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Generation, Transmission & Distribution, IET

Issue 2 • Date February 2014

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Displaying Results 1 - 16 of 16
  • Probabilistic evaluation of failure risk of transmission line surge arresters caused by lightning flash

    Page(s): 193 - 202
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (565 KB)  

    Transmission line surge arresters (TLAs) are vital elements for protection of power networks against the lightning surges. The proper selection of TLAs leads to a reduction of the lightning-related outages as well as the costs imposed to the power utility, because of the undelivered energy and damage to the equipment. The selection of the optimal arrester depends on how well its stresses can be estimated. Although a ground flash very frequently consists of multiple strokes, it is usual to consider only a single lightning stroke to calculate the lightning-related failures. A probabilistic method is presented for risk calculation that considers multiple strokes of each lightning flash to estimate the annual outage rate of TLAs. In the presented method, once the equivalent wave of the flash is computed, the probability of arrester failure is estimated by means of two indices, including total charge and maximum energy stress by the flash, separately. The energy stress caused by the flash is calculated using a few electromagnetic transient program (EMTP) simulations. Then, the obtained results from EMTP simulation are utilised to estimate the probability of failure. The accurate evaluation of failure probability of arresters permits the power utility to select the optimal arresters, considering a desirable average life. View full abstract»

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  • Primary control level of parallel distributed energy resources converters in system of multiple interconnected autonomous microgrids within self-healing networks

    Page(s): 203 - 222
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (2041 KB)  

    To minimise the number of load sheddings in a microgrid (MG) during autonomous operation, islanded neighbour MGs can be interconnected if they are on a self-healing network and an extra generation capacity is available in the distributed energy resources (DER) of one of the MGs. In this way, the total load in the system of interconnected MGs can be shared by all the DERs within those MGs. However, for this purpose, carefully designed self-healing and supply restoration control algorithm, protection systems and communication infrastructure are required at the network and MG levels. In this study, first, a hierarchical control structure is discussed for interconnecting the neighbour autonomous MGs where the introduced primary control level is the main focus of this study. Through the developed primary control level, this study demonstrates how the parallel DERs in the system of multiple interconnected autonomous MGs can properly share the load of the system. This controller is designed such that the converter-interfaced DERs operate in a voltage-controlled mode following a decentralised power sharing algorithm based on droop control. DER converters are controlled based on a per-phase technique instead of a conventional direct-quadratic transformation technique. In addition, linear quadratic regulator-based state feedback controllers, which are more stable than conventional proportional integrator controllers, are utilised to prevent instability and weak dynamic performances of the DERs when autonomous MGs are interconnected. The efficacy of the primary control level of the DERs in the system of multiple interconnected autonomous MGs is validated through the PSCAD/EMTDC simulations considering detailed dynamic models of DERs and converters. View full abstract»

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  • Capacitor allocations in radial distribution networks using cuckoo search algorithm

    Page(s): 223 - 232
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (754 KB)  

    In the present work, a cuckoo search optimisation-based approach has been developed to allocate static shunt capacitors along radial distribution networks. The objective function is adopted to minify the system operating cost at different loading conditions and to improve the system voltage profile. In addition to find the optimal location and values of the fixed and switched capacitors in distribution networks with different loading levels using the proposed algorithm. Higher potential buses for capacitor placement are initially identified using power loss index. However, that method has proven less than satisfactory as power loss indices may not always indicate the appropriate placement. At that moment, the proposed approach identifies optimal sizing and placement and takes the final decision for optimum location within the number of buses nominated with minimum number of effective locations and with lesser injected VArs. The overall accuracy and reliability of the approach have been validated and tested on radial distribution systems with differing topologies and of varying sizes and complexities. The results shown by the proposed approach have been found to outperform the results of existing heuristic algorithms found in the literature for the given problem. View full abstract»

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  • Analysing the effects of different types of FACTS devices on the steady-state performance of the Hydro-Qu??bec network

    Page(s): 233 - 249
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (2087 KB)  

