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Author: search.filters.author.Yutthagowith, PeerawutSubject: search.filters.subject.Curve fitting

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    A Simple Mathematical Expression for Nonlinear Resistive Characteristics of Metal Oxide Elements in Lightning Surge Analysis
    (2025-06-01)
    Yutthagowith, Peerawut
    ;
    Baba, Yoshihiro
    Accurate simulations of transient phenomena in electric power systems with metal oxide varistors (MOVs) or lightning arresters (LAs) using the finite-difference time-domain (FDTD) method for solving Maxwell's equations require simple and accurate representations of MOVs or LAs. By representing a small cell within a MOV or LA with resistivity (ρ) dependent on electric field (E), these components can be modeled in three dimensions and seamlessly integrated into FDTD simulations. Achieving computational efficiency in FDTD simulation necessitates avoiding iterative computations for ρ from E. Hence, there is a significant need for a simple and accurate mathematical expression of ρ in terms of E. This study presents a methodology for deriving a three-coefficient exponential function from experimental data. By using integration properties, this method transforms nonlinear characteristics into linear ones without iterative processes or uniform data sampling. It also incorporates data weighting and outlier discrimination for enhanced accuracy. Comparative analysis with previous methods based on the ordinary least squares method and experimental data, using an applied current with a rise time of approximately 8 μs, confirms high accuracy and effectiveness in computing residual voltages resulting from impulse current injection using the FDTD method.
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    An Effective Approximate Mathematical Expression for Non-Linear Resistance Characteristics of Metal Oxide Elements
    (2025-06-01)
    Yutthagowith, Peerawut
    ;
    Baba, Yoshihiro
    A metal oxide varistor (MOV), manufactured from a blend of zinc oxide and other metal oxides, undergoes changes in resistance or resistivity depending on changes in applied voltage or electric field strength. Typically, the nonlinear resistive characteristics of MOV elements are determined through experimental measurements of voltage and current. This article introduces a mathematical expression comprising two power functions and a constant term with five adjustable coefficients. It is utilized to describe the voltage-current or electric field-current density characteristics across a wide range of current or current density, spanning from microamperes to several tens of kiloamperes or from several hundred A/m<sup>2</sup> to a few hundred of kA/m<sup>2</sup>, respectively. This expression accurately reproduces the observed nonlinear resistive behaviors of several low-voltage MOV elements. A noniterative fitting method is developed to determine the expression’s five coefficients, using integration to linearize nonlinear characteristics without requiring iterations or uniform data sampling. Through comparison with a previously proposed expression and experimental data, the proposed technique demonstrates remarkably high accuracy. Furthermore, the proposed technique is applied to accurately estimate the parasitic inductance of an MOV and its lead wires during a residual voltage test conducted with an 8/20-microsecond impulse current.
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    Fast and Effective Technique in Evaluation of Lightning Impulse Voltage Parameters
    (2021-01-01)
    Yutthagowith, Peerawut
    ;
    Kitwattana, Krit
    ;
    Kunakorn, Anantawat
    This paper presents an approach for the waveform parameter evaluation of lightning impulse voltage in high voltage tests according to the IEC standards. Such waveform parameters are composed of peak voltage (U<inf>p</inf>), front time (T<inf>1</inf>), time to half (T<inf>2</inf>), and the overshoot rate (B<inf>e</inf>). An artificial neural network with a back-propagation learning algorithm was applied to determine a base curve and its parameters from 14 points along the recorded waveform between 20% of the peak voltage on the wave front part to 40% of the peak voltage on the wave tail part. The 29 waveforms recommended by the standard were used in the training process of the development of the network model, and some experimental cases were also utilized for verification of the proposed method. It is found that the waveform parameters evaluated by the proposed approach are in the tolerances of the standard requirements. Maximum absolute deviations of U<inf>p</inf>, T<inf>1</inf>, T<inf>2</inf>, and B<inf>e</inf> are 0.06%, 2.00%, 0.12%, and 0.79%, respectively. Due to that no iteration process in the proposed approach is required, the efficiency in calculation process is significantly faster than the standard recommended approach.
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    Fast curve fitting algorithm for parameter evaluation in lightning impulse test technique
    (2015-10-01)
    Pattanadech, Norasage
    ;
    Yutthagowith, Peerawut
    This paper proposes a fast curve fitting technique for the evaluation of the base curve of lightning impulse voltage and current. The proposed method is based on the waveform parameter estimation employing a numerical integration and linear least square method. This method is derived from an ordinary differential equation. The proposed algorithm is able to fit the base curve of lightning impulse voltage and current. The formula of the base curve is in the complex form of two exponential functions. The proposed form is superior to the conventional real exponential form, since it can be rewritten in a real conventional form used for fitting the impulse voltage or in a damped/undamped sinusoidal form with phase shift for fitting the impulse current. The decomposition base curve procedure was tested with some impulse voltage and current waveforms collected from the test data generator attached with IEC 61083- 2 (2013). The waveform parameters evaluated by the proposed method are compared with those recommended by the standards. The proposed method shows the better performance in computation time than the conventional method recommended by the standards. Due to no requirement of iteration in the proposed curve fitting method, the computation time is much shorter than the conventional iterative method. Moreover, the utilization of the established method does not allow the recorded impulse waveform distortion. Besides, the developed algorithm technique can be done easily with markedly accuracy and noise immunity. For the aforementioned reasons, there is no doubt that the proposed technique is a superior one for impulse parameter evaluation.