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The voltage sag performance of a distribution system has been investigated. A Monte-Carlo procedure has been used to construct the sag density table and estimate the number of unacceptable sags per annum at a sensitive load bus. The subtransmission lines and distribution feeders that largely contribute to the unacceptable sags have been identified. It has been shown that proper protective relay coordination and adequate maintenance of the critical lines and feeders result in significant improvement of the voltage sag performance of the distribution system.Index Terms-Monte-Carlo method, power quality, voltage sags.

A method has been presented for the allocation of responsibilities between a utility and a consumer with reference to the distortion of 3-phase voltage waveforms at the point of common coupling. The input data required for applying this method are the measured voltage and current waveforms at the point of common coupling. The frequencies in the measured waveforms are estimated and a Kalman filter is used to estimate the phasors at these frequencies. Subsequently, the parameters of the electrical system of the industrial load have been estimated using the recursive least-squares technique. With these estimated data, the individual contributions to the distortion of the 3-phase voltage waveforms have been calculated. The proposed method has been illustrated by means ofa practical example.

The voltage sag performance of a distribution system has been investigated. A Monte Carlo procedure has been used to construct the sag density table and estimate the number of unacceptable sags per annum at a sensitive load bus. The sub transmission lines and distribution feeders that largely contribute to the unacceptable sags have been identified. It has been shown that proper protective relay coordination and adequate maintenance of the critical lines and feeders result in significant improvement of the voltage sag performance of the distribution system. Index Terms--voltage sags, power quality, Monte Carlo method.

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