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Generation, Transmission & Distribution, IET

Issue 11 • Date Nov. 2011

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Displaying Results 1 - 13 of 13
  • Starting up rapid-start units for reserve contributions in a system with interruptible loads

    Page(s): 1081 - 1090
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (529 KB)  

    This study presents the effect of starting reliability of rapid-start units (RSUs), such as open-cycle gas turbines (OCGTs) and hydro generators, for energy scheduling and reserve allocation. A method that explicitly integrates unit starting reliability into the expected energy not served (EENS) formulation for non-spinning reserve (NR) contribution is proposed. A unit commitment objective function is used to incorporate the various types of energy/reserve providers and to schedule energy and reserve simultaneously. These providers are conventional thermal units, OCGTs, hydro units and interruptible loads. An EENS model that considers these energy/reserve providers and accounts for their response times is presented pictorially. A penalty cost formulation for RSUs that failed to start up for NR contribution is proposed. This work emphasises the importance of modelling units of varying starting reliability. These results could be used to assist independent system operators and generation companies when selecting energy/reserve sources for power generation and reserve contribution. View full abstract»

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  • Short-term scheduling solved with a particle swarm optimiser

    Page(s): 1091 - 1104
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (581 KB)  

    Unit commitment problem is an important optimising task in daily operational planning of power systems which can be mathematically formulated as a large scale non-linear mixed-integer minimisation problem for which there is no exact solution technique. The solution to the problem can be obtained only by complete enumeration, often at a prohibitively computation time requirement for realistic power systems. This research discusses the planning of short-term scheduling on thermal power systems through the particle swarm optimisation technique. The formulation of the problem considers the operating costs of the units, the minimum up and down times, the spinning reserve and the power balance. A methodology is presented, and a computational tool is developed to solve the problem of unit commitment, which handles the problem constraints with correction operators. In the research also is proposed a new way to update the swarm individuals and a mutation stage of the best solution. The method is applied to standard systems and the results are compared with the ones previously reported in the literature. The results obtained by applying the proposed algorithm to the Chile Large Northern Interconnected System are also discussed. View full abstract»

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  • Assessing the loadability of active distribution networks in the presence of DC controllable links

    Page(s): 1105 - 1113
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (328 KB)  

    This study addresses the benefits of incorporating flexible DC links into radial distribution networks, which are subject to continuous load growth and higher levels of distributed generation penetration. To compare the use of DC links with conventional network reinforcement measures, an optimisation framework is developed. The main feature of the proposed formulation is that, irrespective of the criterion chosen to quantify the benefits of adding DC links, the same objective function is handled. Maximising or minimising a single-objective function, subject to the same set of constraints, allows different planning criteria to be assessed. The proposed optimisation framework is applied to actual networks embedding distributed generation. Two- and three-terminal voltage source converter-based DC links are considered in order to numerically illustrate the potential benefits of this technology in distribution systems. View full abstract»

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  • Power quality of distributed generation systems as affected by electromechanical oscillations - definitions and possible solutions

    Page(s): 1114 - 1123
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (391 KB)  

    Electromechanical oscillations (EMO) are natural responses of synchronous generators to a mismatch in their net torques and therefore are present in every distribution system equipped with such generators. Underdamped oscillations are of major concern for power system stability, and indeed shall be treated as such. However, in this study these oscillations are discussed from the power quality (PQ) point of view. In this work, it is claimed that such oscillations can lead to PQ phenomena. The EMO are characterised in this study using both theoretical and numerical analyses, which lead to the definition of several PQ phenomena that can be induced by such oscillations. The obtained results show that EMO in distribution systems can indeed be a significant source of PQ problems, as opposed to the widespread empirical belief that these two problems (power system stability and PQ) are not linked to each other. As a possible solution to mitigate the defined PQ problems, the usage of classical power system stabilisers is proposed in this study, since these controllers are usually available in the excitation systems of the generators but are not commonly used in distributed generation systems. View full abstract»

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  • Allocating the cost of transient stability constraint relief in bilateral electricity markets

