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Isovaara

The Isovaara 400 kV Series Capacitor: an efficient means for increased power transmission between countries

A series capacitor rated at 515 Mvar has been supplied and installed by Hitachi Energy in the 400 kV grid of the Swedish National Grid at Isovaara in the north of the country. The installation, undertaken on a turnkey base, has the purpose of increasing the power transmission capacity of an existing power corridor between Sweden and Finland by means of increased voltage stability at steady state as well as transient grid conditions.

By these means, extended use of existing facilities is enabled, rendering unnecessary the building of additional lines. The series capacitor is incorporated in the Letsi – Petäjäskoski section of a double circuit 400 kV transborder interconnection Letsi – Petäjäskoski and Svartbyn – Keminmaa north of the Botnian Gulf.

System studies performed prior to the installation showed that with series compensation, it is possible to operate the existing power corridor closer to its thermal limit without jeopardizing its power transmission stability in conjunction with possible system faults.

Main data
System FSC
Commissioning year  1996
 Rated voltage  400 kV
 Rated current  1800 A
 Rated power  515 Mvar
 Degree of compensation  70%
 ZnO varistor rating  104 MJ
 Protective level  2,3 p.u.