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Generation, Transmission and Distribution, IEE Proceedings-

Issue 3 • Date 11 May 2006

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Displaying Results 1 - 15 of 15
  • Expert-system method for automatic reconfiguration for restoration of shipboard power systems

    Page(s): 253 - 260
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (532 KB)  

    The electric-power systems in US Navy ships supply energy to sophisticated systems for weapons, communications, navigation and operation. Faults in a shipboard power system (SPS) may occur owing to material casualties of electrical components or widespread faults owing to battle damage. These faults may interrupt the supply of electrical energy to loads that are not faulty or damaged. To enhance survivability of naval ships and meet reduced manning requirements, automatic reconfiguration for service restoration may be performed to restore the de-energised loads. The paper presents an automatic rule-based expert-system method for reconfiguration of electric-power systems on naval ships which determines the control operations necessary to restore power supply to de-energised loads after battle damage or cascading faults. A case study is presented to illustrate the effectiveness of the proposed method. View full abstract»

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  • Voltage stability analysis in unbalanced power systems by optimal power flow

    Page(s): 261 - 268
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (237 KB)  

    The deregulated market requires a great deal of attention to satisfy reliability, security and optimisation objectives. As is well known, the voltage stability problem may become more and more frequent in this new scenario. Various techniques have been proposed in order to incorporate voltage stability aspects into the classical analysis methods of power systems. However, some technical problems, such as unbalances typical of distribution or transmission systems, require suitable formulations in order to derive critical conditions and their dependence on interest parameters. Hence, a three-phase formulation arises in order to characterise properly the inability of unbalanced power systems to meet heavy load demand. More specifically, a three-phase constrained optimal power flow is proposed in which the load demand at the assigned bus is maximised, simultaneously satisfying power balance equations and various technical constraints. An application is presented with reference to the IEEE 13-bus test system, which highlights the feasibility and the goodness of the proposed technique. Sensitivity analyses are performed in order to capture the dependence of voltage stability on the level of unbalance. View full abstract»

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  • Nonlinear time-response optimisation method for tuning power system stabilisers

    Page(s): 269 - 275
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (242 KB)  

    A power system is an inherently highly nonlinear and complex system. Many tuning methods involving parameter optimisation used in the past, were often based on small-signal stability theory and linearised system equations. Such optimisation usually involves the optimising of frequency-domain characteristics such as damping and damping factors of the system critical eigenvalues. The use of frequency-domain information does not allow for the direct improvement of the time-domain characteristics of the system response, e.g. settling time. A simple method is proposed that directly optimises the nonlinear system by using system time response to large disturbances. The properties of the method and its application specifics are discussed in detail. The effectiveness of the method in the co-ordinated tuning of multiple power system stabilisers is illustrated on a multimachine test power system. View full abstract»

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  • Terminal-voltage and output-power regulation of wind-turbine generator by series and parallel compensation using SMES

    Page(s): 276 - 282
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (428 KB)  

    Utilisation of renewable energy is becoming increasingly important from the viewpoints of environmental conservation and depletion of fossil fuel. However, the generating power always fluctuates owing to its environmental status. Therefore, an energy-storage system is indispensable to compensate for these fluctuations. Superconducting magnetic energy storage (SMES) is useful for compensation of fluctuating power, since it is capable of controlling both the active and reactive power simultaneously and quickly. Control systems for active and reactive power control of the series and parallel compensation using SMES are proposed. The effectiveness of the proposed system is demonstrated through the instantaneous-value-analysis-based computer simulations in which various cases (system interconnection, wind turbulence, three-phase-to-earth fault in the power system interconnecting large-capacity wind turbine generators) are studied. View full abstract»

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  • Novel complex filter with recursive algorithm for phasor computation in power-quality monitoring

    Page(s): 283 - 290
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (302 KB)  

    Accurate on-line tracking of the instantaneous phasor in power-disturbance waveforms is a key element for power-quality monitoring, power-system metering, relaying, control and fault diagnosis in electric power systems. The performance of the measurement techniques in common use or newly developed is briefly reviewed by using three criteria, namely measurement accuracy, dynamic response and real-time capability. Further, a novel complex filter and the associated recursive algorithm for phasor computation are presented, which can achieve both high measurement accuracy in various service conditions and low computational complexity. The proposed method can suppress well signal components other than that selected and is not sensitive to frequency deviation. Its effectiveness and superiority over the Fourier algorithm and the continuous wavelet transform are also ascertained using both simulated and practical power-disturbance waveforms. View full abstract»

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  • Earth conduction effects in systems of overhead and underground conductors in multilayered soils

    Page(s): 291 - 299
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (305 KB)  

