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Generation, Transmission and Distribution, IEE Proceedings-

Issue 4 • Date Jul 2002

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Displaying Results 1 - 18 of 18
  • Electrical generators for direct drive wave energy converters

    Publication Year: 2002 , Page(s): 446 - 456
    Cited by:  Papers (39)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (727 KB)  

    Wave power devices traditionally use conventional rotary electrical machines for power conversion. However hydraulic systems or air turbines are required to convert the low reciprocating motion of the wave device to rotation at 1500 rpm. The concept of a direct drive system is introduced, in which a reciprocating electrical machine is driven at the same speed as the device. A linear permanent magnet synchronous machine is compared to the transverse flux machine in a basic design study for this application. The latter machine is identified as offering the best potential. Electromagnetic and electric circuit models are developed to investigate the performance of the transverse flux machine in a wave energy converter. Measures are suggested to optimise the performance of the machine View full abstract»

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  • Study of four-phase power transmission systems

    Publication Year: 2002 , Page(s): 397 - 401
    Cited by:  Papers (10)  |  Patents (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (456 KB)  

    Multi-phase power transmission is an important method to increase the power density transmitted. The principle of a new four-phase transmission is proposed, and the general characteristics of four-phase overhead power transmission lines are discussed. Four-phase overhead transmission lines have special advantages in multi-phase transmission lines, because of the good symmetry and the simple structure of the lines and poles. Under the same condition of parameters, four-phase transmission lines can increase the transmission capacity by 33.3%, compared with three-phase lines. As the land width occupied by four-phase lines decreases, the capacity transmitted in unit land width by four-phase lines increases by 41.0-88.7%, and the economical and environmental benefits are much more notable. The reliability and transient stability of the transmission system may be improved, because two adjacent phase conductors of four-phase transmission lines can operate. Attention from the power industry is expected View full abstract»

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  • Power system voltage control by multiple STATCOMs based on learning humoral immune response

    Publication Year: 2002 , Page(s): 416 - 426
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (583 KB)  

    An approach for power system voltage control is proposed based on the learning humoral immune response which cannot only fulfil the conventional task of a voltage controller in a power system to keep the voltage at the controller's busbar to a setting reference value at the normal operation mode, but also minimise or eliminate voltage violations at its adjacent busbars in power system contingencies. This dual voltage control function is the major advantage of the approach proposed and is achieved by the capability of the immoral immune voltage control to identify self and nonself antigen intrusion (voltage variations and violations) to the power system. It is proposed that the parameters of a humoral immune voltage controller are trained by learning algorithms via offline simulation. The training is assisted by the injections of artificial reactive loads at relevant busbars in the power system and by the provision of a learning reference signal. An example 10-machine 39-node power system installed with two STATCOMs (static synchronous compensators) is presented. The success of applying the proposed immoral immune voltage control and associated learning algorithms to the design of STATCOMs is demonstrated View full abstract»

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  • Allocation of VAr support using LP and NLP based optimal power flows

    Publication Year: 2002 , Page(s): 377 - 383
    Cited by:  Papers (14)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (541 KB)  

    Characteristics of linear programming (LP) and nonlinear programming (NLP)-based optimal power flows (OPFs) are discussed, which allocate (auctions) reactive power support among competing generators in a deregulated environment. LP-based AC OPF algorithms are frequently used in practice to optimise the operation and reinforcement of power systems owing to their reliability. The alternative methods are NLP-based OPF algorithms, which have developed rapidly in this past decade motivated by the performance of interior-point algorithms. While LP algorithms offer reliable performance, the latter offer computation speed and accuracy for achieving the solution. An LP-based direct reactive OPF and a NLP-based direct reactive OPF using an interior-point algorithm, which concurrently solve load flow and optimisation problems, are developed and analysed. The issue of performance arises from the difficulties associated with the convergence of a direct LP OPF and the need for a technique to enforce the convergence of such an OPF. As the LP OPF may not converge spontaneously to the optimal point, questions arise as to whether such approaches are appropriate for facilitating the provision of VAr support in a competitive environment. Although the overall reactive requirement calculated by the OPF may be reasonably accurate, a generator's individual commitment may vary considerably. In contrast, the NLP OPF shows different characteristics: it converges spontaneously and the solutions are accurate. A comparison between those two streams of algorithms is presented. Extensive case studies are carried out over the IEEE-118 bus system to illustrate the impact of different starting points on the solutions for both LP and NLP algorithms View full abstract»

