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Generation, Transmission & Distribution, IET

Issue 1 • Date Jan. 2011

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Displaying Results 1 - 16 of 16
  • Evaluating opportunities for increasing power capacity of existing overhead line systems

    Publication Year: 2011 , Page(s): 1 - 10
    Cited by:  Papers (4)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1106 KB)  

    Re-tensioning and/or re-conductoring are considered the most popular cost-effective ways to increase the efficiency of power capacity of an existing aerial line. The identification of the most beneficial method requires ampacity and sag calculations to consider all the system factors that influence its performance. A holistic methodology for calculating conductor ampacity and sag at any temperature and power frequency when different conductors are implemented onto a pre-specified overhead line structure is used to illustrate how the properties of the conductors allow opportunities for thermal and voltage uprating on existing overhead line systems. This is achieved through a comparative analysis of the electrical and mechanical behaviour of conductors of different technologies and sizes on a 33 kV wood pole system. The analysis focuses on normal operating temperatures for novel conductors that can operate at elevated temperatures to avoid the increase in losses, and also allow the comparison with conventional conductors in order to identify potential benefits for the investigated overhead lines (OHL) system. View full abstract»

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  • New technique for computation of closest hopf bifurcation point using real-coded genetic algorithm

    Publication Year: 2011 , Page(s): 11 - 18
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (508 KB)  

    Hopf bifurcation in power systems leads to oscillatory instability, and it is desirable to operate the system with sufficiently large loading margin to Hopf bifurcation. A new technique to determine the shortest distance to Hopf bifurcation is developed. The problem of determining the closest Hopf bifurcation point is formulated as an optimisation problem and solved using real-coded genetic algorithm. The advantage of this method is that it is capable of handling various operational constraints and can determine the closest Hopf bifurcation point accurately even if the hypersurface is not smooth. The proposed approach has been applied on two-area and IEEE 14-bus test systems. The details of implementation and simulation results are presented. The effect of load modelling on closest Hopf bifurcation point is also investigated for various loading patterns. View full abstract»

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  • Humidity and contamination severity impact on the leakage currents of porcelain insulators

    Publication Year: 2011 , Page(s): 19 - 28
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (830 KB)  

    The leakage current is the most important information for monitoring the insulator contamination, and especially for forecasting the contamination flashovers. Since the contamination severity and the ambient humidity can both result in the increase of the leakage currents, it is crucial to distinguish the exact reason for the leakage current changes. Experiments, repeated many times, have shown that the normal range of the leakage currents is less than 50 mA at rated operating voltage. This normal range is called the security stage, and it occurs far ahead of the contamination flashover. The characteristics of the leakage currents at that stage have been investigated when changes in the ambient humidity or the contamination severity were introduced in an artificial fog chamber. A joint approach of fast Fourier transform amplitude and power spectrum amplitude estimation is used to analyse the leakage currents in combination with the leakage current waveform. The main purpose is to improve the pre-warning of contamination flashover at the security stage and to obtain more time for the cleaning or replacement of heavily polluted insulators. Fog chamber test results show that there are two frequency spectrum related characteristics. Both characteristics play an important role in the state evaluation of insulator surface, considering the ambient humidity and the contamination severity. The pre-warning thresholds of these two characteristics can be recognised in case of very severe contamination together with high relative humidity conditions. These thresholds are very helpful for pre-warning in advance before contamination flashovers. View full abstract»

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  • Unscented kalman filter for power system dynamic state estimation

    Publication Year: 2011 , Page(s): 29 - 37
    Cited by:  Papers (21)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (487 KB)  

    A new estimation method for power system dynamic state estimation, the unscented Kalman filter (UKF), is presented. It is based on the application of the unscented transformation (UT) combined with the Kalman filter theory. One of the challenges in the process of power system estimation is coping with a highly non-linear mathematical model of network equations, which is usually approximated through a linearisation. The new derivative free estimation method overcomes this limitation using the UT and achieves better accuracy with simpler implementation. The UKF is derived and demonstrated using three different test power systems under typical network and measurement conditions. Its performance is compared with the classical extended Kalman filter. The simplicity of the new estimator and its low computational demand make it a better option to be applied in the next generation of dynamic system estimators. View full abstract»

