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Generation, Transmission and Distribution, IEE Proceedings-

Issue 3 • Date May 1999

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Displaying Results 1 - 19 of 19
  • Inverter controller for HVDC systems connected to weak AC systems

    Publication Year: 1999 , Page(s): 235 - 240
    Cited by:  Papers (5)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (400 KB)  

    The paper presents a new control strategy for the inverter side of an HVDC power system. The new control algorithm is intended for stability improvement of an HVDC system connected to a very weak receiving AC system. A root-locus analysis based on a detailed analytical system model determines the eigenvalues which are mostly affected by the reduction in strength of the inverter AC system. The feedback signal for the new controller is selected by considering possible movement of eigenvalues of importance. The controller is designed as a second-order filter placed in the feedback loop. Since the robustness of the system with respect to the AC system SCR changes is the main controller aim, the H control theory is used for the controller design. Two cases have been studied: the design of a controller to improve the stability of an HVDC system connected to an AC system susceptible to large variations in its strength; and the design of a controller which enables an HVDC system connection to a very weak AC system (SCR=1.0 is considered). The PSCAD/EMTDC simulation results confirm that the controller meets the design objectives View full abstract»

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  • Fast valving scheme using parallel valves for transient stability improvement

    Publication Year: 1999 , Page(s): 330 - 336
    Cited by:  Papers (4)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (444 KB)  

    A new fast valving scheme of steam turbines using two parallel valves for improving the transient stability of a power system is proposed. The influence of the actuation time parameters of a conventional fast valving scheme using a single valve is first studied in detail to justify the need for a parallel valve scheme. A systematic procedure for selecting suitable valve actuation times, the sequence and the conditions to be monitored for implementing a coordinated parallel valve actuation scheme is presented. The proposed scheme is applied to a typical nuclear power plant connected to an infinite busbar system. A four stroke valve operation mode of the scheme is found to improve the second and subsequent swing stability significantly. A multiple stroke operation mode of the scheme for improving the rotor angle damping over a longer period of transient is also presented View full abstract»

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  • Wavelet-transform-based algorithm for harmonic analysis of power system waveforms

    Publication Year: 1999 , Page(s): 249 - 254
    Cited by:  Papers (60)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (392 KB)  

    The paper develops an approach, based on the wavelet transform, for the evaluation of harmonic contents of power system waveforms. The new algorithm can simultaneously identify all harmonics including integer, noninteger and subharmonics. In the first step of the approach, the frequency spectrum of the waveform is decomposed into subbands using discrete wavelet packet transform filter banks. In the second step, a continuous wavelet transform is applied to nonzero subbands to evaluate the harmonic contents. In the first step, there is the problem of images due to down samplings and up samplings of the waveform. A method for alleviating this image problem is developed in the paper. Methods are developed to accurately quantify harmonics frequency amplitude and phase. The approach is validated by its application to synthesised waveforms and to power system waveforms measured in the Western Australia system. It is found to be powerful and suitable for practical use View full abstract»

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  • Load control services in the management of power system security costs

    Publication Year: 1999 , Page(s): 269 - 275
    Cited by:  Papers (7)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (396 KB)  

    The new climate of deregulation in the electricity industry is creating a need for a more transparent cost structure and within this framework the cost of power system security has been a subject of considerable interest. Traditionally power system security has been supplied by out-of-merit generation in the short term and transmission reinforcement in the long term. This paper presents a method of analysing the role of load demand in the management of power system security costs by utilising load control services (LCS). It also proposes a competitive market to enable bidding from various participants within the electricity industry to supply system security View full abstract»

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  • Reliability worth of distribution system network reinforcement considering dispersed customer cost data

    Publication Year: 1999 , Page(s): 318 - 324
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (376 KB)  

    Reliability cost/worth analysis plays an important role in distribution system planning and operation. The interruption cost model used in the analysis directly affects the predicted reliability worth used to make reinforcement decisions. Two cost models are presented that can be used in reliability cost analysis: an average or aggregate model; and a probability distribution model. A time sequential simulation technique is illustrated for distribution system reliability cost/worth assessment using the two developed cost models and incorporating time-varying loads. The technique is used to evaluate the reliability worth of installing lateral fuses, disconnect switches and alternate supplies in a test distribution system. The results show that using the average or aggregate model can result in underestimating the reliability worth, and that the probability distribution model approach may be more meaningful View full abstract»

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  • Demand-side management opportunities for the UK domestic sector

    Publication Year: 1999 , Page(s): 283 - 293
    Cited by:  Papers (13)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (568 KB)  

    The electricity demand signatures of individual UK dwellings, and of the main types of domestic appliance employed by households, have been collected and analysed. Means for modulating these electricity demands have been investigated experimentally. Peak power reductions of up to 60% have been achieved by developing `load conscious' control algorithms for individual cooking and washing appliances, without adversely affecting their performances. Peak avoidance via an integrated control philosophy (for managing a household's coincident peak power demands) and thermal storage, have also been assessed. If widely applied in UK housing, the findings of this investigation could serve to substantially smooth local and national electricity demand profiles View full abstract»

