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Rapporto RSE 16001371

Analisi di perturbazioni sulla rete continentale a partire da misure di frequenza



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S. Canevese (RSE SpA), A. Gatti (RSE SpA), M. Rossi (RSE SpA)

GRID RESILIENCE 2015 - Security and vulnerabilities of the electrical system


Monitoring of electricity networks is a fundamental task to ensure that stability conditions and power quality requirements are met, both in normal operating conditions and in case of faults. One of the most effective indicators of the state for AC systems is of course the frequency, whose measurement plays a significant role in many critical applications and services (system protection schemes, power balancing, inertia control of energy resources, etc.). Frequency reflects the instantaneous balance of generated and absorbed power in AC systems. Large power balance disturbances can cause large and fast frequency deviations over the whole synchronously interconnected system, which, in the case of continental Italy, is the Continental European system. If such deviations are not suitably counteracted (by the frequency regulation actions carried out by generating plants, for instance), several risks for network stability and continuous operation arise, such as load shedding or generation shedding, line opening with grid separation into islands, blackouts.

A deep literature review of the frequency real-time estimation techniques that are currently adopted for power system monitoring is reported. The performance of the most effective methods is compared to the requirements for Phasor Measurement Units (PMUs) defined by IEEE Std C37.118.1 and it is also evaluated by applying them to real-field signals: voltage waveforms acquired in a primary substation, from the MV side of the power transformer, and measurements carried out on a derived LV network and GPS-synchronized with the former ones. Some of the currently adopted estimation techniques for the Rate Of Change Of Frequency (ROCOF) are also described. ROCOF evaluation is important for the “synthetic inertia” control functions by generators interfaced to the grid via electronic converters, such as PV and wind plants.

In the second part of the deliverable, a one-year-long frequency series, derived from one-phase measurements collected on the derived LV network, is considered. First, statistical analyses are carried out on this series. Then the ROCOF is computed and large plant outage events, causing significant ROCOF variations, are searched for. By comparison with data recorded in the ENTSO-E Transparency Platform, the analysis of these events allows an evaluation and discussion on the impact on frequency of large plant outage events.