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Generation, Transmission and Distribution, IEE Proceedings-

Issue 2 • Date March 2003

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Displaying Results 1 - 19 of 19
  • Short-circuit impedance measurement

    Page(s): 169 - 174
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (429 KB)  

    Methods for estimating the short-circuit impedance in the power grid are investigated for various voltage levels and situations. The short-circuit impedance is measured, preferably from naturally occurring load changes in the grid, and it is shown that such a measurement system faces different kinds of problems at different locations in the grid. This means that the best measurement methodology changes depending on the location in the grid. Three typical examples with different measurement problems at 400 kV, 132 kV and 400 V voltage level are discussed. View full abstract»

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  • Fast power transformer fault classification methods based on protection signals

    Page(s): 205 - 210
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (435 KB)  

    A fast estimation of the operating status of the power transformer is essential for power system monitoring. Three methods are presented, which enable the classification of faults affecting power transformer protection, based on its signals. The first method is based on a modelled relationship between faults and protection action, which is formulated as a matrix function. A pseudoinversion is used to obtain the transformer diagnosis indices. The second method uses the norm in the Banach space as a measure for the most probable event. The third method exploits the Bayes probability calculation based on statistical data on faults and protection operation. Results of all these methods show that they yield a fast and successful identification of power transformer faults. View full abstract»

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  • Modelling and analysis of a cascade 11-level inverters-based SVG with control strategies for electric arc furnace (EAF) application

    Page(s): 217 - 223
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (406 KB)  

    The application of cascaded multilevel inverters-based SVG for EAF compensation is investigated. A mathematical model for 11-level cascaded inverters-based SVG is carried out, and a control method based on adjusting both the modulation index (MI) and the phase angle is proposed. Furthermore, to shorten the SVG response time and improve its accuracy, a feed forward neural network to be employed for on-line applications is developed, calculating the MI/switching patterns that are currently found using a conventional look-up table. MATLAB simulation results are provided to validate the proposed schemes. View full abstract»

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  • Exploiting voltage support of voltage-source HVDC

    Page(s): 252 - 256
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (427 KB)  

    The inherent voltage support in voltage-source converters (VSCs) which form a back-to-back VSC-HVDC asynchronous link can increase the power transmissibility by a factor of 1.68 if the installation is sited at the midpoint of the radial AC transmission line. The figure of 1.68 is the limit set by the 'transient stability' which is reached by simulations using HYPERSIM, a real-time digital simulator. The transmission line is modelled by the telegraph equations. The hydraulic turbine, speed governor, generator, field-excitation system, power-system stabiliser (PSS) and transformers are modelled in detail. View full abstract»

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  • Damping of power system oscillations with unified power flow controller (UPFC)

    Page(s): 129 - 140
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (624 KB)  

    A comprehensive approach to the design of UPFC controllers (power-flow controller, DC-voltage regulator and damping controller) is presented. Studies reveal that damping is adversely affected by the incorporation of a DC-voltage regulator. Investigations were carried out to understand the relative effectiveness of modulation of the UPFC control signals mB, δB, mE and δE on damping of the system oscillations, using a controllability index. A dual damping controller based on simultaneous modulation of UPFC control signals mB and δE is proposed. Investigations reveal that alternative damping controllers (damping controller mB, damping controller δE and dual damping controller) provide robust dynamic performance under wide variations in loading condition and system parameters. View full abstract»

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  • Calculation of risk and statistical indices associated with available transfer capability

    Page(s): 239 - 244
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (407 KB)  

    A complete evaluation of available transfer capability (ATC) involves the determination of total transfer capability (TTC), transmission reliability margin (TRM) and capacity benefit margin (CBM). Due to the stochastic nature of power system behaviour, which is considered by TRM, it is important to assess ATC from a statistical and risk analysis point of view. Based on a combination of repeated AC power flow and Monte Carlo methods, risk assessment of the ATC value is described and a set of statistical indices and plots is presented, which provides important information for transmission customers, system operators and power marketers. In addition, two methods of incorporating CBM into ATC are presented and compared. Case studies with the IEEE Reliability Test System (RTS) demonstrate the effectiveness of the proposed methods, indices and plots. The impact of uncertainty, CBM and methods of incorporating CBM on ATC are also investigated. View full abstract»

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  • Oscillation transient energy function applied to the design of a TCSC fuzzy logic damping controller to suppress power system interarea mode oscillations

    Page(s): 233 - 238
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (409 KB)  

    An oscillation transient energy function (OTEF) is proposed for the analysis and damping of power system area-mode oscillations. The OTEF interprets an area-mode oscillation as the conversion between oscillation kinetic energy and potential energy. Based on this interpretation, an OTEF descent method has been developed to design a supplementary fuzzy-logic thyristor controlled series compensator (TCSC) controller to damp the area-mode oscillation. Since the proposed method guarantees the continuous descent of oscillation energy, the fuzzy-logic TCSC damping controller designed is robust to the variations of power system operating conditions. A 4-generator 2-area interconnected power system is presented to demonstrate the effectiveness and robustness of the TCSC fuzzy logic damping controller installed in the power system. View full abstract»

