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Generation, Transmission and Distribution, IEE Proceedings-

Issue 1 • Date Jan. 2003

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Displaying Results 1 - 20 of 20
  • Frequency and time domain analysis of unit connected generators to HVDC converters

    Page(s): 1 - 6
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (413 KB)  

    The steady-state performance of the 'direct connection' of a synchronous generator to an HVDC converter, without AC filters or AC bus bar, is analysed. This system is also referred to as a unit connection' (UC). Despite the existence of subtransient saliency, the distorted terminal voltage of the machine and its harmonic components could be fully determined by simple analytical expressions. The harmonic components and the operation limits of the converter are also derived. The rectified voltage in UC systems has been shown to be essentially as in conventional HVDC converters. Some time domain simulation results of the unit connected system voltages waveforms are presented to confirm the validity of the analytical model obtained. Also, it is shown that it is possible to determine the actual firing delay angle of the converter and the limits of the minimum firing angle due to the UC operation. The analysis presented is highly useful in assessing the machine terminal voltage waveform and its harmonics. View full abstract»

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  • Radiation from coupled multiconductor transmission lines

    Page(s): 15 - 22
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (378 KB)  

    Based on the reciprocity theorem, a simple method for analysis of the radiated electromagnetic fields from an arbitary configuration of coupled multiconductor transmission fines with linear terminations is presented. The radiation problem is solved using the reciprocity theorem and the solution of the coupling problem. The method of solution for the coupling problem is based on the quasi-TEM assumptions. Some examples for several coupled structures of coupled transmission lines are then solved to show the capabilities of the method. View full abstract»

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  • Calculation of rightmost eigenvalues in power systems using the block (BACM) Arnoldi Chebyshev method

    Page(s): 23 - 27
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (318 KB)  

    Small-signal stability analysis of a power system needs the calculation of the rightmost eigenvalues of a system state matrix. The block Arnoldi Chebyshev method (BACM) is used to calculate the rightmost eigenvalues, which is an improved version of the Arnoldi Chebyshev method (ACM). This method constructs an optimal ellipse containing unwanted eigenvalues and uses the Chebyshev iteration to acquire a restart matrix rich in basis vectors associated with the rightmost eigenvalues. Using the restart matrix including many more basis vectors, this method is good for calculating the clustered rightmost eigenvalues. The proposed algorithm is applied to the IEEE39 New England test system and the results of the experiment are described. View full abstract»

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  • Translationally adaptive fuzzy classifier for transformer impulse fault identification

    Page(s): 33 - 40
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (466 KB)  

    The determination of transformer fault categories using soft-computing based techniques has been the subject of much research in the recent past. The development of an adaptive fuzzy classifier which can effectively determine various classes or categories of series and shunt impulse faults in a wide range of power transformers is described. The system employs a self-generating module to automatically derive a fuzzy rule base from predefined input and output membership functions (MFs) and a given data set for different fault classes. The accuracy of the system is further improved by translationally adapting output MF(s) either forward or backward, keeping their size and shape invariant. The database for different classes of faults is developed from FFT operation on current and voltage waveforms, obtained for different possible fault conditions simulated for given transformer models (EMTP) using an electromagnetic transients program. This database is used to create training and testing data sets required to design the fuzzy based classifier system. The usefulness of the proposed fuzzy based classifier is demonstrated on the basis of performances shown for four example power transformers of 1 MVA, 3 MVA, 5 MVA and 60 MVA ratings. View full abstract»

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  • Frequency-domain modelling of interharmonics in HVDC systems

    Page(s): 41 - 48
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (465 KB)  

    A fast and accurate method for the direct calculation of noncharacteristic frequencies occurring around HVDC links is presented. The technique calculates small signal linearised frequency crosscoupling interrelationships for both converters about a base operating point, modelling the coupling with matrix transfers. The full system, including AC and DC systems, is modelled by connecting all individual transfers together with appropriate system equations and nodal analysis. The resulting equation set is rearranged and solved directly for the unknown interharmonic quantities. Returned subsynchronous frequencies and the effect of switching instant variation are discussed. The method is validated against time-domain simulation, for two different asynchronous links, with excellent results. View full abstract»

