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Generation, Transmission and Distribution, IEE Proceedings-

Issue 6 • Date November 2006

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Displaying Results 1 - 14 of 14
  • Coordinated AVR and tap changing control for an autonomous industrial power system

    Page(s): 617 - 623
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (171 KB)  

    A strategy for voltage and reactive power control of an autonomous industrial power system including distributed generators and loads is presented. The investigation is based on time-domain simulations and aims to define the main functions for the power management system (PMS) that will govern the operation of the power system. Inter-bus transformers (IBTs) are used to limit the fault level but will affect the sharing of the total load reactive power between distributed generators. Generator AVR and on-load tap changing of the IBTs, both supervised by the PMS, are used together to regulate the local load voltages and at the same time to allow reactive power flow through the IBTs for the purpose of equalised sharing. A coordinated strategy is obtained. The knowledge gained from this study can be useful in future cases View full abstract»

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  • Enhanced augmented Lagrangian Hopfield network for unit commitment

    Page(s): 624 - 632
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (211 KB)  

    An enhanced augmented Lagrangian Hopfield network (EALHN) for unit commitment (UC) is proposed. The EALHN is an augmented Lagrangian Hopfield network (ALHN) enhanced by unit classification to allow decommitment of excess spinning reserve units caused by the minimum up and down time constraints. First, the ALHN is used to solve the UC problem when neglecting the minimum up and down time constraints. Then, a heuristic-based algorithm is applied to satisfy the minimum up and down time constraints and decommit excess spinning reserve units. Finally, the economic dispatch problem is solved using an augmented Lagrangian-relaxation-based continuous Hopfield network (ALRHN). The EALHN is tested on several systems ranging from 10 to 100 units and compared to several methods. The total production costs from the proposed method are smaller those obtained using existing methods, especially for the large systems. Moreover, the computational times of the proposed method are also much faster than these for existing methods and slightly increase with the system size, which is very favourable for large-scale implementation View full abstract»

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  • Identification of a load-frequency characteristic for allocation of spinning reserves on the British electricity grid

    Page(s): 633 - 638
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (219 KB)  

    The transmission-grid system operator must maintain the system frequency of a synchronous transmission system within legislated tolerances. This task becomes of particular importance during large power imbalances. To establish a frequency-reserve scheme that maintains a healthy system frequency, the exact behaviour of generators and load response must be known. The paper provides details of load behaviour during a number of large infeed losses. These results show that the current load-frequency sensitivity factor of 2%MW/Hz is justified, and can even be extended to a value of 2.5%MW/Hz. Therefore, this value can be substituted in the calculation of reserve schemes on the electricity grid in Great Britain View full abstract»

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  • Unsynchronised two-terminal transmission-line fault-location without using line parameters

    Page(s): 639 - 643
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (145 KB)  

    The paper presents a new two-terminal transmission-line fault-location algorithm without requiring line parameters. The voltage and current measurements at both ends of a transmission line during a fault are assumed to be available and no synchronisation of the data is required. The proposed algorithm is suitable for estimating the location of asymmetric faults on a line when line parameters are not available. Evaluation studies using both simulated and field data are reported View full abstract»

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  • Islanding detection of inverter-based distributed generation

    Page(s): 644 - 652
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (426 KB)  

    An active islanding detection technique for an inverter-based distributed generator (DG) is presented. Two control strategies are studied: one in which the DG only supplies active power and one in which the DG supplies both active and reactive power to improve the power factor. The nondetection zone (NDZ) of the over/under voltage and frequency protection (OVP/UVP and OFP/UFP) method for each control strategy is determined. For the presented interface control, it is observed that the NDZ of the OVP/UVP and OFP/UFP is larger when the DG interface is designed to improve the power factor. In order to decrease the NDZ, an islanding detection method is designed that is based on creating a mismatch between the load and DG reactive power, thus forcing the frequency to deviate outside the OFP/UFP limits. It is shown that the proposed islanding detection technique is robust and has a negligible NDZ View full abstract»

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  • Q-adjusted annealing for Q-learning of bid selection in market-based multisource power systems