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  • Nonstandard method for accelerated ageing tests of nonceramic insulators

    Publication Year: 2002 , Page(s): 439 - 445
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (534 KB)  

    A methodology for testing accelerated ageing of nonceramic insulators (NCI) is presented based mainly on polluting the insulators with several substances, such as kaolin, lime, fertilizer and natural field pollutants. The polluted insulators are evaluated inside a salt fog chamber by applying cycles of salt fog, clean fog, drying and constant voltage. During the tests, clear evidence of tracking, erosion, chalking and puncture was observed on the insulators. Flashover takes place on the early damaged insulators in a relatively short time with respect to the test time of 5000 h recommended by IEC 61109. Based on the results obtained it is necessary to modify the standard continuous 5000 h salt fog test to evaluate the long-term performance of NCI. The new test must consider low salinity, clean fog and drying periods and an initial pollution coating. Under these conditions, the leakage current magnitude is smaller and consequently much more discharge activity occurs over the polluted insulator surface leading to surface deterioration, since hydrophobicity recovery of the insulator surface is allowed during the drying period. Measurements show that the leakage current peak values were in a range from 50 to 120 mA View full abstract»

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  • Design of UPFC controllers and supplementary damping controller for power transmission control and stability enhancement of a longitudinal power system

    Publication Year: 2002 , Page(s): 463 - 471
    Cited by:  Papers (17)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (587 KB)  

    The application of unified power flow controllers (UPFCs) to redistribute the power flows over two disproportionate parallel corridors and to boost the low-voltage profile on the transmission networks of the Taiwan power system is examined. A detailed dynamic generator model is used for a UPFC controller design to give more accurate controller parameters. A power system supervisor and conditioner (PSSC) is proposed to determine proper reference busbar voltages and series power flows for the UPFC control system. To improve system dynamic performance under disturbance conditions, a systematic approach based on the root locus method and pole assignment is developed to reach proper proportional-integral (PI) controller gains for the UPFC control system. In addition, a supplementary damping controller is designed to improve the damping for low-frequency electromechanical mode oscillations. To demonstrate the effectiveness of the proposed UPFC control system, computer simulations are performed to reach the steady-state and dynamic responses of the Taiwan power system. It is concluded from the simulation results that not only the requirements on steady-state power transfer and voltage profile can be obtained, but also the satisfactory system dynamic responses can be achieved by co-ordinated application of the designed UPFC control system View full abstract»

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  • Combined wavelet transform and regression technique for secondary current compensation of current transformers

    Publication Year: 2002 , Page(s): 497 - 503
    Cited by:  Papers (18)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (499 KB)  

    A technique is proposed to effectively and efficiently compensate for secondary current of current transformers, particularly in the presence of remanent flux. The technique first utilises the wavelet transform to accurately distinguish the distorted section from the healthy section of a secondary current waveform. Secondly the technique uses the regression method to recover the distorted section making use of features extracted from the healthy section, essentially to restore the secondary current to a scaled down replica of the primary system current. The proposed technique is demonstrated on a sample power system, achieving an average compensation error of 1.5% under varying degrees of saturation caused by different levels of remanent flux View full abstract»

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  • Improvement of precise P/V curve considering effects of voltage-dependent load models and transmission losses for voltage stability analysis

    Publication Year: 2002 , Page(s): 384 - 388
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (380 KB)  

    The P/V (power/voltage) curve of a power system has been often used for the analysis of voltage stability. If the P/V curve is evaluated with improved precision, then it can have an important role in the analysis of voltage stability. An approach is presented to improve the precision of the P/V curve of a power system, considering the effect of voltage dependency of electric loads and power transmission losses. For electric loads, the use of the voltage-dependent load model, expressed in quadratic form of the bus voltage, has been adopted. For the losses, the re-allocation of transmission losses to each generation bus has been used in the process of power flow calculation for obtaining the P/V curve. Case studies demonstrate the performance of the approach View full abstract»

