significant delays and cost overruns. Additional costscaused by the offshore converter stations are reportedfor both ABB and Siemens .However, no finalcosts including the overruns have been published forthese delayed projects.Given the limited availabilityof information, the cost figures presented here rely onpublicly accessible awarded contractual volumes inpress releases.Based on reported additional cost forSiemens and ABB , , the cost overruns arecaptured and included as far as possible.BorWin1was built by ABB as the first HVDCconnectionforoffshorewind,anditistheonlyone based on two-level-converter technology.Theproject’scommissioningphasetookaboutsevenmonthslongerthanexpected.Evenafterthisextendedcommissioningphase,problemscontinued for several years resulting in significantdown-times , , .DolWin1andDolWin2were entirely built by ABB.These each included the two converter stations, thecable system, and the offshore platform.BorWin2,HelWin1,SylWin1andHelWin2were builtby a consortium of Siemens AG and Prysmian Group.Siemens was responsible for the converter stations andthe offshore platforms while Prysmian was in charge ofthe cable system.DolWin3was awarded to a consortium of Alstomand Prysmian Group. The project’s commissioning isexpected in mid-2017.BorWin3differs from its preceding projects to theextent that it has been awarded in two separate tenders,one to Siemens (together with Petrofac) and another toPrysmian Group. Initial power transmission on the linkis to commence in early 2019.6. Evaluation MethodologyBased on the collected data on contracted cost forthe reference projects, the reference investment costfor the individual projects is calculated according toEquation (7).Cref,i=1110Cconref,i∀i∈IB2BCref,i=54Cconref,i∀i∈IITC(7)Cref,i=54Cconref,i∀i∈IOWCTheseestimatedmarkupsareaccountingforthedifferencebetweenreferencecontractualcostCconref,iandtotalprojectreferenceinvestmentcostCref,i.Thesedifferencesarecausedbymanydifferentfactors, including, but not limited to, internal efforts,risk budget, engineering and concession costs, landpurchase, construction etc.The markup values arebasedon,,andunquotablepersonalcommunication with relevant industry stakeholders.Foreachindividualreferenceproject,thecostestimationiscalculatedwitheachavailablecost8
parameterset.Thesecostestimationsarethencompared with the reference investment cost and therelative deviation is expressed on a logarithmic scale,expressed by Equation (8).Dki=log2Ckest,iCref,i(8)Relative deviations guarantee an adequate assessmentof both small and big projects.Using absolute costfigures would undervalue the correct estimation ofsmaller projects.
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Electric power transmission, Cost overrun, VSC, VSC HVDC