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  • z-domain frequency-dependent AC-system equivalent for electromagnetic transient simulation

    Page(s): 141 - 146
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (419 KB)  

    Modern power systems are very complex and to model them completely is impractical for electromagnetic transient studies. Therefore, areas outside the immediate area of interest must be represented by some form of frequency-dependent network equivalent (FDNE). One of the motivations for investigating z-domain fitting is that it can be directly implemented in a digital-simulation program without any loss of accuracy as it is already a discrete formulation. Fitting in the s-domain always requires 'discretising' a continuous system and the inherent approximations. The formulation for developing 1- and 2-port frequency-dependent equivalents of the AC system using z-domain rational-function fitting of the frequency response is presented and its use illustrated. This 1- and 2-port FDNE have been applied to the New Zealand lower South Island AC power system. The electromagnetic transient package PSCAD/EMTDC is used to assess the transient response of the 1- and 2-port FDNE developed under different conditions (linear load, fault and nonlinear loading). The study results have indicated the robustness and accuracy of land 2-port FDNE for electromagnetic transient simulation. View full abstract»

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  • Two electrical models of the lead-acid battery used in a dynamic voltage restorer

    Page(s): 175 - 182
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (546 KB)  

    Two electrical models of a lead-acid battery, a short-term discharge model and a long-term integrated model, were used to investigate the system performance of a battery-supported dynamic voltage restorer (DVR). The short-term model provides a simple but effective description when the DVR compensates voltage sags over a short period. The integrated model can predict accurately the terminal voltage, state of charge, battery capacity and gassing current. It gives a good description of the battery response during both discharge and charge. Parameters of both models can be determined easily from measured battery output voltages obtained from load-step tests. Both models were successfully implemented in EMTDC/PSCAD and interfaced with the digital model of a 10 kVA DVR physical prototype. They gave a very close agreement between extensive experimental data and simulation results. Application issues such as current harmonics and microcycles during charge/discharge are discussed with respect to their impact on loss of capacity and reduced lifetime of the lead-acid battery. View full abstract»

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  • Detailed analysis and experimental results of the control system of a UPFC

    Page(s): 147 - 154
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (446 KB)  

    The decoupled control of the power flow through a transmission line using a PWM-based unified power flow controller (UPFC) is explained. A dynamic model of a UPFC has been developed using the space-vector representation of instantaneous three-phase variables. The Park's transformation and the reference frame selected reduce the control of the real- and reactive-power flows to the control of the d- and q-axis currents, respectively. The proposed control scheme produces fast and decoupled response of the real- and the reactive-power flow through a transmission line. It also achieves tight control of the DC-link capacitor voltage through careful coordination between the control of the series and shunt compensators of the UPFC. A prototype has been built to illustrate the main contributions. The prototype includes a UPFC with 750 Hz switching frequency applied to a reduced model of a transmission line. Experimental results agree closely with the theoretical analysis. View full abstract»

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  • Wireless power transmission and its annexure to the grid system

    Page(s): 195 - 199
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (417 KB)  

    Transmission or distribution of 50 or 60 Hz electrical energy from the generation point to the consumers' end without any physical wire has yet to mature as a familiar and viable technology. Apart from a few demonstrations or feasibility studies the research effort thus far on wireless power transmission (WPT) is inadequate. Moreover, the reported works have not disclosed any design methodology, and this has restricted further advancement in the research on WPT. A unified, consistent and coherent mathematical model for WPT has been synthesised. The output obtained from the model when applied to a case has been compared against the technical specifications partially reported in the literature by a feasibility study of the same case. In addition, it is shown that a potential application of WPT would be in annexing a grid system for radial feed to a demand site in certain scenarios. Also, the specific aspects upon which further research should focus have been identified so that WPT annexure can be viable in the discussed scenarios. The findings are expected to renew interest in WPT among the public in general and among the researchers and the environmentalists in particular. View full abstract»

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  • Sequential design of decentralised control for FACTS devices in large power systems

    Page(s): 162 - 168
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (460 KB)  

    A procedure for sequential design of decentralised FACTS controllers for multimachine power systems is presented. It is shown how to include a simple estimate of the effects of closing subsequent loops into the design problem for the loop to be closed. The focus of the paper is on the design performance where frequency-domain methods prove to be very useful. A comprehensive and systematic way of designing decentralised controllers is presented and the results are illustrated using a 16-machine 5-area system. The methodology to select the input signal used for supplementary control of FACTS devices in large power systems is also addressed. View full abstract»

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  • Development and assessment of a load decomposition method applied at the distribution level

    Page(s): 245 - 251
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (431 KB)  

    The properties of a load decomposition method based on measured current and voltage waveforms and used for obtaining the load composition at distribution level are studied. To improve the precision of the results a generalised nonlinear load model is used which takes into account the harmonic interaction between voltage and current. Several tests have been carried out in laboratory and field environments. Results show that it is possible to obtain information about loads when these are grouped according to their electrical behaviour. View full abstract»

