• Journal of Electrical Engineering and Technology
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• v.1 no.3
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• pp.279-286
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• 2006

A method for estimating the instantaneous phasor of a fault current signal is proposed for high-speed distance protection that is immune to a DC-offset. The method uses a modified notch filter in order to eliminate the power frequency component from the fault current signal. Since the output of the modified notch filter is the delayed DC-offset, delay compensation results in the same waveform as the original DC-offset. Subtracting the obtained DC-offset from the fault current signal yields a sinusoidal waveform, which becomes the real part of the instantaneous phasor. The imaginary part of the instantaneous phasor is based on the first difference of the fault current signal. Since a DC-offset also appears in the first difference, the DC-offset is removed trom the first difference using the results of the delay compensation. The performance of the proposed method was evaluated for a-phase to ground faults on a 345kV 100km overhead transmission line. The Electromagnetic Transient Program was utilized to generate fault current signals for different fault locations and fault inception angles. The performance evaluation showed that the proposed method can estimate the instantaneous phasor of a fault current signal with high speed and high accuracy.

• Proceedings of the KIEE Conference
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• 1987.11a
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• pp.469-473
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• 1987

This paper presents a method to estimate p.d.f.(probability density function) of harmonic phasor voltage. Because the quantity of harmonics is not fixed, stochastic analysis of harmonics is needed. Because it is impossible to obtain p.d.f. of voltage from p.d.f. of current directly, the moments of voltage and current are used. Firstly, the moments of current is calculated from p.d.f. of current. Secondly, the moments of voltage are calculated from the moments of current using the linearity of the moments. Finally, p.d.f. of voltage is estimated from the moments of voltage using Gram-Charlier Type A Series. [1] The moments of the p.d.f. obtained by the series and of the true p.d.f. is same up to given finite moments. Because current and voltage of harmonics are represented as not instantaneous values but phasors, the estimated value can be compared with the measured value and harmonic phasor voltage can be analyzed when the p.d.f. of phase is nonuniform as well as uniform.

• Journal of the Korean Institute of Telematics and Electronics
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• v.13 no.4
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• pp.1-5
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• 1976

Spectrum의 시간기복을 나타내는 시간 및 주파수의 함수 F(w,t,T) 및 W(w,t,T)를 정의하였고, 실례에 적용시켰다. Fourier변환을 f(t)와 Phasor ejwt와의 Correlation으로 정의하였고 그 변환시분이 시간마다의 성분의 합계이어서 t 시각에서의 Spectrum을 그 근거에서의 f(t)값에만 의함을 증명하였다. Two new time functions defining Time Dependent Fourier Transform F(w,t,T) and Time Dependent Spectrum Density W(w,t,T) are deduced. courier transform is defined as the correlation between the time function f(t) and phasor ejwt. Several theorems corncerning the new functions are proved in order to verify the instantaneous cause a effet of the function f(t) and the nuctuating spectrum.

• Journal of Electrical Engineering and Technology
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• v.9 no.1
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• pp.6-14
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• 2014

A new method to determine the total harmonic contributions of several customers and the utility at the point of common coupling is presented. The proposed method can quantify the individual harmonic impact of each suspicious harmonic source at the point of common coupling. The individual harmonic impact index is then used to assess the total harmonic contribution of each harmonic source. This index can be calculated by the results processed from instantaneous harmonic voltage and current phasor values. The results demonstrate the performance of the proposed method in terms of steady-state accuracy and response to time-varying operating conditions. The proposed index can be used for billing purposes to control harmonic distortion levels in power systems.