grounding systems for electric traction

    Page(s): 389 - 393
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (120 KB) |  | HTML iconHTML  

    The traction power supply system consists of the feeder, trolley, rails and static conductors. The traction load is applied between the trolley and rails as a single phase load. In order to maintain near constant voltage along the traction-route, the paralleling stations are equipped with auto-transformers along the track. Further, there are structures such as bridges and platforms along the traction route. The substation and the paralleling stations are provided with grounding grids, which are in turn connected to the static wires. The bridge and the platform grounds are connected to the rails or static wires. The rails and the static wires are connected at certain locations to provide continuity of the return system. The grounding system along the entire power system is designed so that safety of personnel and passengers is assured. The performance of the grounding system is assessed by analysis of the integrated power and grounding system. The maximum touch voltages at different locations are computed and compared with the IEEE Standard 80 values to ensure safety View full abstract»

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  • Estimating the ignition hazard of 100% cotton clothing worn by transmission and distribution line workers

    Page(s): 429 - 432
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (52 KB)  

    This paper describes a method of estimating the fault current magnitude necessary to ignite 100% cotton clothing worn by transmission and distribution line workers inadvertently exposed to the thermal hazards of an electric arc. This paper is intended to suggest methods for initial evaluation of the ignition hazard assessment of clothing normally worn by transmission and distribution line workers when working on overhead lines operating at 4160 volts, phase to phase, and above. Once the hazard has been identified a further risk analysis is required View full abstract»

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  • Condition assessment of power transformer on-load tap-changers using wavelet analysis

    Page(s): 394 - 400
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (156 KB) |  | HTML iconHTML  

    The operation of a power transformer on-load tap-changer (OLTC) produces a well-defined series of vibration bursts as its signature. Due to the harmonic and nonstationary nature of the transient vibration signal, traditional frequency and time-frequency techniques are on longer effective for characterization of this type of vibration signals, as the localized time domain features, such as delays between bursts, the number of bursts, and the strengths of bursts, are essential for the condition assessment of OLTC. A wavelet transform based technique is developed in this paper to characterize the OLTC vibration signals. This technique gives a simplified format for displaying and representing the essential features of the OLTC vibration signatures. Application results from a selector type OLTC demonstrate that the features extracted in the wavelet domain can be utilized to provide reliable indications of the actual heath of an OLTC View full abstract»

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  • Comparing direct and synthetic tests for interruption of line-charging capacitive current

    Page(s): 409 - 414
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (152 KB) |  | HTML iconHTML  

    Using a validated arc model, this paper analyzes current distortion and voltage waveforms during both direct and synthetic tests for interruption of line-charging capacitive current by power circuit breakers. Although the voltage of the electric arc drawn between breaker contacts may produce significant current distortion, it is demonstrated that the most significant parameter affecting the breaking capacity of power circuit breakers in capacitive-current switching tests is the voltage jump appearing across breaker contacts immediately after current interruption. It is essential to correctly define the supply circuit impedances and the associated voltage jump so as not to reduce or increase this test severity unduly View full abstract»

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  • A highly efficient algorithm in treating current measurements for the branch-current-based distribution state estimation

    Page(s): 433 - 439
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (124 KB) |  | HTML iconHTML  

    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 View full abstract»

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  • A novel digital distance relaying technique for transmission line protection

    Page(s): 380 - 384
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (96 KB) |  | HTML iconHTML  

    Parallel transmission lines often pose more difficult protection problems than single lines. In the case of parallel lines, a number of problems arise when using the distance protection. The paper discusses problems associated with parallel line distance relaying schemes and presents a novel technique to overcome these problems. Two relays instead of four are proposed for the double lines, One relay is located at the beginning and another one at the end. Each relay is fed by three voltage and six current signals from the two lines. The suggested technique is based on the comparison of the measured impedance of corresponding phases. So, the complexity of the possible types of faults, high path fault resistance, mutual effects, current in-feed, inter-system faults are solved. Moreover, 100% of line is protected and the problem of balance-point locations is avoided. Alternative Transient Program models the power system and simulates different fault conditions View full abstract»

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  • A de-noising scheme for enhancing wavelet-based power quality monitoring system

    Page(s): 353 - 360
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (140 KB)  

    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 View full abstract»

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  • Improved calculations for no-load transformer switching surges

    Page(s): 401 - 408
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (168 KB) |  | HTML iconHTML  

    This paper deals with a modeling of components and calculation of transient overvoltages that build up on the transformer primary terminals after the transformer has been switched off by a vacuum circuit breaker (VCB). The transformer is connected to the circuit breaker by a cable. The transient overvoltages are calculated for different cable lengths, and the cumulative probability of different arc angles is investigated. In this study two cases are considered: transient overvoltages due to steady-state magnetizing current switching, and transient overvoltages due to inrush current switching. It is shown that the case of inrush current switching is worse, as virtual current chopping is possible. The cable is modeled by pi sections, whereas the transformer model is based on a terminal impedance. The VCB re-ignitions are modeled by means of withstand voltage characteristics and high-frequency quenching capability. Due to shortage of field tests, this work uses only literature references to compare the results with actual measurements View full abstract»

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  • Optimal computation of distance relays second zone timing in a mixed protection scheme with directional overcurrent relays

    Page(s): 385 - 388
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (148 KB) |  | HTML iconHTML  

    This paper describes a technique to determine the optimal time setting for the second zone of distance relays when used in a mixed protection scheme with directional overcurrent relays. The technique consists of including the second zone operation time as a new variable in the original problem statement of optimal computation of directional overcurrent relays settings. It is shown that the influence of distance relays and directional overcurrent relays must be considered when the settings of these relays are computed. Numerical results obtained with the proposed method for a realistic power system are presented 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