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  • Stochastic harmonic analysis of mass rapid transit power systems with uncontrolled rectifiers

    Page(s): 224 - 232
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (561 KB)  

    The stochastic harmonic distortion of a mass rapid transit (MRT) system is investigated by considering the dynamic load behaviour of train sets. A mathematical model of 12-pulse uncontrolled rectifiers without interphase transformers is derived and applied to the harmonic load flow analysis to workout the power demand and the harmonic injection currents at traction substations for each time snapshot. According to the mean values and standard deviation of harmonic currents, the stochastic harmonic load flow analysis is performed to find the average and the confidence interval of harmonic voltage distortion for all system buses. A comparison with the conventional harmonic load flow analysis, which considers only the average load demand and the mean harmonic injection current, reveals that the method proposed can evaluate the voltage harmonic distortion of the system more accurately to provide better guidance for the strategy of harmonic mitigation. View full abstract»

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  • Optimal capacitor switching with fuzzy load model for radial distribution systems

    Page(s): 190 - 194
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (412 KB)  

    An approach which uses fuzzy variables to solve the capacitor-switching (CS) problem in radial distribution systems is proposed. CS is an important measure for loss minimisation of distribution systems via an optimal capacitor dispatch schedule. Uncertainty of forecasted load values are represented as trapezoidal fuzzy numbers via fuzzy sets. The principles of fuzzy set theory are applied to form a methodology suitable for calculations of fuzzy complex numbers while maintaining a fast computational speed. An approach based on successive linear integer programming with fuzzy variables is exploited to optimise the on-off status of each switchable capacitor bank. A computer program has been developed according to this approach, and numerical studies on a radial distribution system are verified in detail. View full abstract»

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  • Versatile model of a unified power flow controller in a simple power system

    Page(s): 155 - 161
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (472 KB)  

    A versatile mathematical model of a unified power flow controller (UPFC) in a single machine infinite bus system is proposed. The model consists of a simple voltage source whose magnitude and angle depend on the UPFC control parameters. The voltage-source model of UPFC can easily be incorporated into the generator output power equation and that simplifies the dynamic analysis of the system. With some appropriate assumptions, the proposed UPFC model can also be used to represent other FACTS devices, such as, static synchronous compensators, static synchronous series compensators, etc. The proposed model is then used to determine and compare the dynamic behaviour of a simple system equipped with various FACTS devices. View full abstract»

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  • Computation of electromagnetic transients on transmission lines with nonlinear components

    Page(s): 200 - 204
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (374 KB)  

    A state-space technique (SST) for the computation of electromagnetic transients on transmission lines with nonlinear components is presented. State equations for the nonlinear system are derived and these equations are converted to a set of algebraic equations using the trapezoidal rule of integration. A state-space formulation and numerical solution steps are described. To show the validity of the method proposed, two illustrative examples are given. In the first example, lightning surges on a single-phase with a corona are analysed. The effect of the presence of a surge arrester is investigated in the second example. The results obtained using the state-space technique are compared with those obtained using the electromagnetic transients program (EMTP) and with experimental results available in the literature. The proposed method is accurate, numerically stable and suitable for the computation of electromagnetic transients on transmission lines with several nonlinearities. View full abstract»

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  • Design of power system stabiliser for single-machine system using robust periodic output feedback controller

    Page(s): 211 - 216
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (414 KB)  

    Power system stabilisers (PSS) are added to excitation systems to enhance the damping of low-frequency oscillations. The design of PSS for a single machine connected to an infinite bus using periodic output feedback is proposed. The nonlinear model of a machine is linearised at different operating points and 16 linear plant models are obtained. For each of these plants an output injection gain is obtained using the LQR technique. A robust periodic output feedback gain which realises these output gains is obtained using an LMI approach. This robust periodic output control is applied to a nonlinear plant model of the machine at different operating (equilibrium) points. This method does not require the complete set of states of the system for feedback and is easily implementable. View full abstract»

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  • Application of immune algorithm to optimal switching operation for distribution-loss minimisation and loading balance

    Page(s): 183 - 189
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (523 KB)  

    The application of an immune algorithm for the optimal switching search problem to achieve loss minimisation and loading balance among feeders and main transformers is presented. This algorithm prevents the possibility of stagnation in the iteration process and achieves fast convergence for global optimisation. The efficiency of the immune algorithm to solve the problem is verified by comparing the computing time of the conventional binary integer programming for decision making of the switching operation. An interactive best-compromise method is also applied to solve the multiobjective distribution-feeder reconfiguration. Quantitative measures can be supplied to aid the decision-making process. A Taipower distribution system with 18 feeders is selected for computer simulation to demonstrate the effectiveness of the proposed methodology for solving the optimal-switching operation of distribution systems to minimise the power loss and simultaneously enhance the loading balance. View full abstract»

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