    Hydro-Québec's electrical transmission system is an extensive, international grid located in Québec, Canada with extensions into the northeastern United States of America. For large power systems such as this, one of the major issues is to maintain the steady-state performance of the network. From this point of view, flexible AC transmission system (FACTS) devices could be effective tools to improve power system security by reducing the power flow on overloaded lines, which in turn would result in an increased loadability of the power system, reduced transmission line losses, improved stability and security and, ultimately, a more energy-efficient transmission system. Therefore in this study, the authors will present the effects of different types of FACTS devices on the performance of Hydro-Québec's power system. The optimal locations and rating of these FACTS controllers will be determined with a view to improving network security using an optimisation algorithm based on a genetic algorithm. The effects of six different FACTS devices including static VAR compensator (SVC), thyristor-controlled series capacitor (TCSC), thyristor-controlled voltage regulator (TCVR), thyristor-controlled phase-shifting transformer (TCPST), unified power flow controller (UPFC) and static synchronous compensator (STATCOM) with energy storage are compared. Using the presented results, the effects of different types of FACTS devices on the Hydro-Québec network will be analysed and compared with those of a STATCOM equipped with energy storage from the viewpoints of static loadability and losses. View full abstract»

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  • Analytical estimation of short circuit axial and radial forces on power transformers windings

    Page(s): 250 - 260
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1033 KB)  

    In this study, an analytical method is proposed to calculate exerted axial and radial forces on the high and low voltage (LV) windings in core type power transformers. Hence, an analytical modelling approach is proposed to compute short circuit currents in the transient mode and steady state. The proposed model includes non-linear characteristics of the core materials, eddy currents effects, symmetrical and asymmetrical hysteresis loops of the used laminates. Then, exerted axial and radial forces on the high and LV windings are analytically computed in the transient mode and steady state. In order to certify obtained analytical results, the two-dimensional (2D) time stepping finite element method (TSFEM) is utilised to determine aforementioned forces. In this modelling approach, the geometrical, electrical and magnetic characteristics of the core type transformer under short circuit fault are taken into account. Furthermore, three-dimensional TSFEM is employed to verify the analytical and 2D TSFEMs results. View full abstract»

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  • Optimal power flow algorithm and analysis in distribution system considering distributed generation

    Page(s): 261 - 272
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (760 KB)  

    This study investigates the optimal power flow (OPF) problem for distribution networks with the integration of distributed generation (DG). By considering the objectives of minimal line loss, minimal voltage deviation and maximum DG active power output, the proposed OPF formulation is a multi-object optimisation problem. Through normalisation of each objective function, the multi-objective optimisation is transformed to single-objective optimisation. To solve such a non-convex problem, the trust-region sequential quadratic programming (TRSQP) method is proposed, which iteratively approximates the OPF by a quadratic programming with the trust-region guidance. The TRSQP utilises the sensitivity analysis to approximate all the constraints with linear ones, which will reduce the optimisation scale. Active set method is utilised in TRSQP to solve quadratic programming sub-problem. Numerical tests on IEEE 33-, PG&E 69- and actual 292-, 588-, 1180-bus systems show the applicability of the proposed method, and comparisons with the primal-dual interior point method and sequential linear programming method are provided. The initialisation and convergence condition of the proposed method are also discussed. The computational result indicates that the proposed algorithm for DG control optimisation in distribution system is feasible and effective. View full abstract»

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  • Fault line detection in neutral point ineffectively grounding power system based on phase-locked loop

    Page(s): 273 - 280
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (719 KB)  

    Fault line detection timely and accurately when single-phase-to-earth fault occurs in neutral point ineffectively grounding power system is still a focus of research. To perfect these existing detection methods and enhance their accuracy, an improved phase-locked loop (IPLL) is used to extract the fifth harmonic zero-sequence currents in this study and fifth harmonic current characteristics are employed to select the fault line. Through relative processing, the fifth harmonic data differences of all lines are more noticeable, which is better for fault line detection. The line-detection function of IPLL is shown based on Matlab/Simulink. Simulation result reveals the good performance of this proposed method in effectively fault line detection. This method is able to detect different types of grounding faults in power system. This study gives a new train of thought for fault line detection. View full abstract»

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  • Strategic placement of distribution network operator owned wind turbines by using market-based optimal power flow

    Page(s): 281 - 289
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (475 KB)  