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  • Optimal design of low-voltage distribution networks for CO2 emission minimisation. Part I: model formulation and circuit continuous optimisation

    Publication Year: 2011 , Page(s): 38 - 46
    Cited by:  Papers (5)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (405 KB)  

    This study presents a novel model and relevant applications for optimal environmental design of distribution networks. The presentation of the concepts is divided into two papers, of which this paper represents Part I. The proposed methodology is based on a trade-off between emission embodied in the circuit and emissions related to operational losses. Hence, the CO2 emission minimisation problem is developed and analysed for a single circuit in terms of continuous optimisation, and is solved in closed form. This leads to establish a continuous optimal environmental capacity for distribution circuits, and allows identification of the key parameters involved in the analysis. Numerical applications for typical low-voltage (LV) cables used in the UK highlight some numerical aspects of the discussed design. Sensitivity analyses are also run in order to test the robustness of the results found, and to estimate how the design characteristics could change in the presence of different generation mixes. The analyses are completed in Part II, illustrating the application of the model to LV radial networks and relevant environmental and economic implications in comparison to alternative design strategies. View full abstract»

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  • Optimal design of low-voltage distribution networks for CO2 emission minimisation. Part II: Discrete optimisation of radial networks and comparison with alternative design strategies

    Publication Year: 2011 , Page(s): 47 - 56
    Cited by:  Papers (4)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (684 KB)  

    This study extends the model for optimal environmental design of distribution systems presented in Part I to network analyses. In particular, a specific algorithm is developed to apply the proposed circuit design for CO2 emission minimisation to radial networks, the great majority of low-voltage ones, taking into account the presence of only discrete capacities available for cable selection. The implementation of the network design algorithm is illustrated for a realistic large low-voltage urban network in a UK framework. The results found are compared to two benchmark networks designed according to a peak-based minimum investment strategy and an optimal economic strategy that minimises the network life-cycle cost. The specific emission reduction cost due to larger asset investment when applying an optimal environmental design strategy is then quantified with respect to the two alternative strategies. In addition, the results are checked against different discount rates that indicate the attitude of the network operator towards the cost of capital. The analyses illustrated provide clear-cut insights on the environmental and economic implications of adopting different design strategies (in particular, the optimal environmental one introduced here) and represent a key asset for network operators and policy makers in the path towards designing more sustainable energy systems. View full abstract»

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  • Kalman filtering based approach for light flicker evaluation of power systems

    Publication Year: 2011 , Page(s): 57 - 69
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1052 KB)  

    In this study, a Kalman filtering based approach is proposed to measure the light flicker of the electricity transmission systems. Analytical expressions of the instantaneous light flicker sensation are used to obtain a flicker estimation method based on the International Electrotechnical Commission (IEC) flickermeter. In the proposed method, the frequency domain components of the voltage waveform are obtained by Kalman filtering and these components are used to obtain the light flicker. The method is tested on both simulated data and field data obtained from three different electrical arc furnace (EAF) plants, where the flicker level is considerably high compared to other types of loads. The comparison of the results with the digital realisation of the IEC flickermeter shows that the method gives satisfactory estimations with low computational complexity. The method is especially useful for conditions such as disturbances and subsequent system transients where the system frequency deviates significantly. Since the frequency decomposition is obtained by using Kalman filtering, no leakage effect of the fast Fourier transform (FFT) method is involved in case of frequency deviations. View full abstract»

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  • Application of biogeography-based optimisation to solve different optimal power flow problems

    Publication Year: 2011 , Page(s): 70 - 80
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (279 KB)  