    Page(s): 1124 - 1131
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (177 KB)  

    In this study, the issue of allocating the cost of transient stability relief in a bilateral electricity market is investigated. The results of a constrained generation scheduling problem can be utilised in two ways to price the cost of a constraint. In the first method, which is the basis of nodal pricing, the Lagrange multipliers of the nodal power balance constraint are used as the price of electricity at various buses. In the second method, which is used in this study, the constraint relief scheme is based on a bid-based adjustment market of increments and decrements offered by generators to be involved in the constraint relief process. In the scheme used in this study, the cost of transient stability relief is first allocated to the individual constraints by different methods and the allocated costs are then allocated to the transactions in proportion to the degree of involvement in that constraint. Three methods are proposed and discussed for allocation of cost to the constraints and the results are compared and commented. The transient energy function (TEF) method is used to calculate the contribution of transactions in the constraints. View full abstract»

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  • Modelling and simulation of voltage source converter-based interphase power controller as fault-current limiter and power flow controller

    Page(s): 1132 - 1140
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (845 KB)  

    In this study, a new FACTS device is proposed, which is based on the topology of the conventional interphase power controller (IPC). The proposed topology replaces the conventional phase-shifting transformers (PSTs) with the static synchronous series compensator. The equivalent circuit model for this new voltage source converter-based IPC (VSC-based IPC) is developed. Although the injected voltages of SSSCs are almost perpendicular to the branch currents and cannot maintain a constant amplitude line voltage as PSTs, it is shown that the VSC-based IPC can effectively control the line power flow, without exceeding the line voltage regulation limits. Based on the simulations, the abilities of the device for the short-circuit current mitigation and power flow control are presented for the Iran electric network. View full abstract»

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  • Adequacy equivalent development of composite generation and transmission systems using network screening

    Page(s): 1141 - 1148
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (590 KB)  

    Reliability evaluation of a large composite generation and transmission system involves extensive and time-consuming calculations. Application of reliability equivalent networks therefore seems necessary in the reliability evaluation of large power systems. An approach is presented to develop an adequacy equivalent of a composite system using network screening. In the proposed method, a power system is divided into two portions designated as the study area and the external area. The goal is to find the adequacy equivalent of the external area in order to facilitate extensive reliability studies in the study area. The elements in the external area are ranked or screened based on their impacts on power flows in the tie lines between the two areas. Owing to their less impact, the lower ranked elements are considered to be involved in a network reduction technique. Simulation studies are conducted on the IEEE-RTS-96 and the performance of the developed procedure is thoroughly discussed. View full abstract»

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  • Sequential quadratic programming based differential evolution algorithm for optimal power flow problem

    Page(s): 1149 - 1154
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (232 KB)  

    This study proposes a hybrid algorithm combining sequential quadratic programming (SQP) and differential evolution (DE) algorithm for solving the optimal power flow (OPF) problem. In this hybrid method, SQP is used to generate an individual, which is a member of an initial population, for DE algorithm. Having generated an individual by SQP, which will be nearer to the optimal solution, DE algorithm can reach the optimal solution more effectively than the classical evolutionary algorithms can. The proposed method has been used to solve the OPF problem on the standard IEEE 30- and IEEE 118-bus test systems to validate the effectiveness. Two different objectives, namely fuel cost considering valve-point effects and the transmission line losses, have been considered. The simulation results obtained from the proposed hybrid method reveal that this algorithm gives better solution for the problem having more non-convexity. View full abstract»

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  • Effects of strong resonance in tuning of multiple power system stabilisers

    Page(s): 1155 - 1164
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (237 KB)  

    The phenomena of strong resonance occur due to dynamic modal interaction between the power system's modes when one/two system or controller parameters are varied. This study presents the effect of strong resonance while designing a single or multiple power system stabilisers (PSS) in multi-machine power systems that can lead to instability of the system. The effect of strong resonance is investigated in test and practical power systems. It is studied with full-order and reduced-order system models based on the method of perturbations suggested by Seiranyan. The authors also suggest a mechanism to mitigate strong resonance while tuning one or more PSS. The test systems considered are three-machine, ten-bus system and a four-machine, 11-bus practical system, a part of the southern-grid Indian power system. View full abstract»

