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Generation, Transmission & Distribution, IET

Issue 2 • Date February 2009

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Displaying Results 1 - 9 of 9
  • Statistical evaluation of lightning-related failures for the optimal location of surge arresters on the power networks

    Page(s): 129 - 144
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (419 KB)  

    Direct lightning strokes cause unscheduled supply interruptions in power systems because of a failure of the insulation. Metal oxide surge arresters, as a proper protective device, have been widely adopted in power systems to reduce lightning initiated flashovers and, hence, increase the power quality and reliability of the systems. Based on a genetic algorithm approach, a cost effective solution is described to find the optimum location of surge arresters on a power network in order to minimise the global risk of the network, and to improve its reliability. A statistical approach to evaluate lightning failures has been introduced and an optimisation procedure developed to analyse the network in order to satisfy the power utility requirement for a specific value of risk and/or line performance with a minimum set of arresters, that is, at minimum cost. Not only the insulation flashover but also the failure of the arrester can affect the reliability of power systems. Therefore, both the failure of the insulation and that of the arrester are considered in the proposed method. View full abstract»

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  • Simplified probabilistic selectivity technique for earth fault detection in unearthed MV networks

    Page(s): 145 - 153
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (851 KB)  

    A novel selectivity technique to identify the faulty feeder in unearthed Medium Voltage (MV) networks is introduced. The proposed technique is based on a simplified probabilistic method applied to transient features extracted from the residual currents only using the discrete wavelet transform (DWT). DWT will enhance the accuracy of localising fault events with different fault resistances and the probability will give the protection decision (detection/selectivity). The standard deviation of a window of the DWT detail coefficient is used to detect the fault and an adaptive threshold is used as input to the probability function to estimate the faulty feeder. A faulty unearthed 20 kV network is simulated by ATP/EMTP imitating practical fault cases such as arcing and tree leaning faults. The time-domain test cases provide evidence of the efficacy of the proposed technique. View full abstract»

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  • A variable scaling hybrid differential evolution for solving large-scale power dispatch problems

    Page(s): 154 - 163
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (471 KB)  

    A variable scaling hybrid differential evolution (VSHDE) is used to solve the large-scale power dispatch problems. The hybrid differential evolution (HDE) method has been presented as a method using the parallel processors of the two-membered evolution strategy ((1+1)-ES). In this way, the global search ability for the HDE can be inspected. To accelerate the search for the global solution, the concept of the variable scaling factor based on the one-fifth success rule of evolution strategies is embedded in the original HDE. The use of the variable scaling factor in the VSHDE can overcome the drawback of the need for fixed and random scaling factors in an HDE. To realise the dynamic economic dispatch (DED) system, the valve-point loading effect, system load demand, power losses, spinning reserve capacity, ramp rate limits and prohibited operation zones are considered here. Two test problems and two DED systems including those of 10 units and 20 units are used to compare the performance of the proposed method with an HDE. Numerical results show that the performance of the proposed method is better than that of the HDE method. View full abstract»

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  • Control strategies against voltage collapse considering undesired relay operations

    Page(s): 164 - 172
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (394 KB)  

    Control strategies as countermeasures against voltage collapse considering undesired relay operations are mainly discussed here. In the experiences of blackouts, undesired relay operations have played a very important role in cascading events leading to a voltage collapse. An algorithm for quick identification of critical relays is first depicted, the operations of which may significantly deteriorate the systems in terms of voltage stability. Then, the proposed approach determines a control strategy satisfying a relay margin criterion. For this purpose, a combinatorial optimisation formulation with a utility function evaluated by a quasi-steady-state simulation is used, and a local search algorithm to deal with binary control variables in the formulation is employed. The methodology is demonstrated with the modified New England 39-bus system. View full abstract»

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  • Unified computational tool for transient and long-term stability studies

    Page(s): 173 - 181
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (442 KB)  