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  • General steady-state analysis of three-phase self-excited induction generator feeding three-phase unbalanced load/single-phase load for stand-alone applications

    Page(s): 49 - 55
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (406 KB)  

    A general steady-state analysis of a three-phase self-excited induction generator (SEIG) feeding a three-phase unbalanced load or single-phase load is presented. Symmetrical component theory is used to obtain relevant performance equations through sequence quantities. While the analysis of the system is inherently complicated due to unbalance and magnetic saturation, valid simplifications incorporated in the equivalent circuit for both forward and backward fields result in manageable equations suitable for computer simulation. Suitable nonlinear parameters are chosen corresponding to appropriate saturation levels. Using this technique a 7.5 kW, 415/240 V, four-pole, three-phase induction motor operated as a SEIG is analysed under different unbalanced loads and compared with experimental results. The feasibility of using three-phase machines for such unbalanced operations has been critically examined for stand-alone power generation. View full abstract»

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  • Genetic algorithms solution to generator maintenance scheduling with modified genetic operators

    Page(s): 56 - 60
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (293 KB)  

    The applicability of genetic algorithms (GA) to the generator maintenance scheduling (GMS) problem with modified genetic operators (MGO), such as string reversal and reciprocal exchange mutation (REM) is demonstrated. The main contribution is the use of 'probabilistic production simulation' (PPS) with an equivalent energy function method, which outperforms other methods in terms of computation time and accuracy. The performance of the algorithm has been tested on 5- and 21-unit test systems with integer encoding, binary for integer encoding, and real encoding. The GMS problem is solved to minimise the expected energy production cost (EEPC) and maximising the reserve objectives under a series of constraints. Results are compared with solution by conventional methods. This paper places in proper perspective the effect of MGO, with an explicit case study and simulation results. It is placed in evidence that only integer coding GA finds the global optimum solution, irrespective of the nature of the objective function and system size. Faster convergence is enhanced with the implementation of MGO for integer GA only. View full abstract»

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  • Implementation and assessment of physically based electrical load models: Application to direct load control residential programmes

    Page(s): 61 - 66
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (398 KB)  

    The purpose of the paper is to describe physically based electrical models of heating, ventillation and air conditioning residential loads. These models are based on energy balances between the internal air, the dwelling constructive elements, the conditioner appliances and the external environment through a discrete state-space equation system. The main objective of these dynamic models is to evaluate load management programmes, above all direct load control actions. The models have been implemented and tested to assess their accuracy and suitability in this specific kind of applications. In this way, simulated results have been compared with data collected over a period of one year in different cities and for different load performances - steady state as well as response to remote control actions. The advantages of the models proposed here are also compared with models previously developed and described in the literature. View full abstract»

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  • Unit commitment using a stochastic extended neighbourhood search

    Page(s): 67 - 72
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (444 KB)  

    A simulated annealing approach is combined with a tabu search, to develop a robust and powerful optimisation technique for solving the unit commitment problem. The problem is broken down into a combinatorial subproblem in unit status variables and a quadratic programming subproblem in unit power output variables. The combinatorial subproblem is solved using the proposed method. In the hybrid algorithm, which is referred to as a stochastic extended neighbourhood search, simulated annealing is used as the main stochastic algorithm, and a tabu search is used as an extended neighbourhood search, to locally improve the solution obtained by simulated annealing. The neighbourhood search uses local domain-knowledge, which results in rapid convergence of the simulated annealing algorithm. The results obtained for several example systems illustrate the potential of the hybrid approach. View full abstract»

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  • Small-scale embedded generation effect on voltage profile: an analytical method

    Page(s): 78 - 86
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (479 KB)  

