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Generation, Transmission & Distribution, IET

Issue 9 • Date September 2010

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Displaying Results 1 - 9 of 9
  • Dynamic adaptive bacterial foraging algorithm for optimum economic dispatch with valve-point effects and wind power

    Page(s): 989 - 999
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (205 KB)  

    This study presents a dynamically adapted bacterial foraging algorithm (BFA) to solve the economic dispatch (ED) problem considering valve-point effects and power losses. In addition, wind power is included in the problem formulation. Renewable sources and wind energy in particular have recently been getting more interest because of various environmental and economical considerations. The original BFA is a recently developed evolutionary optimisation technique inspired by the foraging behaviour of the Escherichia coli bacteria. The basic BFA has been successfully implemented to solve small optimisation problems; however, it shows poor convergence characteristics for larger constrained problems. To deal with the complexity and high-dimensioned search space of the ED problem, essential modifications are introduced to enhance the performance of the algorithm. The basic chemotactic step is adjusted to have a dynamic non-linear behaviour in order to improve balancing the global and local search. The stopping criterion of the original BFA is also modified to be adaptive depending on the solution improvement instead of the preset maximum number of iterations. The proposed algorithm is validated using several test systems. The results are compared with those obtained by other algorithms previously applied to solve the problem considering valve-point effects and power losses in addition to wind power. View full abstract»

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  • Non-dominated sorting genetic algorithm-II for robust multi-objective optimal reactive power dispatch

    Page(s): 1000 - 1008
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (615 KB)  

    The concept of robust optimal solution is incorporated into multi-objective optimal reactive power dispatch (MORPD) for the consideration of uncertain load perturbations during system operations. Robust MORPD searches for solutions that are immune to parameter drifts and load changes. It uses information of load-increase directions to promote the stability of optimal solutions in the presence of load perturbations. Non-dominated sorting genetic algorithm-II (NSGA-II) is adopted to search for the robust Pareto solutions on a standard IEEE 118-bus system. The simulation validated the effectiveness of NSGA-II for robust MORPD. NSGA-II obtained Pareto solutions over the trade-off surface. The experimental results also indicated that the robust Pareto solutions are comparatively less sensitive to load perturbations in their neighbourhoods and can maintain their objective values against uncertain load perturbations. Robust MORPD can provide optimal solutions with a higher degree of stability in the face of perturbations and can be more practical in reactive power optimisation of the real-time operation systems. View full abstract»

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  • Numerical calculation of the negative onset corona voltage of high-voltage direct current bare overhead transmission conductors

    Page(s): 1009 - 1015
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (512 KB)  

    The negative onset corona voltage of high-voltage direct current bare overhead transmission conductors has been studied by numerical calculations and gas discharge experiments. First, the charge simulation method, an accurate numerical method, is employed to calculate the distribution of the electrical fields in the vicinity of a bare conductor. Then, the electrical field values calculated and a criterion from the gas discharge theory are utilised to evaluate the onset voltage of the negative corona on the bare conductor. Furthermore, a formula for a high altitude correction factor is used to calculate the negative onset corona voltage of a bare conductor located at a high altitude. Finally, it is found that the calculated onset-voltage values agree satisfactorily with the data measured on laboratory models and full-scale test lines. View full abstract»

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  • Intelligent identification of flicker source in distribution systems

    Page(s): 1016 - 1027
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (867 KB)  

    The authors propose a new intelligent method to identify the source of flicker in distribution systems. By measuring and sampling the bus voltages, a flicker index is extracted using multi-resolution S-transform. Time-frequency resolution characteristic of S-transform is shown to be a suitable candidate for assessment and identification of flicker source. The new flicker index is selected from complex S-transform matrix, which takes into account both amplitude and frequency of flicker. An multi level percepteron (MLP) neural network as a powerful classifier is trained with the bus flicker indices to detect existence of flicker source in contaminating bus. The source of flicker is modelled with an amplitude modulation scheme, and both flickers without harmonics and with harmonics are considered. A 14-bus distribution system was simulated in ATP/EMTP to test the method. Results show that by measuring voltages in proper buses, contaminating bus or zone can be detected using a few measuring points. View full abstract»

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  • Optimal design for control coordination of power system stabilisers and flexible alternating current transmission system devices with controller saturation limits

    Page(s): 1028 - 1043
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1001 KB)  