    Page(s): 653 - 660
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (259 KB)  

    The electric power industry is confronted with a major restructuring in which operation scheduling is decided based on a competitive market. In this new arrangement, bidding strategy becomes an important issue. Participants of the deregulated energy marketplace may be able to compete better by choosing a suitable bidding strategy for trading electricity. In such a deregulated market, coalition formation with other participants may change the diffusion of profit. Therefore the problem changes to the selection of the best participant for coalition and joint bidding strategies. Different classic methods for decision making in the uncertain environment of the market can be applied to select a suitable strategy. Most of these methods, such as game theory that insures reaching the optimal solution for all market participants, require a lot of information about other market players and the market. However, in a real marketplace only a little information such as the spot price is available for all participants. A modified reinforcement-learning approach based on Q-adjusted annealing has been applied to determine the optimal strategy for a power supplier in an electricity market with multiple sources. A modified IEEE 30-bus system has been considered and the simulation results are shown to be the same as with standard game theory. The main advantage of the proposed method is that no information about other participants is required. Investigation shows that if all participants use this method they will stay in Nash equilibrium View full abstract»

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  • Inclusion of voltage drop and feeder loading constraints in the evaluation of reliability indices for radial distribution networks

    Page(s): 661 - 669
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (217 KB)  

    A model that includes voltage drop and feeder loading constraints in the evaluation of reliability indices for radial distribution networks is proposed. The model estimates the nodal voltages using a compensation technique and a simplified version of the power summation load flow for radial networks. The main advantage of this models over existing models is that the post-restoration voltages can be evaluated without modifying the data structure used to evaluate the reliability indices. Results obtained on a large-scale distribution network demonstrate that the proposed methodology can assess the impact of network constraints on reliability indices with an acceptable accuracy whilst incurring a small computation cost View full abstract»

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  • Allocation of the cost of transmission losses in a multimarket framework

    Page(s): 670 - 676
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (176 KB)  

    The paper addresses the issue of apportioning of the cost of transmission losses to generators and demands in a multimarket framework. Line flows are unbundled using equivalent bilateral exchanges on a DC-network model and allocated to generators and demands. Losses are then calculated based on unbundled flows and straightforwardly apportioned to generators and demands. The proposed technique is particularly useful in a multimarket framework, where all markets have a common grid operator with complete knowledge of all network data, as is the case of the Brazilian electric-energy system. The methodology proposed is illustrated using the IEEE Reliability Test System and compared numerically with an alternative technique. Appropriate conclusions are drawn View full abstract»

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  • Back-to-back HVDC system using a 36-step voltage source converter

    Page(s): 677 - 683
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (674 KB)  

    A novel 36-step voltage source converter, that allow the number of steps in the output voltage to be increased is proposed. The operational feasibility of the 36-step converter is verified using computer simulations performed with the PSCAD/EMTDC programs and experimental studies performed on a 2 kVA hardware prototype. The propsed 36-step back-to-back converter is shown to be able to independently control the active and reactive power of HVDC systems View full abstract»

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  • Short-term real-power scheduling considering fuzzy factors in an autonomous system using genetic algorithms

    Page(s): 684 - 692
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (197 KB)  

    Distributed generation has several advantages such as reducing required transmission capacity and real power losses, and in terms of traditional generation expansion etc. An autonomous system is an independent system that may include diesel generators, a wind park, solar photovoltaic (PV) modules and/or batteries etc. serving its loads. The paper presents a new method for dealing with short-term power scheduling of an autonomous system. The fuel cost of diesel units is required to be smaller than an expected value and all operational constraints are satisfied. In particular, wind and solar PV power generation with uncertainties are modelled by a fuzzy set. The genetic algorithm is used to solve this problem formulated as symmetrical fuzzy programming. Simulation results based on an autonomous system show the applicability of the proposed method View full abstract»

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  • Short-term scheduling of hydrothermal power system with cascaded reservoirs by using modified differential evolution

    Page(s): 693 - 700
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (204 KB)  

