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Report RSE 18000015

Sardinian electric system operation at 2030 with presence of three terminal VSC HVDC

Report

2017.

Request Document (3.37 MB, .pdf)

D. Cirio (RSE SpA) , A. Pitto (RSE SpA), A. Iaria (RSE SpA), M. Rapizza (RSE SpA)

T&D-C.C. 2017 - Transmission and Distribution in Continuous Current

Analysis, by means of proper grid models, of the behaviour and of the operational bounds of the Sardinian transmission system, in case of refurbishment of the multi-terminal HVDC link SA.CO.I. with the adoption of voltage source converters VSC.

The increase of variable generation from renewable energy sources “RES” implies the reduction ofinertia, short-circuit power and voltage-frequency regulating capacity. In Sardinia, the perspectiveconcerning the interconnection toward the mainland gains high importance for the ancillary servicesprovision. The herein reported activity, carried out in synergy with the project “BEST PATHS”, isaimed to analyse the impact, on the Sardinian system operation, by the replacement of the three-terminalHVDC SA.CO.I.2 (300 MW), based on “LCC” Line Commutated Converters, with a new SA.CO.I.3assumed to have double transmission capacity and be based on “VSC” Voltage Source Converter technology.

A realistic model (year 2030) of the Sardinian electrical system, implemented in the DigSILENTPowerFactory® environment and including the two HVDC links SA.CO.I.3 and SA.PE.I. toward themainland, was improved in order to represent: i) the RES generation with its control/protection logics;ii) the load shedding schemes; iii) special protection schemes based on the remote tripping of windgeneration; iv) the “LVFRT” Low Voltage Fault Ride Through characteristics for the SA.CO.I.3; v)control functions, in the Sardinian converters of the SA.CO.I.3, for the supply of fast frequency primaryregulation “FFR” and for the supply of synthetic inertia “SI”.

Dynamic simulations concerning the possible generation loss highlighted that the FFR is suitable for theSardinian system because it allows highly containing the frequency deviation whereas the SI allows areduction of the frequency derivative in an amount of 0,4 Hz/s.

In a scenario with high export from Sardinia, simulations were performed in order to represent ACthree-phase short circuits and the loss of one pole of the SA.PE.I.. These simulations proved theusefulness of the wind generation’s remote tripping, with the aim to contain the over-frequency in caseof loss of transmission capacity toward the mainland, and of the FFR to contain the under-frequency andthe possible consequent need of load shedding. It was observed that the AC faults can involve highvoltage dips, close to the minimum requirements stated by the LVFRT characteristics of SA.CO.I..

In low export conditions, an operational security analysis, based on the availability’s verification ofsufficient power reserve margins, pointed out that the fast power reversal, a VSC technology’sprerogative, could be necessary in the 3.7% of the yearly hours. Finally, a procedure was proposed toassess the maximum ranges of coordinated operation of SA.CO.I. and SA.PE.I., compatible with theminimum reserve requirements.

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