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  • Migration path study of a distribution SCADA system

    Publication Year: 1999 , Page(s): 313 - 317
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (364 KB)  

    Owing to competitive changes in the electric power industry, it is essential to protect the large financial and human resources investment a utility makes when acquiring a SCADA/EMS. Past experience has indicated that, with proper planning, an obsolete SCADA/EMS can be incrementally augmented. The migration approach provides immediate access to new technology while capital costs are spread over a number of years. To evaluate the different migration options of an area dispatch and control system, a discrete event simulation method is used to study the performance of different migration designs. A thorough analysis of a functionally distributed architecture under realistic conditions is conducted, and the results are reported View full abstract»

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  • Direct load control using fuzzy dynamic programming

    Publication Year: 1999 , Page(s): 294 - 300
    Cited by:  Papers (19)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (364 KB)  

    The paper develops a fuzzy dynamic programming (FDP) approach to solving the direct load control (DLC) problem of large air conditioner loads (ACLs). In the formulation, the cycling capacities of the ACLs and the system load demands are all regarded as fuzzy variables. The scheduling of the DLC and the unit commitment (UC) is integrated into an FDP structure to reduce the system peak loads as well as the system operation costs. The solution approach has been tested on the data for the Taiwan Power (Taipower) 38-unit system with 15 ACL groups. In the tests, the Monte-Carlo simulation technique is employed to assess the robustness of the solution obtained from the proposed FDP approach for various load uncertainties. The results are presented and compared to those without consideration of the load uncertainties View full abstract»

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  • Influence of load on operating conditions of third harmonic ground-fault protection system of unit connected generators

    Publication Year: 1999 , Page(s): 241 - 248
    Cited by:  Papers (5)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (548 KB)  

    The influence of the load of the unit connected generator on the operating conditions of the ground-fault protection of the stator windings of the generator, excited by the ratio of the third harmonic voltage in the generator neutral and at the generator terminals to ground, was analysed. On the basis of the theoretical analysis, experimental tests and computer simulations, relations between the voltage feeding the measuring element of the ground-fault protection and the load of the unit during ground faults along the entire length of the stator windings were determined. The influence of the method of balancing ground-fault protection on the third harmonic voltage feeding its measuring element was determined. It has been found that correct operation of the ground-fault protection calls for the the influence of the load on the resolution of the third harmonic voltages in unit connected generator circuits to be taken into account View full abstract»

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  • Fuzzy-logic method for adjustment of variable parameters in load-flow calculation

    Publication Year: 1999 , Page(s): 276 - 282
    Cited by:  Papers (4)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (376 KB)  

    The paper presents a new approach using fuzzy logic to adjust variable parameters so as to meet constraints during load flow studies. Parameters to be adjusted include transmission line impedance, phase angle and transformer tap position and the constraints are transmission line power flow and bus voltage magnitude. Versatile apparatus which are used to tune these parameters include the thyristor-controlled series compensator, thyristor-controlled phase shifter, unified power flow controller and on-load tap changer. The proposed approach is particularly aimed at assisting convergence in load flow programs. The parameters to be adjusted are decoupled from the main body of the load flow formulation. The methodology for parameter adjustment is conducted by using fuzzy logic View full abstract»

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  • Integrated approach to transmission services pricing

    Publication Year: 1999 , Page(s): 255 - 260
    Cited by:  Papers (5)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (428 KB)  

    The paper presents an intuitively logical split between: (a) embedded; (b) operating; and (c) expansion cost based pricing and methodologies for implementation, for transmission services. A conceptually straightforward mechanism for the equitable allocation of transmission network embedded cost recovery based on capacity-use and reliability benefit is proposed, expansion cost is charged on a long-run marginal cost basis and finally, operating cost recovery is based on short-run marginal pricing. This is followed by co-ordinating these alternatives and integrating the pricing mechanisms to achieve appropriate price signals for bulk power users of transmission systems View full abstract»

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  • Application of algorithms and artificial-intelligence approach for locating multiple harmonics in distribution systems

    Publication Year: 1999 , Page(s): 325 - 329
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (324 KB)  

    A new method is proposed for locating multiple harmonic sources in distribution systems. The proposed method first determines the proper locations for metering measurement using fuzzy clustering. Next, an artificial neural network based on the backpropagation approach is used to identify the most likely location for multiple harmonic sources. A set of systematic algorithmic steps is developed until all harmonic locations are identified. The simulation results for an 18-busbar system show that the proposed method is very efficient in locating the multiple harmonics in a distribution system View full abstract»

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  • Nonlinear adaptive control of TCSC to improve the performance of power systems

    Publication Year: 1999 , Page(s): 301 - 305
    Cited by:  Papers (5)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (284 KB)  