    A modified differential evolution (MDE) algorithm, for solving short-term hydrothermal scheduling problem is presented. Hydrothermal scheduling involves the optimisation of a nonlinear objective function with a set of operational and physical constraints. Differential evolution, an improved version of a genetic algorithm, is a very simple, fast and robust global optimisation technique. The differential evolution algorithm is modified in order to handle the reservoir end volume constraints in the hydrothermal scheduling. The transmission losses are also accounted for through the use of loss coefficients. The study is extended for the combined economic emission dispatch. The performance of the proposed approach is validated by illustration with two test systems. The results of the proposed approach are compared with those of dynamic programming, nonlinear programming, genetic algorithm and evolutionary programming techniques. From the numerical results, it is found that the modified DE based approach is able to provide a better solution at a lesser computational effort View full abstract»

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  • Power quality and stability improvement of a wind farm using STATCOM supported with hybrid battery energy storage

    Page(s): 701 - 710
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (885 KB)  

    A large penetration of wind generation info the power system will mean that poor power quality and poor stability margins cannot be tolerated from wind farms. This requires that methods to improve power qualify and stability for such systems be found. The static compensator (STATCOM) with hybrid battery energy storage (BES) has great potential to fulfil this role, though considerable advances in the control of this system are still to be made. From an economic point of view, rating the STATCOM for steady-state power-quality improvement duty is appropriate. Rating the STATCOM to absorb large amounts of additional power in excess of its transient overload capability during network faults is inappropriate. A hybrid of BES and braking resistor is therefore proposed. A new hybrid STATCOM-BES control technique is developed and discussed in the context of improving the stability and power quality to fixed speed, induction generator, wind turbines. The variation of the network voltage, active and reactive power with the fluctuation of the wind generation is studied. A wind generation system with a STATCOM battery energy storage unit and the new control was simulated and the results demonstrate that both power quality and the stability margin can be improved significantly for wind farms View full abstract»

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  • Design and evaluation of a directional algorithm for transmission-line protection based on positivesequence fault components

    Page(s): 711 - 718
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (301 KB)  

    A directional relay algorithm for EHV transmission lines using positive-sequence fault components is presented. By comparing the phase relationship between the voltage and current measured at the relay point, the algorithm can determine correctly whether a fault is in the forward or backward direction. Specially designed techniques and logic are adopted to solve the difficult problems that exist in a real system. The signal-processing procedure for extracting the required fault components is provided in detail. Extensive simulation studies were conducted on a 500 kV system model using EMTDC. Theoretical analysis and simulation results show that the proposed algorithm provides adequate sensitivity, reliability and a fast operating response under a variety of system and fault conditions. In addition, it provides significant advantages over conventional directional relays, and these are discussed in the paper View full abstract»

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  • Probabilistic reliability criterion for planning transmission system expansions

    Page(s): 719 - 727
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (239 KB)  

    Probabilistic reliability criteria, such as LOLP, LOLE, EENS etc., have been used extensively for generation expansion planning throughout the world. Typically, only deterministic reliability criteria, such as (N-1) or (N-2) contingencies, have been used for grid expansion planning until now. The main reason is the difficulty in determining the optimum design of a grid expansion plan using probabilistic reliability criteria and in developing the appropriate mathematical model that incorporates the chosen reliability criterion for the transmission system. Optimum design in grid expansion planning is still an important element of overall electric power system planning in deregulated electricity markets. One of the potential improvements in generation and grid expansion planning comes from the use of a more realistic reliability level as a criterion to constrain the form of the optimum expansion problem. A methodology is proposed that uses a probabilistic reliability criterion to determine an optimum plan for transmission system expansion using a criterion that minimises the expected cost, which includes both construction and outage costs, using a probabilistic reliability criterion loss of load expectation RLOLE. The optimum value of the reliability criterion RLOLE* is determined at the minimum value of the combined total of the cost of constructing new transmission and the customer outage cost associated with supply interruptions. The characteristics and effectiveness of this methodology are illustrated by a case study using a 21-busbar test system View full abstract»

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