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Generation, Transmission & Distribution, IET

Issue 12 • Date December 2011

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Displaying Results 1 - 10 of 10
  • Development of an industrial non-linear robust power system stabiliser and its improved frequency-domain testing method

    Page(s): 1201 - 1210
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (735 KB)  

    The modern control methods, such as linear optimal control and non-linear control, for the generator excitation systems in state space have been dramatically developed during the past few decades. However, the lack of frequency-domain testing methods baffles the engineering applications of the modern controllers. In this study, a practical parameter configuration method as well as its frequency-domain testing method is proposed for the industrial non-linear robust power system stabiliser (industrial NR-PSS) for large synchronous generators. Furthermore, a two-machine, infinite-bus system is used to verify the effectiveness of the proposed method and the comprehensive performances of the industrial NR-PSS. A series of experiments are carried out on the real-time digital simulator to confirm its better performance comparing with the proportion integration differentiation (PID) controller and the conventional power system stabiliser (PSS). All the simulation and experimental results demonstrate that the industrial NR-PSS can improve system damping characteristic, enhance large disturbance stability and so has promising prospects in the applications to excitation systems. View full abstract»

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  • Control of static synchronous compensator with supplementary damping enhancement for wind farm voltage regulation

    Page(s): 1211 - 1220
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (954 KB)  

    This study presents a new control design approach for the wind farm voltage regulation using static synchronous compensator (STATCOM). A mode decoupling proportional plus integral (PI) controller, in which the control gains are synthesised by eigenstructure assignment (EA), is proposed for the STATCOM. EA is a state-space approach, which is used to improve system damping by eigenvalue assignment and alter system mode shape by eigenvector assignment. To embed the physical PI control loops in the state-space model, an equivalent transformation is proposed to map the feedback gain matrix to the PI controller. Owing to the presence of the physical PI control loops, the control signals would not mire into saturation when appropriate limiter according to the STATCOM capacity is placed in the control variables. To further alleviate the undesired oscillation mode excited by transient disturbance, a lead-lag-based supplementary damping controller (SDC) is adopted. Simulation comparisons are provided to show that the proposed technique can be an effective method for mitigating the voltage fluctuation in the wind farm because of the load changes and the wind gust. View full abstract»

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  • Subsynchronous resonance in single-cage self-excited-induction-generator-based wind farm connected to series-compensated lines

    Page(s): 1221 - 1232
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1073 KB)  

    Integration of large wind farms may get constrained owing to the available transfer capacity of existing transmission networks. This transmission capacity may be enhanced by incorporating series compensation. However, series capacitors are known to cause subsynchronous resonance (SSR) oscillations in synchronous generators. In this study, the potential of SSR is investigated with series-compensated lines connected to wind farms based on single-cage self-excited induction generators. A small-signal mathematical model is developed for the prediction of SSR oscillations in such a wind farm for a study system similar to the IEEE First SSR benchmark system. Eigenvalue analysis is performed through MATLAB at various operating points. This is validated by detailed time-domain simulation through electromagnetic transient simulation software EMTDC/PSCAD for a three-phase-to-ground (LLLG) fault at the remote end of the compensated line. An equivalent circuit analysis is performed to examine the impact of a similar fault at the terminals of the wind farm. It is shown from detailed non-linear simulation that even at a realistic level of series compensation a three-phase fault at generator terminals for low levels of wind farm power generation may subject the generator shafts to potentially dangerous magnitudes. View full abstract»

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  • Experimental investigation on steady-state and transient performance of a self-excited induction generator

    Page(s): 1233 - 1239
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (420 KB)  

    This study presents a novel approach to determine the steady-state performance of a self-excited induction generator (SEIG). The method gives an intuitive understanding of the effects of loading on the steady-state performance of the SEIG, without requiring any major mathematical effort. The steady-state no-load voltage of the SEIG is determined as the intersection between the generator no-load curve and the capacitor characteristics. The proposed method extends this approach to a loaded generator by replacing the no-load characteristic by a new generator-load curve. The method is initially applied in a lab environment, but a suitable algorithm to be used instead is also introduced. The algorithm has been validated through laboratory measurement showing an excellent agreement between theoretical and experimental results. Furthermore, an experimental investigation of the demagnetisation process of the SEIG is performed, showing how remanent flux depends on applied fault or load resistance. This analysis reveals some issues not previously reported in the literature. The relationship between remanent flux and speed at which self-excitation occurs is shown to contain a discontinuity, above which a fixed minimum speed is required for re-excitation given a certain capacitance. Below the discontinuity the minimum re-excitation speed is dependent on how the generator was demagnetised. View full abstract»

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  • Enhanced transmission line pilot impedance and pilot protection

    Page(s): 1240 - 1249
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (334 KB)  

    This study proposes a novel pilot protection for transmission lines by using enhanced transmission line pilot impedance (ETLPI). The ETLPI is defined by the ratio of the voltage difference of fault-superimposed component to the current summation of fault-superimposed component at both terminals of the protected line and used to distinguish the internal faults from the external faults. For the external fault, the amplitude of ETLPI is greater than the positive-sequence impedance of the protected line, whereas it is smaller than the positive-sequence impedance for the internal faults. The pilot protection scheme based on the ETLPI has the feature of avoiding the influence of line distributed capacitance and the saturation of current transformer (CT) as well as the transient response of coupling capacitor voltage transformers (CCVT). Therefore the pilot protection is suitable for different length transmission lines. Both theoretical analysis and test results obtained from EMTP digital simulation and the physical simulation have demonstrated that the pilot protection is of high reliability and good adaptability. View full abstract»

