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Power Delivery, IEEE Transactions on

Issue 4 • Date Oct 1993

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Displaying Results 1 - 25 of 54
  • Minimal transient switching of capacitors

    Page(s): 1988 - 1994
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    Capacitor banks are used to compensate the reactive power demand of large commercial and industrial loads. When used to switch capacitor banks mechanical breakers generate large current transients. These transients may cause serious system disturbances, premature wear of the breaker contacts and, possibly, shorten the life of the capacitors. While thyristor switches are not new and industry has successfully used them to obtain transient-free switching of capacitor banks, there are very few papers describing this application. This paper tries to fill the void and presents a comparative study of various three-phase configurations of semiconductor switches intended for low voltage (600 V and less) distribution systems. Simple theoretical analysis enables the calculation of the optimal switching times to minimize transients. These calculations take into account the system impedance and the initial capacitor voltages View full abstract»

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  • An investigation into major factors in shunt capacitor switching performances by vacuum circuit breakers with copper-chromium contacts

    Page(s): 1789 - 1795
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    The performance of vacuum circuit breakers in switching shunt capacitors depends much more on in-rush current than on interrupting current. This is because when contacts that were fused together by pre-arcs during contact closing are forcibly separated, large protrusions are formed on the contact surface, making it easier for microparticles to be detached from the protrusions. Microparticles are also produced on the entire surface of contacts by mechanical impact or cold weld. Current interruption of a certain magnitude, however, has a conditioning effect because moderate arcs can eliminate such microparticles and lower the protrusions. To clarify the relationship between the behavior of microparticles and the dielectric breakdown, a laser scattering technique was employed. The authors found a microparticle-induced breakdown phenomena that could explain the mechanism of long delayed restrikes that is occasionally observed in vacuum circuit breakers View full abstract»

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  • Network reconfiguration algorithm for automated distribution systems based on artificial intelligence approach

    Page(s): 1933 - 1941
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    This study develops an expert system to solve the problems of the main transformer (MTr) or feeder overload and the feeder constraint violation in automated distribution systems, where each feeder is subject to the thermal overload and voltage-drop limits. The objective is to perform the network reconfiguration by switching the tie and sectionalizing switches so that the system violation is removed, while achieving load balance of the MTrs and feeders with a fewer number of switching operations. Since the switching operation in a practical system does not cause a large change in the voltage, an approximation method is used in order to check the voltage violation, instead of a full AC load flow solution. To reduce the search space, an expert system based on heuristic rules is presented, and implemented in PROLOG. This system adopts the best first tree search technique. List processing and recursive programming techniques are then utilized to solve the combinatorial type optimization problem. The computational results are also prepared to show the performance of the heuristic algorithms developed View full abstract»

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  • Multi-infeed HVDC transient response and recovery strategies

    Page(s): 1995 - 2001
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    Should two or more DC transmission systems terminate in close electrical proximity in the same AC system, there is the potential for degradation of DC transient performance due to interaction in response to common AC system disturbances. This paper presents the digital simulation of a test system and shows the DC responses to AC faults at various locations. Control strategies are evaluated to enhance the recovery of the DC systems from the disturbances View full abstract»

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  • Solid-state current limiter for power distribution system

    Page(s): 1796 - 1801
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    To prevent voltage decrease of distribution systems, the principle and fundamental characteristics of a solid-state current limiter using GTO thyristors were investigated. Basic components of the apparatus were a fast solid-state switch and a current limiting impedance of low resistance in parallel with the switch. Experimental results of the test current limiter showed the fault current was limited successfully, regardless of DC component size. The time from detection of fault occurrence to interruption of the fault current by the solid-state switch was 40 μs. This time was very short in comparison with that before the fault current reached a large value. Thermal rise of the solid-state switch for conduction was solved by a self-cooling apparatus using a noncombustible cooling liquid. The results indicated that the solid-state current limiter was a valuable protecting device for high fault current distribution systems View full abstract»

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  • Impedance of a double submarine cable circuit using different types of cables within a single circuit