    The installation of thyristor controlled series compensation (TCSC) is planned in the Yimin-Fengtun 500 kV transmission lines of the Northeast China power system. To improve the transient stability and dynamic performance of the system, the authors present a nonlinear control scheme for the TCSC. The control scheme is derived by employing a nonlinear theory, the differential geometry theory. Thus, it can reflect the nonlinearity of power systems and has better adaptability. To reduce the influence of operation limitations of the TCSC equipment, such as limitation owing to the voltage protection of the metal oxide varistor (MOV), or the firing-angle of thyristors, an adaptive strategy of choosing parameters of the controller is applied. Thus, in any power transfer level, satisfactory performance of the power system can be acquired with the control scheme. A local control approach is also proposed so that all input variables can be obtained locally and easily. Simulations have proved the effectiveness of the nonlinear adaptive control strategy View full abstract»

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  • Extended Petri net models for fault diagnosis for substation automation

    Publication Year: 1999 , Page(s): 229 - 234
    Cited by:  Papers (28)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (344 KB)  

    In previous work, Petri net models were developed by the authors (1977) for detecting fault locations in general. In the current paper, the models have been modified to include backup protection as well as primary protection. The modification overcomes many limitations of the original models. Hence, the advanced models are more capable of analysing faults in a highly meshed network or network with more than one layer of protective devices, such as those in substations. The developed methodology is tested using an actual substation network. Fast and accurate results are obtained, and the proposed method has great potential for online applications View full abstract»

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  • Power-frequency magnetic shielding of heavy-current conductors by rectangular shields

    Publication Year: 1999 , Page(s): 223 - 228
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (376 KB)  

    Metallic enclosures of rectangular shape (e.g. galvanised iron trunking) are often installed in large buildings for the purpose of mechanical protection. Recently shielding performance of such enclosures has been of interest as a result of concerns about power-frequency magnetic field interference. The paper addresses shielding characteristics of rectangular shields, based on theoretical discussion, numerical simulations and laboratory experiments. It is found that both field reflection and field attenuation are two key factors, determined by impedance and skin depth ratios, respectively. Galvanised iron trunking can be approximately modelled as a linear shield with a constant equivalent relative permeability, the value of which is proportional to current magnitude. The shielding impact of shield parameters and source orientation, as well as guidelines for trunking design, is also discussed View full abstract»

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  • Applications of modelling UPFC into multi-machine power systems

    Publication Year: 1999 , Page(s): 306 - 312
    Cited by:  Papers (18)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (328 KB)  

    The paper establishes a nonlinear dynamic model of a multi-machine power system with a unified power flow controller (UPFC) installed. The linearised Phillips-Heffron model of the system is then derived and used to study oscillation stability. To demonstrate the applications of the models developed in the paper, a case study of a three-machine power system to be installed with a UPFC is presented. The impact of various UPFC control functions upon the power system oscillation stability is investigated based on the linearised model with confirmation by simulation from the nonlinear dynamic model. It is found that the basic control function within the UPFC, the voltage control of the DC link capacitor, interacts negatively with PSS. Results of counteracting the negative interaction by the readjustment of PSS or the introduction of a damping function into the UPFC itself to regain a satisfactory damping of power system oscillations are given in the paper View full abstract»

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  • Feature extraction methods for neural network-based transmission line fault discrimination

    Publication Year: 1999 , Page(s): 209 - 216
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (496 KB)  

    The suitability of conventional distance relays to operate correctly under variations in such factors as source impedance, prefault load and fault resistance is still a problem. This paper describes an alternative approach to nonunit protection of transmission lines using artificial neural networks (ANNs). Particular emphasis is placed on describing a methodology whereby the extraction of the input features (from the measured voltage and current signals) to the ANNs is near optimal; with this approach, the results presented clearly demonstrate that the protection technique gives satisfactory performance under a wide variation in practically encountered system operating and fault conditions View full abstract»

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  • Modelling of DC drives for power system harmonic analysis

    Publication Year: 1999 , Page(s): 217 - 222
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (348 KB)  

    A three-phase equivalent circuit model is developed to model DC motor drives for power system harmonic analysis. The validity and accuracy of the model were verified by comparing simulation results with field test results. Sensitivity studies are then conducted to determine the key factors affecting the harmonic characteristics of DC drives. Guidelines on modelling DC motor drives for harmonic distortion assessment are developed based on the results View full abstract»

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  • More sophisticated synchronous machine model and the relevant harmonic power flow study

    Publication Year: 1999 , Page(s): 261 - 268
    Cited by:  Papers (5)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (416 KB)  

    A more sophisticated Park equation-based synchronous machine model, used in harmonic load flow study, is proposed. From the physical interpretation of this model, it can be noticed that synchronous machines should also be considered as harmonic sources in power flow study, only if the power network is asymmetrical. This model is then incorporated with the extended `decoupling-compensation' network model used for harmonic power flow analysis. Several cases are studied, including harmonics caused by asymmetry of transmission lines and nonlinear elements like static VAr compensators (SVCs). A computed result verifies the effectiveness of the proposed model and the conclusion that more sophisticated synchronous machine models should be employed to obtain the correct, full scenario of harmonics distribution in power system is drawn View full abstract»

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