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Generation, Transmission and Distribution, IEE Proceedings-

Issue 1 • Date Jan 2001

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Displaying Results 1 - 14 of 14
  • Efficient two-level interior point method for optimal pumped hydrostorage scheduling exploiting the nonsparse matrix structure

    Page(s): 41 - 47
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (552 KB)  

    The primal-dual interior point method (PDIPM) has proven to be an efficient tool for power system optimisation problems. Its computational efficiency heavily relies on sparsity techniques. Hence, when optimisation problems cannot be formulated into sparse form, PDIPM then may not be the right choice for these problems, because the computational efficiency drops significantly in factorisation of a dense matrix. A nonsparse power-system optimisation problem containing either-or constraints, pumped hydrostorage (PHS) scheduling, is presented and a two-level predictor-corrector version of PDIPM (PCPDIPM) is proposed to cope with this nonsparse and NP hard problem. To overcome the difficulty associated with the dense matrix structure, a special data transformation is proposed. By further exploiting the dense matrix structure, the performance of PCPDIPM is not deteriorated by the nonsparse structure. On the contrary, the computational efficiency is dramatically improved due to exploiting this structure. Moreover, to solve the difficulty associated with either-or constraints. An effective two-level LP procedure is proposed. To illustrate the performance of the proposed methodology, numerical results are carried out on two test cases. These results show that the presented two-level PCPDIPM solves the PHS scheduling effectively View full abstract»

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  • Dynamic equivalents of distribution systems for voltage stability studies

    Page(s): 49 - 53
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (332 KB)  

    Dynamic equivalents of distribution systems, including the dynamics of electric loads and on-load tap changers, are needed in voltage stability studies. A method for a dynamic equivalent of a radial distribution system for voltage stability studies and an equivalent model are proposed. The procedure and detailed formulae for separate aggregation of dynamic loads and network with OLTCs are derived. Case studies show the accuracy of the equivalent model and the availability of the method View full abstract»

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  • Allowable tension levels for overhead-line conductors

    Page(s): 54 - 59
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (652 KB)  

    Optimised design of overhead transmission lines requires the selection of appropriate stringing tensions for conductors. The percentage of rated-tensile-strength and tension-over-mass criteria for determining these stringing tensions are discussed and analysed in terms of the static tensile stresses in the aluminium component of the conductor. It is demonstrated that the CIGRE tension-over-mass method of specifying vibration constraints does not maintain constant initial aluminium stress for conductors with various steel-to-aluminium ratios in all climates. In place of methods based on a percentage of rated strength or the tension-over-mass method, it is proposed that vibration constraints be based on specified values of static tensile aluminium stress. The `aluminium-stress method' may be applied by specifying a stress constraint in a sag-tension program that is equipped to apply one. If such a program is not available to a line engineer, a simple method is provided for computing the initial tension constraint based on the steel and aluminium areas, the average temperature of the coldest month and specified constraints on initial aluminium stress and built-in stress. The effect of built-in stresses on initial stringing tensions is discussed View full abstract»

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  • Parallel operation of passive power filter and hybrid power filter for harmonic suppression

    Page(s): 8 - 14
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (540 KB)  

    Harmonic pollution has been serious in recent years. Passive filters have been used to suppress harmonic current conventionally. However, passive power filters have the problem of resonance. To solve the resonance problem, active power filters and hybrid power filters were developed. After considering the power capacity and cost, the hybrid power filter is the better choice for the future. Many passive power filters have already been installed in the industry power systems. However, the elements of these passive power filters are often destroyed due to the resonance or the harmonic current injection of a neighbouring harmonic source. To improve the performance of passive power filters, a small capacity of hybrid power filter is proposed to connect in parallel with the existing passive power filters. The combined power filter system, which contains the parallel operation of existing passive power filters and hybrid power filters, is analysed and simulated. The simulation results show that the filter performance and resonance problem of existing passive power filters can be improved by applying the hybrid power filter View full abstract»