    Nowadays, deep concern is focused on the introduction of small-scale embedded generation (SSEG) in LV networks, since some technologies have a natural inclination to be easily integrated into urban LV distribution networks. As a consequence, studies on the effects produced on LV distribution systems by SSEG are gaining more and more relevance. Some aspects regarding the quality of the power supplied to customers are dealt with, taking into consideration long-duration voltage variations in the presence of SSEG. In particular, the effect on the voltage profile in a LV distribution feeder is examined with reference to both distributed loads and lumped loads. Some analytical expressions are derived to determine the limit value of the power that can be injected into a single node of a distribution feeder without causing overvoltages. The expressions derived for distributed loads are compared to those for lumped loads in order to assess if the analytical evaluation of the current threshold can be performed by means of an equivalent model based on continuous quantities with a negligible error, since actually, the analysis of real cases implies dealing with lumped loads. View full abstract»

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  • Reliability evaluation of small stand-alone wind energy conversion systems using a time series simulation model

    Page(s): 96 - 100
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (370 KB)  

    A time series simulation model for the reliability evaluation of small stand-alone wind energy conversion systems (SSWECS) containing battery storages is presented. The performance of such a system is quite different from one containing conventional generating units due to the dispersed nature of the wind at the specific site location. The reliability of a SSWECS depends on various factors such as the reserve margin, the battery size and charging (discharging) characteristics, the wind speed, the wind turbine generator's failure/repair characteristics and power ratings, the system load profile and the system operating philosophy. The results and discussions presented should prove useful in planning, designing, and operating small stand-alone wind energy conversion systems for electricity supply in remote areas. View full abstract»

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  • Data structure for radial distribution system load flow analysis

    Page(s): 101 - 106
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (367 KB)  

    Owing to the radial nature and high R/X ratio, radial distribution systems (RDS) employ a special recursive technique for distribution load flow (DLF). An efficient method for DLF plays a critical role in automation algorithms of RDS whose scope encompasses fault isolation, network reconfiguration and service restoration. The ability of automation algorithms to handle these complex tasks that require frequent topology changes in the RDS demands a dynamic topology processor based on a well-defined data structure. The purpose of this paper is to formulate a dynamic data structure (DDS) and an algorithm that generates the DDS of the RDS as an R-tree. The proposed DDS algorithm generates the DDS and is used as a topology processor in the DLF algorithm. The resulting DLF algorithm is computationally efficient and can handle rapidly changing topology by updating the R-tree. The pseudocodes for the DDS algorithm and the overall recursive algorithm for DLF are presented. Various RDS have been tested with the proposed method and the results demonstrate its efficiency over other known methods of DLF. View full abstract»

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  • On-line monitoring of maximum permissible loading of a power system within voltage stability limits

    Page(s): 107 - 112
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (418 KB)  

    Online determination of the maximum permissible loading of a power system is essential for operating the system with an adequate security margin. A very simple and straightforward method of determining the maximum permissible loading and voltage stability margin of a power system using information about the current operating point is proposed. The method simply requires some locally measurable quantities, such as bus voltage magnitude, and active and reactive components of load power. The measured data are carefully processed to estimate the maximum permissible loading and voltage stability margin of a system. The proposed method was vigorously tested on the IEEE 14- and 30-bus systems and the simulation results indicated that the method can correctly estimate the maximum permissible loading of the systems at the verge of voltage collapse. View full abstract»

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  • Reactive control in a deregulated environment with static VAr compensators improving voltage stability

    Page(s): 113 - 118
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (373 KB)  

    The deregulated market requires great attention to be paid to analysis and control methodologies. This evolution has to satisfy reliability, security and optimisation objectives. In this context the importance of reactive control has to be highlighted. Power electronic devices can be efficiently employed to solve this crucial problem. A co-ordinated control strategy for the reactive power based upon a hierarchical structure is considered. An optimisation procedure is effected at a high level maximising the economic gain and avoiding the possibility of critical conditions deriving from voltage instabilities. The optimisation output data are used as reference signals for static VAr compensators. The rationale behind the static VAr compensator control design is the invariant manifold theory, allowing the reference signal to be tracked with accuracy and robustness. An application is presented with reference to the IEEE 118-bus system which outlines the flexibility and goodness of the proposed technique. View full abstract»

