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Electric Power Applications, IET

Issue 1 • Date January 2009

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Displaying Results 1 - 8 of 8
  • Algorithm to identify the excitation inductance of power transformer with wye-delta connection

    Publication Year: 2009 , Page(s): 1 - 7
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (591 KB)  

    An algorithm to identify the excitation inductances of three-phase power transformer with wye-delta connection is proposed. Existing methods of determining the excitation inductances of three-phase transformers require that all winding currents to be known, making them impractical on some wye-delta transformers where the delta winding currents are not measured. Based on the transformer equivalent circuit, the proposed algorithm eliminates the influence of the delta circulating current, allowing the excitation inductances to be calculated using the line currents of the delta connection side directly. The algorithm's accuracy has been verified by electromagnetic transients program including direct current (EMTDC) simulations, which show that the proposed algorithm is able to differentiate accurately and sensitively between transformer inrush and fault conditions. This lends itself to applications in the area of transformer protection. View full abstract»

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  • Model reference adaptive control-based adaptive current control scheme of a PM synchronous motor with an improved servo performance

    Publication Year: 2009 , Page(s): 8 - 18
    Cited by:  Papers (6)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (752 KB)  

    A model reference adaptive control (MRAC)-based current control scheme of a PM synchronous motor with an improved servo performance is presented. Although the predictive current control is known to give ideal transient and steady-state responses among various PWM inverter-fed current control schemes for a PM synchronous motor, its steady-state response may be degraded under the motor parameter variations. To overcome such a limitation, the disturbances caused by the parameter variations will be estimated using an MRAC technique and compensated by a feedforward manner. Thus, the steady-state control performance can be effectively improved, while retaining its good dynamic performance. The proposed control scheme does not require the measurement of the phase voltage unlike the conventional disturbance estimation scheme using observer. This can be an effective way considering the phase voltage contains much harmonics as well as noise. The asymptotic stability of the overall system is proved and the adaptation laws are derived by the Lyapunov stability theory. The proposed scheme is implemented using DSP TMS320C31 and the effectiveness is verified through the comparative simulations and experiments. View full abstract»

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  • Three-phase transformer modelling for unbalanced conditions Part II: general formulation

    Publication Year: 2009 , Page(s): 19 - 39
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (992 KB)  

    Part I of this two-part paper proposed a model for two-winding three-phase transformers under steady-state unbalanced conditions. Although the model is very simple (it only uses two parameters), it is valid for different core designs (three-legged, five-legged and triplex). The nodal equations for four examples are developed step by step in Part I. In part II, phase and sequence nodal equations are systematically obtained for all possible phase shifts and all winding connections, including the isolated wyes and the impedance grounded wyes on one or both transformer sides. The proposed model encompasses the usual model in the literature. The formulation has been tested with the IEEE 4 node test feeder. Three numerical application examples illustrate that the model provides accurate results (compared with the results of a non-linear model) if the transformer is not highly saturated. View full abstract»

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  • New sensorless commutation technique for brushless DC motors

    Publication Year: 2009 , Page(s): 40 - 49
    Cited by:  Papers (5)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (409 KB)  

    In brushless DC (BLDC) drives commutation is performed by power electronic devices forming part of an inverter bridge. Switching of the power electronic devices has to be synchronised with rotor position. Determination of position, with or without sensors is an essential requirement. The most common sensorless method is based on detection of the zero crossings of back EMF signals. This technique works only above a certain speed. BLDC systems which rely solely on back EMF signals for commutation suffer from relatively poor starting performance characterised by back rotation of up to one hundred and eighty electrical degrees and fluctuations in electromagnetic torque. The aim of this project has been to investigate the possibility of a sensorless technique which is cost effective but with a performance at start-up comparable with that obtained when Hall sensors are used. Initial investigations led to a saliency based method. Theoretical analysis is presented which shows that the method is insensitive to variations in operational parameters such as load current and speed or circuit parameters such as power device voltage drops and winding resistances. Also a starting strategy, relying on saliency related measurements, is proposed which offers starting performance as good as Hall sensor based techniques. View full abstract»

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  • Effects of pulse-width-modulated supply voltage on eddy currents in the form-wound stator winding of a cage induction motor

    Publication Year: 2009 , Page(s): 50 - 58
    Cited by:  Papers (9)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (611 KB)  

    The eddy currents of a form-wound multi-conductor stator winding because of the non-sinusoidal supply voltage in a cage induction motor are studied. The time and space dependence of the field, circuit variables and the motion of the rotor are modelled with the time-discretised finite-element analysis. A pulse-width-modulated voltage is used to supply the motor. The eddy-current loss distribution of the stator bars and the total eddy-current losses are studied. The radial distance of the stator bars from the air gap is re-emphasised as a design parameter because of its effect on the losses and the hot spots. The means for minimising the losses and avoiding the local hot spots are studied. View full abstract»

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  • Heat transfer in power transformer windings with oil-forced cooling

    Publication Year: 2009 , Page(s): 59 - 66
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (485 KB)  

    Power transformer outages have a considerable economic impact on the operation of an electrical network. One of the most important parameters governing a transformer's life expectancy is the hot-spot temperature (HST) value. The classical approach has been to consider the HST as the sum of the ambient temperature, the top-oil temperature rise and the hot-spot-to-top-oil temperature gradient. Temperature distribution is solved using the heat conduction equation. Finite element method is used in the numerical solution. The transformer selected for simulation is 32 MVA transformer with non-directed oil-forced cooling and directed oil-forced cooling. Comparing the results with those obtained from finite integral transform and experimental test checks the validity and accuracy of the proposed method. View full abstract»

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  • Rotor position estimator for stator flux-oriented sensorless control of slip ring induction machine

    Publication Year: 2009 , Page(s): 67 - 76
    Cited by:  Papers (4)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (645 KB)  

    A rotor position estimation scheme for stator flux-oriented speed sensorless control of slip ring induction machine (SRIM) is presented in this paper. Position of the rotor is estimated by integrating the rotor back-electromotive force. The problem of DC drift during integration is eliminated using an error-decaying mechanism in the estimator. This estimation scheme reduces the propagation of noise in the sensed current to the estimated rotor side unit vectors. This scheme also eliminates the need for differentiating the unit vectors for estimating slip frequency. The proposed scheme is simulated and experimentally verified. View full abstract»

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  • Application of interval analysis and evidence theory to fault location

    Publication Year: 2009 , Page(s): 77 - 84
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (238 KB)  

    The technique of fast fault clearance for railway power transmission lines is an urgent and noticeable problem. According to the segmented structure characteristic of the lines, a novel fault location scheme based on the interval analysis and evidence theory is proposed. First, the interval model is addressed. The interval analysis is applied to deduce three interval algorithms, which implement interval location. Then, in terms of the characteristic of interval set, the difference matrix of deviation degree is used to represent quantitatively the degree of similarity between interval numbers, and construct an expression of basic probability assignment function. Finally, the evidence theory is introduced to combine the results of three interval algorithms and infer the fault segmented interval. The simulated results and practical application have effectively verified the accuracy and reliability of the proposed location scheme, which is suitable for all segmented structure lines. View full abstract»

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