Skagerrak 1-3 HVDC Interconnections

An electric DC power transmission between Norway and Denmark (using the Thury system) was proposed as early as 1922. But it lasted 54 years until the first 500 MW was realized in 1977. The Skagerrak 1&2 with 500 MW was commissioned in 1976-77 and Skagerrak 3 with 440 MW in 1993. The link goes between Kristansand in southern Norway and Tjele on Denmark's Jutland peninsula. The link is owned by Statnett in Norway, and Energinet.dk in Denmark.

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Aerial overview of Tjele converter station with the converters for Pole 1&2 to the left and Pole 3 to the right. Valve hall in the first Skagerrak link

The converter stations for Skagerrak 1&2 (1976-77) were the first stations to employ the modern circuitry and station design that is employed even today. The first stations with thyristor valves were designed according to the principles adopted for mercury arc valve stations. But ABB adopted new design principles for the converter stations of the Skagerrak 1&2 link: twelve pulse converters quadruple thyristor valves no 5th or 7th harmonic filters on the AC-side converter transformers close to the valve-hall with the valve-side bushings in the valve-hall The Skagerrak 1&2 link was the first one to employ ABB´s second generation of air-cooled valves (which also were used in the CU and Inga-Shaba transmissions). The Skagerrak 1&2 link went through a control and protection system upgrade in 2007, when the advanced MACH2 control system was installed.

When Skagerrak 3 (1993) was built it was decided to reconfigure the existing bipole so that Pole 1 and Pole 2 operate with the same current direction. Thereby achieving a better current balance, since the Pole 3 has a higher current than Pole 1 and 2.

The converter stations of Pole 3 was the first in the series of ABB cable projects during the 1990's that also includes Baltic Cable, Kontek and SwePol.

In 2011, ABB was awarded the Skagerrak 4 link - read more about it here.

Main data
Commissioning year:	Pole 1&2: 1976-77 Pole 3: 1993 Pole 4: 2014
Power rating:	Pole 1+2: 500 MW Pole 3: 440 MW Pole 4: 700 MW
No. of poles:	4 (2 bipoles)
AC voltage:	Pole 1&2: 300 kV (Kristiansand), 150 kV (Tjele) Pole 3: 300 kV (Kristiansand), 400 kV (Tjele) Pole 4: 400 kV (Kristiansand), 400 kV (Tjele)
DC voltage:	Pole 1&2: 250 kV (HVDC Classic) Pole 3: 350 kV (HVDC CLassic) Pole 4: 500 kV (HVDC Light)
Length of DC submarine cable routes:	Skagerrak 1-3: 127 km Skagerrak 4: 140 km
Lenth of DC land cable route:	Skagerrak 4: 104 km
Length of DC overhead line:	Skagerrak 1-3: 113 km
Main reason for choosing HVDC:	Length of sea crossing, asynchronous link. For pole 4, HVDC Light was chosen for its premier power quality features.