    This study presents a biogeography-based optimisation (BBO) algorithm to solve optimal power flow (OPF) problems of a power system with generators that may have either convex or non-convex fuel cost characteristics. Different operational constraints, such as generator capacity limits, power balance constraints, line flow and bus voltages limits and so on, have been considered. Settings of transformer tap ratio and reactive power compensating devices have also been included as the control variables in the problem formulation. Biogeography describes how a species arises, migrates from one habitat to another and eventually gets wiped out. The algorithm developed using this concept is known as BBO, which searches for the global optimum mainly through two steps: migration and mutation. BBO has been implemented for three different objectives that reflect fuel cost minimisation, voltage profile and voltage stability improvement with the OPF embedded on IEEE 30-bus system. The superiority of the proposed method over other methods has been demonstrated for these three different objectives. Considering the quality of the solution obtained by the proposed method seems to be a promising alternative approach for solving the OPF problems. View full abstract»

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  • Seeker optimisation algorithm: application to the solution of economic load dispatch problems

    Publication Year: 2011 , Page(s): 81 - 91
    Cited by:  Papers (4)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (304 KB)  

    This study presents a seeker optimisation algorithm (SOA) for the solution of the constrained economic load dispatch (ELD) problems in different power systems considering various non-linear characteristics of generators. In the SOA, the act of human searching capability and understanding are exploited for the purpose of optimisation. In this algorithm, the search direction is based on empirical gradient by evaluating the response to the position changes and the step length is based on uncertainty reasoning by using a simple fuzzy rule. A comparison of simulation results reveals the optimisation efficacy of the algorithm over the prevailing optimisation techniques for the solution of the multimodal, non-differentiable, highly non-linear and constrained ELD problems. View full abstract»

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  • Unbalanced distribution network fault analysis with hybrid compensation

    Publication Year: 2011 , Page(s): 92 - 100
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (505 KB)  

    Fault analysis with hybrid compensation for unbalanced distribution systems is proposed. The method employs the unbalanced three-phase model to analyse faults. Two matrices containing information of the topological characteristics of distribution networks were built along with the proposed hybrid-compensation method for analysis. Appropriate boundary conditions can be obtained for a fault to solve various types of single or simultaneous faults. The time-consuming lower upper (LU) decompositions, the Jacobian matrix or the Y admittance matrix, required in the traditional algorithms, are not needed in the new development. Test results show that the proposed method is efficient, easy to program, also with advantages of high speed, robustness, improved accuracy and lower memory requirements. View full abstract»

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  • Incorporating superconducting fault current limiters in the probabilistic evaluation of transient recovery voltage

    Publication Year: 2011 , Page(s): 101 - 107
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (560 KB)  

    A Monte Carlo based approach to evaluate the transient recovery voltages (TRVs) induced across circuit breaker poles during clearing faults on transmission lines equipped with a superconducting fault current limiter is presented here. In this context, investigations have been conducted on a sample power system model taking into consideration the uncertainty of several factors associated with the practical operation of a power system. Risk indices that reflect the likelihood that the TRV induced across a circuit breaker poles as well as its rate of rise exceed their design values are also presented. The EMTP-RV (Electro Magnetic Transients Program) was used in the simulation studies. View full abstract»

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  • Voltage enhancement in industrial distribution systems using narrow-band filters

    Publication Year: 2011 , Page(s): 108 - 118
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1092 KB)  

    This study presents a novel and efficient technique for extracting the most common voltage disturbances in distribution systems. The new technique depends on a new recursive implementation of the digital second-order narrow-band filters. The proposed extraction technique is accurate and simple. In addition, a generalised compensation strategy is developed and utilised for mitigating the most common voltage quality problems such as voltage harmonics, voltage unbalance, voltage sags, voltage swells and voltage flicker. The suggested technique and the mitigation results are validated by digital simulation results obtained from an industrial distribution system. Also, the experimental results are provided to prove the practicality of the proposed concepts. View full abstract»

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  • Evidence theory-based fake measurement identification and fault-tolerant protection in digital substations

