Adaptation of the control equipment to permit 3-terminal operation of the HVDC link between Sardinia, Corsica and mainland Italy

After more than 20 years of service as a conventional two-terminal HVDC link, the Sardinia-mainland Italy HVDC link (200 MW, 200 kV) is now operating as a three-terminal system. The original control equipment has been modified to allow the introduction of a tapping station on the line for three-terminal operation. The adaptations to the control equipment, including means to ensure that the converters are operated within their capabilities, are explained. It is concluded that the successful addition of a tapping station to the existing Sardinia-mainland Italy HVDC link demonstrates the ease with which an HVDC link with frequency control can be adapted to provide for a third terminal, even though it utilizes a different generation of technology. It also demonstrates the practicality of allowing two separate converter stations (Sardinia and Corsica) to modulate their power flow according to the demands of local frequency, within the limitations imposed by plant ratings and system load dispatching