    Electromagnetic interference calculations in the case of overhead lines and underground insulated conductors require the determination of the self and mutual impedances of all conductors in the arrangement. For the calculation of these impedances in nonhomogeneous soils, the use of the finite-element method is suggested. However, this is generally a complicated and time-consuming task. Analytic expressions for these impedances are derived by a solution of the electromagnetic field equations for the case of n-layer soil. The infinite integrals involved are evaluated using a numerically stable and efficient integration scheme. A typical transmission line/underground insulated pipeline arrangement is examined for various two-layer earth models and over a wide frequency range. The validity of the proposed methodology is justified by a proper finite-element method formulation. The inclusion of earth stratification leads to substantially different results for the calculated impedances. These differences affect significantly the levels of voltages and currents induced on the pipeline, even for power frequencies, justifying the need for a more detailed earth model representation. View full abstract»

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  • Continuation load flow using automatically determined branch megawatt losses as parameters

    Page(s): 300 - 308
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (239 KB)  

    The conventional Newton's method is considered to be inadequate for the computation of the maximum loading point (MLP) of power systems since: (i) it encounters difficulties in the vicinity of the MLP: and (ii) the load flow Jacobian matrix becomes singular at the MLP. It is well known that continuation methods are powerful and useful tools that are able to trace the solution PV curve without experiencing such difficulties. However, continuation methods require a parameterisation so that a modified, well conditioned set of load flow equations is obtained. In particular, the Jacobian matrix associated with this modified set of equations should not be singular at the MLP. The authors propose that the actual power losses in transmission branches (lines and transformers) are used to parameterise the approach. Specific procedures for the automatic determination of the most appropriate parameter (branch) are proposed. Such procedures include the utilisation of fast voltage-stability indices. Simulation results are presented to show that the proposed method is able to trace the whole solution PV curve very efficiently. View full abstract»

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  • Application of an immune algorithm to the short-term unit commitment problem in power system operation

    Page(s): 309 - 320
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (274 KB)  

    An immune algorithm, which includes a fuzzy system and an annealing immune operator is presented. The proposed immune algorithm (PIA) is applied to the short-term unit commitment (UC) problem in power system operation. The PIA differs from its counterparts in three main aspects: (i) the crossover and mutation ratios are changed from having fixed values and become a variable that is determined by the fuzzy system; (ii) it uses a memory cell; and (iii) it uses an annealing immune operator. These modifications result in three major advantages for the PIA: (i) it does not fall into locally optimum solutions; (ii) it can quickly and correctly find the full set of globally optimum solutions; and (iii) it can easily obtain the most economic solution to the UC problem. In particular it can determine the start-up and shutdown schedules for the generation units so that they are able to meet forecasted demands at the minimum cost while satisfying adverse range of constraints. The PIA is used to generate schedules for cases containing 10, 20, 50, 70 and 90 generators. The schedules generated by the PIA are compared to those generated using the dynamic programming, Lagrangian relaxation, genetic algorithm, simulated annealing and tabu search methods. It is shown that the proposed method is valid and that it is able to produce excellent solutions. View full abstract»

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  • Determination of load shedding for power-flow solvability using outage-continuation power flow (OCPF)

    Page(s): 321 - 325
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (169 KB)  

    The paper proposes a methodology that determines control strategies of load shedding for restoring power-flow solvability in unsolvable cases using a new tool of outage-continuation power flow (OCPF). A specified outage from a set of multiple contingencies is modelled with a homotopy function, including a parameter representing the outage. The new tool traces the path of solutions satisfying the power-flow equations with respect to variations of the parameter. At the nose point, it performs a sensitivity analysis with a normal vector to identify the most effective control variables. With the sensitivity information, location of load shedding is determined; then, an adequate amount of control is decided by applying a searching method. In numerical simulation, an illustrative example of the proposed framework is shown applied to the New England 39-bus system. View full abstract»

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  • Transmission planning in a deregulated environment

    Page(s): 326 - 334
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (464 KB)  

    The worldwide trend for the deregulation of the electricity generation and transmission industries has led to dramatic changes in system operation and planning procedures. The optimum approach to transmission-expansion planning in a deregulated environment is an open problem especially when the responsibilities of the organisations carrying out the planning work need to be addressed. To date there is a consensus that the system operator and network manager perform the expansion planning work in a centralised way. However, with an increasing input from the electricity market, the objectives, constraints and approaches toward transmission planning should be carefully designed to ensure system reliability as well as meeting the market requirements. A market-oriented approach for transmission planning in a deregulated environment is proposed. Case studies using the IEEE 14-bus system and the Australian national electricity market grid are performed. In addition, the proposed method is compared with a traditional planning method to further verify its effectiveness. View full abstract»

