Fault distribution modeling using stochastic bivariate models for prediction of voltage sag in distribution systems

Abstract

This paper presents a new method on fault distribution modeling for stochastic prediction study of voltage sags in the distribution system. Two-dimensional stochastic models for fault modeling make it possible to obtain the fault performance for the whole system of interest, which helps obtaining not only sag performance at individual locations but also system sag performance through system indices of voltage sag. By using bivariate normal distribution for fault distribution modeling, the paper estimates the influence of model parameters on system voltage sag performance. The paper also develops the modified SARFI X regarding phase loads that creates better estimation for voltage sag performance for distribution system.Index Terms--distribution system, power quality, voltage sag frequency, stochastic prediction, fault distribution modeling, bivariate normal distribution, phase loads.

Prediction of voltage sag in the transmission system of Vietnam, A case study

“…Therefore, this work only considers faults that occur in the transmission system. According to [1], [3], [7], basing on the concept of "area of vulnerability", fault positions should be generally chosen in the manner that a fault position should be the representative for other nearby shortcircuit faults in a portion of network that cause voltage sags to load nodes with the similar characteristics (similar magnitudes). Voltage sag magnitude normally divides in 9 ranges : 0-0.1, 0.1-0.2,…, 0.8-0.9 p.u.…”

“…-Fault rate: The occurrence of short circuits depends on many factors [3] and the rates of occurrence of different faults (fault position, fault type) are normally not the same. However, because, in reality, recorded fault data does not consider detailed fault distribution, this work assumes that fault distribution for each fault type follows uniform model within each regions in Vietnam.…”

“…The permissible voltage tolerance for electric equipment, normally defined by the manufacturers and the well-known PQ curves for susceptibility of computer equipment displays are CBEMA, ITIC or SEMI [1] whereas power quality assessment of power supply system is utilities duty. This paper is the first effort to assess the voltage sag performance in the transmission system of Vietnam by using the method of stochastic prediction of voltage sags [1], [2], [3] using SARFI CURVE-X that is derived from SARFI X with regard to fault clearing time of protective devices currently used in the transmission system in Vietnam.…”