    Page(s): 1668 - 1674
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    The interconnection between the Upper and Lower Peninsulas of Michigan has recently been upgraded from a single 138 kV circuit to a double 138 kV submarine power cable circuit. The original circuit consisted of four single-conductor cables, the fourth cable serving as a spare phase conductor. The second circuit was formed by adding two new single conductor cables and combining them with the spare cable from the original circuit. The use of two different types of cables in one circuit causes that circuit to be unbalanced. The series impedance and shunt admittance matrices of the circuits were studied to investigate the degree to which they were unbalanced, so that the impedance relays protecting the cable could be properly set. Measurements were made on the cables after they were installed and these were compared to calculations made with the ATP EMTP Cable Constants program View full abstract»

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  • An expert system for transmission substation event analysis

    Page(s): 1942 - 1949
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    Digital fault recorders (DFRs) are used in substations to capture recordings of various disturbances and fault events. Protection engineers use these recordings to identify reasons for particular operation of protection relays and circuit breakers. In performing this task protection engineers use their expertise related to specific power system conditions, equipment and operations. This paper describes implementation of an expert system which performs fault detection and diagnosis automatically and can aid operators in their task of analyzing disturbances and fault events View full abstract»

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  • Motor bus transfer

    Page(s): 1747 - 1758
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    The Motor Bus Transfer Working Group of the IEEE Power System Relaying Committee has performed a survey on industry practices for implementing automatic motor bus transfers in various power plant applications and the application of supervisory and control relays for these transfer schemes. This report summarizes automatic transfer methods for primary auxiliary buses that supply major rotating machinery loads. Fast, slow, parallel, residual voltage, and in-phase transfer methods are covered in this report. Information is also included on methods and criteria of acceptance testing of the motor bus transfer scheme View full abstract»

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  • Planning and installation of the 138 kV South Padre Island submarine cable

    Page(s): 1675 - 1681
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    This paper describes the planning, design and installation phases of a 138 kV submarine power cable project which was recently completed by Central Power and Light (CPL) to improve the service reliability of South Padre Island and the town of Port Isabel. The project presented unique installation problems due to the shallow water depths combined with the necessity to minimize the environmental impact to sea grasses during the cable installation View full abstract»

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  • Control of tap change under load transformers through the use of programmable logic controllers

    Page(s): 1759 - 1765
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    This paper describes a method developed by Pennsylvania Power and Light Company (PP&L) for applying programmable logic controllers to control tap change under load (TCUL) power transformers. Equipment was identified, and a set of software programs developed, to completely replace the existing analog-based TCUL control systems. There is a significant cost savings from this approach, and PP&L expects an increase in the reliability of the TCUL controls from this design, as well as fewer operations of the TCUL equipment. Several additional functions and alarms were implemented in the new design which will enhance the operation of these transformers View full abstract»

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  • Practical aspects of distribution automation in normal and emergency conditions

    Page(s): 2002 - 2008
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    In this study, the practical aspects of the real-time analysis and control of distribution systems in normal and emergency conditions are presented. A load flow algorithm based on loop currents, which is numerically more stable and would require a smaller number of iterations, is considered in distribution systems calculations. In order to obtain an optimal solution within a reasonable time, the problem is decomposed into feeder reconfiguration and volt/VAr optimization subproblems and uses an iterative process between these two subproblems. For feeder reconfiguration, an efficient procedure based on a closed loop resistive scheme which utilizes fast branch removal is proposed. For volt/VAr optimization, a procedure based on the gradient search is developed. The proposed software is devised for interaction with human operators which will provide advice in real-time normal and emergency practices View full abstract»

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  • On-line reactive power compensation schemes for unbalanced three phase four wire distribution feeders

    Page(s): 1958 - 1965
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    A new reactive power compensation method is developed to reduce the negative and zero sequence components of load currents and to improve the load bus power factor of unbalanced three-phase four-wire distribution feeders. Negative and zero sequence currents may cause additional losses and damage to power systems. Load compensation at the load bus is an effective method to eliminate those undesired sequence currents. The compensation technique uses a Y-connected and a Δ-connected static reactive power compensators (SVCs) to give a different amount of reactive power compensation to each phase. The compensation formulas are very suitable for on-line control by measurement of phase voltages and currents in real time. The compensation effect can also be achieved even if one leg of the SVCs is out of service. In addition to balancing effect and power factor improvement at the load bus, the SVCs can also be used to support the load bus voltage and to maintain the substation feeder at unity power factor. Digital simulations are made with the load data measured from an 11.4 kV secondary substation feeder View full abstract»