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  • Supplier risk analysis in the day-ahead electricity market

    Page(s): 335 - 342
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (213 KB)  

    In the deregulated marketplace, generation companies sell energy through auctions or bilateral contracts in a daily market. The daily-price volatility creates the need to perform risk assessment. A procedure able to detect the profitability and risk of bidding in a day-ahead energy market is proposed for power producers. In a pool/bilateral market structure, generation companies are assumed to submit supply bids for the auction in the market pool and report the power amount involved in bilateral contracts to the market operator. The market-clearing process is simulated by solving an OPF-based problem that maximises the social welfare. Then, the expected profits are evaluated by running a Monte Carlo simulation, and the value at risk and conditional value at risk are calculated for quantifying risk of the producer portfolio. The proposed procedure provides suppliers with an efficient tool able to handle daily market-price uncertainties and to capture, in powerful aggregate risk measures, all relevant portfolio effects of market-risk exposure. Simulations are carried out in a 24-hour time frame to analyse the profit and the risk faced by one of the generating companies of the Italian electric-power system. View full abstract»

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  • Potential and electric-field calculation along an ice-covered composite insulator with finite-element method

    Page(s): 343 - 349
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1091 KB)  

    A two-dimensional finite-element model for potential and electrical-field calculation along an ice-covered composite insulator is presented. To find the influence of the ice on the potential and electrical-field distribution, various thicknesses of the ice and various lengths of the icicles are simulated in the condition of dry ice and wet ice, respectively. In addition, the present study investigates the influence of the discrete water film and the dry band on the potential and electrical-field distribution of the iced composite insulator. Finally, a comparison between the electric-field distribution along the ice-covered composite insulator and that of ice-covered ceramic insulator string is presented. View full abstract»

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  • Harmonic mitigation throughout a distribution system: a distributed-generator-based solution

    Page(s): 350 - 358
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (404 KB)  

    The paper investigates the use of ancillary services from inverter-interfaced distributed generators (DGs) to achieve harmonic mitigation across a network. The approach is to include the functionality of a resistive active-power filter (R-APF) within several DGs. The R-APF provides adjustable damping at harmonic frequencies. In a realistic network, which has feeder sections of different characteristic impedances, it is impractical to damp with a single value of resistance. Instead, feeders are split into harmonic sections based on the standing waves of the highest-order harmonic, and DG ancillary services are called up for each section. Co-ordination of services from each DG is arranged through adaptation of the harmonic resistance according to target THD levels. The primary purpose of each DG is the supply of real power and this is respected through a further aspect of the resistance adaptation which reduces the harmonic duty of an individual DG if it approaches the apparent-power rating of the inverter. The harmonic VA required of the inverter is dependent on both the chosen harmonic resistance and the harmonic-voltage component present at the connection bus. The system is demonstrated through a simulation of an irregular feeder using Simulink and PLECS. View full abstract»

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  • Development of a fuzzy inference system based on genetic algorithm for high-impedance fault detection

    Page(s): 359 - 367
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (485 KB)  

    A novel method for high-impedance fault (HIF) detection in distribution systems is presented. Using this method HIFs can be discriminated from isolator leakage current (ILC) and transients such as capacitor switching, load switching (high/low voltage), ground fault, inrush current and no-load line switching. Wavelet transform and principal component analysis are used for feature extraction/selection. A fuzzy inference system is implemented for fault classification and a genetic algorithm is applied for input membership functions adjustment. HIF and ILC data was acquired from experimental tests and the data for other transients was obtained by simulation of a real 20 kV distribution feeder using EMTP. Results show that the proposed procedure is efficient in identifying HIFs from other events. View full abstract»

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  • Sensitivity-based hybrid approach for assessment of stability-constrained generation limit

    Page(s): 368 - 374
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (213 KB)  

    Based on an improved hybrid method for transient stability assessment, a new sensitivity-based approach for stability-constrained generation limit assessment is proposed. The variation characteristic of minimum kinetic energy (KE) in post-fault duration against generation of severely disturbed generators is studied. The study shows that the active minimum KE is much more sensitive to a generation change of severely disturbed generators than inactive KE is, and the sensitivity factor of minimum KE could be used to predict generation limit. With this knowledge, a method for evaluating sensitivity factors of minimum KE in conjunction with trajectory and trajectory-sensitivity simulation is presented. It has the advantage that the approach is usable for systems represented by complex models. The effectiveness of the sensitivity-based hybrid approach is shown through case studies on the ten-generator New England test system. View full abstract»

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