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6 System Coupling by High Voltage Direct Current (HVDC) Technology
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The main focus of the project was on the investigation of a synchronous coupling between the IPS/UPS and the UCTE. The study has however also considered the possibility of coupling both systems via High Voltage Direct Current (HVDC) technology. This could provide backing for the creation of a joint electricity market platform between the UCTE and the IPS/UPS. The construction of HVDC back-to-back links between the interface countries might also be considered in the medium term.
HVDC technology has been successfully proved in various specific applications worldwide. The major difference of a DC solution compared to an AC coupling concerns the decoupling character of the link. When system disturbances occur, neither a dynamic interaction between the coupled systems, nor the factor of the CPFM (which reduces the installed interface capacity) has to be considered, as is the case with a synchronous coupling. Additionally, DC links allow the control of the power flow which is used for discharging the grid under overload and emergency situations. Ultimately, due to their technical features, back-to-back links could result in an “easier to realise” perspective. However, in order to assist further decisions relating to a possible DC-coupling of the IPS/UPS and the UCTE, further detailed investigations will be required in addition to any bilateral agreements and studies.
Although no specific system simulations were carried out by means of DC coupling of the IPS/UPS with the UCTE, the investments for DC coupling have been determined. The specific investment costs estimated for a back-to-back link are in the region of € 12.5m per 100 MW. Typical unit sizes for conventional HVDC back-to-back links vary between 600 and 1000 MW. Assuming that three back-to-back stations of 600 MW each would be placed at the interface the investment for these stations – not considering costs for network improvements – would amount to € 225m.
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