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  • Improvement of transmission line ground circuit current carrying limit after system interconnections

    Page(s): 2023 - 2030
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    When one or more transmission lines are added to an existing transmission system, the intensity of the fault currents flowing along the ground wires near the substations may exceed the ground wire thermal limit. In such cases, it is generally preferred to improve the existing ground wire conductivity by replacing say a steel groundwire with an ACSR ground wire along the first spans near the substation. Generally, this procedure requires that the transmission line be de-energized, what may sometimes be considered unacceptable. This paper deals with optional procedures which can be implemented in the first line kilometers near the substations keeping the existing lines energized. Such procedures include sectionalizing of groundwires, use of continuous counterpoise and use of additional overhead ground wires installed below the conductors. This paper introduces also a technique known as "tower foot resistance adjustment", which complements the corrective effects of the aforementioned procedures View full abstract»

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  • A study of polyphase watthour meter accuracy comparing single phase series to polyphase calibration

    Page(s): 1712 - 1720
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    This paper examines the accuracy of polyphase watthour meters derived from two methods of calibration. The standard single phase series method is compared to the three phase method of calibrating polyphase transformer rated and self-contained induction type watthour meters. A total of seventy two meters from four different manufactures are tested. Sixty of these meters are tested at full load, full load with 0.5 lagging power factor and light load for each of the calibration methods. Twelve meters are further tested over a greater range of loading conditions. Also, the effect of rotating the phase of the input conductors on the meter's accuracy is examined View full abstract»

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  • State estimation for electric power distribution systems in quasi real-time conditions

    Page(s): 2009 - 2015
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    This paper proposes a new method for the state estimation of electric power distribution system conditions oriented towards working with minimum number of remote measurements available in the network. This approach will require information concerning the network reconfiguration, remote measurements of voltages, real and reactive power as well as feeder currents in distribution substations. All kinds of statistical information pertaining to distribution transformer loads are used together with real-time remote measurements. In the proposed method, the existing scheme configuration is examined by a configuration pre-screening process based on the addressed references in an oriented graph. The permissible intervals for remote measurement errors and the reliability of statistical information are discussed. A practical example is presented and the exploitation of results has proved its accuracy and efficiency View full abstract»

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  • Harmonic power flow for unbalanced systems

    Page(s): 2052 - 2059
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    A harmonic power flow method that analyzes harmonics in unbalanced power systems is presented. The developed algorithm has two steps which are executed successively: the first is a fundamental frequency power flow for the AC linear network in which nonlinear loads are represented by current sources; the second is a frequency domain iterative Newton-Raphson method to calculate the harmonics generated by nonlinear loads. In this second step, the AC linear network is represented by a generalized Thevenin equivalent with respect to the nonlinear loads, obtained from the power flow solution. Both linear and nonlinear loads are considered in terms of power View full abstract»

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  • Exponential fitting algorithms for digitally recorded HV impulse parameter evaluation

    Page(s): 1727 - 1735
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    Standard analysis of high voltage impulses comprises determination of parameters describing the recorded impulses. These include peak value, front time, and time to half-value. This paper describes several fitting algorithms intended to facilitate extraction of these parameters from recorded data. These algorithms were used to fit bi-exponential models to smooth lightning and switching impulses, to lightning impulses having oscillatory fronts or peaks where the evaluation of the waveform parameters is based on the construction of a smooth curve, and to tail-chopped lightning impulses. The overall effectiveness of these algorithms and their influence on parameter estimates are presented and discussed View full abstract»

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  • A color graphics display of the field intensity around the insulator on 13.2 kV distribution lines

    Page(s): 1696 - 1702
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    Covered conductors have been used, especially in wooded areas on low as well as high voltage overhead distribution lines for preventing brush contact and short circuit faults between conductors. Burndown on covered conductors has become a significant problem. The burndown mechanism is complicated since it is determined by combinations of the various types of insulators, ties, and conductors. In order to investigate the burndown mechanism, a finite element analysis is carried out to identify the electric field around the insulator. A newly developed electric field digital simulation system is reported in which a finite element analysis method considering isoparametric triangular and line elements is developed. A new color display method for electric potential and electric field distributions with lines of electric force is also described as a means of observing the results View full abstract»

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  • The performance of demand meters under varying load conditions

