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Generation, Transmission and Distribution, IEE Proceedings-

Issue 2 • Date 4 March 2005

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Displaying Results 1 - 21 of 21
  • Static VAR compensator-based voltage control implementation of single-phase self-excited induction generator

    Page(s): 145 - 156
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (705 KB)  

    A single-phase static VAR compensator (SVC) is proposed to regulate smoothly the output voltage of a single-phase self-excited induction generator (single-phase SEIG) driven by a variable-speed prime mover (VSPM) due to inductive load and prime mover speed variations. A PI feedback closed-loop voltage regulation scheme is presented to adjust the equivalent excitation capacitance of the single-phase SVC. The SVC is composed of a fixed excitation capacitor (FC), thyristor switched capacitor (TSC) and thyristor controlled reactor (TCR). The steady-state single-phase SEIG output voltage and the TCR triggering angle responses of the proposed scheme are simply evaluated and discussed. A small-scale single-phase SEIG voltage control prototype is designed in order to verify system viability and assess its performance. System dynamic operation is studied based on experimental results. Simulation and experimental results prove system practical effectiveness in terms of fast response and high performance. View full abstract»

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  • Mathematical morphology based phase selection scheme in digital relaying

    Page(s): 157 - 163
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (613 KB)  

    The speed and accuracy of digital relays of transmission lines can be improved by accurate and fast fault phase selection, and this also allows single pole tripping and autoreclosure to be employed. Current phase selection schemes, however, have defects. A fault phase selector based on a new technique, series multiresolution morphological gradient (SMMG) transformation, is proposed in this paper. The proposed scheme identifies fault phases by using a SMMG filter to extract the power frequency fault components (PFFC) of the modular currents. The computational burden is lighter than that of conventional methods. The approach has high speed, sensitivity and reliability. EMTP simulation result verifies its feasibility. View full abstract»

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  • Emergent electricity customer classification

    Page(s): 164 - 172
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (903 KB)  

    Various techniques for electricity customer classification are presented and discussed, with the focus on highlighting the behaviour of electricity customers. The surveyed techniques include classical approaches (applications of statistics and deterministic clustering algorithms), as well as methods based on artificial intelligence (neural networks and fuzzy systems). The classification techniques are illustrated by using various sets of features characterising the shape of the load patterns. Different approaches for feature selection, both in the time and in the frequency domain, are discussed. A number of specific metrics, some of which were originally developed by the authors, are applied in order to quantify the classification adequacy and to identify the most suitable classification techniques. Detailed results obtained from real life applications are provided. View full abstract»

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  • Finding core solutions for power system fixed cost allocation

    Page(s): 173 - 179
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (655 KB)  

    The cost allocation problem faced by an operator of an electricity network, where the fixed cost of the network has to be allocated among its users is discussed. Usage-based methods, such as the postage stamp rate method and the MW-mile method, are easy to understand and compute, but may yield cost allocations for which some transactions are subsidising others. Formally, this is equivalent to allocations outside of the core of the corresponding co-operative cost game. The main contribution of this paper is to present a method, similar to a well known method for computing the nucleolus of a cooperative game, by which several usage-based methods may be combined to produce allocations that are in, or as close as possible to, the core. Simulation results are conducted using two test systems. View full abstract»

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  • Down-conductor fault detection and location via a voltage based method for radial distribution networks

    Page(s): 180 - 184
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (501 KB)  

    A method to detect and locate a high-impedance fault caused by a downed conductor on a distribution primary feeder cone is presented. The protection system in radial networks generally consists in placing current detectors along each feeder line. A down-conductor fault typically has a very low current values which is often not detectable by conventional overcurrent protection devices. The proposed method is not based on current measurement but instead on voltage measurements performed at MV/LV stations. This method may be particularly interesting if LV potential transformers are already present in the network. The method is divided into two steps. The first step consists in determining whether each sensor is above or below the fault. The second step consists in determining the fault section, from a purely topological method. EMTP simulations are presented to highlight the effectiveness of the proposed technique. View full abstract»

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  • Multilevel-converter-based VSC transmission operating under fault AC conditions

    Page(s): 185 - 193
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (810 KB)  