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  • Practical method for computing the maximum loading point using a load flow with step size optimisation

    Page(s): 1250 - 1258
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (427 KB)  

    A fast, practical maximum loading point (MLP) calculation method is proposed in this study. The calculation process is based both on the geometrical properties of the load parameter space feasibility boundary and a load flow method with step size optimisation. Moreover, a practical procedure is added to the overall calculation process to include the operator's information on the acceptable error in the final result. The basic process is characterised by obtaining consecutive approximations of the MLP within the infeasible region. In each step, a correction factor based on the maximum acceptable error in the final MLP is applied. Reactive power generation limits are taken into account. The MLP is accurately obtained after just a few iterations, demonstrating that the proposed method is very efficient. Simulation results for IEEE test and realistic systems are shown to validate the proposed method. View full abstract»

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  • Determinant-based feature extraction for fault detection and classification for power transmission lines

    Page(s): 1259 - 1267
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (533 KB)  

    This study proposes a novel fault feature extraction that could be used in fault detection and classification schemes for power system transmission lines, based on single-end measurements using time shift invariant property of a sinusoidal waveform. Various types of faults at different locations, fault resistance and fault inception angles on a 400 kV 361.65 km power system transmission line are investigated. The determinant function is used to extract distinctive fault features over various data window sizes namely, 1/4, 1/2 and a cycle of post-fault data. In addition, various delays were introduced before taking the post-fault measurements. The performance of the feature extraction scheme was tested on a machine intelligent platform WEKA by using three types of feature selection techniques: information gain, gain ratio and SVM. The result shows that, the determinant function defined over the phase current and neutral current is sufficient to classify ten types of short-circuit faults on doubly fed transmission lines; however, the scheme did not differentiate between 3 phase line faults (LLL) and 3 phase lines to ground faults (LLLG), the two types of faults are treated as the same type of fault, balanced fault. An accuracy between 95.95 and 100 is achieved. View full abstract»

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  • Assessing the proximity of time evolutions through dynamic time warping

    Page(s): 1268 - 1276
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (673 KB)  

    Comparing time-series is a frequent task in many scientific fields. In power systems, in particular, it may be of interest to compare the outputs of a simplified and a detailed model, or to validate the output of a model with respect to a measured time response. The classical Euclidean distance, involving pairs of points of the two data series aligned in time, is not suited to the practical time evolutions met in power systems, which often involve variable time delays and jumps at discrete times. In this study, an alternative measure of proximity, stemming from other scientific fields, is proposed for power system applications. It consists in warping the time axis to guarantee the best match between the two time-series, that is it maps points on two curves that are not aligned in time so as to minimise the sum of squared differences of their ordinates. Modifications and adaptations of the classical algorithm to better fit power system problems are discussed. The method is illustrated through three representative curve comparison problems. A multi-dimensional extension allowing system-wide measures of similarity is also proposed. View full abstract»

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  • Fast recursive Gauss-Newton adaptive filter for the estimation of power system frequency and harmonics in a noisy environment

    Page(s): 1277 - 1289
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (956 KB)  

    This study presents a new recursive Gauss-Newton method-based adaptive filter for estimating the time-varying amplitude, phase, and frequency of fundamental and harmonic components of power system voltage or current corrupted by noise. The coefficients of the adaptive filter are obtained from unconstrained optimisation of an error function weighted by a variable forgetting factor, and using suitable approximation of the recursive Gauss-Newton algorithm for reducing computational complexity. To improve the tracking speed and accuracy of the filter, the forgetting factor is tuned iteratively. This approach is very much suitable for a large variety of applications in the distributed generation control and protection, synchronised phasor measurement of voltage and current signals using phasor measurement units, power electronic converters etc. Several computational issues like the time-varying nature of the power system voltage and frequency parameters, noise and distortion, presence of decaying dc and inter-harmonics are considered to evaluate the fast operation and robustness of the proposed approach. View full abstract»

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  • High-speed superimposed-based protection of series-compensated transmission lines

    Page(s): 1290 - 1300
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (766 KB)  

    This study presents a sub-cycle power frequency-based fault direction discrimination and fault classification algorithm for the series-compensated transmission lines. Also, it provides an accurate estimation for the fault occurrence instant which is helpful in synchronised waveforms-based pilot protective schemes. The proposed algorithm is based on capturing the initial change in the voltage and current waveforms caused by occurrence of a fault. The high-frequency components of the fault signals are first filtered out, and then the signals are sampled at a relatively low sampling rate. Unlike the conventional relative-phase-angle-based directional relays, the proposed algorithm is not affected by the current and voltage inversion phenomena due to the presence of series capacitor in the fault loop. Extensive simulation studies are performed to evaluate the proposed algorithm performance. The obtained results show that the proposed algorithm provides a simple and a very fast and reliable protection technique for power transmission lines. This algorithm also covers non-compensated transmission lines and is able to well discriminate the fault direction even if the post-fault voltage amplitude becomes too small. It is also tested using some real data recorded from a high-voltage transmission 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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