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  • Review of research on lightning-induced voltages on an overhead line

    Page(s): 91 - 95
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (392 KB)  

    Two methods of analysis of the voltage induced on an overhead line by a lightning stroke to a nearby ground have been widely used. These analyses are based on modelling lightning return stroke as well as on coupling the electromagnetic fields of the stroke channel to the line. The return-stroke models and models of the coupling mechanisms of these two methods are reviewed View full abstract»

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  • Design considerations on the line-side filter used in the dynamic voltage restorer

    Page(s): 1 - 7
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (596 KB)  

    The effects of harmonic voltages generated by the voltage source inverter within a dynamic voltage restorer can be mitigated through the use of a line-side filter. However, injudicious design of the harmonic-filtering system can degrade the power-quality-enhancement capability of the restorer. Inappropriate filter design may also result in the need for the inverter current rating to be increased significantly, The purpose of the investigation is therefore to carry out a systematic analysis of the filter design by considering first the selection of the filter-capacitor on the basis of meeting a prespecified harmonic-performance criterion. The effect of the capacitor on the inverter rating is then evaluated and the method of determining the filter capacity is presented. An example, which involves electromagnetic transient studies, is included to demonstrate the efficacy of the proposed design method View full abstract»

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  • Proposed wavelet-neurofuzzy combined system for power quality violations detection and diagnosis

    Page(s): 15 - 20
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (500 KB)  

    A system for the identification of power quality violations is proposed. It is a two-stage system that employs the potentials of the wavelet transform and the adaptive neurofuzzy networks. For the first stage, the wavelet multiresolution signal analysis is exploited to denoise and then decompose the monitored signals of the power quality events to extract its detailed information. A new optimal feature-vector is suggested and adopted in learning the neurofuzzy classifier. Thus, the amount of needed training data is extensively reduced. A modified organisation map of the neurofuzzy classifier has significantly improved the diagnosis efficiency. Simulation results confirm the aptness and the capability of the proposed system in power quality violations detection and automatic diagnosis View full abstract»

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  • Co-ordination of spark-gap protection with zinc-oxide surge arresters

    Page(s): 21 - 28
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (644 KB)  

    Zinc-oxide (ZnO) surge arresters are now well established as a very efficient and reliable form of overvoltage protection against both fast surges, such as those generated by lightning and gas-insulated switchgear, and high-energy surges generated by switching operations and temporary faults on the network. The addition of ZnO surge arresters to existing protection schemes reinforces the system's reliability and the security of supply. The protection characteristics of the parallel configuration formed by arresters and existing spark gaps at distribution voltages are studied. Tests on various spark-gap geometries, with and without surge arresters in parallel, have been carried out to determine breakdown characteristics, probability curves and voltage-time characteristics for different impulse shapes. It is found that the introduction of the arrester in the circuit modifies the prospective impulse which results in the shift of the breakdown characteristics towards higher voltages. A proposed circuit model, based on laboratory test data, is used to simulate such parallel configurations. Good agreement between test and simulated results is obtained. As a result of these tests, it is recommended that gap-sparkover characteristics based on short-tail (about 5 μs) impulses are used for insulation co-ordination. The role of parallel air gaps in preserving the arrester energy-rating limits is also discussed View full abstract»

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  • Multi-agent co-ordination for the secondary voltage control in power-system contingencies

    Page(s): 61 - 66
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (492 KB)  

    The secondary voltage control of power systems initiated by EDF has been developed successfully and applied mainly for the generator AVRs to improve power system voltage stability. Work on secondary voltage control is presented involving various types of power system voltage controllers, AVRs, SVCs and STATCOMs, for a new application: power system voltage management in system contingencies. The secondary voltage control is proposed, to be implemented based on the principles of multi-agent system theory, an active branch of applications in distributed artificial intelligence. An example power system is presented to demonstrate the necessity of the secondary voltage control among an AVR, an SVC and a STATCOM installed in the power system, and also to illustrate the success of applying the multi-agent co-ordination for their secondary voltage control in system contingencies View full abstract»