    A study of a floating-capacitor (FC) multilevel-converter-based VSC transmission system operating under unbalanced AC conditions is presented. The control strategy is based on the use of two controllers, i.e. a main controller, which is implemented in the synchronous d-q frame without involving positive and negative sequence decomposition, and an auxiliary controller, which is implemented in the negative sequence d-q frame with the negative sequence current extracted. Automatic power balancing during AC fault is achieved without communication between the two converters by automatic power modulation on the detection of abnormal DC voltages. The impact of unbalanced floating capacitor voltages of the FC converter on power devices is described. A software-based method, which adds square waves whose amplitudes vary with the capacitor voltage errors to the nominal modulation signals for fast capacitor voltage balancing during faults, is proposed. Simulations on a 300 kV DC, 300 MW VSC transmission system based on a four-level FC converter show good performance of the proposed control strategy during unbalanced conditions caused by single-phase to ground fault. View full abstract»

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  • Harmonic domain approach to STATCOM modelling

    Page(s): 194 - 200
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1081 KB)  

    Previous work conducted in the unified harmonic domain has been primarily focused on HVDC systems. The paper outlines the extension of this technique to a hard switched FACTS device. A unified harmonic domain model is developed for a STATCOM and solved using a Newton solution based on DC side current mismatches alone. This generic formulation maintains modularity, allowing the interaction between multiple STATCOMs to be studied. The model has been verified against a time domain solution using PSCAD/EMTDC. The proposed technique provides practically identical results, without the time domain's inherent problems with respect to steady-state simulation. View full abstract»

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  • Improved hybrid approach to transient stability assessment

    Page(s): 201 - 207
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (549 KB)  

    The characteristics of the minimum transient kinetic energy of post-fault trajectories are studied in order to develop a tool for dynamic security assessment during the operation mode analysis of power systems. Using available commercial software a strategy for the transient stability study is introduced to enable harmless contingencies to be screened out and the classification of high-risk and harmful contingencies to be performed. Based on these characteristics, an approach to transient stability assessment is proposed and applied to the assessment at the hybrid transient energy margin for high-risk and harmful contingencies. The significant advantage of this approach is that the identification of a critical machine group is completely unnecessary. Case studies on a small test system, the ten-generator New England test power system and a realistic system, the middle-China power network are presented to verify the effectiveness and efficiency of this method. View full abstract»

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  • Transmission loss allocation through a modified Ybus

    Page(s): 208 - 214
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (520 KB)  

    A methodology to allocate the active power transmission loss among agents of a power pool is proposed. The approach is based on the inclusion of the admittances equivalent to bus power injections in the bus admittance matrix. For a given power-flow solution, the relationship between the branch currents and the load/generator current injections is determined using a modified bus admittance matrix, which allows the power loss of each transmission line to be expressed in terms of bus current injections. The proposed technique is simple to implement and flexible enough to allow the assignment of loss parcels to a preselected set of buses. An example, with a six-bus system illustrates the main steps of the proposed allocation strategy, and numerical results obtained with the IEEE 57-bus system are used to assess the quality of the loss allocation. View full abstract»

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  • Fuzzy financial analyses of demand-side management alternatives

    Page(s): 215 - 226
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (649 KB)  

    Fuzzy financial models are derived for the profitability analyses of demand-side management (DSM) alternatives. The present value of cost and equivalent uniform annual cost models are selected to determine the least-cost solution, while the net present value, payback year and benefit/cost ratio models are proposed for the execution of cost-benefit analyses. The means and variances of the fuzzy financial indexes associated with DSM alternatives are evaluated by Mellin transform in order to determine their relative ranking in a decision-making process. The performance of the proposed models is verified through the simulation of a numerical example and by considering their application to two practical DSM programmes: the choice of a suitable air-conditioning system for an office building and the evaluation of different cogeneration alternatives for a synthetic rubber corporation in Taiwan. These investigations confirm not only that the results of the proposed fuzzy financial models are consistent with those of the conventional crisp models, but they also demonstrate that the proposed methods represent readily implemented possibility analysis tools for use in the arena of uncertain financial decision-making. View full abstract»

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  • Incorporating station-related outages in composite system reliability analysis

    Page(s): 227 - 232
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (515 KB)  

    A technique to incorporate station-related outages in composite system reliability analysis is presented. The technique is used to evaluate composite system performance as a function of station configuration. The basic technique used to evaluate station-related outages is explained in detail using a ring bus configuration. A small composite test system is used to examine the impact of ring bus, double-bus double-breaker, one and one-half breaker and one and one-third breaker configurations. View full abstract»