    In this study, a new methodology to optimally allocate wind turbines (WTs) in distribution networks is proposed. A market-based optimal power flow is used to determine the optimal numbers and capacities of WTs in a way that maximises the social welfare. The method is conceived for distribution network operators to strategically allocate WTs in distribution networks. The proposed method by yielding location-specific WTs capacity settlement both in terms of cost reduction and consumers' benefits is consistent with distribution network topology and constraints. The method is solved by using step-controlled primal dual interior point method considering network constraints. The effectiveness of the proposed method is demonstrated with two radial distribution systems including an 84-bus 11.4 kV and a 69-bus 11 kV network. View full abstract»

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  • Frequency/voltage wide-area measurements over transmission control protocol/internet protocol communication network for generator trip identification concerning missed data

    Page(s): 290 - 300
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1324 KB)  

    Wide-area frequency/voltage measurements are used to observe and record changes in power system operating conditions. This study introduces an application of the frequency/voltage (F/V) wide-area measurements for identifying the generator trips. These measurements are received from the frequency disturbance recorders (FDRs). The FDRs transmit their measurements over the transmission control protocol/internet protocol-based communication network to the data concentrator server (DCS) hosted at Helwan University. The transmitted data from FDRs to the DCS using IP protocol cannot guarantee the quality of service while it provides the best effort delivery for data packets. Missed data at the DCS are expected as a result of number of factors including packet drop because of network congestion, buffer overflow at the source or destination, corrupted packets rejected in-transit or faulty networking hardware. The study introduces a new technique to compensate the missed data using principal component analysis in order to determine a specific signature and properties for each generator trip in the power system network. These signatures are compared with recorded signatures using minimum distance classification to determine a probable match. The real-time measurements collected at DCS showed that some data are missed because of the previously mentioned factors. View full abstract»

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  • Advanced DC zonal marine power system protection

    Page(s): 301 - 309
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (778 KB)  

    A new active impedance estimation based protection strategy which is suitable for utilisation in a DC zonal marine power distribution system is presented. This method uses two triangular current `spikes' injections for system impedance estimation and protection when faults are detected. By comparing the estimated impedance with the pre-calibrated value, the fault location can be predicted and fault can be isolated without requiring communication between two injection units. Using co-ordinated double injections and line current measurement (directional fault detection), faults in the system with same impedance and different fault positions can be distinguished, located and isolated. The proposed method is validated using experimental test results derived from a 30 kW, 400 V, twin bus DC marine power system demonstrator. The experimental tests were applied to both faults during normal operation and faults that occur during system restoration. View full abstract»

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  • Time-frequency transform-based differential scheme for microgrid protection

    Page(s): 310 - 320
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (937 KB)  

    The study presents a differential scheme for microgrid protection using time-frequency transform such as S-transform. Initially, the current at the respective buses are retrieved and processed through S-transform to generate time-frequency contours. Spectral energy content of the time-frequency contours of the fault current signals are calculated and differential energy is computed to register the fault patterns in the microgrid at grid-connected and islanded mode. The proposed scheme is tested for different shunt faults (symmetrical and unsymmetrical) and high-impedance faults in the microgrid with radial and loop structure. It is observed that a set threshold on the differential energy can issue the tripping signal for effective protection measure within four cycles from the fault inception. The results based on extensive study indicate that the differential energy-based protection scheme can reliably protect the microgrid against different fault situations and thus, is a potential candidate for wide area protection. View full abstract»

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  • Laboratory simulation of naturally polluted high-voltage transmission line insulators

    Page(s): 321 - 327
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (512 KB)  

    This study represents experimental techniques for testing the high-voltage polluted insulators under conditions simulating the natural environment. International Electrotechnical Commission (IEC) fog method is used for testing the insulators of type π-φ-E4.5, but it does not simulate the desert pollution environments. For that reason, other two suggested techniques are added to explain the performance of the polluted insulators under dew and under simultaneous fog and dew, respectively. The leakage current bursts are recorded in each test type. Also the effect of the wetting method of the insulators under testing on the flashover voltage is investigated. The results of the three types of tests are compared with each other, under different surface layer conductivities. It is concluded that the analysis of leakage current bursts can be used to monitor the severity of pollution on the electrical network. View full abstract»

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  • Reduction of low-frequency harmonics in modular multilevel converters (MMCs) by harmonic function analysis

    Page(s): 328 - 338
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (773 KB)  

