Stefan Florjancic, Senior Manager
Ansaldo. The scope of supply of Ansaldo Energia, as head of the Temporary Association of Companies, included design, supply, commissioning and maintenance of three 250 MVAR synchronous compensators for installation in Garigliano, Matera and Foggia, plus an option for two more synchronous compensators, to be exercised within a maximum of 36 months of the order issue date.
Construction is currently in progress, and commissioning of the three compensators will be completed in 2022. The synchronous compensator represents a special application of electricity generators which, connected to Terna's transmission grid, exchange reactive energy with the grid and increase short circuit power. They are also capable of contributing inertia to the electricity grid to increase its stability: a strategic advantage in view of the energy transition and increase in power generation from renewable sources which are naturally subject to discontinuities in delivered power, with little or no inertia.
The synchronous compensators supplied by Ansaldo Energia also feature a "flywheel system", an innovation designed and implemented entirely by Ansaldo Energia. The flywheel connected to the compensator rotor guarantees an overall inertia of the rotating system that is four times greater than that of the compensator rotor alone. To reduce friction losses due to rotation, the flywheel is contained in a vacuum chamber at a pressure of less than 200 mbar.
Ansaldo Energia's solution stands out for:
- A flywheel diameter of about 2 metres and a high peripheral speed of 3000 rpm, permitting the required inertia to be achieved with limited axial extension of the flywheel, saving on the cost of forging, supports and civil works. This is a very challenging achievement in terms of rotor dynamics, in view of the torsional stresses in the event of electrical failure that must be taken into account when determining the size of the shafts.
- The seals between the vacuum chamber and the flywheel shaft use liquid ring technology, drastically reducing air leakage and the rating of the vacuum pumps. The immediate benefits are lower costs for Ansaldo and lower power consumption for Terna.
- The vacuum chamber has a nominal pressure of 50 mbar to reduce friction losses. The total losses of the compensator/flywheel system are assessed in the tender phase with a specific scoring system.
The contract also includes a twenty-year maintenance and assistance service for both plants.