Implementation of a New Method for an Improved Voltage Dips Evaluation by the Italian Power Quality Monitoring System in Presence of VT Saturation Effects

Abstract

The paper deals with a recent measurement improvement introduced into the Italian power quality monitoring system, concerning voltage dips detection and their proper evaluation in the presence of voltage transformer VT saturation phenomena. Saturation effects, essentially on network operated with isolated neutral, can give origin to “false” voltage dips, which can affect the on-line voltage monitoring during a few specific events (i.e. single line-to-ground faults). The “false dip” problem, on the other hand, can be considered negligible in compensated neutral networks. A new criterion has been developed in cooperation with the Polytechnic of Turin, based on the detection of a second harmonic component in the measured voltages, which, once provided with the proper setting parameters, can succeed in identifying “false” dips. The criterion effectiveness has been evaluated on field. The major advantage of the filter implementation in the monitoring system is that, from now on, network operated with isolated neutral could be considered quite similar to those operated with neutral compensation from the point of view of voltage dip performance.