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Generation, Transmission & Distribution, IET

Issue 2 • Date Feb. 2013

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Displaying Results 1 - 12 of 12
  • Energy harvesting for a wireless-monitoring system of overhead high-voltage power lines

    Page(s): 101 - 107
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (674 KB)  

    For electric power transmission the overhead power line monitoring system plays an important role in operating security for grid operators as well as high supply availability at optimised cost. In this study, an approach to harvesting energy from the electric field around the conductor to supply the wireless sensor nodes was investigated. Special requirements in functionality, reliability and limited accessibility at the power line result in the development of a specific energy management strategy. A prototype of the power module was realised and tested under high voltage laboratory conditions. Then, a field test was carried out under real operating conditions. The test results confirm that the power module can collect enough energy to power the sensor nodes. The contribution in this study presents theoretical considerations of energy availability from the electric field, design of energy management and results from measurements with the prototype in a high voltage laboratory and in field test. The field test results demonstrate that the energy harvester can collect enough energy to power the sensor nodes by 16 mW. View full abstract»

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  • Data size reduction with symbolic aggregate approximation for electrical load pattern grouping

    Page(s): 108 - 117
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1171 KB)  

    Data size reduction techniques may be helpful in the process of categorising the electrical load consumption patterns on the basis of their shape. Starting from a macro-class of consumers defined according to certain general criteria on the type of consumers and the period of the year or week, the representative load pattern (RLP) of each consumer can be built by considering the data points in the time domain or a reduced number of features. This study exploits the effects of using the symbolic aggregate approximation (SAX) method to form the reduced set of features. The portion of the time-amplitude plane defining the RLP is partitioned into sub-portions on the basis of the characteristics of the whole data set. A specific partitioning of the time axis is proposed on the basis of the cumulative distribution function of the RLP variations in time. Each RLP is then coded according to the SAX principles. The resulting codes are then used into a hierarchical clustering procedure. The validity of the clustering results obtained by using the SAX data representation with the proposed non-uniform partitioning of the time axis is presented and discussed, including comparisons with the results obtained from other data size reduction techniques. View full abstract»

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  • Reliability improvement of power system observability with minimum phasor measurement units

    Page(s): 118 - 129
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (792 KB)  

    The size and complexity of power network and the cost of monitoring equipments, make it unfeasible to monitor the whole system variables. Conventional system analysers use voltages and currents of the network for monitoring purposes, which affects the system analysis, control and protection. A strategic placement of phasor measurement units (PMUs) is crucial to monitor the whole system with minimum number of devices. This study improves a topological circuit observation method to find essential PMUs. Besides the observability of the normal network, observability of abnormal network is considered. Consequently, a high level of system reliability is achieved. The reliability is maintained by observability under bad current data (CT errors) and all possible single single-line outage. These limitations are taken into the account in a hybrid genetic particle swarm optimisation strategy to minimise monitoring cost and avoiding unobservability under abnormal conditions. Proposed algorithm is tested on 14, 30, 39 and 118-bus IEEE standard test systems and a 24-bus network of Mazandaran Regional Electric Company located in north of Iran. View full abstract»

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  • Flexible load shedding strategy considering real-time dynamic thermal line rating

    Page(s): 130 - 137
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (271 KB)  

    In recent years, real-time dynamic thermal line rating (RT-DTLR) technology has been developed and implemented in operations to improve transmission line capacity, so that congestion costs and/or risk of load shedding can be reduced. Power systems obviously benefit from this technology but also bear the risks because of thermal overload of transmission lines. To involve RT-DTLR technology into conventional power system load shedding strategies, this study explains the concept of flexibility in power system analysis, expresses transmission line capacity constraints into flexible forms and proposes a flexible load shedding strategy considering RT-DTLR. The two sub-objective functions, representing load shedding quantity and system risk increment, are normalised and expressed as the confidence levels from system security consideration and load loss consideration, respectively. The proposed method takes advantage of both the advanced hardware and software technologies in smart grids and the simulation results showed that it can trade off the benefits and risks brought about by RT-DTLR in load shedding. View full abstract»

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  • Guaranteed state estimation of power system via interval constraints propagation

    Page(s): 138 - 144
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (277 KB)  

    This study deals with guaranteed state estimation of power systems in the bounded-error context, which avoids the effect of inexact matching of the assumed statistical hypotheses on the error. A new approach, based on interval constraint propagation, is proposed to compute guaranteed estimates of state variables and measurements. According to the feature of power systems, two improvements based on interval constraint propagation are presented to improve contraction and obtain narrow interval images. First, a monotonicity-based contractor is exploited because of the monotonicity of measure function to part of state variables. Second, the constraints set are extended by combining the measurement constraints. The improved method is guaranteed, contraction efficient and time efficient. The results, achieved using the proposed method, are compared with those typical existing methods to demonstrate its effectiveness. Tests are carried out on the IEEE 14-bus system and the IEEE 118-bus system, respectively. View full abstract»

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  • Study on fog flashover performance and fog-water conductivity correction coefficient for polluted insulators

    Page(s): 145 - 153
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (519 KB)  

    The pollution flashover performance of insulators is generally tested by the steam fog method. However, environmental temperature in tests differs greatly, so the dispensability of test results is high. Moreover, the influence of fog-water conductivity has not been taken into account. Compared with the steam fog method, the cold-fog method simulating natural fog is more consistent with the actual operating conditions of transmission line insulators. This deals with the influence of salt deposit density (SDD) and fog-water conductivity on pollution flashover performance. The influence of the two factors is determined by analysing the results of laboratory experiments where polluted insulators were tested by using the cold-fog method. The results show that the 50% AC pollution flashover voltage (U50) decreases as SDD and fog-water conductivity increase. The correction coefficient (K) indicating the influence of fog-water conductivity on U50 can be expressed as an exponential function, where the factors are 0.0476, 0.0587 and 0.0567 for samples A, B and C, respectively. View full abstract»

