A New Concept for HVAC Underground Transmission with a Low Magnetic Field

The planned offshore-windparks in the North Sea and the Baltic Sea must be connected to the onshore grid by means of submarine high voltage cable routes. The efficiency of these connections are crucial for the economy and success of the whole wind energy. It is discussed whether to apply HVAC, HVDC-classic or the new HVDC-light/plus systems. Recently a new concept of bipolar cable systems was presented in order to overcome the given limitations of the state of the art techniques. A further decisive advantage of such bipolar transmission systems is the possibility of bulk power transmission with very low magnetic fields. The magnitude of the magnetic field and the efficiency of steel pipe shieldings for a further field reduction is calculated by means of finite-element method considering the nonlinear behaviour of ferromagnetic materials. It will be shown that the magnetic induction at a chosen test point will decrease significantly when replacing the conventional HVAC-system by a bipolar HVAC-system. With a steel pipe shielding a further decrease of the magnetic induction can be reached to comply with the strictest limit values.