単独運転領域における柱上変圧器の磁気特性の推定

概要

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For the detection of islanding, it is very important to choose the threshold value of harmonic voltage change. In this paper, we propose an analytical model of the pole transformer using a Fourier series, and will clarify the nonlinear magnetizing characteristics of the pole transformer in islanding area. After determining the proposed model coefficients from the tests of the pole transformer excited by sinusoidal voltage, the distorted wave voltage tests were performed under the condition that the third harmonic voltage or the fifth harmonic voltage was superimposed. The results of the testing showed that the magnetic properties vary greatly upon increasing the harmonic component of the voltage. The analysis and measurement results were in good agreement. By using the proposed method, the distributed generators (DGs) can estimate the magnetizing characteristics of the pole transformer by monitoring the connected terminal voltage. So, as the active signal for islanding detection, DGs can inject the harmonic current synchronized to exciting current harmonics of the pole transformer into the distribution network. In the case of the DGs equipped with the above functions, there is no need to change the settings about the islanding detection threshold of harmonic voltage change, even when there is an excitation voltage change or an increase in the number of DGs.