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  • Robust state estimation method based on maximum exponential square

    Page(s): 1165 - 1172
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (573 KB)  

    State estimation is a fundamental function of energy management system (EMS) and has been practically used for many years. However, traditional weighted least square (WLS)-based state estimator still suffer problems when conforming errors exist. In this study, a maximum exponential square (MES) state estimation method is proposed, which is formulated as a maximisation problem with an exponential square objective function. As a special type of M-estimator, the main characteristic of an MES estimator is that it can automatically suppress bad data and its calculation is fast, and so it is suitable for practical applications. A large number of tests have been performed to verify the performance of an MES estimator in suppressing bad data. Tests on a real provincial power system have also been performed to verify the calculation efficiency and estimation accuracy of an MES estimator. View full abstract»

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  • Probabilistic dynamic multi-objective model for renewable and non-renewable distributed generation planning

    Page(s): 1173 - 1182
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (431 KB)  

    This study proposes a probabilistic dynamic model for multi-objective distributed generation (DG) planning, which also considers network reinforcement at presence of uncertainties associated with the load values, generated power of wind turbines and electricity market price. Monte Carlo simulation is used to deal with the mentioned uncertainties. The planning process is considered as a two-objective problem. The first objective is the minimisation of total cost including investment and operating cost of DG units, the cost paid to purchase energy from main grid and the network reinforcement costs. The second objective is defined as the minimisation of technical risk, including the probability of violating the safe operating technical limits. The Pareto optimal set is found using non-dominated sorting genetic algorithm method and the final solution is selected using a max-min method. The model is applied on two distribution networks and compared with other models to demonstrate its effectiveness. View full abstract»

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  • Phasor-measurement-unit-based transmission line fault location estimator under dynamic conditions

    Page(s): 1183 - 1191
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (461 KB)  

    When power system is under dynamic condition such as power oscillation, the fault voltage and current cannot be expressed as a standard sinusoidal function, so error, in the form of oscillation of estimate, will arise as conventional fault location algorithms ignore the dynamic characteristics of supplied signals. A novel algorithm extended from conventional fault location algorithms is proposed in this study. This approach not only can express the spatial characteristic of supplied signals but also considers them as time-variant signals whose magnitude and frequency are changing against time. Therefore it possesses the ability of describing spatial property and time property of signals, simultaneously. By using the adjoining phasor estimate from synchrophasor phasor measurement units (PMUs) to express the dynamic characteristics in terms of derivatives, an accurate estimate of fault location can be attained via Newton iteration method. The performance of the proposed algorithm is evaluated by computer Power System Computer Aided Design/Electromagnetic Transient including DC (PSCAD/EMTDC)-generated signals under various situations. The evaluation results indicate that the proposed technique yields an accurate fault location estimate under dynamic conditions independent of fault types, fault impedance and fault locations. The maximal estimate error of the proposed algorithm is less than one-tenth of that of the conventional fault location algorithm in most cases. View full abstract»

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  • Integration of clustering analysis and reward/penalty mechanisms for regulating service reliability in distribution systems

    Page(s): 1192 - 1200
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (431 KB)  

    This study proposes an approach for improving service reliability in the distribution network based on establishing competition among electric distribution utilities. The idea behind this approach is to categorise the utilities and compare the performance of utilities located in one cluster with the other members of the same cluster. The reward/penalty mechanism (RPM) as a quality regulating instrument is designed for each cluster and used to penalise the utilities with a performance worse than the benchmark and to reward them for providing a performance better than the benchmark. Based on the RPM, utilities located in one cluster compete to make more profit by serving customers in better reliability level. The setting of a RPM in an ex-post manner is also proposed to provide incentives for utilities to improve their reliability in an active manner. The system reliability indices are utilised to measure the utilities performance. The proposed method is applied to 39 electric distribution utilities in Iran. The results show the effectiveness of combining clustering analysis with a reward/penalty instrument in reliability improvement. 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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