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  • Uncertainty modelling in power system state estimation

    Page(s): 233 - 239
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (520 KB)  

    A method for uncertainty analysis in power system state estimation is proposed. The two-step method uses static weighted least-squares analysis to compute 'point' state estimates. Linear programming is then employed to obtain the upper and lower bounds of the uncertainty interval. It is shown that the method can provide useful additional information for both metered and nonmetered elements of the system. The effects of network parameter errors are also studied. For illustrative purposed, the proposed method is tested using the six-bus and IEEE 30-bus standard systems. Results show that the proposed method is an accurate and reliable tool for estimating the uncertainty bounds in power system state estimation. View full abstract»

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  • Measurement location for state estimation of distribution networks with generation

    Page(s): 240 - 246
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (687 KB)  

    State estimation is important for the automatic management and control of complex distribution networks with significant distributed generation. State estimation has been used extensively on transmission systems where, generally, measurements of busbar voltages and line power flows exist. However, distribution systems normally have only a limited number of measurements. In such systems additional measurements are expensive and careful selection of location becomes important. The paper presents a heuristic approach to identify potential points for location of voltage measurements for state estimation as part of a proposed distribution management system controller. The developed technique identifies measurement locations to reduce the voltage standard deviation of the busbars which do not have a measurement. It addresses the problems of classical transmission meter placement methods, which are not directly applicable to distribution systems due to limited measurements, and unobservability of the network. View full abstract»

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  • Development and application of a multi channel current integrator-cum-peak classifier for online monitoring of leakage current on RTV coated insulators

    Page(s): 247 - 252
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (521 KB)  

    Room temperature vulcanising (RTV) silicone rubber coated porcelain insulators and nonceramic insulators have a good anti-pollution performance in the field due to their excellent leakage current suppression capability. However, because of ageing, the material characteristics deteriorate and thus lose the property of hydrophobicity of the coating material. Diagnostically, leakage current monitoring is an indicator, amongst others, for assessing the life of the coating and thus continuous monitoring of the leakage current for longer periods is called for, warranting the necessity for an online personal computer (PC)-based data acquisition system. The PC-based data acquisition system is called a multi-channel current integrator-cum-peak classifier (MCIC). This paper discusses the complete development of the MCIC system, in terms of hardware and software, and its successful application for conducting artificial ageing tests on RTV coated porcelain insulator samples, in the pollution ageing chamber. View full abstract»

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  • Wind generation optimisation algorithm for a doubly fed induction generator

    Page(s): 253 - 263
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1163 KB)  

    In recent years, there has been a strong trend towards wind energy production and therefore, new problems related to the efficient production of renewable energy, to the management and operation of energy transfer and to the energy distribution are arising. Hence, the optimisation of wind energy production and consequently the economic benefits derived from its connection to the grid becomes one of the most important problems to be solved in the very near future. Two control strategies are developed in this paper for the active power regulation of wind farms comprising doubly fed induction generators, to obtain the maximum active power from the wind hitting the blades of a mill. View full abstract»

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  • Operating modes and control interaction analysis of unified power flow controllers

    Page(s): 264 - 270
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (533 KB)  

    In order to simplify the description of the operating status at a unified power flow controller (UPFC) the authors propose that the UPFC has three operating modes: (1) an uncontrolled mode; (II) an inductive mode; and (III) a capacitive mode. An application example demonstrates that the effect in the changes in the UPFC operations on the power system stability can be described more systematically and explained more clearly when they are represented by changes in these UPFC operating modes. It is shown that the linkage pattern of the UPFC series and shunt parts decides whether or not the control functions implemented by the UPFC series and shunt parts conflict with one another. This linkage pattern can be described by the flow of active power through the UPFC at steady-state operation of the power system. Hence, the direction and amount of active power flow through the internal link of the UPFC series and shunt parts at steady-state operation of the power system is suggested to be an indicator adds to predict the possibility of UPFC control interactions. This proposed interaction indicator is calculated from a power system load flow solution without having to run simulations on the power system with UPFC controllers installed. An application example to demonstrate the analytical results on UPFC control interactions is presented. View full abstract»