    Here, the authors intend to apply a numerical method of integration with changing steps into dynamic simulations of power systems. The focus is on the transient and long-term periods represented by the set of algebraic-differential equations into the numerical algorithm predictor-corrector. The developed algorithm is based on the proposal of implicit integration step and it makes use of the Newton-Raphson method with the integration step obtained iteratively through the process. As the step size is important for the transient and long-term simulations, the authors propose to identify successive increases of integration steps and trigger the quasi-dynamic process, where the equations are purely algebraic. Therefore to control the step size and modify the techniques of simulation during the process has increased the speed of the simulation process with lower computational costs and more accuracy. View full abstract»

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  • Semi-definite programming-based method for security-constrained unit commitment with operational and optimal power flow constraints

    Page(s): 182 - 197
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (426 KB)  

    Considering the economics and securities for the operation of a power system, a semi-definite programming (SDP) model for the security-constrained unit commitment (SCUC) problem is described here, which is directly solved by the interior-point method for SDP within the polynomial times. The proposed method is promising for the SCUC problems because of its excellent convergence and the ability of handling the non-covex integer variables. No model decomposition and initial relaxation are needed when applying the SDP-based method. When the solution contains minor mismatches in the integer variables, a simple rounding strategy is used to correct the non-integer into integer efficiently. Different test cases from 6 to 118 buses over a 24 h horizon are presented. Extensive numerical simulations have shown that the proposed method is capable of obtaining the optimal UC schedules without any network and bus voltage violations, and minimising the operation cost as well. View full abstract»

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  • Fast and secure breaker failure detection algorithms

    Page(s): 198 - 205
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (233 KB)  

    In a power system, every apparatus is equipped with a primary protection to detect faults and isolate the equipment by opening the circuit breaker. Breaker failure (BF) protection is employed as a means of local backup protection to detect failure of a circuit breaker. In this research work, a critical challenge facing numerical BF relays namely longer reset time of current based BF algorithms is examined by means of simulations and realistic experiments. Two new fast resetting algorithms for BF protection with reset time of less than half a power system cycle are proposed as means of enhancing BF protection. Simulations and experiments reflecting realistic conditions were used for performance evaluation of the enhanced BF algorithms. The proposed algorithms have a reset time of around half a cycle compared to 2-3 cycles in the case of a commercial numerical BF relay selected. Results indicate that the new algorithms significantly enhance the numerical BF protection. View full abstract»

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  • N-1 security in optimal power flow control applied to limited areas

    Page(s): 206 - 215
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (388 KB)  

    Blackouts in recent years have demonstrated that a reliable and secure power system is a key component of an efficient economy. Therefore control devices such as flexible AC transmission system devices (FACTS) are placed in the system and utilised to improve the security of the system. A method to determine appropriate settings for these devices is optimal power flow control. As the area of influence of a FACTS device is usually limited, it is sufficient to include only a reduced area in the optimisation problem. Here, such an optimal power flow problem is formulated where the considered area is defined using sensitivity analysis. To include N - 1 security as an objective, a current injection method is applied, which facilitates the determination of the system state in the case of a line outage, without having to carry out a full-load flow simulation. View full abstract»

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  • Feasibility of online collaborative voltage stability control of power systems

    Page(s): 216 - 224
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (392 KB)  

    The authors present the results of feasibility study of a novel concept of power system online collaborative voltage stability control. Online collaboration between power system controllers is proposed in order to enhance their overall performance and efficiency to cope with the increasing operational uncertainty of modern power systems. The framework of the proposed online collaborative voltage stability control is first presented, which is based on the deployment of multi-agent systems and real-time communication for online collaborative control. Then, two of the most important issues in implementing the proposed online collaborative voltage stability control are addressed: (1) Error-tolerant communication protocol for fast information exchange among multiple intelligent agents; (2) Deployment of multi-agent systems by using graph theory to implement power system post-emergency control. Results of testing the proposed online collaborative voltage stability control in the case of the 10-machine 39-node New England power system are presented. Results of a feasibility study by means of a simulation are given that take into consideration low-probability cascading faults in the power system. 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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