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Generation, Transmission & Distribution, IET

Issue 7 • Date July 2009

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Displaying Results 1 - 8 of 8
  • Stage pre-warning based on leakage current characteristics before contamination flashover of porcelain and glass insulators

    Page(s): 605 - 615
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (756 KB)  

    Contamination flashover is the ultimate result of the creeping discharge of polluted insulators. Since there are close ties between the contamination flashover and the leakage currents, it is critical to research the leakage current characteristics during the entire contamination discharge process. The leakage currents of porcelain and glass insulators are monitored and analysed through a number of laboratory tests in various polluted cases. The goal is to find the characteristics that are useful for the pre-warning of the contamination flashover. The emphasis of this paper is on the leakage current root-mean-square values and waveforms and power spectrum estimation of the leakage currents. Results of the experiments (repeated several times) show that the progress of the contamination discharge process can be classified into three stages, that is, security stage, forecast stage and danger stage. In addition, the boundaries of the three stages in both the time domain and the power spectrum domain are given based on the analysis of the test results of various insulators. That is very helpful for the stage pre-warning of the contamination flashover. Also, a new characteristic index, K, is introduced. It is the rate of rise of the maximum peak value of the power spectrum. It can provide a more comprehensive theoretical guidance for the contamination flashover stage pre-warning together with the leakage current and waveforms. The three-stage classification for the entire flashover process is also meaningful in order to perfect the prediction of the contamination flashover. Finally, other characteristics of the power spectrum estimation are also discussed based on the three-stage classification. View full abstract»

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  • FPAA-based MHO distance relay considering CVT transient supervision

    Page(s): 616 - 627
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (778 KB)  

    Present-day numerical relays provide remarkable capabilities such as monitoring, recording and communication. These capabilities are considered as secondary priority whereas speed and reliability are the two most important characteristics of a protective relay. Even though present-day numerical relays have provided considerable capabilities and advantages, they have not improved speed of operation in comparison to their solid-state counterparts. The idea of applying mixed signals processing using advanced analogue and digital technology in several applications has started. Use of advanced programmable analogue technology, which is known as field programmable analogue arrays (FPAAs), seems to have the potential to be used in protective relays. Hybrid hardware using both digital signal processor (DSP) and FPAAs is proposed to implement mho distance relay considering capacitor voltage transformer (CVT) transient supervision for low and high system impedance ratio (SIR) systems. Test results are reported and compared with a commercial relay test results. View full abstract»

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  • Reliability assessment of restructured power systems using optimal load shedding technique

    Page(s): 628 - 640
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (352 KB)  

    Power system restructuring and deregulation has changed the strategy of reliability management of a power system. Load shedding, and generation and reserve re-dispatch methods used in the existing reliability evaluation techniques have to be improved to incorporate these changes. An optimisation technique, incorporating those changes, is proposed in this study to determine load curtailment and generation re-dispatch for each contingency state in the reliability evaluation of restructured power systems with the Poolco market structure. The problem is formulated using the optimal power flow (OPF) technique. The objective of the problem is to minimise the total system cost, which includes generation, reserve and interruption costs, subject to market and network constraints. A model for the contingency management of a Poolco power market is presented to include generation and reserve biddings, reliability considerations and transmission network constraints in reliability evaluation. Both supply side reliability for a generation company (Genco) and demand-side reliability for a customer can be calculated using the technique. The proposed technique can be used to evaluate both conventional and restructured power systems, and can provide both economic and reliability information for the independent system operator to manage system reliability, for Gencos to enhance their reliability, and for customer to select suppliers. The modified IEEE-RTS with the Poolco market has been analysed to illustrate the techniques. The results obtained using the proposed technique have been compared with those from the existing load shedding techniques. View full abstract»

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  • Real-coded genetic algorithm and fuzzy logic approach for real-time tuning of proportional-integral - derivative controller in automatic voltage regulator system