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  • Lightning surge analysis using nonuniform, single-phase line model

    Page(s): 85 - 90
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (504 KB)  

    In the analysis of lightning surges, transmission towers are usually simulated by nonuniform lines, but overhead lines are assumed uniform. If the effect of line sags is considered, the variation of the overhead line parameters with respect to space should also be treated as nonuniform. Tower surge response is computed using nonuniform, single-phase line models for both transmission tower and ground wire. Using boundary conditions for these lines, total response of the system in s-domain is obtained. A fast inverse Laplace transform is used for the frequency-to-time domain conversion. The effect of line losses is included View full abstract»

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  • Fuzzy logic application in load flow studies

    Page(s): 34 - 40
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (424 KB)  

    Fuzzy logic is used to solve the load flow problem, so decreasing computing time. Consequently, the repetitive solution of the proposed fuzzy load flow (FLF) method requires only 2 m calculations per iteration, where m is the number of buses of the system. In the FLF method, the real and reactive power mismatches per voltage magnitude at each node of the system are chosen as the crisp input values, which are fuzzified into the fuzzifier. The process logic uses a rule base to explode the fuzzy output signals, which are defuzzified and the crisp values are chosen as the corrections of voltage angle and magnitudes at each node of the system. The efficiency of the proposed method is demonstrated on various test systems View full abstract»

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  • Dynamic optimal power flow by interior point methods

    Page(s): 76 - 84
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (740 KB)  

    An algorithm based on nonlinear interior point methods is developed for the dynamic optimal power flow (DOPF) problem in which both time-separated and time-related constraints are considered and solved as a single optimisation problem. A border blocked power system is derived and further decomposed into time-separated submatrices whose sizes merely rely on network sizes and the 4×4 block structure is the same as the nodal admittance matrices. Thus, the supersparsity technique of the Newton OPF can be fully utilised. A three-stage solution procedure is proposed to implement the proposed algorithm. The numerical examples of the systems with sizes from 30 to 118 busbars with up to 24-hour period are employed to demonstrate the efficiency and robustness of the proposed method View full abstract»

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  • Electrothermal model for complete metal-oxide surge arresters

    Page(s): 29 - 33
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (384 KB)  

    A computational electrothermal model for a complete metal-oxide surge arrester based on the implicit form of the finite-differences method is presented. The model is used to calculate the cooling curve after the application of overvoltages and the temperature variations during standard test. The model has been checked against experiments carried out on a test section and a complete surge arrester and the behaviour of a hypothetical surge arrester during standard tests simulated View full abstract»

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  • Initialisation, decoupling, hot start, and warm start in direct nonlinear interior point algorithm for optimal power flows

    Page(s): 67 - 75
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (684 KB)  

    Effective approaches dealing with four important issues in a direct nonlinear interior point algorithm (DNIPA) for optimal power flows (OPF) are presented. The first issue, initialisation, is important for the robustness of DNIPA, the second issue, decoupling, is important for OPF applications. The other two issues are particularly important to OPF performance in energy management systems. The approaches enhance the performance of DNIPA for OPF problems in terms of iteration counts and CPU times. Extensive numerical tests are performed on two different sizes of real-life systems: 244- and 2423-bus systems. Based on these results, the initialisation approach improves direct nonlinear predictor-corrector primal-dual interior point algorithm (PCPDIPA) by 24%, in term of CPU times. The decoupling approach enhances PCPDIPA (with initialisation) by 27%,. The hot start and warm start solve the problems about 2.0 and 2.7 times, respectively, faster than PCPDIPA with initialisation, and 2.5 and 3.3 times, respectively, faster than PCPDTPA without using initialisation View full abstract»

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