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  • Influence of semiconducting layers on the attenuation behaviour of single-core power cables

    Page(s): 271 - 276
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (847 KB)  

    Travelling electromagnetic waves in power cables are strongly influenced by frequency-dependent attenuation. For many applications in overvoltage protection, knowledge of the attenuation is very important. Especially in long cable systems the attenuation can be so high that lightning or switching voltages will be reduced to an innocuous level. Another area is the power line communication which uses the energy power grid for signal transmission in a frequency range up to 30 MHz. Here an indepth analysis of the attenuation of the transmission line is very important. In particular, the admittance of the cable, composed of insulating and semiconducting materials, is very important for the attenuation of high frequencies. Simulation results agree well with measurements for a 20 kV XLPE cable, if the semiconducting layers between the conductor and screen are thoroughly modelled. The material parameters of the commonly used carbon-polyethylene compound and conductive paper layers were measured for the calculations. Measurements at a test setup show the attenuation for several plys of conducting paper layers on the inner conductor of a coaxial pipe system. The effect of different numbers of plys on the impulse rise time was investigated. View full abstract»

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  • Constructive heuristic algorithm for the DC model in network transmission expansion planning

    Page(s): 277 - 282
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (567 KB)  

    A novel constructive heuristic algorithm to the network expansion planning problem is presented. The basic idea comes from Garver's work applied to the transportation model, nevertheless the proposed algorithm is for the DC model. Tests results with most known systems in the literature are carried out to show the efficiency of the method. View full abstract»

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  • Digital distance protection for composite circuit applications

    Page(s): 283 - 290
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (621 KB)  

    An approach to numeric distance relaying is proposed that is suitable for EHV composite overhead line and underground cable circuit applications. The proposed relay incorporates a circuit shunt capacitance in addition to a series resistance and inductance. By modelling the protected circuit as a series of RLC sections within the relaying algorithm, greater reach point accuracy can be achieved. Unlike conventional distance relays that sense the fault loop impedance and compare this against a reach point value, the proposed relay uses a directional element that is based on the calculated reach point voltage and current values. Results are presented based on a composite 500 kV application study comprising two overhead line sections and two cable sections. Comparisons with conventional numeric distance relay algorithms show that overreach is virtually eliminated in the proposed relay. The simulation results have been verified with an implementation of the relay based on modern digital signal processing hardware. View full abstract»

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  • Improved evolutionary programming with dynamic mutation and metropolis criteria for multi-objective reactive power optimisation

    Page(s): 291 - 294
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (507 KB)  

    Reactive power optimisation is an important technique, which is concerned with the security and economy of operation of the power system. The appropriate distribution of reactive power can elevate voltage rating, decrease network losses and maintain network running under proper conditions. An improved evolutionary programming method with dynamic mutation and metropolis selection to solve the multi-objective reactive power optimisation under the deregulation environment is presented. The multi-objective function includes the minimisation of network losses, voltage deviation and compensation cost. To solve the problems of convergence and robustness in the conventional evolutionary programming method, the mutation operators and the selection criteria that affect the convergence and robustness are considered and a dynamic mutation and metropolis selection evolutionary programming method is suggested. Introducing chaos dynamics into mutation operators of evolutionary programming, the new method adopts the certainty method of like-stochastic to obtain mutation operators which break through the conventional thought with mutation by stochastic numbers of fixed distribution. Also, it introduces the metropolis selection in evolutionary programming to construct new selection operators. Thus, the new method not only accelerates convergence but also increases precision, so is an efficient way to optimise the capacitor banks and the adjustable transformer ratio. Tested by the IEEE-30 bus system, the method is effective. View full abstract»

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  • Application of S-model learning automata for multi-objective optimal operation of power systems

    Page(s): 295 - 300
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (606 KB)  

    A learning automaton systematically updates a strategy to enhance the performance of a system output. The authors apply, a variable-structure learning automaton to achieve a best compromise solution between the economic operation and stable operation in a power system when the loads vary randomly. Both the generation cost for economic operation and the modal performance measure for stable operation of the power system are considered as performance indices for multi-objective optimal operation. In particular, it is shown that the S-model learning automata can be applied satisfactorily to the multi-objective optimisation problem to obtain the best trade-off between the conflicting objectives of economy and stability in the power system. View full abstract»

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