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Article RSE 14001722

Flexible operation of combined cycles - new research and development incentives


L'Energia Elettrica, vol. 91 N.3, pp. 11-20, Maggio/Giugno-2014.

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M. Benini (RSE SpA) , G. Guagliardi (RSE SpA), A. Cammi (RSE SpA) , V. Casamassima (RSE SpA)

EVOLRETE 2014 - Evolution and planning of the national electric system

Criticality and impact on ancillary services caused by the increase in non-programmable renewable energy production.Combined cycles responsiveness and research contribution to enhance the flexibility of the operating plants.

In the last years, the utilization factor of the combined cycle plants has decreased dramatically, despite their high efficiency. This is an effect of the reduction of their competitiveness in the electricity market, as consequence of the strong increase in the share of production from not programmable renewable sources, which have dispatching priority, and the reduction in energy demand due to the economic crisis.

The decrease in the share of production from thermoelectric plants has the reduction in the regulation capacity of the grid primary frequency and the decrease in the inertia of the rotating masses (TG,TV) as consequence, This involves risks for safe operation of the grid during the frequency transients. A concrete example is the transient recorded on May, 18th 2011, in Sicily, during of which it has had to resort to load shedding to prevent a widespread black out. In this context, the combined cycle profitability has shifted toward the “Dispatching Services Market” (MSD), on which, the shortening of the startup/shutdown time, the increase of the startup/shutdown cycling and high gradients of load variation are needed to compete profitably.

This operating mode, hugely flexible, was not taken into account in the design of most of the running plants, even if since a few years, it is not operable immediately and it increases thermo-mechanical stresses of most of the relevant equipment of the combined cycles resulting in the early consumption of their lifetime. In this framework, RSE carries on material characterization activities by tests of Low Cycle Fatigue (LCF) and Thermo-Mechanic Fatigue (LMF), to develop “material damage laws” to use for the diagnostics and the evaluation of the material wear. And it also carries on studies about the plant operating procedures and their effects on the machinery lifetime, which are based on the combined use of “multi-physics” dynamic simulation tools and “high fidelity” power plant dynamic simulators.

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