    Modular multilevel converter (MMC) is troubled by the inherent second harmonic of single-phase ac power. By adding feedforward to the modulation signal, low-frequency harmonic voltages are significantly reduced thus overcoming an important weakness of MMC. Capacitors of sub-modules do not have to be over-sized. If desired for protection, transformers can be wye-connected with grounded neutral. The reduction method is based on harmonic function analysis. In addition to deriving algebraic formulae of harmonic voltage components of `open loop' control, this study makes original contributions by deriving formulae which include feedforward control. Analytical insights from the formulae have shown the way to design feedforward methods to reduce low-frequency harmonics. Validation is by simulations using SIMULINK/MATLAB. View full abstract»

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  • Damping of low-inertia machine oscillations using Takagi-Sugeno fuzzy stabiliser tuned by genetic algorithm optimisation to improve system stability

    Page(s): 339 - 352
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (909 KB)  

    The implementation of distributed generation (DG) in a power network may introduce undesirable transients or network oscillations in power networks due to low or no inertia. These undesirable transients and oscillations may be dampened through the use of power system stabiliser (PSS), if properly designed. In this study, an intelligent PSS comprising of Takagi-Sugeno (TS) fuzzy-logic control and genetic algorithm optimisation is proposed to effectively dampen these oscillations. Eigenstudy and participation factor analysis have been carried out to determine critical issues relating to angle instability such that the intelligent PSS can be designed accordingly. The proposed fuzzy-logic stabiliser is tested on an Australian power network using network data provided by an industry participant. To demonstrate the effectiveness of the proposed fuzzy-logic PSS, a number of disturbances have been simulated and the response of the interconnected DG units of rotary type is assessed in terms of rotor angle and rotor speed. The results demonstrate that the proposed fuzzy-logic controller substantially improves the performance of the network transients with DG by effectively damping local oscillations in the machine rotor angle and machine rotor speed. View full abstract»

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  • Power signal disturbance identification and classification using a modified frequency slice wavelet transform

    Page(s): 353 - 362
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1062 KB)  

    This study presents a novel approach to localise, detect and classify non-stationary power signal disturbances using a modified frequency slice wavelet transform (MFSWT). MFSWT is an extension of frequency slice wavelet transform (FSWT), which provides frequency-dependant resolution with additional window parameters for better localisation of the spectral characteristics. An advantage of the MFSWT is attributed to the fact that the modulating sinusoids are fixed with respect to the time axis, whereas a localising scalable modified Gaussian window dilates and translates. Several practical power signals are considered for visual analysis using MFSWT, and the disturbance patterns are appropriately localised with unique signature corresponding to each type. This work also evaluates the detection capability of the proposed methodology and a comparison with earlier FSWT and Hilbert transform to show the superiority of proposed technique in detecting the power quality disturbances. A probabilistic neural network (PNN) based classifier is used for identifying the various disturbance classes. The spread parameter of the Gaussian activation function in PNN is tuned and its effect on the classification at different strengths of noise is studied. View full abstract»

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  • Study on the effect of artificial radiation simulating terrestrial solar ultraviolet radiation on negative DC discharge performance of air gap

    Page(s): 363 - 372
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (650 KB)  

    It is important to reveal the effect of terrestrial solar ultraviolet radiation (TSUVR) on discharge performance of external insulation for the design and operation of a power system in regions with strong TSUVR, especially in Tibet. However, no research was carried out in this field until now. In this study, an artificial UV lamp was used to imitate TSUVR in the relevant experiments to research on the effect of negative DC discharge. It was found that artificial radiation simulating terrestrial solar UV radiation (STSUVR) does not affect appreciably the negative DC corona characteristics and breakdown voltage of short rod-plane air gaps of several electrode materials. That is because the wavelength of the STSUVR is in the range of 290-400 nm, and its intensity is less than 200 W/m2. Thus, air, Cu and Fe cannot be photoionised by STSUVR. There is also no effect of the STSUVR on arc propagation because of energy. Although a part of the photons in the TSUVR has higher energy than the work function of Al, it is very easy for the Al to be oxidised, and the oxide film (Al2O3) can prevent Al from being ionised by TSUVR. Therefore the TSUVR does not have an obvious effect on negative DC discharge performance of air gap. View full abstract»

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