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  • Iterative solvers in the Newton power flow problem: preconditioners, inexact solutions and partial Jacobian updates

    Publication Year: 2002 , Page(s): 479 - 484
    Cited by:  Papers (7)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (541 KB)  

    A comparative study of available iterative solvers (for linear systems of equations) applied to the solution of the nonlinear Newton power flow problem is presented. Iterative solvers are combined with Newton's method and an optimal stopping strategy is included to obtain an efficient solution for large power systems. Using the solvers and preconditioners available in Matlab, it is shown that iterative solvers are more efficient than the direct LU solution for large power systems. An easy to implement refinement is the introduction of partial Jacobian updates to avoid additional computations when an equation has reached the convergence tolerance. For large power systems (3000 buses and more), we have obtained savings (in flops) in the order of 25% compared to the direct LU solution. A convergence characterisation of the Newton power flow based on the Jacobian's spectrum and its condition number is also presented View full abstract»

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  • Investigation of the performance of a photovoltaic AC module

    Publication Year: 2002 , Page(s): 472 - 478
    Cited by:  Papers (8)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (494 KB)  

    Details of a converter and control system used in a photovoltaic AC module is presented. The sizing of the DC link capacitor, the DC/DC converter design and the maximum power point algorithm are discussed. An overview of system integration including the converter and its control is given. Throughout, the choices of system components are supported with analysis and simulation, as well as experimental tests using a solar emulator test system View full abstract»

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  • Method for computing probability distributions of available transfer capability

    Publication Year: 2002 , Page(s): 427 - 431
    Cited by:  Papers (14)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (419 KB)  

    With the advent of open transmission access, power transfers in interconnected networks have increased. The transfer capability between two buses or areas is a random variable, but the current available transfer capability (ATC) postings by the transmission service providers are deterministic. For a market participant, managing transmission risks requires a statistical forecast for the expected range of transfer capability. From this viewpoint, it is worthwhile to approach the ATC problem as a probabilistic one. A simple bootstrap technique is proposed to determine the probability distribution of an ATC which reflects the market activities and operational risks. The proposed method draws with replacement from recent bus injection datasets many times to create a pseudo-population of system situations from which ATCs are calculated. The obtained ATC distributions can be used to evaluate the risk of curtailment for incremental levels of transfers, thus permitting more informed decisions in arranging transmission services View full abstract»

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  • Decentralised congestion management of interconnected power systems

    Publication Year: 2002 , Page(s): 432 - 438
    Cited by:  Papers (6)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (500 KB)  

    A method for the decentralised solution of the congestion management problem in large interconnected power systems is presented. The multi-area congestion management is achieved through crossborder co-ordinated redispatching by regional transmission system operators. The coordination is performed through a pricing mechanism inspired by Lagrangian relaxation. The prices used for the co-ordination of the regional subproblem solutions are the prices of electricity exchanges between adjacent areas. Test results from the application of the method to the three-area RTS96 are reported View full abstract»

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  • Robust damping controller design for a static compensator

    Publication Year: 2002 , Page(s): 491 - 496
    Cited by:  Papers (4)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (423 KB)  

    A robust controller for providing damping to power system transients through static compensator (STATCOM) devices is presented. The method of multiplicative uncertainty has been employed to model the variations of the operating points in the system. A loop-shaping method has been employed to select a suitable open-loop transfer function, from which the robust controller is constructed. The design is carried out applying robustness criteria for stability and performance. The proposed controller has been tested through a number of disturbances including three-phase faults. The robust controller designed has been demonstrated to provide extremely good damping characteristics over a range of operating conditions View full abstract»

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  • Self-correction two-machine equivalent model for stability control of FACT system using real-time phasor measurements

    Publication Year: 2002 , Page(s): 389 - 396
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (584 KB)  