    Publication Year: 2011 , Page(s): 119 - 126
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (616 KB)  

    Protective relay is designed to make a trip decision based on calculation of collected measurements, and thus, the quality of data plays an important role in ensuring the reliability of protective relay. However, abnormity of any part of the data acquisition system (DAS), especially cyber risk, may make the protection system receive fake measurements and misoperate. Besides those efforts spent on the reliability of DAS and cyber security, protective relay itself should be able to tolerate fake measurements and actively minimise the impacts associated with bad data. Based on evidence theory, this study proposes an approach taking advantage of abundant information in digital substations to identify fake measurements and avoid misoperation of protective relay. When protective relay is prone to misoperate after the analysis of fake measurements from several current transformers (CTs) or voltage transformers (VTs), measurements from other CTs/VTs are rapidly collected to indicate whether there is a real fault in the power system. In this way, misoperation because of fake measurements can be prevented and CTs/VTs providing bad data can also be identified. Simulation tests demonstrate the effectiveness of the proposed approach. View full abstract»

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  • Optimal voltage support mechanism in distribution networks

    Publication Year: 2011 , Page(s): 127 - 135
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (443 KB)  

    Optimal scheduling of voltage regulators (VRs), fixed and switched capacitors and voltage on customer side of transformer (VCT) along with the optimal allocation of VRs and capacitors are performed using a hybrid optimisation method based on discrete particle swarm optimisation and genetic algorithm. Direct optimisation of the tap position is not appropriate since in general the high voltage (HV) side voltage is not known. Therefore, the tap setting can be determined given the optimal VCT once the HV side voltage is known. The objective function is composed of the distribution line loss cost, the peak power loss cost and capacitors' and VRs' capital, operation and maintenance costs. The constraints are limits on bus voltage and feeder current along with VR taps. The bus voltage should be maintained within the standard level and the feeder current should not exceed the feeder-rated current. The taps are to adjust the output voltage of VRs between 90 and 110' of their input voltages. For validation of the proposed method, the 18-bus IEEE system is used. The results are compared with prior publications to illustrate the benefit of the employed technique. The results also show that the lowest cost planning for voltage profile will be achieved if a combination of capacitors, VRs and VCTs is considered. View full abstract»

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  • Unsymmetrical open-conductor analysis for unbalanced weakly meshed distribution systems

    Publication Year: 2011 , Page(s): 136 - 143
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (412 KB)  

    An efficient and effective unsymmetrical open-conductor analysis for unbalanced weakly meshed distribution systems is proposed in this study. Some efficient and accurate formulae used to analyse the effects of adding or removing branches on unbalanced weakly meshed distribution system are conducted. Unsymmetrical open-conductor analysis, such as the open of one phase or two phases of a three-phase branch, is then derived accordingly. Traditionally, unsymmetrical open conductors are analysed by the symmetrical-component-based methods, as are usually time consuming. The proposed method provides novel viewpoints in calculating the effects of unsymmetrical open conductors on unbalanced weakly meshed distribution systems. Test results demonstrate that the proposed method is systematic, efficient, accurate and easily programmable. View full abstract»

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  • Experimental studies on discharge initiation from an icicle tip under DC voltage

    Publication Year: 2011 , Page(s): 144 - 152
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (938 KB)  

    Electric discharge between the tip of an icicle and a plane electrode has been studied because of its relevance to the flashover of high voltage ice-covered insulators. Using an icicle/iced-plate system, the corona discharge at the icicle tip was investigated under DC voltage. The influence of different parameters such as gap distance, temperature and water conductivity on the corona inception voltage (Vinc) was examined and analysed. The corona discharge process was depicted and the influence of the corona discharge on the icicle tip was illustrated. A novel discharge characteristic under the icicle tip was found when T=-5°C according to under the metal electrode, which needs to be verified further. All results will improve our understanding on discharge activities under atmospheric icing and are available to find solutions to improve insulators characteristics. 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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