    Page(s): 1708 - 1711
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    The influence of load variations on the performance of four different types of electricity demand meters was studied using a computer controlled test system capable of reproducing load profile data recorded in the field. Results of the tested meters are compared with computer calculated demand values based on readings of a fast response reference multimeter. Differences in readings in the range of -9.3% to +5.3% were observed during the tests of the four demand meters. For the load profiles considered, demand calculations based on one minute subintervals resulted in values closer to the true peak demand than calculations with five minute subintervals View full abstract»

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  • A study on the characteristics of various conductive contaminants accumulated on high voltage insulators

    Page(s): 1842 - 1850
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    In the assessment of the conductive materials of the natural contaminants accumulated on insulators in terms of equivalent salt deposit density (ESDD), not much attention has been paid to the basic consideration, such as its solubility in water, correction of the conductivity of its water solution to the standard temperature, etc. A study was made on these important factors through repeated measurements of the actual contaminants on the insulators. As a result, practical precautions for the measurement of ESDD are indicated. Also, it is pointed out that the difference in the performance of the naturally and artificially contaminated insulators even with the same ESDD may be explained by the solubility of the materials and that the ambient temperature has a significant influence on the contamination flashover voltage View full abstract»

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  • An improved modeling technique for distribution feeders with incomplete information

    Page(s): 1966 - 1972
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    This paper proposes an improved technique for modeling of an electrical distribution system in the presence of incomplete information. By considering the different behavior and coincident factors of commercial and residential loads, this paper formulates a ratio factor technique to acquire an improved power-flow model. A load distribution relationship between the entire load and less than 50% of the total load on a feeder is also formulated. The technique only requires annual peak loads for each feeder and substation which are readily available. In addition, the method uses the results of the conventional technique and produces better results through a set of simple computation. It is shown that the accuracy of the new technique is significantly better than the traditional technique View full abstract»

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  • Dynamic model of a three-phase power transformer

    Page(s): 1811 - 1819
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    An adequate mathematical model of a three-phase power transformer is one of the important elements in the programs for the computer analysis of power system transients. Featured in this paper is the simulation model of a three-phase, three-limb core-type power transformer. Nonlinear effects of saturation, hysteresis and eddy currents are considered. Two ways of creating major and minor hysteresis loops are presented. The transformer model, described by a system of time dependent differential equations, is solved by an efficient numerical algorithm. The behaviour of the transformer model during switching-in and fault transients, as well as other types of transients, has been tested. The computed transient waveforms are compared with the measured ones and there exists very close agreement between them View full abstract»

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  • Application of a new arc model for the evaluation of short-circuit breaking tests

    Page(s): 1921 - 1925
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    A new arc model is introduced, which describes the behaviour of a circuit breaker using four constant parameters. Comparison of measurement and calculation shows that the description is relatively exact. By means of this model more information about the arc quenching capability of a circuit breaker can be obtained from switching tests than was possible up to now. Examples are given View full abstract»

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  • Comparative studies of lightning performance of a quadruple-circuit dual voltage 275/132 kV transmission line design with wooden crossarms

    Page(s): 1973 - 1980
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    This paper describes a transmission line lightning performance analysis program QCORTL which is able to predict single and multi-circuit flashover and outage types and rates of a quadruple circuit transmission line. It employs the Monte Carlo statistical technique to select lightning and system parameters and the dynamic travelling wave technique to calculate overvoltages on transmission line towers. The program has also incorporated nonlinear corona effects, the dynamic response of soil and the modelling of wooden-crossarms for arc-quenching in its calculations. The assessment of a Malaysian quadruple circuit dual voltage 275/132 kV transmission line using this program is demonstrated to illustrate the detailed nature of the analysis that is suitable for insulation design of transmission lines View full abstract»

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  • High impedance fault detection in low voltage networks

    Page(s): 1829 - 1836
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    High impedance faults are those with fault current magnitude similar to load currents. Experimental results were obtained that confirm operating experience that such faults can occur in the low voltage (600 V and below) underground distribution networks typically found in urban power systems. These faults produce current waveforms qualitatively similar to those found on overhead feeders, but quantitatively smaller. Loose connectors can produce similar, but cleaner current characteristics. Noisy loads remain a major impediment to reliable detection. Design and installation of an inexpensive prototype fault detector on the Seattle City Light street network is described 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