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  • Risk/investment-driven transmission expansion planning with multiple scenarios

    Page(s): 154 - 165
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (353 KB)  

    This study presents a new methodology based on risk/investment to solve transmission network expansion planning (TNEP) problem with multiple future scenarios. Three mathematical models related to TNEP problems considering multiple future generation and load scenarios are also presented. These models will provide planners with a meaningful risk assessment that enable them to determine the necessary funding for transmission lines at a permissible risk level. The results using test and real systems show that the proposed method presents better solutions compared with scenario analysis method. View full abstract»

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  • Research on lightning performance of AC/DC hybrid transmission lines on the same tower

    Page(s): 166 - 174
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (438 KB)  

    Rapid expansion of power system and the limitation of transmission corridor resources have indispensably promoted the development of AC/DC hybrid transmission lines on the same tower under special situations, especially for ultra-high voltage systems being established in China. A hybrid tower model incorporating a double-circuit AC transmission and a bipolar DC transmission is proposed in the study. The lightning performance of AC/DC hybrid transmission lines is investigated based on electro-magnetic transient program (EMTP) and leader progression model, taking into account the operating voltage of transmission lines as well as the competition of multiple upward leaders. The impact of tower's height, footing resistance, arrangements of ground wires and ground obliquity on lightning protection performance is also analysed. In accordance with the ± 800 kV bipolar DC and the 500 kV double-circuit AC transmission lines on the same tower, the results show that the back flashover and the shielding failure is relatively serious for a 500 kV AC transmission line, which should be paid more attention to. Finally, several methods that may be used to improve lightning protection performance of the AC/DC hybrid transmission lines are presented, such as reducing the tower's height, using a negative protection angle and installing additional ground wires. View full abstract»

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  • Maximum loadability of droop regulated microgrids - formulation and analysis

    Page(s): 175 - 182
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (444 KB)  

    This study extends the methodologies presented in other study concerned with the modelling and stability analysis of autonomous microgrids. It elaborates on a continuation method for finding the equilibria states through the entire loading range of an autonomous microgrid. The continuation method is based on the conventional continuation power flow (CPF) employed in the analysis of large power systems. However, the dissimilarities between conventional, simplified models of large power systems employed in CPF and those of detailed dynamics employed in microgrids make it necessary to reinterpret the CPF methodology. The methodology followed employs modelling procedures of microgrids previously published so as to build the Jacobians required by the predictor step. The procedure is quite expeditious, speeding up the solutions. The study also discusses revisions conducted on the CPF to warrant convergence of the corrector step to the particular case of islanded microgrids. View full abstract»

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  • Dynamic fault locator for three-terminal transmission lines for phasor measurement units

    Page(s): 183 - 191
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (560 KB)  

    The study presents a fault locator for three-terminal transmission lines under dynamic conditions such as power oscillation based on synchronised phasor measurement units. This approach based on conventional static fault locator can express the dynamic characteristics of supplied signals and consider them as time-variant signals whose magnitude and frequency are changing against time. Therefore the authors can apply its ability of describing dynamic characteristics to three-terminal transmission lines and get the dynamic parameters of transmission lines under the dynamic conditions. By using Newton iteration, the proposed dynamic fault locator can acquire the three-terminal fault-location indices to identify a fault section and estimate the distance to fault. The performance of the proposed method is evaluated by Power Systems Computer Aided Design/Electromagnetic Transients including DC (PSCAD/EMTDC)-generated signals under various situations. An extensive set of simulation results show that the distinctive features of this method are that it performs with better accuracy than the conventional method for all types of faults at different fault locations and is practically immune to fault resistance. View full abstract»

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  • Reliability evaluation of restructured power systems using a novel optimal power-flow-based approach

    Page(s): 192 - 199
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (372 KB)  

    Power system planning and operation has been considerably affected by restructuring of power systems and high penetration of renewable energy resources. In the new environment, customers are at the centre of attention and their concerns need to be addressed properly. The conventional techniques are not usually able to address both segregation of power system components and uncertainty of renewable energy resources. A novel technique is proposed in this study to determine load point reliability in restructured power systems considering the effect of renewable generators. This technique is based on modified optimal power flow and represents generation and transmission system with their equivalent multistate models and investigates the effect of each one on the load point reliability, separately. Furthermore, this approach remarkably relieves the reliability evaluation process, especially when loads and generations are subject to changes in the power system. The proposed method can assist the planners in reaching an optimal load allocation plan by providing valuable information. The proposed approach is applied to the Roy Billinton test system to illustrate the applications and advantages of the new approach. View full abstract»

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  • Adaptive neuro-fuzzy controller for static VAR compensator to damp out wind energy conversion system oscillation

    Page(s): 200 - 207
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (514 KB)  

    Wind shear and tower shadow produce a periodic pulse reduction in mechanical torque captured from wind energy resulting in wind energy conversion system (WECS) active power oscillations. In this study, an adaptive neuro-fuzzy controller for static VAR compensator, used in power networks integrated with WECS, is presented to address the torque oscillation problem. The proposed controller consists of a radial basis function neural network representing a third-order auto-regressive and moving average system model and performing the prediction, and a main controller with adaptive neuro-fuzzy inference system providing the damping signal. A modified two-area four-machine power network with WECS integration is applied to validate the proposed implementation, compared with conventional lead/lag compensation. Time-domain simulations prove that the proposed controller can provide a damping signal to improve the active power oscillation and system dynamic stability, influenced by torque oscillations under WECSs synchronised operating condition. 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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