Effect of PQ-monitor connection on voltage dip indices: PN vs PP voltages

This work addresses the influence of the PQ-monitor connection on the estimation of voltage dip site and system indices. Voltage dip indices are estimated for a set of events obtained from simulation and measurement of voltage dips. The simulated dips are obtained applying the method of fault positions on a large transmission network and the measured dips come from a one-year survey realized on three buses of a sub-transmission and distribution network. The site and system indices estimated to compare phase-to-phase and phase-to-neutral dips are SARFI-90, SARFI-70, SARFI-ITIC, expected voltage dip amplitude (µ[VDA]), and the cumulative distribution frequency of voltage dip amplitude. These indices are estimated at the bus level and then they are aggregated to estimate the system performance. The comparison of phase-to-phase and phase-to-neutral indices indicates that, at high voltage level, phase-to-neutral dips are more frequent and more severe than phase-to-phase ones. However, these differences are damped at low voltage level, where the monitored bus presented similar indices for phase and line voltages. These observations must be taken in consideration to compare voltage dip benchmark because the lack of information about the type of the measured voltages may lead to derive inaccurate conclusions about the site and system performance regarding voltage dips.