    Page(s): 641 - 649
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (330 KB)  

    Optimal tuning of proportional-integral-derivative (PID) controller parameters is necessary for the satisfactory operation of automatic voltage regulator (AVR) system. This study presents a combined genetic algorithm (GA) and fuzzy logic approach to determine the optimal PID controller parameters in AVR system. The problem of obtaining the optimal PID controller parameters is formulated as an optimisation problem and a real-coded genetic algorithm (RGA) is applied to solve the optimisation problem. In the proposed RGA, the optimisation variables are represented as floating point numbers in the genetic population. Further, for effective genetic operation, the crossover and mutation operators which can deal directly with the floating point numbers are used. The proposed approach has resulted in PID controller with good transient response. The optimal PID gains obtained by the proposed GA for various operating conditions are used to develop the rule base of the Sugeno fuzzy system. The developed fuzzy system can give the PID parameters on-line for different operating conditions. The suitability of the proposed approach for PID controller tuning has been demonstrated through computer simulations in an AVR system. View full abstract»

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  • Neural network-based approach for early detection of cascading events in electric power systems

    Page(s): 650 - 665
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (577 KB)  

    This study proposes neural modelling and fault diagnosis methods for the early detection of cascading events in electric power systems. A neural-fuzzy network is used to model the dynamics of the power transmission system in fault-free conditions. The output of the neural-fuzzy network is compared to measurements from the power system and the obtained residuals undergo statistical processing according to a fault detection and isolation algorithm. If a fault threshold, defined by the fault detection and isolation (FDI) algorithm, is exceeded then deviation from normal operation can be detected at its early stages and an alarm can be launched. In several cases fault isolation can be also performed, that is the sources of fault in the power transmission system can be also identified. The performance of the proposed methodology is tested through simulation experiments. View full abstract»

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  • Choice of estimator for distribution system state estimation

    Page(s): 666 - 678
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1214 KB)  

    In this study, a statistical framework is introduced to assess the suitability of various state estimation (SE) methodologies for the purpose of distribution system state estimation (DSSE). The existing algorithms adopted in the transmission system SE are reconfigured for the distribution system. The performance of three SE algorithms has been examined and discussed in standard 12-bus and 95-bus UK-GDS network models. View full abstract»

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  • Independent marginal losses with application to locational marginal price calculation

    Page(s): 679 - 689
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (397 KB)  

    A new kind of power system marginal loss (or loss sensitivity) for nodal MW/Mvar is developed. First the electricity transmission loss is expressed in terms of source currents. It is thus an analytical function. Then the marginal loss with respect to source current is derived based on calculus and vector algebra. Using each source/load power represents its nodal injection current, the marginal loss with respect to source current is then transformed into the marginal loss with respect to source/load power. The new kind of marginal loss is based on load flow solution. It is exact in algorithm and independent of reference bus, thus called independent marginal loss (IML). The IML exactly leads to double collection of actual system loss. It makes loss components of locational marginal price small in spatial fluctuation compared to the existing marginal losses. Numerical examples including the IEEE 118-bus and PJM 5-bus systems are presented to demonstrate the calculation and effectiveness of the IML. View full abstract»

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  • Induction motor load impact on power system eigenvalue sensitivity analysis

    Page(s): 690 - 700
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (532 KB)  

    Load modelling plays an important role in power system dynamic stability assessment. One of the widely used methods in assessing load model impact on system dynamic response is parametric sensitivity analysis. A composite load model-based load sensitivity analysis framework is proposed. It enables comprehensive investigation into load modelling impacts on system stability considering the dynamic interactions between load and system dynamics. The effect of the location of individual as well as patches of composite loads in the vicinity on the sensitivity of the oscillatory modes is investigated. The impact of load composition on the overall sensitivity of the load is also investigated. View full abstract»

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IET Generation, Transmission & Distribution is intended as a forum for the publication and discussion of current practice and future developments in electric power generation, transmission and distribution.

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