The Italian system for Power Quality (PQ) monitoring of MV distribution networks described in the previous paper 0042 of the 19th International Conference on Electricity Distribution [1] has been working for almost 3 years on 600 instruments distributed all over the Italian territory. The paper illustrates the results of monitoring over the last three years and shows how the monitoring of events, (especially voltage dips) is going to consolidate the characterization of the Italian MV network from the PQ point of view.

No abstract

The aim of the work is to compare the advantages and disadvantages of two feasible methods of evaluation of voltage dips "origin" intended as the network where the "fault" has probably occurred. The first method, mainly based on the simultaneous monitoring of an event by nearby primary substations connected to a common high voltage network, has been extensively applied since 2009 to the QuEEN (Quality of the Electric Energy) monitoring system data, by RSE within its research activity. The second one requests the monitoring of both primary substation medium voltage bus-bars and has been proposed as a possible method for the new ongoing Italian national monitoring system, developed by the Italian DSOs, by a technical committee on National Monitoring. This method, which has been shared as a possible and feasible method by all the participants to the committee (DSOs, TSO, researchers and the Italian regulator), can be applied at a few QuEEN substations compliant with its requirements. The first method requires the knowledge of the high voltage network topology and, when applied at research level, requires time-expending visual analysis of voltage dips waveforms to compensate the lack of "confidential" information. The second method has lower effectiveness but, being a local method, can be applied also to networks including only one substation.

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.

The Italian MV networks voltage quality monitoring system has been collecting power quality data since 6 years by 600 instruments, 400 of which installed on HV/MV substations MV bus-bars and statistical representative of the network, the other 200 installed at some nodes of the MV lines [1]. The paper is focused on the analysis of voltage dips monitored at some of the 200 measuring points considered more significant. The aims were to confirm, on a wider scale, the representativeness of the statistics gathered on the HV/MV stations MV bus-bars with respect to that expected along the MV lines and to investigate the events way of propagation along different voltage levels. The analysis has been performed by both statistical methods on real data and DIgSILENT 1 simulations. The possibility to get the MV network voltage dip performance along the lines by measurements at HV/MV stations level has been widely confirmed. Measurements at MV lines have also confirmed the percentages of probable HV origin voltage dips, evaluated at national and macro area levels. The voltage dips duration distributions have shown a good accordance with the typical tripping times of the HV and MV protection system.