    A self-correction two-machine equivalent model for the stability control of a flexible AC transmission (FACT)-based transmission system is developed. Shaping of the self-correction two-machine equivalent model uses only the real-time phasor signals available from the synchronous phasor measurement units (PMUs). The errors between the proposed model and practical power system are corrected by real-time measurements. The adaptive and robust behaviours both get involved in this model. In addition, linearity approximation is not used in its development. The proposed model is appropriate for transient stability control. Via the self-correction two-machine equivalent model, this work successfully applies the direct feedback linearisation (DFL) technique to a multimachine interconnected power system for transient stability control. The parameters and model uncertainties are also considered in the proposed DFL controller. This approach is then successfully applied to a three-area six-machine test system that installed two thyristor-controlled switch capacitors (TCSCs) controllers. Simulation results indicate that the proposed model and DFL controller are effective and robust in stabilising the transient swings between interconnected systems under various system conditions and the occurrence of severe faults View full abstract»

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  • Capability charts for combined cycle power plants

    Publication Year: 2002 , Page(s): 407 - 415
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (562 KB)  

    Thermal power plants, based on combined gas and steam turbine cycles, are now worldwide. In a competitive generation market, power plants are required not only to inject active power but also to support secure operation of the transmission system, providing adequate ancillary services. To determine power plant capability for supporting voltage/reactive power regulation of the power system, the active and reactive powers that a combined cycle power plant can inject into the power system must be evaluated. The concept of capability charts is therefore extended from synchronous generators to the whole combined cycle power plant, including the effects of the operating conditions of the thermal and electrical components of the power plant, as well as of the plant connection to the electrical power system. Steady-state mathematical models are presented and a modular algorithm is proposed to evaluate the power plant capability charts numerically. Some numerical results are presented to show the effective synthetic information that can be obtained by adopting the proposed approach in practical cases View full abstract»

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  • A simple control scheme for hybrid active power filter

    Publication Year: 2002 , Page(s): 485 - 490
    Cited by:  Papers (21)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (399 KB)  

    A simple control scheme for hybrid active power filters connected in parallel is presented and analysed. The hybrid active power filter combines the compensation characteristics of resonant passive and active power filters. The series active power filter is implemented with a three-phase pulse-width modular (PWM) voltage-source inverter. The proposed scheme is able to compensate displacement power factor and current harmonics simultaneously. The combination of passive and active power filters allows a better performance compensation of high-power nonlinear loads. The proposed control scheme is discussed in terms of principles of operations under steady-state and transient conditions. The design and implementation of the power and control circuits are reported. Finally, key predicted results are verified experimentally on a 5 kVA prototype model View full abstract»

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  • Bus-oriented transmission loss allocation

    Publication Year: 2002 , Page(s): 402 - 406
    Cited by:  Papers (11)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (387 KB)  

    As a result of deregulation, energy transfers increase in both volume and geographical span. Parallel flows begin to exert serious operational and economic effects. In system loss allocation calculation, it is desirable to match the calculation results and actual power flows as closely as possible. Three bus-oriented schemes, based on generalised generation distribution factors (GGDFs) and generalised load distribution factors (GLDFs), are proposed to allocate the transmission losses to market participants. This bus-oriented method is aimed at reducing the distribution factor computation and reflecting the activity in a competitive market. AC power flow-based injection shift distribution factors are exploited for computing GGDFs and GLDFs. Instead of using an incremental loss concept, system total loss is allocated directly to each bus by the proposed schemes. Several systems have been used to test the proposed methods, and numerical examples based on a 14-bus system are presented View full abstract»

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  • Voltage distribution studies on ZnO arresters

    Publication Year: 2002 , Page(s): 457 - 462
    Cited by:  Papers (11)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (464 KB)  

    The voltage distribution in a zinc oxide (ZnO) surge arrester under normal operating conditions has been observed to be nonuniform. The discs at the top are subjected to a higher voltage and hence thermal stresses, leading to a faster thermal ageing of these highly stressed discs. Therefore, efforts are generally made to make the voltage distribution as uniform as possible. The voltage distribution in the arrester is governed by the geometry as well as the electrical properties of the materials used. To improve the voltage distribution, some changes in geometry are relatively easier to implement. The authors employ a numerical field computation approach to ascertain the influence of the geometry of different components of the arrester on its voltage distribution. Practical geometries of a 220 kV and a 400 kV class arrester are considered under both clean and uniformly polluted conditions. Some optimum values for the geometry of the components are obtained View full abstract»

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