    This study develops a new method by which the controller output limits are taken into account in the eigenvalue-based control coordination design for achieving optimal dampings of the electromechanical oscillations for specified disturbances. The method combines the non-linear time-domain simulations with the constrained optimisation of the eigenvalue-based objective function. The time-domain simulations are used to derive the linearised relations between the maximum controllers outputs and controllers parameters, for any specified disturbances. The relations combined with specified controller output limits lead to additional set of constraints in the design. The time-domain simulations are performed independent of one another and outside the optimisation procedure. These features lead to lower computing time requirement and the possibility of using parallel processors for implementing the design algorithm. From many design studies in which linearised relations are derived and used, the number of constrained optimisations required is relatively low (about 5). The results of representative design cases with a multimachine power system having power system stabilisers and supplementary damping controllers of thyristor-controlled series capacitors are presented. The performance of the designed controllers is verified by non-linear time-domain simulations. View full abstract»

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  • Optimal generation rescheduling with sensitivity-based transient stability constraints

    Page(s): 1044 - 1051
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (528 KB)  

    A new generation rescheduling model is proposed for transient stability enhancement of power systems, which can optimally reallocate power generations for eliminating potential transient stability threat. The idea of angle norm has been introduced to develop a sensitivity-based transient stability constraints of the rescheduling model. Trajectory sensitivity mapping technique is studied to evaluate the sensitivity factor of the angle norm at maximum swing angle to the power input of generators. The augmented Lagrangian method is employed to solve the rescheduling problem in an iteration manner. Case studies on the IEEE 50-generator test power system are reported to verify the effectiveness of the proposed generation rescheduling method. View full abstract»

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  • Online estimation and application of power grid impedance matrices based on synchronised phasor measurements

    Page(s): 1052 - 1059
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (464 KB)  

    Grid impedance matrices estimation is important in monitoring and protection of wide-area power systems. In this study, a recursive least-squares estimation algorithm with a forgetting factor is presented to identify impedance parameters of power grids. This approach is based on synchronised phasor measurements and makes it possible to track changing parameters. The algorithm is tested on two power systems using MATPOWER-generated data, and case studies are conducted for estimation of grid impedances followed by voltage stability margin analysis and fault detection. The results show that the proposed method is effective for online estimation of grid impedances, fault detection and voltage stability monitoring. View full abstract»

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  • Protection, faulted phase and winding identification for the three-winding transformer using the increments of flux linkages

    Page(s): 1060 - 1068
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (744 KB)  

    The ratio of the increments of flux linkages (RIFLs) of the primary-secondary, primary-tertiary and secondary-tertiary windings is the same as the corresponding turns ratio during normal operating conditions, magnetic inrush and over-excitation. The RIFL differs from the turns ratio during an internal fault. In this study, the authors propose an algorithm for protection, a faulted phase and winding identification for the three-winding transformer using the increments of flux linkages (IFLs). The IFLs of each pair of windings are estimated for a single-phase and a three-phase transformer with wye-connected windings. For a three-phase transformer with delta-connected windings, the differences of the IFLs are estimated to use the line currents because the delta winding currents are practically unavailable. In this study, six detectors are suggested for fault detection; three additional detectors and a rule for the faulted phase and winding identification are presented as well. The proposed algorithm can not only detect an internal fault, but also identify the faulted phase and winding of a three-winding transformer. The various test results with electromagnetic transients program (EMTP) generated data show that the proposed algorithm successfully discriminates the internal faults from normal operating conditions including magnetic inrush and over-excitation. This study concludes by implementing the proposed algorithm into a prototype relay based on a digital signal processor. View full abstract»

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  • Efficient procedure to evaluate electromagnetic transients on three-phase transmission lines

    Page(s): 1069 - 1081
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (675 KB)  

    This paper presents a hybrid way mixing time and frequency domain for transmission lines modelling. The proposed methodology handles steady fundamental signal mixed with fast and slow transients, including impulsive and oscillatory behaviour. A transmission line model is developed based on lumped elements representation and state-space techniques. The proposed methodology represents an easy and practical procedure to model a three-phase transmission line directly in time domain, without the explicit use of inverse transforms. The proposed methodology takes into account the frequency-dependent parameters of the line, considering the soil and skin effects. In order to include this effect in the state matrices, a fitting method is applied. Furthermore the accuracy of proposed the developed model is verified, in frequency domain, by a simple methodology based on line distributed parameters and transfer function related to the input/output signals of the lumped parameters representation. In addition, this article proposes the use of a fast and robust analytic integration procedure to solve the state equations, enabling transient and steady-state simulations. The results are compared with those obtained by the commercial software Microtran (EMTP), taking into account a three-phase transmission line, typical in the Brazilian transmission system. View full abstract»

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IET Generation, Transmission & Distribution is intended as a forum for the publication and discussion of current practice and future developments in electric power generation, transmission and distribution.

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