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.