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  • Advanced three-phase static VAr compensator models for power flow analysis

    Page(s): 119 - 127
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (499 KB)  

    The development of new static VAr compensator (SVC) models and their implementation in a power flow program is presented. The modelling is carried out in the phase domain considering the SVC delta-connected physical structure. The SVC is assumed to be a continuous, variable susceptance, which is adjusted in order to achieve a specified nodal voltage magnitude in an adaptive fashion. A polyphase Newton-Raphson power flow program is modified in order to implement the proposed models. Validation of these models is carried out in a benchmark network operating under balanced conditions. SVC performance is assessed in both balanced and unbalanced power network operating conditions. The power flow implementation exhibits a very strong convergence characteristic regardless of the network size. View full abstract»

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  • Addendum

    Page(s): 128
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (169 KB)  

    First Page of the Article
    View full abstract»

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  • Disturbance data compression of a power system using the Huffman coding approach with wavelet transform enhancement

    Page(s): 7 - 14
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (474 KB)  

    A Huffman coding approach enhanced with wavelet transform is applied to compress power system disturbance data. The acquired data of the disturbance signal is first decomposed into higher frequency and lower frequency components by wavelet transform. The Huffman coding technique is then used to reduce the amount of data more effectively. The data transmission and storage capability can also be enhanced. This method has been tested under disturbance scenarios that include: voltage sag, voltage swell and momentary interruption. Test results demonstrated the feasibility of the method. View full abstract»

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  • Dynamic Leapfrog algorithm for power system state estimation

    Page(s): 28 - 32
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (390 KB)  

    Power system state estimation is a very large-scale, sparse and non-linear problem. The following methods to solve the problem will be tested and compared: Gauss-Newton and the Dynamic Leapfrog method. The IEEE 14-bus power system is used to compare the different solvers. Cases when Gauss-Newton does not converge are identified. The Dynamic leapfrog method is proposed to be used in state estimation to solve these nonconvergent cases. For this small-scale power system the dynamic method proves to be numerically robust compared to Gauss-Newton. View full abstract»

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  • Optimal transmission pricing with generation uncertainty and transmission losses

    Page(s): 73 - 77
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (415 KB)  

    A technique to include uncertainties in generation availability in transmission price calculations based on the optimal pricing methodology and probabilistic production costing methodology is proposed. The method considers the possible outages of generators and their effect on meeting the system load and, thus, on the transmission prices. Transmission losses in the problem formulation are considered. A case study is presented using the IEEE 24-busbar reliability test system, where the effect of the proposed technique and that of transmission losses on the optimal transmission prices are demonstrated. It is concluded that the inclusion of generation uncertainty and proper treatment of transmission losses is an important part in the calculation of transmission charges and the presented model provides a possible approach in this regard. View full abstract»

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  • Optimal load-frequency control in restructured power systems

    Page(s): 87 - 95
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (598 KB)  

    A framework for optimal load-frequency control (LFC) in deregulated environments is proposed. The objective function of optimisation incorporates both the indices of economy and stability with their own physical meanings. Under this framework, the problem of market-based optimal LFC is formulated to be an optimisation problem of functional extremum. Since the structure-preserving model of power systems is adopted in order to consider the characteristics of loads, the optimisation problem is constrained by differential algebraic-equation systems (DAEs). Then a quasi-Newton algorithm is put forward to solve the formulated optimal DAEs-constrained optimisation problem. Simulation is carried out on the IEEE 30-bus system with different market structures. It is shown that the proposed framework and the corresponding algorithm are effective, and can achieve optimal operation of power systems in terms of both security and economy. View full abstract»

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